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Clim. Past, 12, 2087–2106, 2016
www.clim-past.net/12/2087/2016/
doi:10.5194/cp-12-2087-2016
© Author(s) 2016. CC Attribution 3.0 License.
Jens Esmark’s Christiania (Oslo) meteorological observations
1816–1838: the first long-term continuous temperature record
from the Norwegian capital homogenized and analysed
Geir Hestmark1and Øyvind Nordli2
1Centre for Ecological and Evolutionary Synthesis, CEES, Department of Biosciences, Box 1066 Blindern,
University of Oslo, 0316 Oslo, Norway
2Norwegian Meteorological Institute (MET Norway), Research and Development Department, Division for Model and
Climate Analysis, P.O. Box 43 Blindern, 0313 Oslo, Norway
Correspondence to: Geir Hestmark (geir.hestmark@ibv.uio.no)
Received: 1 June 2016 – Published in Clim. Past Discuss.: 20 June 2016
Revised: 17 October 2016 – Accepted: 19 October 2016 – Published: 18 November 2016
Abstract. In 2010 we rediscovered the complete set of me-
teorological observation protocols made by Jens Esmark
(1762–1839) during his years of residence in the Norwegian
capital of Oslo (then Christiania). From 1 January 1816 to 25
January 1839, Esmark at his house in Øvre Voldgate in the
morning, early afternoon and late evening recorded air tem-
perature with state-of-the-art thermometers. He also noted air
pressure, cloud cover, precipitation and wind directions, and
experimented with rain gauges and hygrometers. From 1818
to the end of 1838 he twice a month provided weather ta-
bles to the official newspaper Den Norske Rigstidende, and
thus acquired a semi-official status as the first Norwegian
state meteorologist. This paper evaluates the quality of Es-
mark’s temperature observations and presents new metadata,
new homogenization and analysis of monthly means. Three
significant shifts in the measurement series were detected,
and suitable corrections are proposed. The air temperature in
Oslo during this period is shown to exhibit a slow rise from
1816 towards 1825, followed by a slighter fall again towards
1838.
1 Introduction
The current concern with climate change has increased the
interest in early meteorological observation series and eval-
uation of their quality (e.g. Bergström and Moberg, 2002;
Auer et al., 2007). In a recent paper we analysed the temper-
ature record for the Norwegian capital made between 1837
and 2012 by the Astronomical Observatory at the University
of Oslo and the Norwegian Meteorological Institute (MET
Norway) (Nordli et al., 2015). Previous to 1837, long-term
observations of the Oslo weather were known to have been
made by Jens Esmark (1762–1839), professor of mining sci-
ences at the University of Oslo (then Christiania). A first re-
analysis of Esmark’s observations was made by meteorolo-
gist B. J. Birkeland (Birkeland, 1925). Our rediscovery in
2010 of Esmark’s original meteorological observation proto-
cols has provided an opportunity to digitize, homogenize and
analyse his data with modern methods.
Esmark is today mostly remembered for his pioneer as-
cents of many of Norway’s highest peaks (Esmark, 1802,
1812; Hestmark, 2009), his discovery of ice ages, and his
astronomical explanation of such dramatic climate change
as caused by variations in the eccentricity of the orbit of
the Earth, a hypothesis now recognized as a precursor of
the theories of James Croll and Milutin Milankovich (Es-
mark, 1824, 1826; Andersen, 1992; Worsley, 2006; Rudwick,
2008; Berger, 2012; Krüger, 2013). In his own lifetime he
was primarily known as a skilful mineralogist and geologist.
Throughout his life Esmark maintained a passion for mete-
orological observation with instruments he crafted himself
in accordance with the highest contemporary standards. His
main inspiration for this activity was his teachers at Copen-
hagen University, which he attended 1784–1789; first among
them was the Astronomer Royal Thomas Bugge (1740–
1815), who in his observatory tower, Rundetårn, in the mid-
Published by Copernicus Publications on behalf of the European Geosciences Union.
2088 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
dle of Copenhagen, made daily measurements of the weather
(Willaume-Jantzen, 1896). Esmark also befriended Bugge’s
instrument maker, the Swede Johan(nes) Ahl (1729–1795)
(Esmark, 1825; Anonymous, 1839). In addition, Esmark fol-
lowed the lectures of Christian Gottlieb Kratzenstein (1723–
1795), professor of medicine and experimental physics, a
“hands-on” practical man who enjoyed crafting instruments
and all sorts of mechanical machines (Kratzenstein, 1791;
Snorrason, 1974; Splinter, 2007). From 1789 to 1791 Es-
mark studied mining sciences at the Norwegian silver town
of Kongsberg, and after further studies in Freiberg, Saxony,
and Schemnitz in today’s Slovakia, in 1798 he moved back
to Kongsberg to take up a position as assessor in the central
mining administration (Overbergamtet) of the dual kingdom
Denmark–Norway. At Kongsberg he also lectured in miner-
alogy, geology and experimental physics at the Royal Norwe-
gian Mining Seminar, acting as its temporary inspector from
1799, and permanent inspector from 1802 to 1815. From 1
January 1799 he three times a day recorded observations of
the Kongsberg weather – air pressure on mercury barometers
(in inches and lines) and air temperature in degrees Réau-
mur. This was documented in a series of small notebooks
running continuously with some lacunae until 16 Septem-
ber 1810, which were rediscovered by the authors in 2010
(Esmark, 1799–1810). When Esmark in 1815 moved to the
Norwegian capital Christiania (now Oslo) to become the first
professor in the mining sciences at the university, he contin-
ued this habit. At least from January 1816 up to and includ-
ing day before his death on 26 January 1839 he recorded air
temperature and barometric pressure three times a day. The
complete set of his 23 Christiania observation protocols, long
believed lost, was rediscovered in 2010 by the authors, and
is now safely deposited in the Norwegian National Archive
(Riksarkivet) (Esmark, 1816–1838). They provide a unique
and detailed picture of the weather in Oslo in the early 19th
century. From January 1818 to December 1838 tables of Es-
mark’s observations were published every fortnight in the of-
ficial newspaper Den Norske Rigstidende (see Appendix A),
and he thus acquired a semi-official position as Norway’s first
state meteorologist. Based on a number of previously unpub-
lished documents (cited as Document 1, 2 etc., with archival
location in the reference list) we present here new metadata
for Esmark’s meteorological observations from Christiania
and homogenize, analyse and evaluate his original temper-
ature data with modern statistical tools to characterize the
temperature variations in the Norwegian capital in this pe-
riod.
2 Metadata
2.1 The location – No. 308, Vestre Rode – Øvre
Vollgate 7
Esmark’s observations were made at his home (see Esmark,
1823: De ere tagne i min Bopel), and there is no evidence in-
dicating that he changed the location. On 19 August 1815 Es-
mark was registered as owner of property No. 308 in Vestre
Rode (i.e. Western Quarter), one of the four old quarters
of Christiania town (Document 1). It was a modest one-
and-half-storey house built late in the 18th century with an
adjoining garden. Esmark’s continued residence at this ad-
dress until his death is documented in annual censuses and
tax protocols (Document 2). Property No. 308 was situated
on the north-western side of the street Øvre Vollgate (Øvre
Woldgaden), laid out literally on what used to be the outer-
most western rampart (voll) of nearby Akershus Castle and
Fortress (Fig. 1). It was a natural rock promontory above a
meadow to the west where the poor fishing village Pipervi-
gen would develop later in the 19th century, today the site
of Oslo Town Hall. In 1815 Øvre Vollgate constituted the
south-western limit of Christiania, a town with only about
15 000 citizens (Myhre, 1990). Until 1814 the main admin-
istration centre of the dual kingdom was in Copenhagen, but
with Christiania in that year acquiring the new parliament
and government after the separation of Norway from Den-
mark, the town expanded rapidly. When street numbers were
introduced, Esmark’s property was numbered Øvre Vollgate
No. 7. The present Øvre Vollgate 7 – an office high-rise –
comprises previous numbers Øvre Vollgate 3, 5 and 7.
Esmark’s property No. 308 and all neighbouring proper-
ties were measured and mapped for the new matriculation
of Christiania in the summer of 1830, and thus we have
very precise data on his house and the surrounding proper-
ties at the relevant time (Document 3). The whole property
roughly constituted an elongated rectangle, approximately
14 m ×60 m (Fig. 2). The unit used in these measurements
was the “Norwegian alen” (Norsk alen), determined by law
in 1824 to be 62.75 cm. It was divided into 2 feet, each di-
vided into 12 inches, each divided into 12 lines. No. 308 was
measured to 2026 square alen, of which the house (including
a yard) was 733 1/2 and the garden 1292 1/2 square alen
(1 square alen =0.3937 m2). Thus, the whole property was
ca. 800 m2, and the house (including yard) ca. 290m2. The
house had a 22-alen, 6-inch (ca. 14 m) long façade towards
the street Øvre Voldgate, constituting the south-eastern bor-
der of the property, with windows, doors, and a gate leading
into the backyard (Fig. 3). Øvre Vollgate street runs from SW
to NE at an angle of roughly 32◦NE (400 ◦). At the back the
house surrounded a small yard, with a narrow passage open-
ing out to the garden in the NW. As it would have been haz-
ardous to place the meteorological instruments on the street
side of the house, where passers-by could tinker with them,
it is almost certain that they were placed in Esmark’s back-
yard, a well-guarded space. When the house was finally de-
molished in 1938, it was in such a bad condition that the
Oslo city health authorities demanded the whole property be
sprayed with hydrocyanic acid and that none of the fungus-
infected material be used for construction elsewhere (Docu-
ment 4).
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2089
Figure 1. Map of Christiania (now Oslo) 1811 with the location (red star) of Esmark’s house in Øvre Vollgate 7 marked.
