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Well known for his discovery of discontinuity between Earth’s crust and mantle, this all-around
geophysicist also made pioneering observations of rotor-type circulation in bora.
A
ndrija Mohorovičić initiated his cloud ob-
servations on 1 May 1888 while a professor
at the Royal Nautical School in Bakar,
Croatia. Located in the Kvarner region of the
northern Adriatic at the foot of steep coastal
mountains, Bakar (45°18'N, 14°32'E) lies at the
north end of Bakar Bay in the east part of the
larger Rijeka Bay on the northern Adriatic coast
of Croatia (Fig. 1). The Royal Nautical School
there was established in 1849,
1
and Mohorovičić
joined its faculty in late 1882 as a lecturer, shortly
after completing his studies of physics and math-
ematics at the University of Prague (Skoko and
Mokrović 1982).
Mohorovičić’s interest in clouds was moti-
vated by the desire to contribute to the general
theoretical understanding of the dynamics of
upper-air currents and their relation to air move-
ments near the ground. Living at the base of the
coastal mountains in the northern Adriatic,
where the famous bora wind frequently makes
EARLY OBSERVATIONS OF ROTOR
CLOUDS BY ANDRIJA MOHOROVIC
ˇ
IC
´
BY VANDA GRUBIŠIc
´
AND MIRKO ORLIc
´
F
IG. 1. Diagrams of (a) the northern Croatian
coast and (b) the Bakar Bay area. Topography
contours are shown every 200 m. The solid
rectangle marks the inset shown in panel (b).
In (a) are marked the following toponyms: OP
(Opatija), RK (Rijeka), BK (Bakar), and RB (Ri-
jeka Bay). The solid line in (b) represents the
baseline of the vertical section shown in Fig. 2.
1
The Nautical School at Bakar was closed in 1856, but
reopened in 1871, and it has been in continuous opera-
tion since that time under various names.
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its appearance, he also drew his motivation from the
desire to explain the dynamics of bora, recognizing
the need to predict the onset of this severe gusty wind
for the benefit of many communities on the shore and
for nautical operations at sea.
Most of the late-nineteenth-century contempo-
raneous work on cloud observations, including their
physical measurements and classification, had been
done in northern Europe. As noted by Mohorovičić
(1891), there was an absence of similar work in
southern Europe, and he set out to change that. In
his pursuit of cloud observations, he followed in the
footsteps of his Scandinavian colleagues who made
extensive use of a nephoscope for measurements of
cloud movements (Ekholm and Hagström 1887).
In the course of this painstaking observational
work on clouds, and with his general interest in the
bora dynamics, Mohorovičić made observations of a
special type of stationary cumulus clouds that formed
occasionally during bora events over Bakar Bay,
appearing to reside on top of a horizontal vortex down-
wind of the coastal mountain range (Mohorovičić
1889a). In view of the renewed interest in the study of
atmospheric rotors, leading to the recently completed
Terrain-Induced Rotor Experiment (T-REX; Grubišić
et al. 2004), our goal is to bring Mohorovičić’s early
observations of atmospheric rotors into focus and set
them in a wider historical context.
Section 2 contains a summary of Mohorovičić’s
observations of this special type of orographic clouds
in Bakar, including a reproduction of the original
diagram by Mohorovičić, which appears to be the first
published illustration of the entire closed horizontal
circulation of an atmospheric rotor, including the
reversed surface flow branch. In section 3, we pro-
vide a contemporary setting of Mohorovičić’s note
on rotor cloud observations, and emphasize the role
of the nineteenth-century journal editor in fostering
the exchange of scientific ideas. A biographical note
on Mohorovičić and his scientific legacy is presented
in section 4. Section 5 concludes the paper.
