ArticlePDF Available

A positive trend in western Antarctic Peninsula precipitation over the last 50 years reflecting regional and Antarctic-wide atmospheric circulation changes

Authors:

Abstract and Figures

In situ observations of precipitation days (days when snow or rain was reported in routine synoptic observations) from Faraday/Vernadsky station on the western side of the Antarctic Peninsula, and fields from the 40 year European Centre for Medium-Range Weather Forecasts re-analysis (ERA-40) project are used to investigate precipitation and atmospheric circulation changes around the Antarctic Peninsula. It is shown that the number of precipitation days is a good proxy for mean sea-level pressure (MSLP) over the Amundsen-Bellingshausen Sea. The annual total of precipitation days at the station has been increasing at a statistically significant rate of +12.4 days decade−1 since the early 1950s, with the greatest increase taking place during the summer and autumn. This is the time of year when the Southern Annular Mode (SAM) has experienced its greatest shift to a positive phase, with MSLP values decreasing in the Antarctic coastal zone. The lower pressures in the circumpolar trough have resulted in greater ascent and increased precipitation at Faraday/Vernadsky.
Content may be subject to copyright.
A positive trend in western Antarctic Peninsula precipitation
over the last 50 years reflecting regional and Antarctic-wide
atmospheric circulation changes
John TURNER, Tom LACHLAN-COPE, Steve COLWELL, Gareth J. MARSHALL
British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge CB3 0ET, UK
E-mail: j.turner@bas.ac.uk
ABSTRACT. In situ observations of precipitation days (days when snow or rain was reported in routine
synoptic observations) from Faraday/Vernadsky station on the western side of the Antarctic Peninsula,
and fields from the 40 year European Centre for Medium-Range Weather Forecasts re-analysis (ERA-40)
project are used to investigate precipitation and atmospheric circulation changes around the Antarctic
Peninsula. It is shown that the number of precipitation days is a good proxy for mean sea-level pressure
(MSLP) over the Amundsen–Bellingshausen Sea. The annual total of precipitation days at the station has
been increasing at a statistically significant rate of +12.4days decade
–1
since the early 1950s, with the
greatest increase taking place during the summer and autumn. This is the time of year when the
Southern Annular Mode (SAM) has experienced its greatest shift to a positive phase, with MSLP values
decreasing in the Antarctic coastal zone. The lower pressures in the circumpolar trough have resulted in
greater ascent and increased precipitation at Faraday/Vernadsky.
INTRODUCTION
The Antarctic Peninsula is one of the most climatologically
interesting areas of the Antarctic. Over the last 50 years,
annual mean near-surface air temperatures on the western
side of the peninsula have risen by up to 0.68C decade
–1
(statistically significant at less than the 1% level), as large a
warming as anywhere on Earth (King and others, 2003). In
addition, a number of floating ice shelves on both the
eastern and western sides of the peninsula have disinte-
grated (Doake and Vaughan, 1991), and sea-ice extent over
the Bellingshausen Sea has decreased (Zwally and others,
2002). However, we have little knowledge of how pre-
cipitation has changed over the last 50 years.
Precipitation is extremely difficult to measure at the
research stations because of blowing-snow effects, which
can cause snow to be added to or removed from snow
gauges in the absence of precipitation, once the wind speed
exceeds about 10 m s
–1
. Some Antarctic Peninsula stations
have used snow gauges, but the results have not been
satisfactory. A more commonly used procedure has been to
measure net surface mass balance (for a definition of this
term and its relationship to precipitation and accumulation
see Turner and others (2002)) at the stations or remote sites
using a single stake or array of stakes. This method works
well at interior locations on the continent where there is
little blowing snow and the orography is fairly flat.
However, in the coastal region, where the winds are
frequently strong, stake measurements are of less value,
with the greatest increases observed often being associated
with strong wind events rather than heavy precipitation
(Turner and others, 1995).