Figure 2. Matriculation and survey 1830 of Esmark’s property No. 308, Øvre Voldgate 7, in Oslo Byarkiv (Oslo City Archive). Arrow
indicates north. Garden to the left, and house surrounding backyard to the right.
Esmark’s garden on the NW side of the house and court
yard was a continuous slope, dropping 10 alen (6.25 m) down
along 66 alen length towards Pipervika. Here it was most
probably limited by a fence towards the street Præste Gade,
which later changed name to today’s Rosenkrantz’ street.
In 1841, a couple of years after Esmark’s death, most of
this garden was sectioned out and sold to form the new
property Rosenkrantz’ gate 26. In Esmark’s time, however,
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2090 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Figure 3. Street view of Esmark’s house in Øvre Voldgate 7. Photograph from around 1900. Oslo Bymuseum, No. OB.F00897. The high
buildings on each side were built in late 19th century.
the promontory remained an open garden space. His neigh-
bours on both sides (No. 307 and No. 309) had the same ar-
rangement of house and garden, with facades to Øvre Voll-
gate and gardens sloping down on the back to Præstegaden
(Document 5). To the north of the lowermost part of Es-
mark’s property was an open space called Jomfru Wold’s
Løkke (No. 368). South of this lower part of the garden was
the street Pipervigbakken, leading down from Rådhusgaten
street passing by the outer ramparts of Akershus Castle and
Fortress. The sea with Pipervika Bay (Piperviks Bugten) was
less than 200 m south of Esmark’s garden. His garden was
not an entirely constant environment. In 1823, for instance,
he received several fruit trees from a Danish friend which he
planted in the garden (Document 6).
It was a modest residence for a professor, situated in a
comparatively poor part of town, with mainly craftsmen,
tradesmen and artisans in the neighbourhood (Myhre, 1990:
p. 40). Here Esmark, a widower since 1811, moved in with
his three sons Hans Morten, Petter and Lauritz, as well as
a maid and a manservant (Document 2). His daughter Elise
resided with her grandparents in Copenhagen, but later re-
turned to Norway to take up residence in No. 308.
2.2 The observers
The great majority of the Christiania observations were made
and noted down by Esmark himself, who has easily recog-
nizable handwriting. His position as a professor in the min-
ing sciences did, however, sometimes cause him to leave
town on short or long field excursions, some lasting sev-
eral months. He was away from Christiania on long voyages
in 1818 (Hallingdal), 1819 (Kristiansand), 1822 (Bergen),
1823 (round-trip, Southern Norway), 1826 (Setesdalen),
1827 (Trondhjem) and 1829 (Copenhagen). In his absence
his sons seem to have been instructed to continue daily ob-
servations, and there are extremely few missing data points.
The oldest son, Hans Morten Thrane Esmark (b. 1801), in
1825 became a chaplain in Brevig and moved from Christia-
nia; Axel Petter (b. 1804) became a sailor and was often away
from home; and Lauritz Martin (b. 1806), later a professor
of zoology at the Christiania University, and daughter Elise
Cathrine (b. 1800) remained at home until Esmark’s death.
The sons evidently did not fully share their father’s passion,
and although instrument readings were meticulously main-
tained, the qualitative notes on weather are often restricted
to a single word in Esmark’s absence. A claim (Birkeland,
1925: p. 5) that the botanist Martin Flor performed the ob-
servations in Esmark’s absence has not been substantiated.
2.3 The hours of day
Esmark’s Christiania observation protocols do not indicate
the precise hours when the observations were made. The
columns are given as morning, noon (really afternoon) and
evening (Morgen,Middag,Aften). A note on the first pub-
lished table in Den Norske Rigstidende on 24 January 1818
also says Morgen,Middag og Aften without further specifi-
cation (Fig. 5). In a summary table of 15 years (1818–1832)
published in 1833, Esmark is more explicit: “The barome-
ter observations have been made daily in the morning, af-
ternoon and evening; in later years at 8.30a.m., at 3.30p.m.
and at 9.30 p.m.; thermometer observations at the same times
in the afternoon and evening and in the morning with the
help of the night thermometer. From this the middle height
is taken.” (Barometerobservationerne ere dagligen gjorte om
Morgenen, Eftermiddagen og Aftenen; i de senere Aar Kl. 8
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2091
Figure 4. The January page from Esmark’s meteorological observation protocol from 1823, the year he discovered ice ages. Esmark 1816–
1838, protocol 1823.
1/2 Morgen, Kl. 3 1/2 Eftermiddag og Kl. 9 1/2 Aften; Ther-
mometerobservationerne paa samme Tider om Eftermidda-
gen og Aftenen og om Morgenen ved Hjælp af Natthermome-
tret. Heraf er taget Middelhøiden.) (Esmark, 1833: p. 235).
The hour 3.30 p.m. probably coincided with Esmark’s return
to his house from the lectures at the university, just a few
blocks away. He regularly lectured from 2.00 to 3.00 p.m.
The phrasing “in later years” suggests that the hours had not
been constant throughout the whole series, and we address
this problem in the analysis.
2.4 The instruments and their position
In a note to his first table presented in the journal Den Norske
Rigstidende, on 24 January 1818, Esmark provides a few
details of his measurements: “The observations are made
34 Rhinelandic feet [i.e. 10.68 m] above the sea, and are
the middle value of observations made morning, noon and
evening. The barometer heights are corrected as they would
have been if the barometer was subject to a temperature of 0◦.
The thermometer hangs freely facing north.” (Observation-
erne ere anstillede 34 Rhinlandske Fod over Havet, og ere
Middeltallet af Observationer, anstillede Morgen, Middag og
Aften. Barometerhøiderne ere corrigerede saaledes, som de
skulle være, dersom Barometret havde været udsat for 0◦
Temperatur. Thermometret hænger frit imod Nord.) (Fig. 5).
Esmark also notes: “The barometer height is reduced to 0 ◦R.
If one wants it reduced to sea level, one must add a line or
1/12 of an inch to its height, so that the barometer height
at sea level becomes 28.1,20 in French measure.” (Barome-
terhøiden er reduceret til 0◦R. Vil Man have den reduceret
til Havets Overflade, maa Man til den anførte Høide lægge
en Linie eller 1/12 Deel af en Tomme, saa at Barometerhøi-
den ved Havets Overflade bliver 28.1,20 i Fransk Maal.) (Es-
mark, 1833: p. 235).
2.4.1 Thermometers
Esmark all his life used the Réaumur scale, R. The preci-
sion of his Réaumur thermometer was half of a degree. On
a table of averages for the years 1816–1822 Esmark notes:
“The thermometer observations are made in shadow in free
air with a Réaumur thermometer, whose boiling point is de-
termined at 28 inches 2 lines (French measure) barometric
height.” (Thermometerobservationerne ere gjorte i Skyggen
i fri Luft med et Reaumurs Thermometer, hvis Kogepunkt er
bestemt ved 28 Tommers 2 Liniers (fransk Maal) Barome-
terhöide.) (Esmark, 1823). In Esmark’s observation protocol
for the year 1816, some instrumental corrections are given
for what is claimed to be Esmark’s thermometer. They are
not written by Esmark himself; most probably they are notes
written by Birkeland, who says he has the corrections from
Hansteen, but it is not certain that they belong to the ther-
mometer used by Esmark. The corrections are listed in Ap-
pendix B but have not been used in the present paper.
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2092 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Figure 5. Esmark’s first published Christiania weather table, from
Den Norske Rigstidende, 24 January 1818. Maltese crosses are in-
tended as plus signs.
2.4.2 Barometer
Of the barometer used, Esmark (1833: p. 235) states: “The
barometer is a simple barometer, the tube of which is 2 1/2
lines in diameter and whose capsule is 40 lines in diameter,
and calibrated after a siphon barometer.” (Barometret er et
simpelt Barometer, hvis Rør er 2 1/2 Linie i Diameter og hvis
Capsel er 40 Linier i Diameter, samt justeret efter et Hævert-
barometer.)
2.5 The protocols and data recorded
Esmark’s Christiania protocols are handmade, folded sheets
of white paper cut up and sewn in with a thin grey cardboard
cover; there is one protocol for each year, with 23 protocols
in all (Esmark, 1816–1838). Esmark interfoliated the official
printed Almanach for Christiania. This had, for each month,
16 days on each page, and thus Esmark wrote down his data
for 15 or 16 days on the first page of a month and the remain-
ing days from 17 to 28, 29, 30 or 31 on the next page (Fig. 4).
The protocols start on 1 January 1816 and end 31 Decem-
ber 1838, only 26 days before his death; altogether, there are
8401 days of continuous measurements. There are only a few
small lacunae. Photographs of all the protocols are available
at MET Norway (Klimadata samba server, HistKlim scanned
documents), and digitized values, converted from degrees
Réaumur to degrees Celcius, can be downloaded from MET
Norway’s home page: http://www.met.no. Esmark and his
sons continued observations in January 1839 until the day
before his death, on 26 January, but these observations are
only known through the newspaper Morgenbladet, which had
published Esmark’s daily measurements since 1834.
Three times a day, Esmark recorded temperature to a half
degree and air pressure in inches and lines (Fig. 4). In the
right-hand margin he noted the weather (Veirliget) with qual-
itative terms (see also Esmark, 1833). He used a fairly limited
number of categories:
–Precipitation: lidt Regn (a little rain),Fiin Regn (driz-
zle), Regn (rain), Regn Bygger/Bÿgger (showers), Regn
af og til (rain now and then), megen Regn (much rain),
Sne (snow), Sne Flokker (snowflakes), and Sne Bygger
(snow showers).
–Cloud cover: Klart (clear), enkelte Skyer (a few clouds),
tynde Skyer (thin clouds), skyet (cloudy), skyer i Hori-
zonten (clouds on the horizon), disig (haze), and Taage
(fog). The most common category was tykt (thick),
which means a grey day with haze, often with precip-
itation.