MOHOROVIC
ˇ
IC
´
’
S OBSERVATIONS OF
ROTOR CLOUDS. From the outset of his cloud
studies, and in addition to the regular hourly obser-
vations of cloud cover and cloud type carried out in
collaboration with his colleague A. M. Zuvičić from
the Royal Nautical School from 0700 to 2100 LT
daily, Mohorovičić had conducted measurements of
the direction and speed of cloud movement. These
measurements were carried out 4 times daily at
0700 (0800 in winter), 1000, 1400, and 1600 LT, and
whenever a new cloud appeared in the sky, which was
sufficiently often for Mohorovičić (1891) to state
2
Clouds are strange fellows, and you must catch them
when they appear, and not when you would like to.
Their directions and speeds also vary a great deal.
The measurements were made with a nephoscope
that he constructed adapting the school-owned cam-
era obscura (Mohorovičić 1888). Mohorovičić carried
out the measurements of cloudiness, cloud types, and
their movements for 2 yr, from 1 May 1888 to 30 April
1890. Employing elaborate trigonometric consider-
ations, he had also developed a method for quantita-
tive determination of the vertical velocity component
using his measurements of the direction and speed of
cloud movement (Mohorovičić 1889b,c). The analysis
and summary of the cloud observations in the Bakar
area represent the subject of Mohorovičić’s doctoral
thesis, which he successfully defended at the Univer-
sity of Zagreb in 1893.
During this 2-yr period of observation, he noted
a special type of stationary cumulus cloud that
occasionally formed during bora events over Bakar
Bay. A particularly striking example of this type of
cloud, which formed on 18 October 1888, prompted
Mohorovičić to submit a short note to the Meteo-
rologische Zeitschrift (Mohorovičić 1889a).
3
In this
note he delivers a detailed description of orographic
clouds and other meteorological conditions observed,
together with a tabular summary of 4-times-daily
measurements of pressure, temperature, vapor
pressure, relative humidity, wind, cloudiness, and
AFFILIATIONS: GRUBIŠIC´—Desert Research Institute, Reno,
Nevada; O
RLIC´—Andrija MohoroviCˇiC´ Geophysical Institute,
University of Zagreb, Zagreb, Croatia
CORRESPONDING AUTHOR: Dr. Vanda Grubišic´, Division
of Atmospheric Sciences, Desert Research Institute, Reno, NV
89512
E-mail: Vanda.Grubisic@dri.edu
The abstract for this article can be found in this issue, following the
table of contents.
DOI:10.1175/BAMS-88-5-693
In final form 8 January 2007
©2007 American Meteorological Society
2
The English translation of this paragraph comes from Skoko
and Mokrović (1982).
3
The author of this note is presented as Professor H.
Mohorovičić. Because Mohorovičić had only one name—
Andrija—this leads us to conclude that initial H. is the result
of a typographical error.
694
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|
cloud movements during a 3-day period surrounding
this bora event.
4
The key signature of this short note, in addition to
a keen set of observations delivered in Mohorovičić’s
succinct writing style, is a diagram of the observed
clouds and the attendant circulation in a vertical
cross section over Bakar Bay parallel to the bora
flow (Fig. 2). The diagram shows the following
three major groups of clouds:
5
i) a stationary
cumulus cloud with the leading edge over Bakar
Bay, ii) fragmented stratocumulus clouds farther
aloft moving steadily in a strong northeast flow,
and iii) some smaller fragments of disappearing
cumulus coming down the mountain slope. The
large stationary cumulus cloud formed a line par-
allel to the coastal mountains, and “it extended as
far as could be seen [in the northwest–southeast
direction]
6
.” A thick cumulus cloud bank, a bora-cap
cloud, was present over the coastal mountains as
well [not part of the diagram in Fig. 2, but shown
in Mohorovičić (1891)], with some clear skies and
cirrus seen in between the two cloud lines through
the stratocumulus aloft. From the torn peaks and
edges of the mountain-cap cloud, smaller fragments
of cloud broke off and gradually disappeared in
the strongly marked descending motion down the
mountain slope. Over Bakar, near the leading edge
of the stationary cumulus cloud, smaller cumulus
clouds that formed at lower altitudes moved swiftly
(at the estimated 15–16 m s
–1
) before reaching
and merging into the large stationary cumulus.