Estimates of mass balance from ice cores and pits have
proved particularly valuable and have allowed the produc-
tion of maps of mean mass balance for the whole continent
(Bromwich, 1988). With careful analysis, ice cores can yield
annual mean accumulation, although the wind can mix
large amounts of snow on the surface, thus hindering the
identification of annual layers.
Atmospheric models are a powerful tool for examining
the precipitation and precipitation–evaporation (PE) over
the continent, providing data across regions where there are
no in situ observations. Model output has been used to
consider the temporal and spatial variability of these
quantities across the Antarctic (Turner and others, 1999)
and how precipitation may change in coming decades
(Budd and Simmonds, 1991). However, the relatively coarse
horizontal resolution of these models has meant that their
performance has been poor in areas of complex orography.
Recent experiments with high-resolution, limited-area mod-
els have had more success in the Antarctic Peninsula region
(Van Lipzig and others, 2004), but this is still a challenging
area for models.
Atmospheric models have been used as part of data
assimilation schemes incorporating in situ and satellite
observations to produce meteorological analyses. Recently,
some of the major meteorological agencies have re-
analyzed all the observational data using current analysis
schemes to produce the so-called re-analysis datasets
(Gibson and others, 1996; Kalnay and others, 1996). These
provide surface and upper-air meteorological analysis fields
at the four main synoptic hours each day, extending back to
the 1950s. As discussed below, these fields tend to be rather
poor at high latitudes in the pre-satellite era, but never-
theless are an extremely important tool for investigating
recent climate variability.
One final form of data that has been used to examine
precipitation variability and change is the observations of
precipitation occurrence from the stations, made as part of
the synoptic reporting programmes (Turner and Colwell,
1995). These observations cannot provide information on
the amount of precipitation that has fallen, but can yield
valuable data on precipitation frequency and the relative
occurrence of snow and rain in the Antarctic.
In this paper, we investigate the changes in precipitation
that have taken place around the Antarctic Peninsula over
the last 50 years, using the European Centre for Medium-
Range Weather Forecasts (ECMWF) re-analysis (ERA) data
Annals of Glaciology 41 2005 85
and observations from Faraday/Vernadsky station (65.48S,
64.48W). The data on precipitation days provide one of the
few reliable meteorological datasets on precipitation ex-
tending back to the 1950s. We have used this time series in
conjunction with the re-analysis fields to infer atmospheric
circulation variability and change in the pre-satellite era.
DATA AVAILABILITY AND CHARACTERISTICS
The re-analysis fields
The re-analysis fields produced by the ECMWF provide one
of the most reliable and consistent series of surface and
upper-air meteorological analyses available. Fields are
available every 6hours and have been produced with a
current, state-of-the-art data assimilation scheme that has
been run using the historical record of in situ meteorological
observations and satellite data. The fields cover the 44year
period 1957–2001, although the project is still known as
ERA-40.
In the pre-satellite era the only upper-air meteorological
data over the Southern Ocean were from widely spaced
island stations, while surface conditions had to be analyzed
from ship reports, which tended to come mainly from along
the major shipping lanes. It is therefore not surprising that
the quality of the ERA-40 fields around the Antarctic is poor
in the early years. Marshall (2003) compared the ERA-40
fields against the available in situ observations and
concluded that the mean sea-level pressure (MSLP) and
upper-level height fields can be used with confidence as far
back as 1973. However, he also noted that the fields from
over the Southern Ocean contain considerable errors in the
late 1950s and early 1960s. This makes them unsuitable for
investigation of atmospheric conditions around the Antarctic
Peninsula during this period. Figure 1 shows the differences
between the monthly mean MSLP data from Faraday and
ERA-40 at the location of the station, and confirms that from
1979 the Faraday MSLP is well represented in ERA-40,
although there is a small negative trend. From 1974 the
satellite temperature soundings from the Vertical Tempera-
ture Profile Radiometer were included in the analysis
system, so differences were usually limited to several hPa;
but before this, as would be expected given the lack of data,
there are very large differences between the Faraday data
and ERA-40. The Faraday observations themselves were
assimilated, but since the model fields to the west are
essentially climatological there is a mismatch between
conditions at Faraday and further west, hence the difficulty
of fitting the station data to the analysis scheme. It should
also be noted that the ERA MSLP data have a positive bias of
about 3 hPa at the location of Faraday in the period before
about 1970.