–Wind: wind direction was usually recorded only once a
day, in the afternoon, with categories N, S, V and O, and
combinations, e.g. N. O. (nord ost, north-easterly).
–Other: Torden (thunder), Nordlys (northern lights),
Flekker i Solen (sunspots, one or two circles around the
sun), and Høyt vand (high sea level).
In June 1818 Esmark introduced a new parameter, precip-
itation, measured with a rain gauge, and in the June sum-
mary, he announced: “In this month there has, according to
the rain gauge, fallen rain to a height which, if it had been
standing, had constituted a height of 1 inch and 9 and 7/12
lines. The rain gauge is situated 15 feet above sea level.” The
low altitude of the rain gauge suggests that it was placed at
the lower part of the slope in his garden. In October 1820
he presented to the readers of Rigstidende his new design
for a hygrometer – an instrument to measure air humidity
(Esmark, 1820). It was modified from a model developed by
John Livingstone, an M.D. from Canton (today Guangzhou),
China, published in the Edinburgh Philosophical Journal
in 1819 (Livingstone, 1819). The general idea was to put
a moisture-absorbing/releasing chemical substance (Living-
stone used pure sulfuric acid, which was also used to produce
ice) on one side of a balance, balanced against a weight on
the other side. The balance was placed under a glass jar open
at the bottom to let air freely flow in and out and to protect
it from precipitation. Esmark made two new hygrometers ac-
cording to this model. “Anyone who desires to see these hy-
grometers can see them at my house.” (Enhver, som har Lyst
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2093
dertil, kan see disse Hygrometere hos mig.) (Esmark, 1820).
He had tested them for several months and thought they could
be used by farmers to predict weather change as a substitute
for barometers. He did not, however, use the hygrometer data
for his meteorological tables. For the year 1821 he presented
more regular monthly data on precipitation in inches – from 1
May through October – apparently the months without frost.
2.6 The published tables
Starting on Saturday 24 January 1818, with a table presenting
weather data for the first half of the month, the semi-official
daily Den Norske Rigstidende published Esmark’s meteo-
rological observations, which thus acquired an official air
(Fig. 5). It became a regular series, published twice a month
– one table for the first half of the month, one for the second
half – a total of 24 tables each year, all with the same title,
“Meteorologiske Iagttagelser i Christiania [year], anstillede
af Prof. Esmark” (Meteorological observations in Christia-
nia [year], made by Prof. Esmark). This series running from
1 January 1818 to 15 December 1838 is absent from all pre-
viously published bibliographies of Esmark’s works but in
fact runs to no less than 503 published tables (Appendix A).
These tables present present 7665 days of continuous ob-
servations. In addition come the two full years of 1816 and
1817, only published summarily by Esmark (1823) but with
the complete record preserved in the original protocols. The
whole year 1818 was summed up on 8 January 1819 with, for
example, means, and here Esmark also compared the Chris-
tiania data to those obtained by Wargentin in Stockholm, by
Bugge in Copenhagen, and (no observer given) in St. Pe-
tersburg, Russia. It was not a weather forecast but rather a
weather “backlog”, and this may have dimmed their public
interest somewhat. The data given in these published tables
differ from the raw data of the protocols by being daily aver-
ages. For each day he gave the barometric pressure and tem-
perature, averaged from observations made in the morning,
afternoon, and evening (at first without further precision of
hour). To calculate these averages he apparently used the for-
mula
Tm=1/4(TI+2TII +TIII),(1)
where Tmis Esmark’s daily “mean” temperature, and TI,TII,
and TIII are the observed temperature morning, afternoon and
evening, respectively. To the tables, for the second half of
each month, he also appended a note with the mean baro-
metric pressure and temperature for the entire month, and
indicated which days had the maximum and minimum air
pressure and temperature. The mean temperature was given
to 1/100th of a degree (a spurious precision). The series con-
tinued in 1820, now also with the daily wind direction. Es-
mark evidently trusted only himself to calculate the means
and set up the tables, and thus the readers of Rigstidende
sometimes had to wait for months to read the weather for the
last fortnight when he was off on some excursion. From 1834
Esmark’s observations were also published in the Christiania
newspaper Morgenbladet every day, with two days’ delay,
i.e. observations for the first day of the month were pub-
lished on the third, the second on the fifth, etc. This was
initiated after Christiania doctors suspected a connection be-
tween the weather and the cholera epidemics which struck
Norway from 1833 onwards.
3 Methods
3.1 Homogeneity testing
A homogeneous climatic time series shows variations in cli-
mate without being disturbed by other factors involved, like
changes in the environment, observational procedures or in-
strument calibration. For the study of climate variations the
use of homogeneous series is of paramount importance, as
otherwise the climate analysis may be wrong (e.g. Auer et
al., 2007; Moberg and Alexandersson, 1997; Tuomenvirta,
2001). For testing the homogeneity of Esmark’s tempera-
ture series we selected the standard normal homogeneity
test (SNHT) with a significance level of 0.05, which has
been widely used for testing of both precipitation series and
temperature series (Alexandersson, 1986; Alexandersson and
Moberg, 1997; Ducré-Robitaille et al., 2003). The first ver-
sion of the test (Alexandersson, 1986) had one step change
as the only possibility, whereas in the version of 1997 both
double shifts and a trend were possible outcomes of the test.
In any year the significance of a potential break is examined.
The testing followed the principle of comparing a candidate
series (the series under testing) against a reference series. The
reference may be series from one or more neighbouring sta-
tions. A candidate series may also be observations at one par-
ticular time of the day which are compared with other obser-
vation times for the same station. In the latter case we call this
“internal testing”. Contemporary neighbouring series over-
lapping Esmark’s observations are too short to be used in
the homogeneity testing. The nearest stations that could have
been used are Stockholm or Uppsala, about 350 km from
Oslo. The problem with using series so far away is that spa-
tial temperature variations could be interpreted as inhomo-
geneities. Therefore, our chosen method is internal testing.
Later measurement series from observation stations in the
Oslo area may, however, be of some use in some analyses,
and these are listed with Esmark’s in Table 1 with their na-
tional station number (identifier) and name. While the official
names of the stations refer to their sites, for convenience we
will often refer to the names of the observers in the text, i.e.
the column “Additional information” in Table 1. Before the
analysis started, all observations in degrees Réaumur were
converted into degrees Celcius by multiplying by the factor
1.25.
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2094 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
4 Results
4.1 Detection of inhomogeneities
First, we will use SNHT for detection of the inhomogeneities
and will thereafter treat each inhomogeneity in more de-
tail and produce corrections. The testing was performed for
both seasonal (Table 2) and monthly (Table 3) resolutions
where observations taken in the morning (I), midday (II) and
evening (III) were compared with each other. By comparing
several test results it was possible to decide at which obser-
vation time a shift (inhomogeneity) occurred. Most striking
are the huge shifts detected in spring, summer and autumn
when the morning observation was involved. The most prob-
able year for the shift was 1827; in particular, this was true
for the single-shift test. Here we apply the common conven-
tion to define the shift year as the last year before the shift.
We have to conclude that the morning observation is inhomo-
geneous. Further investigation of the daily observations (not
shown) suggested that the change took place in the month of
March 1828.
When the evening observation was tested against the mid-
day observation, a shift seemed to occur in 1820 or 1821,
most probably in 1821. However, this break in homogene-
ity was much less than that of the morning observation (see
Table 2). The shift seems to be absent or very weak during
winter, so exact dating was impossible. For convenience the
end of 1821 was adopted as the time of the inhomogeneity.
Tests including the midday observation revealed no addi-
tional shifts than those already detected. The occurrence of
the shifts in the tests I vs. II and III vs. II seemed to reflect
shifts either in the morning or in the evening observations.
For the winter season a shift in the last part of the series was
detected; possible shift years were 1832, 1833 or 1834.
The large shift in the morning observation could have
masked possible smaller shifts in the series on both sides
of this shift. Therefore, the single-shift SNHT was applied
on two different parts of Esmark’s series: January 1816–
February 1828 and March 1828–December 1838 (parts 2 and
3 in Table 2). However, no further shifts in the series were
detected.
Thus, there are three shifts that seem reliable: one in 1821
for the evening observation, one in 1827 (probably Febru-
ary 1828) for the morning observation and one during winter
with possible shift years of 1832, 1833 or 1834. We now pro-
ceed to propose corrections.
4.2 Correcting the shift in 1821.12 in the evening
observation
This inhomogeneity was corrected by using the midday ob-
servation that came out of the SNHT as homogeneous. The
monthly mean difference between the midday observation
and the evening observation on each side of the shift was
calculated. Then the evening observation was corrected by
adding monthly correction terms so that this mean difference
was constant on each side of the shift. It is most common to
correct the early part of the series, so this was also done here.
Therefore, the period January 1816–December 1821 was cor-
rected, whereas the rest of the series was not. The corrections
are given in Table 4.
The corrections are largest in the months where the daily
temperature wave is largest, so one could hypothesize that a
change in the observation time was the reason for the shift.
Strictly speaking, we know Esmark’s observation times only
in 1833, so this hypothesis is not in contradiction to meta-
data. However, observation times cannot be the only reason
for the shift, because it also appeared in midwinter, when
the daily temperature wave is weak. Moreover, the numbers
of the corrections are so large that only observation times
near midnight would compensate for the low values of the
evening observation. Observation times that late seem un-
likely. There is some indication that a changed environment
could have played a role for this inhomogeneity as Esmark
in 1823 planted fruit trees in his garden (see Metadata). A
1-year mismatch of the shift detected by the SNHT is not
uncommon.