Mohorovičić interpreted the continuous formation
of new clouds at the leading edge of the station-
ary cumulus mass as an indication of a sustained
updraft at that location. The downwind edge of
the stationary cumulus was also fringy, and the
small cloud fragments that were torn from it were
observed to disappear rapidly—a solid indication
to Mohorovičić of a strong downwelling current at
that end. The available surface observations from
Rijeka Bay, where a strong west-northwest wind was
reported (among other sources by a local steamer);
from Bakar, where weak and variable winds were
observed; and from the Kostrena side of Bakar Bay,
4
It was a common practice at that time to provide tabulated observational surface data as core scientific material.
5
The general cloud classification system Mohorovičić used was developed by Luke Howard.
6
Bracketed information within quotes is provided by the authors.
FIG. 2. Clouds and winds observed from Bakar (Buccari in Italian) on 18 Oct 1888 as
reported by Mohorovicˇic´ (1889a). The sea (Meerbusen v. Fiume, i.e., Rijeka Bay) is
on the left, the mountains on the right. Full arrows mark the observed winds, dashed
arrows are the winds deduced on dynamical grounds. The name of the journal in which
this figure was published in 1889 was Meteorologische Zeitschrift. The reason why the
older abbreviated name appears in this figure remains unclear.
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showing winds similar to those over the Rijeka
Bay, allowed Mohorovičić to close his diagram of
attendant circulation, revealing a large horizontally
oriented vortex. This cloud configuration persisted
from the morning hours through the late afternoon
(~1700 LT), with only a short break around local
noon, leading Mohorovičić (1889a) to conclude
7
It is impossible to imagine the existence of such a
permanent mass of cumulus unless on the assump-
tion of a rotary motion about a horizontal axis.
Mohorovičić speculated that the vortex formation
was probably due to the particular geometry of the
lee-slope terrain, which descends to the sea surface
in a series of terraces.
While likely unaware of the precedent he was
setting by providing a diagram of the circulation in
what appears to be an atmospheric rotor, Mohorovičić
was clearly aware that a large vortex with a horizontal
axis is a rather unusual atmospheric phenomenon,
opening his note by stating
We do not often read of a whirlwind with its axis
horizontal, and I have not been able to find any
notice of such a phenomenon in the Meteorologische
Zeitschrift. I think, therefore, that what I say may
be of interest.
Indeed, this short note by Mohorovičić was of
great interest to the journal editor Julius von Hann,
who appended it with his commentary on observa-
tions of stationary orographic clouds associated with
horizontal circulations in the lee of complex terrain
in various locations worldwide.
CONTEMPORANEOUS OBSERVATIONS
OF STATIONARY OROGRAPHIC CLOUDS:
ROLE OF THE NINETEENTH-CENTURY
JOURNAL EDITOR. Mohorovičić’s note on sta-
tionary orographic clouds in bora was published in
Meteorologische Zeitschrift,
8
which at that time was
the leading meteorological journal in continental
Europe. In its stature and rating this journal was
only equaled by the Quarterly Journal of the Royal
Meteorological Society (RMS) published in the United
Kingdom. Julius von Hann, the director of the
Zentral Anstalt für Meteorologie und Geodynamik
(ZAMG) in Vienna, Austria, served as the editor of
the Meteorologische Zeitschrift for more than 50 yr
(1866–1920). At the time when the peer review pro-
cess was not yet known,
9
the journal editor played a
pivotal role in determining the profile of a journal
by personally selecting the material for publication.
In the Meteorologische Zeitschrift, research articles
were mixed with short contributions, often dealing
with interesting observations, as was the case with
Mohorovičić’s note. Described as a “living encyclo-
pedia of his chosen [meteorological] science” (Ward
1922), Hann himself used to provide commentary and
notes to accompany journal contributions in which
he brought related material to the reader’s attention.