In this study, we have used the ERA-40 precipitation fields
and determined the number of precipitation days at the
location of Faraday. We have taken a precipitation day to be
any day with >0.1 mm of precipitation. This amount was
chosen to exclude the extremely small amounts of pre-
cipitation generated within the model by numerical in-
stabilities.
Although a number of studies of the quality of the ERA-40
MSLP and height fields have been carried out, it is unclear
how accurate the precipitation data, and especially the time
series of precipitation days, are for the Antarctic. Figure 2
shows the annual totals of the number of precipitation days
at Faraday and in ERA-40 at the location of Faraday. It shows
that in the period up to 1983 there was little correlation
between the two time series, as a result of the lack of
humidity data being assimilated into the analysis system.
However, from 1984 onwards there is good agreement
between the number of ERA and Faraday precipitation days
(correlation coefficient 0.8), indicating that the ERA analysis
system accurately simulates the hydrological cycle around
the Antarctic Peninsula. In the following we have there-
fore only used the ERA precipitation data over the period
1984–99.
Precipitation-day information
For this study we have used the time series of the number of
precipitation days occurring each month at Faraday/
Vernadsky station. We have defined a precipitation day as
any day when there was at least one report of snow, rain,
drizzle, hail or a shower in the past or present synoptic
weather reports. Reports of blowing snow and clear-sky
precipitation (‘diamond dust’) were not regarded as pre-
cipitation reports, and were therefore ignored.
The meteorological observing programme at the station
began in 1947, but for the first 3 years the weather reports
were made at different frequencies, so the number of
precipitation days is lower than in later years. A similar
marked drop in the number of precipitation days occurred
after 2000, indicating another change in observing practice.
Fig. 1. Differences between the monthly mean MSLP data from
Faraday and ERA-40 at the location of the station.
Fig. 2. Annual totals of the number of precipitation days at Faraday
and in ERA-40 at the location of Faraday.
Turner and others: Positive trend in western Antarctic Peninsula precipitation86
In the following we have therefore only used Faraday/
Vernadsky precipitation-day data for the period 1950–99,
when regular 3 hourly synoptic reports were made.
Although the synoptic reports provide information on
precipitation intensity, examination of the time series of
these observations shows marked jumps in the frequency
with which particular intensities, slight, moderate or heavy,
are reported, especially when there was a change of
observer. Although the World Meteorological Organization
guidelines on making observations provide information on
how to estimate snowfall intensity from the reduction in
visibility, this is still a very subjective process and dependent
on the observer. In this study we have therefore not used the
observations of precipitation intensity made by the ob-
servers. However, the question arises as to how the statistics
on precipitation days relate to the actual amount of
precipitation that fell. Figure 3 shows a scatter diagram of
the number of precipitation days at Faraday vs the monthly
totals of precipitation from ERA-40. The data are for all
months over the period 1984–99. It can be seen in Figure 3
that for any particular number of Faraday precipitation days
during a month there is a broad spread of ERA-40
precipitation amounts, but this is to be expected, as a
precipitation day can range from a few snowflakes to many
hours of heavy snowfall. However, Figure 3 does illustrate
the general increase in precipitation amount that is found
with a greater number of precipitation days in a month.
A further illustration of the value of precipitation-day data
from Faraday can be seen in Figure 4, which shows a
comparison of monthly precipitation-day totals from the
station and ERA-40. There is some scatter since the
precipitation-day values are produced by such different
means, but the correlation between these two datasets
indicates that the model reasonably represents the variability
of this quantity at the location of the station. The smaller
number of precipitation days in the Faraday record is to be
expected, as the observer does not watch the weather
continuously and observing conditions become difficult
during the long, dark winter nights.