4.3 Correcting the shift in 1828.02 in the morning
observation
Esmark (1833) relates that he uses “a night thermometer” for
the morning observation. Our hypothesis is that in Esmark’s
terminology the “night thermometer” was a minimum ther-
mometer. That means that he at some point started to note
the night minimum temperature in the column for the morn-
ing temperature, rather than the actual morning temperature
when he read the barometer. This hypothesis was tested by
studying the difference between Esmark’s evening observa-
tion and the morning observation the following day for the
three homogeneous intervals (Table 5; the winter inhomo-
geneity in the 1830s was ignored). For comparison we used
the hourly observations (September 1993–September 2015)
at the modern station Oslo – Blindern (18700 Oslo), where
the difference between the observation at 21:00UTC and the
minimum temperature for the following night is presented in
row 4 in Table 5. The interval for the night minimum was
from 21:00 to 08:00 UTC, i.e. the same observation times as
Esmark used at least for his barometric observations in 1833.
In the earliest time interval (row 1) the differences in Es-
mark’s observations are very much smaller than those from
Blindern, so it is impossible that Esmark in this early inter-
val could have recorded the nightly minimum temperature in
the column for the morning observation. In the next inter-
val (row 2) the differences are somewhat larger, but far too
small compared to Blindern, so the same conclusion has to
be drawn: no minimum thermometer was in use. However, in
the third interval (row 3) the differences are nearly the same
as those for Blindern. Even the monthly variations through-
out the year correlate well. We conclude that Esmark for the
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G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2095
Table 1. Esmark’s station at Øvre Vollgate 7 as well as other observation stations used in this article: national station number (identifier)
and name, period of observation, station altitude and some additional information. The asterisk before the start year marks the start of hourly
observations. Hsis metres above sea level.
No. and name Period (from...to; year, month, day) Hs(m) Additional information
18651 Oslo II 1837.04.02–1933.12.31 25 Astronomical Observatory
18654 Oslo – Øvre Vollgate 1816.01.01–1838.12.31 11 Esmark’s observations
18655 Oslo – Pilestredet 1822.10.19–1827.02.28 16 Hansteen’s observations
18700 Oslo – Blindern ∗1993.01.05 to present 94 Main building, MET Norway
18815 Oslo – Bygdøy ∗2012.01.01 to present 15 Mainly rural station
Table 2. The SNHT used for comparison of observations at time xvs. observations at time y(xvs. y). The shifts (◦C) are given by the last
year of each part of the series. For the single-shift test, the corrections needed for the xseries to be homogeneous with yseries are also given.
Corrections should be applied from the start year to the end year of the inhomogeneity (non-significant results are given in italic).
SNHTs Obs. times Winter Spring Summer Autumn Year
Part 1, 1816.01–1838.12: the whole length of the series
Single shift I vs. II 1833; −1.1 1827; −2.1 1827; −3.3 1824; −1.4 1827; −1.8
Single shift I vs. III 1832; −1.5 1826; −2.8 1827; −4.0 1827; −1.7 1827; −2.4
Single shift III vs. II 1821; 0.7 1820; 1.5 1821; 1.3 1821; 0.6 1821; 0.9
Double shift I vs. II 1826; 1834 1818; 1827 1817; 1827 1824; 1829 1823; 1827
Double shift I vs. III 1819; 1832 1820; 1826 1818; 1828 1823; 1829 1818; 1827
Double shift III vs. II 1821; 1832 1819; 1835 1821; 1835 1817; 1834 1821; 1835
Part 2, 1816.01–1828.02
Single shift II/I 1826; 0.8 1818; 0.7 1817; 0.8 1824; 1.0 1823; 0.5
Single shift I/III 1818; −1.0 1820; −1.7 1818; −1.7 1821; −0.9 1818; −1.3
Single shift III/II 1821;−0.6 1819; −1.4 1821;−1.2 1817;−0.8 1821; −0.8
Part 3, 1828.03–1838.12
Single shift I/II 1834; −1.0 1834; 0.4 1830;−0.4 1829;−0.4 1830;−0.5
Single shift I/III 1832; −1.3 1836;−0.6 1836;−0.8 1829;−0.9 1836;−0.8
Single shift III/II 1833; 0.4 1835; 0.8 1835; 0.9 1834; 0.6 1835; 0.7
“morning observation” used a minimum thermometer in the
period March 1828–December 1838. Before that he observed
temperature in the morning with an ordinary thermometer.
Minimum thermometers were certainly available by 1828.
As early as 1790, a spirit thermometer with a glass index,
very much like what is used up to this day at manual stations,
was described to the Royal Society in Edinburgh (Middleton,
1966: p. 152).
If the minimum thermometer was set at the evening ob-
servation, the values in the column for morning observation
should always be equal to or lower than the evening temper-
ature the previous day. In December this is not true for 26 %
of the observations and in June for 6 %. These figures reduce
to 6 and 2 % in December and June respectively for viola-
tions of no more than 1 ◦C. In practice, different exposure of
the two thermometers may violate this test, and one should
also take into account the possibility of instrumental errors in
Esmark’s thermometers. We may conclude that the percent-
age of violation is not large enough to contradict our con-
clusion that a night minimum thermometer was in use. The
normal procedure for meteorological institutes when mini-
mum thermometers are introduced is to change the formula
for monthly mean calculation. Therefore, the morning tem-
perature will not be corrected. Homogeneity in the monthly
means will be obtained by changing formula for monthly
mean calculation (see Sect. 4.5).
4.4 Correcting the shift in the 1830s
A significant inhomogeneity in winter for the morning ob-
servation (in this period identified as minimum temperature)
was detected by the SNHT double shift (Table 2 part 1 I vs.
II) and also by the single-shift test when the time window
was March 1828–December 1838 (Table 2, part 3). A signif-
icant shift in spring was also formally detected (Table 2 III
vs. II), but with only 3 years on one side of the shift, its sig-
nificance was considered doubtful. The shift in winter was
firstly examined by plotting the morning temperature against
the evening temperature, which revealed that there was not
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2096 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Table 3. The same as Table 1 but with the single-shift test used at monthly resolution. In the first and third rows the years of the shifts are
shown, and in the second and fourth rows the adjustments. Period of observation: January 1816–December 1838.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
I/II 1834 1826 1826 1830 1827 1827 1827 1827 1825 1827 1824 1833
−1.2 −1.4 −1.0 −2.2 −3.3 −3.4 −3.5 −2.9 −1.9 −1.1 −1.5 −1.2
III/II 1828 1832 1820 1819 1819 1826 1821 1821 1821 1820 1834 1820
0.6 0.7 1.1 1.7 1.8 1.3 1.3 1.3 0.8 0.9 0.6 0.7
Table 4. Corrections (◦C) of the evening observation during the period January 1816–February 1821.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.6 0.6 1.0 1.2 1.3 1.2 1.3 1.3 0.9 0.8 0.3 0.5
0
1
2
3
1830 1832 1834 1836 1838 1840
Temperature (ᵒC)
Years
Figure 6. The temperature difference (◦C) between Esmark’s
evening observation and the morning observation the following day
for the winter season (December–February) in the period 1831–
1838.
an abrupt shift in the difference but rather a steady state
during 1829–1931 followed by a trend. The graphical plot-
ting was followed by applying the multiple linear regression
(MLR) procedure, also known as the Vincent test (Vincent,
1998). The significant inhomogeneity was confirmed, as was
the change point year of 1831. The trend line was found by
least-squares regression analysis (Fig. 6). An explanation for
the trend may be a change in the observation times. Accord-
ing to Esmark (1833), his observation times were as follows
(see Metadata):
–morning: 08:30 ChT =08:43 CET =07:43 UTC;
–midday (afternoon): 15:30 ChT =15:43 CET =
14:43 UTC;
–evening: 21:30 ChT =21:43 CET =20:43 UTC.
(ChT: Christiania time, i.e. local time for Christiania
(Oslo); CET, Central European Time; UTC, Universal
Time Coordinated)
These observation times were for the barometric pressure,
but in the afternoon and evening the thermometer was read
at the same time as the barometer; however, Esmark does not
explicitly say that the morning thermometer was read at the
same time as the barometer. He also uses the term “in the
later” years, so we do not know from which year these obser-
vation times were introduced or whether he also continued to
use them in the following years of 1834–1838.
Our hypothesis is that Esmark had another observation
time for the temperature observations in the morning than for
the pressure observations. Pressure could be observed inside
the house, but for the temperature observations he possibly
had to leave the house for his garden. Esmark might orig-
inally have observed temperature and pressure at the same
time in the morning also, but with the introduction of the
minimum thermometer he could have thought that the ob-
servation time for the morning temperature was not impor-
tant. In spring, summer and autumn he obviously was right
in his thinking as minimum temperature occurs earlier than
the morning observation (08:30ChT), but in winter the min-
imum temperature often occurs later in the day as the sys-
tematic daily temperature wave is weak. This can explain the
changing difference during winter and the stable differences
during the other seasons. As Esmark grew older and more
frail, he may have got up in the morning later and later. Pro-
gressive illness and susceptibility to cold in his later years
(Anonymous, 1839) could have made it less convenient to
leave the house for the garden in the morning. Following this
hypothesis, the minimum temperature was corrected, 1T , by
use of Eq. (2) for the winter season in accordance with the re-
gression line shown in Fig. 6, where a=year (period 1832–
1838). No correction was undertaken for the period 1829–
1831.
1T =0.2861 ·a−523.85 (2)
4.5 Homogenization of the monthly mean temperature
Esmark observed only three times a day, so it is far from ob-
vious how monthly mean temperature should be calculated
without bias. This problem confronts meteorological insti-
tutes worldwide, so formulas for such calculations have been
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G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2097
Table 5. Difference (Diff, ◦C) of median temperature between Esmark’s evening observations and the observations the following morning.