In the commentary following Mohorovičić’s note,
Hann lists observations of similar features observed
in South Africa, Greenland, and north of the United
Kingdom.
Perhaps the most interesting of these locations
is that of Cross Fell in Cumberland in the north of
England. The local wind there, known as helm,
10
has
a long history of documentation [Brunskill (1884)
contains appended earlier observations dating back
to 1777]. Similar to bora, this gusty, violent, easterly
cold wind is associated most often with bad weather
as illustrated by a common saying from Penrith, a
town located some 10 km west of Cross Fell (RMS
Committee 1885): “The Helm is on, we shall have no
good weather till the Helm is gone.” Characteristic
cloud formations associated with the helm wind
consist of a helm(et) cloud over the high peaks, a
horizontal slim bar of a cloud (helm bar) that forms
several miles to the west of and parallel to the moun-
tains (with sometimes four of five of these bars being
present downwind of Cross Fell), and a gap with clear
skies in between (Fig. 3). The diagram in Fig. 3 was
published in Marriott (1889), which is the full report
to the RMS “Helm Wind Inquiry,” which contains the
translation to English of all of Mohorovičić’s (1889a)
Meteorologische Zeitschrift note.
11
7
The English translation comes from Marriott (1889).
8
Up to volume 18 (1883), the name of this journal was Zeitschrift der Österreichischen Gesellschaft für Meteorologie or abbrevi-
ated Zeitschrift für Meteorologie. In subsequent volumes, the journal was renamed the Meteorologische Zeitschrift, with the
change of name coinciding with the Deutsche Meteorologische Gesellschaft joining the effort of journal publication.
9
This touchstone of modern scientific method has been in place only since the middle of the twentieth century.
10
The name “helm wind” most likely derives from the helmet-looking cloud that forms over Cross Fell during these events.
11
An earlier version of this diagram, which is almost identical to the one in Fig. 3, except for the reversed-flow branch under-
neath the bar opposing the helm wind, was published in Marriott (1886).
696
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That Hann was not just familiar with unusual
cloud formations associated with the helm wind but
also quite intrigued by them is clear from his note
in the discussion section of Brunskill (1884). There,
as in the commentary to Mohorovičić’s note, Hann
(an honorable member of the Royal Meteorological
Society) points to a similarity between the helm
cloud formations and those in the flow past Table
Mountain in South Africa (Herschel 1862) and
over the center of the Ivigtut Fjord in southwest
Greenland (Fritz 1883). He also offers a possible ex-
planation for the helm cloud and helm bar as being
part of a sinusoidal airflow response to an isolated
mountain, and suggests that, perhaps, in the case of
helm wind there are vortices with horizontal axes.
“A sketch, no matter how rough,” summarizing all
the essential elements of this phenomenon with
respect to the local terrain, “would be of great use,”
states Hann. Given his statement of need for the
diagram that shows all aspects of airflow and clouds
in relation to the local terrain and his hypothesis
about vortices with horizontal axes, we can only
imagine his delight in seeing such a diagram and
reading the conjectures in Mohorovičić’s (1889a)
note, prompting him to publish these observa-
tions and his commentary in the Meteorologische
Zeitschrift.
MOHOROVIC
ˇ
IC
´
—
AN ALL-AROUND
GEOPHYSICIST.