TRENDS IN THE FARADAY/VERNADSKY RECORD
OF PRECIPITATION DAYS
Figure 5 shows the time series of the total number of
precipitation days over the year from Faraday/Vernadsky,
along with the annual mean temperature. It can be seen that
both quantities have increased over the 50year period:
temperatures at a rate of +0.568C decade
–1
and precipitation
days at a rate of +12.4decade
–1
, with both increases being
statistically significant at less than the 1% level. However,
there is only a relatively low correlation of 0.25 between the
two datasets, due to the different factors determining these
two quantities in a particular year and the timescales on
which they operate.
Temperatures at the station, especially during the winter,
are highly correlated with the sea-ice extent to the west of the
Antarctic Peninsula (King, 1994), years of extensive (little) sea
ice being characterized by low (high) temperatures. The sea-
ice extent in a particular year is heavily influenced by the
frequency of winds from the north or south, with northerlies
(southerlies) inhibiting (aiding) the advance of the ice. The
Fig. 3. Faraday precipitation days vs total monthly precipitation
from ERA-40. The data are for all months during the period
1984–99.
Fig. 4. Comparison of monthly totals of precipitation days from
Faraday and ERA-40. The data are for all months during the period
1984–99.
Fig. 5. Faraday/Vernadsky annual mean temperature and total
number of precipitation days, 1951–99.
Turner and others: Positive trend in western Antarctic Peninsula precipitation 87
winds affecting the area are in turn determined by the
synoptic conditions over the Amundsen–Bellingshausen Sea
(ABS) with low- (high-)pressure systems resulting in generally
northerly (southerly) flow. However, the sea ice does not
respond instantaneously to changes in the wind direction and
it has been shown that sea-ice anomalies, once created, can
last for long periods (King, 1994).
The number of precipitation days at Faraday is dictated to
a large extent by the air masses that arrive at the station:
moist, north-to-northwesterly (dry, southerly) air masses
result in a large (small) number of precipitation days (Turner
and others, 1995). So, as with sea-ice extent, the winds over
a year will influence the number of precipitation days
recorded at Faraday. But this quantity will respond almost
immediately to changes in wind direction and be more of a
direct measure of air-mass origin, and hence depression
activity over the ABS, than sea-ice extent or temperature.
This can be seen in Figure 6, which shows the monthly mean
number of precipitation days recorded throughout the year
at Faraday for the period 1951–99. This figure shows that the
greatest number of precipitation days occurs in the spring
and autumn, in association with the peaks in depression
activity as the circumpolar trough moves south and
intensifies as a result of the semi-annual oscillation.
Examination of the standard deviation of the number of
precipitation days throughout the year (not shown) does not
suggest any seasonal signal, which would be expected if the
quantity were being heavily influenced by the sea-ice extent
(as occurs with the temperature record) which has its largest
variability during the winter.
The close association between the number of precipita-
tion days at Faraday and depression activity over the ABS
can be further appreciated by noting that one of the largest
totals of precipitation days in the record occurs in 1979
(Fig. 2). This was the year of the First GARP (Global
Atmospheric Research Programme) Global Experiment,
when Physick (1981) noted that there were many deep
depressions and low MSLP values in the circumpolar trough.
The seasonal trends in the Faraday mean temperatures
and number of precipitation days are shown in Table 1. Here
it can be seen that the temperature trend has a clear
maximum in the winter, when it has almost double the
magnitude of any other season, then rapidly decreases
towards the spring. On the other hand, the trend in the
number of precipitation days is largest during the autumn,
although as can be seen in Figure 6, it varies considerably
over the year and does not have the smooth form of the
temperature trend as shown in King and others (2003).
RELATIONSHIP BETWEEN ATMOSPHERIC
CIRCULATION AND NUMBER OF PRECIPITATION
DAYS
In order to gain insight into the relationship between the
number of precipitation days at Faraday and the broad-scale
atmospheric circulation, the annual totals of precipitation
days from the station and the ERA-40 data at the location of
Faraday were correlated with the annual mean values of
MSLP across the whole of the Southern Hemisphere (Fig. 7).