For comparison the differences between the observation at 21:00UTC and the minimum temperature the following night are shown for the
modern station Oslo – Blindern. The night is defined by the interval 21:00–08:00UTC. SD (◦C) is the standard deviation for the differences.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Esmark Diff 0.0 0.0 0.0 −0.7 −1.8 −1.6 −1.3 −1.2 0.0 0.5 0.0 0.0
1816.01–1821.12 SD 3.4 2.6 2.4 2.1 2.4 2.3 2.6 2.1 2.1 2.0 2.6 2.2
Esmark Diff 0.9 0.7 1.2 0.6 0.6 −0.7 −0.6 0.0 1.2 0.6 0.8 0.6
1822.01–1828.02 SD 3.1 2.5 2.3 1.8 2.2 2.4 2.2 2.1 2.9 2.5 2.5 2.4
Esmark Diff 1.3 1.5 1.9 2.2 3.1 3.1 3.1 3.1 2.5 1.9 1.6 1.3
1828.03–1838.12 SD 2.6 2.3 2.5 1.8 2.1 2.2 2.4 2.3 2.2 2.1 1.9 2.7
Blindern Diff 1.0 1.5 2.3 2.6 3.2 3.0 2.7 2.4 2.0 1.5 1.0 1.0
1993.09–2015.09 SD 1.7 1.8 1.8 1.7 1.8 1.8 1.7 1.6 1.6 1.6 1.5 1.6
0.00
0.10
0.20
0.30
0.40
0.50
1815 1820 1825 1830 1835 1840
Correction (ᵒC)
Annual Winter Spring Summer Autumn
Figure 7. Corrections added to Esmark’s series for each season dur-
ing his period of observation, 1816–1838.
developed (see Appendix C). The formulas contain specific
constants valid for each month and site. Strictly speaking,
the constants were unknown for Esmark’s observation site
at Øvre Vollgate, but they are well known for the station
18700 Oslo – Blindern, situated 3.4 km to the north of Es-
mark’s site. Fortunately, there are indications that the con-
stants for Blindern could also be used for Øvre Vollgate (see
Appendix C). Given the constants, the calculation of homo-
geneous monthly mean temperature was trivial when the ho-
mogenized version of the observations at fixed hours was
used. We found that the corrections for seasonal means vary
from 0.0 to +0.4 ◦C and the annual corrections from 0.0 to
+0.3 ◦C. How the corrections changed throughout the period
of observation is shown in Fig. 7. For the period Decem-
ber 1822–December 1831, no corrections were applied.
4.6 The Christiania (Oslo) climate in Esmark’s period of
observation, 1816–1838
Esmark’s observations exhibit a long-term variation pattern
characterised by lower values in the start and in the end of
the period, whereas the middle of the period was somewhat
warmer (see Fig. 8). This is true not only for the annual
means but also for all seasons of the year except for win-
ter. For individual years 1822 is warmest except in summer
and autumn. The coldest year is 1838, followed by the years
1816, 1829 and 1820.
The year 1816 is of particular interest as it has gone
into history as “the year without summer”, with an aver-
age decrease in global temperatures often ascribed to vol-
canic activity, resulting in a food shortage in many places
in the Northern Hemisphere. However, Esmark’s observa-
tions show that this summer (JJA) was not extraordinary in
Oslo, as the following summers of 1817 and 1821 were ap-
proximately 1 ◦C colder. The spring temperature in 1816 is,
however, the coldest one in the series. The first 3 years of
Esmark’s series must have been very unfavourable for agri-
culture due to low temperature. In the grain-growing months
(AMJJA) the mean temperature was about 10◦C for the three
consecutive years 1816, 1817 and 1818, i.e. the lowest tem-
peratures in Esmark’s series of observation.
5 Discussion
5.1 Overheating of the midday observation?
The midday observation turned out to be homogeneous, but
it may have been overheated by insufficient radiation protec-
tion in Esmark’s yard or simply the confined space allow-
ing less air flow (wind). This was tested by comparison with
the Oslo – Blindern station (18700), which is well protected
by a Stevenson screen. Differences between the midday ob-
servation and the evening observation exhibit characteristic
variations throughout the year, not only for Blindern but also
for the Esmark series and the Oslo II series (Astronomical
Observatory, 18651) (see station list Table 1 and Fig. 9).
Whereas the differences between the Blindern series and Es-
mark’s series were relatively small in the months August–
April, they are much larger in the months May–July, when
the sun is highest in the sky and the radiation reaches its an-
nual maximum. Therefore, one possible interpretation is that
Esmark’s thermometer was overheated at the midday obser-
vation in midsummer, MJJ, by (reflected) shortwave radia-
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2098 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Figure 8. Annual and seasonal means of Esmark’s temperature se-
ries (symbols) and Gaussian filter (curves) with 3 standard devia-
tions in the Gaussian distribution (e.g. Nordli et al., 2015), corre-
sponding roughly to a 10-year rectangular filter.
0
1
2
3
4
5
6
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Temperature difference (ᵒC)
Blindern Esmark Oslo II
Figure 9. Temperature differences (◦C) between the observations at
15:00 and at 21:00 UTC for the following stations: Oslo – Blindern
for the period January 1993–September 2015 and Esmark for Jan-
uary 1816–December 1838. The corrections of the evening obser-
vations (Table 4) are added to the data for the period January 1816–
December 1821 before the calculation of the differences and Oslo
II (Astronomical Observatory) April 1837–December 1867.
tion. However, when compared to the diurnal pattern at the
Oslo II station (Astronomical Observatory), it is seen that the
curve representing Esmark’s observations quite closely fol-
lows the Oslo II curve, also in midsummer (Fig. 9). At the
Astronomical Observatory there were three thermometers on
different walls – the north, east and west walls (Nordli et al.,
2015). At least one of these thermometers was in the shade
and therefore available for use at every observation time. This
is our main reason for not correcting for a possible overheat-
ing of Esmark’s midday observation (see also the following
Sect. 5.2 and 5.3). The deviation of the Blindern station may
be due to this site being more exposed to wind chill and its
situation significantly higher above sea level than Esmark’s
house and the Astronomical Observatory (see Table 1).
The meteorological observations at the Astronomical Ob-
servatory started in April 1837 (Nordli et al., 2015), so this
series overlaps with Esmark’s series by 21 months. The dif-
ference of their uncorrected monthly means is shown in
Fig. 10. It is evident that for all seasons but winter Esmark’s
temperatures are somewhat lower than those from the obser-
vatory. Esmark died on 26 January 1839 (see Metadata), so
the quality of the latest months of his series may possibly
be questioned. However, we cannot see any decline in qual-
ity directly from his observation protocols. This is also rele-
vant for the discussion of a possible correction of Esmark’s
midday observation due to overheating. If Esmark’s midday
observation had been corrected, the discrepancy between Es-
mark’s series and observatory series would have been larger.
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G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2099
-4
-3
-2
-1
0
1
2
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Temperature difference ( ᵒC)
Esmark - Oslo II
Figure 10. Differences in mean monthly temperature between Es-
mark’s observations at Øvre Vollgate and those at the Astronom-
ical Observatory (Esmark minus observatory) during the period
April 1837–December 1838. Temperatures are not corrected.
5.2 Comparison with Hansteen’s observations at the
street Pilestredet in Oslo
During the period November 1822–February 1827 the Chris-
tiania professor Christopher Hansteen carried out observa-
tions at his home in Pilestredet at the corner of Keysers-
gate, at the centre of town (Hansteen, 1823, 1824, 1828;
Birkeland, 1925: p. 12) (see Table 1 for some further in-
formation). The distance from Esmark’s site was only about
600 m. Hansteen’s observation times varied much but for
each month he gives the observation times together with the
data (Hansteen, 1824). The distribution of the observation
times in UTC is as follows:
–morning: 06:00, 4 %; 07:00, 44 %; 08:00, 52 %;
–midday: 13:00, 20 %; 14:00, 78 %; 15:00, 2 %;
–evening: 21:00, 6%; 22:00, 88%; 23:00, 6%.
Hansteen’s observations were corrected to Esmark’s ob-
servation times, approximately 08:00, 15:00 and 21:00UTC
by use of the mean daily temperature wave at Blindern, so
that Esmark’s observations could be compared with the cor-
rected ones of Hansteen (Fig. 11). It is seen that Hansteen’s
morning observation is much warmer than that of Esmark
except during winter. Most likely, the thermometers of
Hansteen had been overheated as they were hanging at the
southern and northern side of the house (Birkeland, 1925:
p. 12). Then it must have been difficult to find shadow in
the morning. Also, the midday observation is warmer at
Hansteen’s site than by Esmark. This is probably due to the
fact that Hansteen’s garden was protected by the surrounding
houses and gardens of the town, which reduced wind, while
Esmark’s garden was directly exposed to the winds from the
adjacent bay. The evening temperatures at Hansteen’s house,
however, agree well with those from Esmark during summer,
-4
-3
-2
-1
0
1
2
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Temperature ( ᵒC)
Morning Midday Evening Monthly mean
Figure 11. Difference between Esmark’s observations at Øvre
Vollgate and Hansteen’s observations at Pilestredet (Esmark mi-
nus Hansteen) during the period November 1822–February 1827
at 08:00, 15:00 and 21:00 UTC.
unlike for the two other observation times. The evening ob-
servations occurred after sunset at both sites, whereas the two
other observations occurred after sunrise.
Unlike the situation during summer, Hansteen’s tem-
peratures are lower than those of Esmark in the period
November–March (Fig. 11). In many weather situations the
air loses energy by longwave radiation because the shortwave
radiation is too small to compensate for the loss. The result
is that the coldest air is found at the lowest places in the lo-
cal terrain, not necessarily at the lowest sites above sea level.