Who was Andrija
Mohorovicˇ ic´? Andrija
Mohorovičić was born
on 23 January 1857 in
Volosko near Opatija,
a coastal resort town in
Croatia, then part of the
Austrian (Habsburg)
Empire (Skoko and
Mokrović 1982). After
graduating from the
high school (gymna-
sium) in Rijeka in 1875, Mohorovičić enrolled in the
study of physics and mathematics at the University
of Prague. There he attended classes offered by Ernst
Mach, the famous physicist and philosopher who sub-
jected classical mechanics to thorough criticism, and
Heinrich Durège, a well-known mathematician with
a particular interest in complex analysis and elliptical
functions. Following graduation from the University
of Prague, Mohorovičić returned to Croatia and
taught at high schools in Zagreb and Osijek, but
finally settled in 1882 as a lecturer of mathematics,
physics, and meteorology at the Royal Nautical School
in Bakar, in close proximity to his birthplace. As
already mentioned, in Bakar he started the research
on clouds and related air motion, which led to his first
scientific publications (Mohorovičić 1888, 1889a,b,c,
1891)
12
and, eventually, to the doctoral thesis defended
at the University of Zagreb in 1893.
In 1892 Mohorovičić succeeded Ivan Stožir as the
head of the Meteorological Observatory in Zagreb
(Fig. 4) and remained there until his retirement
30 yr later. During this period he expanded work
at the observatory and gradually added to it new
components—seismology, geomagnetism, and time
keeping
13
—so that the observatory was renamed
the Geophysical Institute in 1921.
14
Moreover, he
introduced geophysical courses at the University of
12
As the capital of the Austro-Hungarian Empire, as well as of its predecessor the Austrian Empire, Vienna was the most impor-
tant center of politics and science in Central Europe at that time. It is not surprising then to find Mohorovičić, an ambitious
scientist from Croatia who was educated in Bohemia (Prague), both of which were parts of the Austro-Hungarian Empire,
to seek recognition by publishing in the most prominent journal in his field in continental Europe, published in Vienna.
13
Mohorovičić had introduced observations of star passage through the meridian using a passage instrument and, later, had
initiated synchronization of the observatory clocks utilizing the time coincidence signal received from an astronomical
observatory. The clocks he maintained were used to time stamp the data collected at the observatory, but also to provide
information on accurate time to the public.
14
Today, the Geophysical Institute in Zagreb, which carries his name, continues the tradition of geophysical research in a broader
sense, including the solid earth, oceans, and atmosphere, within the Department of Geophysics at the University of Zagreb.
FIG. 3. Airflow and clouds in helm wind of Cross Fell (England). (From Marriott
1889.)
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Zagreb in the 1894/95 academic year and taught them
by himself for over more than two decades. After
arriving at the observatory, Mohorovičić continued
with meteorological research. His published papers
from that period cover such diverse topics as a whirl-
wind (tornado) observed in the continental part of
Croatia, the climate of Zagreb, and the decrease of
air temperature with height. Around the turn of the
century, however, he switched from meteorology to
seismology and soon arrived at his most important
discovery.
While analyzing seismograms of the earthquake
near Zagreb that occurred on 8 October 1909,
Mohorovičić noticed that at epicenter distances
ranging from 300 to 720 km two longitudinal and
two transverse waves were recorded, and that at other
locations only one longitudinal and one transverse
wave were observed. With the flash of a genius he con-
cluded that, in addition to a continuous increase in the
speed of seismic waves with depth, the interpretation
these observations demanded is that of the existence
of a discontinuity where the waves are reflected and
refracted. By applying a simple model he determined
the depth of the discontinuity as well as the speed of
the seismic waves above and below it. The existence
of the surface that separates the Earth’s crust from
the mantle was thus demonstrated
for the first time (Mohorovičić
1910). After publishing the seminal
finding, Mohorovičić continued to
do important work in seismology
by proposing construction of a new
seismograph, developing an original
method for the location of epicen-
ters, constructing reliable travel-time
tables for distant earthquakes, and
studying the response of buildings
to earthquakes. Mohorovičić’s work
in seismology established him as one
of the leading Earth scientists of all
times. He died on 18 December 1936
in Zagreb. Today, the discontinuity
he discovered is named after him
(the Mohorovičić discontinuity or
MOHO), as is a crater on the moon
and asteroid 8422.
Mohorovicˇic´’s scientific legacy. Obvi-
ously, Mohorovičić was scientifically
active in two fields of geoscience
research: in meteorology until his
40s and in seismology subsequently,
with almost no overlap of the two
sets of activities. Many of his biographers assumed
implicitly, and some stated explicitly (e.g., Maksić
1960), that while both lines of research were stimu-
lated by regional phenomena, they differed in their
impact; whereas the seismological work influenced
the development of Earth science worldwide, the
meteorological work was only relevant regionally.
The truth, however, is more complex.
As we have seen, the note in which he describes
rotary motion of the air about a horizontal axis
(Mohorovičić 1889a) was translated into English
and published in the same year in the Quarterly
Journal of the Royal Meteorological Society (Marriott
1889). The note was subsequently cited in some of
the most influential meteorological textbooks of the
time, for example, in those published by Hann (1901;
and later editions) and Wegener (1911; and a later
edition). This note is also cited in seminal papers on
aerial observations of mountain lee waves (Küttner
1938, 1939). In his review of early observations of
stationary clouds and circulations on the lee side of
mountains, Kuettner
15
cites Mohorovičić (1889a) and
FIG. 4. Hitherto unpublished picture showing (from right to left)
Andrija Mohorovicˇic´, Spas Vatzov (1856–1928, founder of the Bulgarian
Meteorological Service), and Ivan Stožir (1834–1908, founder of the
Zagreb Meteorological Observatory and Mohorovicˇic´’s predecessor at
the observatory). The picture was taken in Zagreb in the 1890s, a few
years after Mohorovicˇic´ had performed observations at Bakar.
15
Joachim Küttner changed the spelling of his last name to
Kuettner after emigrating to the United States after World
War II.
698
MAY 2007
|
his diagram of a “Bora Roller,”
16
stating a similarity
with circulations and stationary clouds observed in
the lee of Cross Fell, Greenland, and later observa-
tional accounts in the lee of Riesengebirge.
17
After this time, Mohorovičić’s note disappears from
international literature; for example, Mohorovičić
was neither cited in Queney et al. (1960) in their
overview of studies addressing airflow over moun-
tains, nor by Yoshino (1976) in the only monograph
published to date on the bora wind. Thus, by the time
Mohorovičić became subject of biographical research,
he was no longer cited in widespread meteorological
publications,
18
although his work was by then firmly
incorporated into the existing knowledge on atmo-
spheric rotors.
While Mohorovičić was clearly a pioneer of atmo-
spheric rotor research, this field of research was slow
in developing and his direct contribution gradually
faded away. Instead, much later observational work by
Kuettner from the 1930s in the lee of the Riesengebirge
is remembered today—the work that had directly mo-
tivated and led to subsequent research on mountain
waves and rotors,
19
including both theoretical and
further observational studies (Grubišić and Lewis
2004). On the other hand, Mohorovičić’s pioneering
work in seismology had a strong, immediate impact,
and his contribution to this field is regarded as seminal.
Although in both cases he showed an ability to do first-
class research, it was only in seismology that his skill in
combining empirical and theoretical approaches would
be fully employed. His scientific approach, however,
makes it clear that objective, reasoned thinking in the
presence of careful observations remains the hallmark
of discovery in science.
OUTLOOK. From the time of Mohorovičić to today,
illustrations of atmospheric rotors remain dominated
by two-dimensional diagrams indicating the presence
of anticyclonic rotary motion underneath the crests
of mountain lee waves in a stable airstream over a
mountain ridge (Doyle and Durran 2004). Paralleling
the advancements in understanding of the rotor phe-
nomenon, these diagrams have morphed from early
attempts to grasp an unusual atmospheric behavior
using sharp observations and thoughtful deduc-
tions to schematic diagrams representing concep-
tual models of time-averaged behavior of turbulent
rotors. Very detailed observations by a multitude of
sophisticated airborne and ground-based, in situ,
and remote sensors deployed in the recently com-
pleted Terrain-Induced Rotor Experiment (T-REX;
Grubišić et al. 2004), combined with the power of
high-resolution numerical simulations, offer a unique
and an unprecedented opportunity to obtain a more
realistic depiction of the spatially and temporally
varying terrain-induced rotors.