Esmark’s house lies high in the local terrain at the edge of a
slope down to Pipervika (see Metadata), whereas Hansteen’s
house lies low in the local terrain at a floor of a small valley.
The difference in winter temperature is therefore possibly an
effect of topography.
5.3 Comparison with Stockholm and Copenhagen
The Stockholm and Copenhagen series were not used as
reference stations for the homogeneity testing. Their dis-
tances from Oslo were considered to be too long, 350 and
450 km respectively. However, comparison with the Stock-
holm Observatory and Copenhagen Old Botanical Garden
(Closter et al., 2006) with Esmark’s observations may pro-
vide some indications of the quality of the homogenization
(see Fig. 12). Compared to Esmark, Stockholm seems to be
relatively warmer in the first four years, 1816–1819, than the
rest of the series. Without correction for the years 1816–1821
the differences would have been even larger. Therefore, com-
parison with Stockholm supports the correction of the series.
It is possible that there is another shift in the series in 1819.
Some support for this is seen in the homogeneity testing (see
Table 2, part 2). However, the may also be due to spatial
temperature differences between Stockholm and Oslo, with
the long distance between the stations taken into account.
www.clim-past.net/12/2087/2016/ Clim. Past, 12, 2087–2106, 2016
2100 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Table 6. The rank of mean temperature in 1816 for months and seasons during the years 1816–1838 for Oslo (Esmark’s observations). For
comparison Stockholm is also included. The rank runs from low to high values, so that the lowest temperature is ranked 1.
Jan Feb Mar Apr Mar Jun Jul Aug Sep Oct Nov Dec Year Winter Spring Summer Autumn
Oslo 14 6 1 5 1 7 13 3 2 3 8 11 2 1 5 2
Stockholm 14 3 6 9 1 16 18 9 13 5 8 12 7 6 4 17 3
-1
0
1
2
3
4
5
1810 1815 1820 1825 1830 1835 1840
Temperature differences (ᵒC)
Stockholm-Esmark Copenhagen-Esmark
Figure 12. Annual mean temperatures from Stockholm Observa-
tory and Copenhagen old Botanical Garden compared to Esmark’s
observations at Øvre Vollgate in Oslo.
Furthermore, in spite of homogenization, there may also be
small inhomogeneities in the Stockholm series.
Comparison between Copenhagen and Oslo gives no rea-
son for expecting any shift in the series, but 4 years are miss-
ing from the Botanical Garden series
5.4 The summer of 1816 in Christiania (Oslo)
Several volcanic eruptions affected global climate in the first
years of Esmark’s period of observation, the Tambora erup-
tion in Asia in 1815 being the largest in terms of sulfur mass
ejected and general impact (Stothers 1984; Oppenheimer,
2003). It has given rise to the paradigm for 1816: “the year
without a summer”. Esmark’s observations show, however,
that the summer of 1816, though cold, was not extraordi-
narily cold in Oslo. Moreover, in Stockholm (“Bolin Centre
Database”, 2016) that summer was rather warm, No. 17 of
the 23 summers from 1816 to 1838, ranked from low to high
(Table 6). May, however, was very cold in both cities, and
July quite warm in both cities, but in June and August Oslo
was much colder relative to the mean value than Stockholm.
Esmark’s observations may also be compared to other in-
dependent reconstructions of temperature in Norway in the
period 1816–1838 (Table 7). One reconstruction for FMA
for Austlandet, south-eastern Norway, is based upon ice loss
mainly from Lake Randsfjorden (Nordli et al., 2007). Four
reconstructions are based upon the first date of grain har-
vest: Austlandet (Nordli, 2001a); Vestlandet (western Nor-
way; Bergen), (Nordli et al., 2003); Lesja (Nordli, 2001b);
and Trøndelag (central Norway; Nordli, 2004). The grain
harvest date is a proxy for AMJJA temperature in the south-
ern lowland areas, whereas in the mountain valleys (Lesja)
and northern areas (Trøndelag) it is a proxy for MJJA tem-
peratures. We also included a gridded multi-proxy series for
the nearest grid point to Oslo (Luterbacher et al., 2004).
The three reconstructions for Austlandet all have the spring–
summer of 1816 as the coldest one in the period, whereas
in the Esmark series it is listed as No. 3. The reconstruc-
tions for the two other regions, Vestlandet (western Norway)
and Trøndelag, show a very different picture with relatively
warm 1816 summers like the summer in Stockholm based
on instrumental observations (Nordli et al., 2003; Nordli,
2004). Vestlandet and Trøndelag belong to other climate re-
gions than Austlandet (Hanssen-Bauer and Førland, 2000),
so for a specific summer it may reflect real temperature dif-
ferences. The very low temperature for spring in 1816 seems
to have had a strong influence on agriculture, so the harvest
had been delayed in south-eastern Norway. This is reflected
in the AMJJA temperature reconstruction. In Fig. 13, proxy
and instrumental summer temperatures (JJA) are shown for
the whole period of Esmark’s observations. The proxy data of
Oslo (Luterbacher et al., 2004) agree with the homogenised
Esmark’s series that the three summers of 1816–1818 were
quite cold, not warm like those in Stockholm. The summer
of 1819, however, was warm in Oslo (and also in Stockholm)
but not in the reconstruction. It is also evident that the vari-
ability in the reconstructed series is too small.
The summer temperatures of 1816 have recently been
analysed by Luterbacher and Pfister (2015). Their study
shows a positive gradient from a cold core of air lying over
France with a positive temperature gradient towards eastern
and northern Europe, so the paradigm of the severe summer
of 1816 has to be modified when it comes to Scandinavia and
eastern Europe to take into account significant geographical
variation. The authors state that “in eastern Europe, western
Russia and parts of eastern Scandinavia, summer tempera-
tures were normal or slightly warmer than average”.
6 Conclusions
Homogeneity testing (SNHT) of Esmark’s temperature ob-
servations 1816–1838 in Christiania (Oslo) demonstrated
three significant shifts, and we propose corrections for these.
First there is a shift in the evening observation in 1821–
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2101
Table 7. The rank of 1816 temperature for seasons during the period 1816–1838 for Oslo (Esmark’s observations), and for climate re-
constructions from proxy data at different places in Norway. For comparison Stockholm is also included. The rank runs from low to high
values, so that the lowest temperature is ranked 1. The grid point (59.75◦N, 10.75◦E) differs only slightly from Esmark’s house (59.91◦N,
10.74◦E).
Place, county Feb–Apr Apr–Aug May–Aug Jun–Aug References
Oslo, south-eastern Norway 2 3 3 5 Esmark’s observations
Austlandet, south-eastern Norway 2 Nordli et al. (2007)
Austlandet, south-eastern Norway 1 Nordli (2001a)
Lesja, south-eastern Norway 1 Nordli (2001b)
Bergen, western Norway 18 Nordli et al. (2003)
Trøndelag, central Norway 18 Nordli (2004)
Stockholm, Sweden 3 10 9 17 Bolin Centre Database, 2016
Grid point (59.75◦N, 10◦75 E) 1 Luterbacher et al. (2004)
10
12
14
16
18
20
1810 1815 1820 1825 1830 1835 1840
Summer temperature (ᵒC)
Oslo, Esmark Oslo (59.75ᵒ N, 10.75ᵒ E) Stockholm
Figure 13. Summer mean temperature (JJA) for Stockholm Obser-
vatory, for Øvre Vollgate in Oslo (Esmark’s observations), and also
for grid point 59.75◦N, 10.75◦E (Oslo) reconstructed by Luter-
bacher et al. (2004).
1822. Before the shift, the evening observation was corrected
by about +1.3◦for the summer months, but only by about
+0.5 ◦C in winter.
A very large shift in the morning temperature was detected
in 1827–1828. From Esmark himself we know that he used a
“night thermometer” in 1833, identified as a minimum ther-
mometer. This change in instrumentation explains the lower
values for the morning observation. During the years 1831
to 1838 the nightly minimum temperature decreased steadily
in the winter season – i.e. it was inhomogeneous. The reason
seems to be later and later reading of the minimum tempera-
ture in the morning. The seasonal corrections of the series are
less than 0.5 ◦C, and for annual means less than 0.4 ◦C. In the
time interval 1822–1831 no corrections are applied. The ho-
mogenized temperature series 1816–1838 exhibits low tem-
perature at both ends, with higher temperature in the middle,
i.e. in the 1820s. The starting year, 1816, is of particular inter-
est as it has been referred to as “the year without a summer”.
That summer in Oslo was cold, but not extraordinary cold,
as it was only the fifth coldest in the period of observation.
However, March and May that year were the coldest ones
in the period of Esmark’s data, and 1816 and 1838 had the
lowest annual means. The first 3 years of Esmark’s observa-
tion, 1816–1818, were particularly cold in the grain-growing
season, April–August, which lends support to the historians’
view that these were years of hardship and famine.
7 Data availability
The underlying data for this analysis of Esmark’s data are
stored in the database of the Norwegian Meteorological
Institute (www.met.no). The original data are in degrees
Réaumur, but transformed to degrees Celcius by multiply-
ing by 1.25. There are three data sets: (1) sub-daily data,
(2) monthly means, and (3) homogenized monthly means,
resulting from the corrections described in the present pa-
per. All data sets may be accessed through the national sta-
tion numerical identifier 18654 or the place name Øvre Voll-
gate. The program for accessing the data is at present at
www.met.no. In the future the program may be changed
but there will always be programs available for download-
ing Norwegian meteorological data from the institute’s home
page.
www.clim-past.net/12/2087/2016/ Clim. Past, 12, 2087–2106, 2016
2102 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
Appendix A: Esmark’s meteorological tables in Den
Norske Rigstidende
Esmark, J. 1818/19. Meteorologiske Iagttagelser i Christia-
nia 1818, anstillede af J. Esmark. Den Norske Rigstidende
1818, No. 7 (24 January); No. 10 (4 February); No. 14 (18
February); No. 18 (4 March); No. 23 (21 March), No. 28
(8 April), No. 32 (22 April); No. 37 (9 May); No. 40 (20
May), No. 45 (6 June), No. 49 (20 June), No. 54 (8 July);
No. 59 (25 July); No. 63 (8 August); No. 67 (21 August);
No. 71 (5 September); No. 83, (17 October); No. 84 (21 Oc-
tober), No. 86 (28 October); No. 88 (4 November); No. 95
(28 November); No. 98 (9 December); No. 102 (23 Decem-
ber); No. 3 (8 January 1819).
Esmark, J. 1819/20. Meterologiske Iagttagelser i Christia-
nia 1819, anstillede af J. Esmark. Den Norske Rigstidende
No. 6 (19 January); No. 11 (5 February); No. 16 (23 Febru-
ary); No. 19 (5 March); No. 24 (23 March); No. 26 (6 April);
No. 33 (23 April); No. 36 (4 May); No. 41 (21 May); No. 48
(15 June); No. 49 (18 June); No. 54 (6 July); No. 62 (3 Au-
gust); No. 65 (13 August); No. 67 (20 August); No. 78 (28
September); No. 79 (1 October) No. 82 (12 October); No. 84
(19 October); No. 89 (5 November); No. 95 (26 November);
No. 99 (10 December); No. 103 (24 December); No. 2 (7
January 1820).
Esmark, J. 1820/21. Meteorologiske Iagttagelser i Chris-
tiania 1820, anstillede af J. Esmark. Den Norske Rigstidende,
No. 7 (25 January); No. 11 (8 February), No. 14 (18 Febru-
ary); No. 18 (3 March); No. 24 (24 March); No. 28 (7 April);
No. 32 (21 April); No. 37 (9 May); No. 41 (23 May); No. 47
(13 June); No. 50 (23 June); No. 54 (7 July); No. 58 (21 July);
No. 63 (8 August); No. 68 (25 August); No. 72 (8 Septem-
ber); No. 77 (26 September); No. 81 (10 October); No. 85
(24 October); No. 88 (3 November); No. 94 (24 November);
No. 98 (8 December); No. 103 (26 December); No. 3 (9 Jan-
uary 1821).
Esmark, J. 1821/22. Meteorologiske Iagttagelser i Chris-
tiania 1821, anstillede af J. Esmark. Den Norske Rigstidende,
No. 7 (23 January), står bare snee, men ikke mengde; No. 11
(6 February); No. 16 (23 February); No. 21 (13 March);
No. 23 (20 March); No. 29 (10 April); No. 33 (24 April),
No. 38 (11 May); No. 41 (22 May); No. 45 (5 June); No. 52
(29 June); No. 55 (10 July); No. 58 (20 July); No. 63 (6 Au-
gust); No. 68 (24 August); No. 72 (7 September); No. 76
(21 September); No. 80 (5 October); No. 85 (22 October);
No. 89 (5 November); No. 93 (19 November)(nytt moderne
plusstegn); No. 98 (7 December); No. 102 (21 December);
No. 2 (7 January 1822).
Esmark, Jens 1822/23. Meteorologiske Iagttagelser i
Christiania 1822, anstillede ved J. Esmark. Den Norske
Rigstidende, No. 5 (18 January); No. 10 (4 February); No. 15
(22 February); No. 18 (4 March); No. 23 (22 March); No. 28
(8 April); No. 32 (22 April); No. 36 (6 May); No. 42 (27
May); No. 45 (7 June) not nedbørmåling; No. 50 (24 June);
No. 81 (11 October); No. 82 (14 October); No. 83 (18 Oc-
tober); No. 84 (21 October); No. 87 (1 November); No. 89
(8November); No. 90 (11 November); No. 92 (18 Novem-
ber); No. 94 (25 November); No. 96 (2 December); No. 98 (9
December); No. 102 (23 December); No. 2 (6 January 1823).
Esmark, J. 1823/24. Meteorologiske Iagttagelser i Chris-
tiania 1823, anstillede ved J. Esmark. Den Norske Rigsti-
dende No. 7 (24 January); No. 11 (7 February); No. 15 (21
February); No. 20 (10 March); No. 24 (24 March); No. 27 (4
April); No. 31 (18 April); No. 36 (5 May); No. 40 (19 May);
No. 46 (9 June); No. 49 (20 June); No. 75 (19 September);
No. 76 (22 September); No. 77 (26 September); No. 78 (29
September); No. 79 (3 October); No. 81 (10 October); No. 82
(13 October); No. 84 (20 October); No. 88 (3 November);
No. 93 (21 November); No. 98 (8 December); No. 102 (22
December); No. 2 (5 January 1824).
Esmark, J. 1824/25. Meteorologiske Iagttagelser i Chris-
tiania 1824, anstillede ved J. Esmark. Den Norske Rigsti-
dende No. 6 (19 January); No. 11 (5 February); No. 15 (19
February); No. 20 (8 March); No. 24 (22 March); No. 29 (8
April); No. 33 (22 April); No. 37 (6 May); No. 42 (24 May);
No. 45 (3 June); No. 50 (21 June); No. 54 (5 July); No. 59
(22 July); No. 64 (9 August); No. 68 (23 August); No. 74
(13 September); No. 77 (23 September); No. 80 (4 Octo-
ber); No. 86 (25 Oktober); No. 89 (4 November); No. 96 (29
November); No. 98 (6 December); No. 103 (23 December);
No. 2 (6 Januar 1825).
Esmark, J. 1825/26. Meteorologiske Iagttagelser i Chris-
tiania 1825, anstillede ved J. Esmark. Den Norske Rigsti-
dende No. 7 (24 January); No. 11 (7. February), No. 15 (21
February); No. 18 (3. March); No. 24 (24 March); No. 29 (11
April); No. 33 (25 April); No. 36 (5 May); No. 40 (19 May);
No. 45 (6 June); No. 49 (20 June); No. 53 (4 July); No. 70 (1
September); No. 71 (5 September); No. 73 (12 September);
No. 74 (15. September); No. 76 (22 September); No. 79 (3
October), No. 85 (24 October); No. 89 (7 November); No. 93
(21 November); No. 97 (5 December); No. 102 (22 Decem-
ber); No. 2 (5 January 1826).
Esmark, J. 1826/27. Meteorologiske Iagttagelser i Chris-
tiania 1826, anstillede ved J. Esmark. Den Norske Rigsti-
dende No. 8 (26 January); No. 12 (9 February); No. 17 (27
February); No. 19 (6 March); No. 23 (20 March); No. 28
(6 April); No. 33 (24 April); No. 36 (4 May); No. 43 (29
May); No. 45 (5 June); No. 50 (22 June); No. 55 (10 July):
No. 58 (20 July); No. 62 (3 August); No. 67 (21 August);
No. 72 (7 September); No. 77 (25 September); No. 80 (5 Ok-
tober); No. 84 (19 October); No. 88 (2 November); No. 93
(20 November); No. 97 (4 December); No. 102 (21 Decem-
ber); No. 2 (4 January 1827).
Esmark, J. 1827/28. Meteorologiske Iagttagelser i Chris-
tiania 1827, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 7 (22 January); No. 11 (5 February); No. 16 (22
February); No. 19 (5 March); No. 24 (22 March); No. 28 (5
April); No. 32 (19 April); No. 37 (7 May); No. 43 (28 May);
No. 48 (14 June); No. 50 (21 June); No. 54 (5 July); No. 58
(19 July); No. 79 (1 October); No. 80 (4 October); No. 81 (8
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2103
October); No. 82 (11 October); No. 83 (15 October); No. 84
(18 October); No. 89 (5 November); No. 94 (22 November);
No. 97 (3 December); 102 (20 December); No. 2 (7 January
1828) – also sums up last 10 years and compares with Stock-
holm; the coldest years were 1819 and 1820, and the mildest
1822 and 1826.
Esmark, J. 1828/29. Meteorologiske Iagttagelser i Chris-
tiania 1828, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 6 (21 January); No. 10 (4 February); No. 15 (21
February); No. 18 (3 March); No. 24 (24 March); No. 27 (3
April – mange solpletter); No. 32 (21 April); No. 36 (5 May);
No. 40 (19 May); No. 45 (5 June); No. 49 (19 June); No. 53
(3 July); No. 59 (24 July); No. 63 (7 August); No. 78 (29
September); No. 79 (2 October); No. 81 (9 October); No. 84
(20 October); No. 88 (3 November); No. 94 (24 November);
No. 98 (8 December); No. 102 (22 December); No. 2 (5 Jan-
uary 1829).
Esmark, J. 1829/30. Meteorologiske Iagttagelser i Chris-
tiania 1829, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 8 (26 January); No. 11 (5 February); No. 15 (19
February); No. 19 (5 March – den strengeste vinter på mange
år); No. 24 (23 March); No. 27 (2 April); No. 33 (23 April);
No. 37 (7 May); No. 42 (25 May); No. 46 (8 June); No. 50
(22 June); No. 54 (6 July); No. 78 (28 September); No. 79 (30
September); No. 80 (5 October); No. 81 (8 October); No. 85
(22 October); No. 87 (29 October); No. 89 (5 November);
No. 90 (9 November); No. 94 (23 November); No. 99 (10
December); No. 103 (24 December); No. 2 (7 January 1830).
Esmark, J. 1830/31. Meteorologiske Iagttagelser i Chris-
tiania 1830, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 7 (25 January); No. 11 (8 February); No. 14 (18
February); No. 18 (4 March); No. 22 (18 March); No. 27 (5
April); No. 31 (19 April); No. 36 (6 May); No. 40 (19 May);
No. 46 (9 June); No. 50 (23 June); No. 53 (5 July); No. 57
(19 July); No. 63 (9 August); No. 70 (1 September); No. 73
(13 September); No. 78 (29 September); No. 81 (11 Octo-
ber); No. 84 (21 October); No. 91 (15 November); No. 95
(29 November); 98 (9 December); No. 102 (23 December);
No. 3 (10 January 1831).