From those early days of Mohorovičić’s keen
deductions on rotary motion about a horizontal
axis, unraveling the mysteries of atmospheric
rotors continues to the present day. Continued also
is the effort to understand the complex mesoscale
structure of the bora flow. Significant progress
has been achieved with aerial observations of bora
in the Alpine Experiment (ALPEX; Smith 1987)
and the Mesoscale Alpine Programme (MAP;
Grubišić 2004), which have, respectively, offered a
two-dimensional view of bora as the hydraulically
controlled severe downslope wind
20
and revealed
its three-dimensional variation along the coastal
mountain range with a number of individual bora
jets and wakes within the Dinaric Alps wake. Today,
availability of high temporal and spatial resolution
observations and high-resolution numerical simula-
tions offers new possibilities for investigating small-
16
This was called the “Bora Walze” in the original German publication (Küttner 1938).
17
One of those observations that has made a particularly strong impression on Kuettner is that of H. Koschmieder, the well-
known dynamicist, who had photographed some rotor clouds and had subsequently carried out a thorough analysis of these
cloud observations, similar to what Mohorovičić undertook decades earlier with a different set of observations on clouds, to
obtain an estimate of a 10 m s
–1
updraft at the leading edge of the rotor (Koschmieder 1920).
18
Even in Croatia, where Mohorovičić’s note has been regularly cited from at least the 1930s, his diagram of a bora-related rotor
seemingly fell into oblivion, probably because it was not published along with the text, but in an appendix to the 1889 issue of
the Meteorologische Zeitschrift. The diagram was rediscovered in 2005, which prompted the present study of Mohorovičić’s
early contributions to meteorology.
19
Subsequent observational documentation of atmospheric rotors is closely tied to observations of mountain waves. This is not
surprising given that the earliest aerial documentation of mountain lee waves was done with gliders, which had to pass through
turbulent rotors on their way to smooth wave updrafts (Kuettner and Hertenstein 2002; Grubišić and Lewis 2004).
20
Incidentally, elongated cumulus cloud lines downwind of and parallel to the coastal mountain range are shown in Smith
(1987), who refers to them as “turbulent lee clouds” or “lee-side ‘jump’ or ‘rotor’ clouds.” In T-REX terminology, this likely
represents a reference to the hypothesized type II or a hydraulic jump rotor (Grubišić et al. 2004).
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MAY 2007AMERICAN METEOROLOGICAL SOCIETY
|
scale structures within the bora flow. And, thus, it
is not surprising to see studies of bora rotors emerge
again (Gohm and Mayr 2005), nearly 120 years after
Mohorovičić discovered them.
ACKNOWLEDGMENTS. The authors are indebted
to Joachim Kuettner for his thoughts on early research on
rotors. John Lewis is thanked for his careful review of the
early version of the manuscript and thoughtful comments.
We thank our two reviewers and BAMS History Editor
James Flemming for many constructive comments that have
improved our presentation. We thank also Branka Penzar for
her translation of early Mohorovičić’s papers from German
to Croatian, and Zoran Pasarić for providing data for Fig. 1.
Haraldur Olafsson’s and Idar Barstad’s efforts in providing
us with a copy of the 1882 Meteorologiske Aaborg are much
appreciated. John Ford (DRI librarian) is thanked for valu-
able technical assistance. Vanda Grubišić’s work on this
project has been supported in part by the National Science
Foundation, Division of Atmospheric Sciences, Grants
ATM-0242886 and ATM-0524891. Mirko Orlić has received
support from the Ministry of Science, Education and Sports
of the Republic of Croatia.
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