Esmark, J. 1831/32. Meteorologiske Iagttagelser i Chris-
tiania 1831, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 10 (3 February); No. 11 (7 February); No. 17 (28
February); No. 20 (10 March); No. 25 (28 March); No. 28 (7
April); No. 33 (25 April); No. 39 (12 May); No. 43 (22 May);
No. 52 (12 June); No. 57 (23 June); No. 63 (7 July); No. 70
(24 July); No. 75 (4 August); No. 85 (28 August); No. 88 (4
September); No. 97 (25 September); No. 102 (10 October);
No. 110 (3 November); No. 112 (10 November); No. 118 (1
December); No. 119 (4 December); No. 1 (1 January 1832);
No. 2 (5 January 1832).
Esmark, J. 1832/33. Meteorologiske Iagttagelser i Chris-
tiania 1832, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 10 (2 February); No. 11 (5 February); No. 19 (4
March); No. 20 (8 March); No. 26 (26 March); No. 30 (12
April); No. 33 (22 April); No. 37 (6 May); No. 43 (20 May);
No. 52 (10 Juni); No. 57 (21 Juni); No. 63 (5 July); No. 70
(22 July); No. 78 (9 August); No. 86 (28 August – usedvanlig
kold sommer); No. 92 (11 September); No. 98 (25 Septem-
ber); No. 103 (7 October); No. 108 (25 October); No. 111 (4
November); No. 117 (25 November); No. 122 (13 Decem-
ber); No. 127 (30 December); No. 4 (13 January 1833).
Esmark, J. 1833/34. Meteorologiske Iagttagelser i Chris-
tiania 1833, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 10 (3 February); No. 12 (10 February); No. 18 (3
March); No. 24 (24 March); No. 25 (28 March); No. 30 (14
April); No. 35 (2 May); No. 37 (9 May); No. 44 (26 May);
No. 50 (9 June); No. 58 (27 June); No. 63 (9 July); No. 77 (11
August); No. 80 (18 August); No. 86 (1 September); No. 91
(12 September); No. 97 (26 September); No. 103 (13 Octo-
ber); No. 105 (20 October); No. 110 (7 November); No. 115
(24 November); No. 120 (12 December); No. 123 (22 De-
cember); No. 2 (5 January 1834).
Esmark, J. 1834/35. Meteorologiske Iagttagelser i Chris-
tiania 1834, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 7 (23 January); No. 10 (2 February); No. 16 (23
February); No. 18 (2 March); No. 24 (23 March); No. 27 (3
April); No. 32 (20 April); No. 37 (4 May); No. 43 (18 May);
No. 53 (10 June); No. 60 (26 June); No. 68 (15 July)(regnet
som falt på en kvadratfods flate utgjorde 4 rhinlandskae tom-
mer eller 576 kubikktommer); No. 71 (22 July); No. 79 (10
August), No. 83 (19 August); No. 90 (7 September); No. 96
(21 September); No. 102 (5 October); No. 107 (23 October);
No. 111 (6 November); No. 117 (27 November); No. 119 (4
December); No. 126 (28 December); No. 2 (8 January 1835).
Esmark, J. 1835/36. Meteorologiske Iagttagelser i Chris-
tiania 1835, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 10 (1 February); No. 12 (8 February); No. 15 (19
February); No. 20 (8 March); No. 24 (22 March); No. 28 (5
April); No. 34 (26 April); No. 40 (10 May); No. 50 (2 June);
No. 54 (11 June); No. 58 (21 June); No. 65 (7 July); No. 72
(23 July); No. 79 (9 August); No. 88 (30 August); No. 91 (6
September); No. 99 (24 September); No. 105 (11 October);
No. 107 (18 October); No. 112 (5 November); No. 118 (26
November); No. 120 (3 December); No. 126 (24 December);
No. 3 (10 January 1836).
Esmark, J. 1836/37. Meteorologiske Iagttagelser i Chris-
tiania 1836, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 7 (24 January); No. 15 (21 February); No. 17 (28
February); No. 19 (6 March); No. 23 (20 March); No. 27 (3
April); No. 32 (21 April); No. 38 (5 May); No. 45 (22 May);
No. 50 (2 June); No. 59 (23 June); No. 66 (10 July); No. 70
(19 July); No. 78 (7 August); No. 85 (23 August?); No. 92
(8 September); No. 98 (22 September); No. 105 (9 October);
No. 111 (30 October); No. 112 (3 November); No. 119 (27
November); No. 125 (18 December); No. 126 (22 Decem-
ber); No. 3 (5 January 1837).
Esmark, J. 1837/38. Meteorologiske Iagttagelser i Chris-
tiania 1837, anstillede ved J. Esmark. Den Norske Rigsti-
dende, No. 10 (22 January); No. 17 (7 February); No. 22 (19
February); No. 22 (2 March); No. 34 (19 March); No. 41 (4
www.clim-past.net/12/2087/2016/ Clim. Past, 12, 2087–2106, 2016
2104 G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838
April); No. 48 (20 April); No. 53 (2 May); No. 61 (21 May);
No. 67 (4 June); No. 74 (20 June); No. 82 (9 July); No. 86 (18
July); No. 93 (3 August); No. 100 (20 August); No. 106 (3
September); No. 113 (19 September); No. 120 (5 October);
No. 126 (19 October); No. 132 (2 November); No. 139 (19
November); No. 145 (3 December); No. 152 (19 December);
No. 2 (4 January 1838).
Esmark, J. 1838. Meteorologiske Iagttagelser i Christia-
nia 1838, anstillede ved J. Esmark. Den Norske Rigstidende,
No. 10 (18 January); No. 19 (3 February); No. 29 (20 Febru-
ary); No. 36 (4 March); No. 45 (20 March); No. 53 (3 April);
No. 62 (19 April); No. 70 (3 May); No. 79 (19 May); No. 87
(2 June); No. 98 (19 June); No. 108 (4 Junly); No. 117 (19
July); No. 127 (2 August); No. 137 (19 August); No. 148 (6
September); No. 156 (20 September); No. 164 (4 October);
No. 173 (20 October); No. 181 (3 November); No. 190 (18
November); No. 199 (4 December); No. 207 (18 December).
Appendix B: Corrections of Esmark’s thermometer?
The corrections are very small for the frequent winter tem-
peratures but as high as 0.5 ◦C for frequent summer temper-
atures. Due to the uncertainty with the identification of Es-
mark’s thermometer, we have not applied these corrections
to his observations. It should also be kept in mind that Es-
mark used another thermometer, i.e. a minimum thermome-
ter for the period March 1828–December 1838, which may
also have instrumental corrections. However, he was a skilled
instrument builder, so it is not likely that he used a thermome-
ter with larger corrections that those in Table B1.
Table B1. Instrument correction (Corr.) for thermometer readings (Temp.). The thermometer may have been used by Esmark between 1816
and 1838.
Temp. (◦C) 25.00 18.75 12.50 6.25 0.00 −6.25 −12.50 −18.75 −25.00
Corr. (◦C) +0.50 +0.50 +0.38 +0.38 +0.13 +0.13 +0.13 +0.13 +0.63
Appendix C
Table C1. Formulas for calculation of monthly mean temperature,
T, where T08,T15, and T21 are monthly means at observation times
08:00, 15:00 and 21:00 UTC respectively; Tnis monthly mean night
temperature; and kgand kfare constants. Mohn’s formula is also
often called the Cformula.
Mohn’s formula T=Tc+C Tc=T08+T15+T21
3
Köppen’s formula T=Tf−k(Tf−Tn)Tf=T15 +T21
2
MET Norway calculates monthly mean temperatures for
manual stations by Mohn’s (also called the Cformula) and
Köppen’s formulas (Birkeland, 1936; Gjelten et al., 2014;
Nordli et al., 2015), so we also chose to use those formu-
las for Esmark’s observations: the monthly mean tempera-
ture, T, may be calculated by Mohn’s formula and a modified
Köppen’s formula (Table C1).
A “true” monthly mean temperature, T, may be calculated
by the arithmetic mean of hourly observation according to
definition, so for a station that has hourly observations the
constants, Cand kf, are easily calculated by rearranging
Mohn’s and Köppen’s formulas. For Esmark’s series from
Øvre Vollgate the constants were unknown. It was assumed
that the constants from Blindern could also be used for Øvre
Vollgate. An indication of the robustness of this assumption
was tested by comparison with a short series of hourly obser-
vations from the station 18815 Oslo – Bygdøy (15ma.s.l.).
The test procedure started with calculation of the constants
for the Blindern series based on the period December 2012–
September 2015. These constants were then used for the cal-
culation of mean monthly temperatures for Bygdøy for the
same period, which were compared with the “true” monthly
means, i.e. those calculated using the hourly observations.
For Mohn’s formula the deviation from the true means var-
ied from −0.06 ◦C in December to +0.31 ◦C in September,
giving +0.10 ◦C for the whole year. For seven of the months
the deviation from the true value was less than ±0.1 ◦C. Cor-
responding figures for Köppen’s formula were −0.06 ◦C in
July, +0.16 ◦C in September and +0.01 ◦C for the whole
year.
Clim. Past, 12, 2087–2106, 2016 www.clim-past.net/12/2087/2016/
G. Hestmark and Ø. Nordli: Jens Esmark’s Christiania (Oslo) meteorological observations 1816–1838 2105
Edited by: S. Bronnimann
Reviewed by: R. Przybylak and two anonymous referees
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