The two fields are very similar considering the means by
which the number of precipitation days was computed using
the in situ data and ERA-40 fields. The greatest negative
correlations (a large number of precipitation days associated
with low MSLP) are over the ABS where values of –0.6 to
–0.8 are found with both the ERA and Faraday data,
although the area of correlation in this range is larger in
ERA. This picture of low MSLP over the ABS during periods
of greater number of precipitation events at Faraday is
consistent with our understanding of the means by which
warm air masses can arrive at the station. Case studies of the
arrival of different types of air mass on the western side of
the Antarctic Peninsula have shown that the location of the
low-pressure centres over the ABS is critical in determining
whether the area is affected by air of warm, mid-latitude or
cold Antarctic origin (Marshall and others, 1998). The
location of the highest values of negative correlation in the
southeastern corner of the Bellingshausen Sea is just about
optimal in ensuring that air arriving at Faraday has a long
fetch over the relatively warm Southern Ocean.
Around the rest of the Antarctic coastal zone the
correlations are quite low, indicating that over the year as
a whole it is synoptic activity over the ABS that mainly
determines the number of precipitation days at Faraday and
that conditions across the rest of the continent play a
relatively small role. However, it should be noted that
determining MSLP under the high-Antarctic orography has
little physical meaning, and correlations across the higher
parts of the Antarctic should be ignored.
Some areas of large positive correlation are found north
of the Antarctic in the Western Hemisphere, with values
from the ERA data being in excess of 0.8 over the South
Fig. 6. Faraday/Vernadsky mean monthly number of precipitation
days and the trend of 1951–99.
Table 1. Mean data and trends for Faraday/Vernadsky station. Data are for 1951–99
Annual Summer
(Dec–Feb)
Autumn
(Mar–May)
Winter
(Jun–Aug)
Spring
(Sep–Nov)
Mean number of precipitation days 267.1 58.7 67.3 65.6 70.6
Trend in precipitation days (days decade
–1
) +12.4 +2.8 +3.9 +3.2 +1.9
Trend in surface temperature (8Cdecade
–1
) +0.56 +0.25 +0.60 +1.08 +0.28
Turner and others: Positive trend in western Antarctic Peninsula precipitation88
Atlantic. Again this is to be expected since there is often an
anticorrelation between mean MSLP values in the Antarctic
coastal region and the 50–608S zone (Marshall and King,
1998), depending on the storm tracks over the South Pacific.
Similar maps of correlation between precipitation days
and MSLP have been produced for each month of the year.
In several of the months the area of high correlation has a
circular or wavenumber-3 form, with correlation values in
excess of 0.6 being found around much of the Antarctic
coastal region. This is particularly the case in summer and
autumn, as can be seen from the January map shown in
Figure 8. In January there is still a regional maximum of
correlation in the southeastern Bellingshausen Sea, but
similar high correlation values are found around much of the
coast of East Antarctica. This pattern suggests that changes in
the number of precipitation days at Faraday during certain
months are linked to Antarctic-wide, as well as local
synoptic, forcing factors in the immediate ABS region.
Figure 8 also shows that in January there were areas of high,
positive correlation in the 40–608S zone, suggesting Ant-
arctic–mid-latitude linkages play a role in modulating the
Faraday precipitation.
During the second half of the year, the maximum
correlation is generally located in the southeastern Bellings-
hausen Sea, with low correlations around the rest of the
continent, suggesting that at this time of the year local
synoptic conditions have most influence on Faraday
precipitation.
DISCUSSION
The number of precipitation days as determined from the
Faraday synoptic observations is clearly a valuable measure
of meteorological conditions over the ABS. The close
agreement between the time series of this quantity from
the station and similar measures derived from ERA-40 in
recent years suggests that it is a reliable measure of the
precipitation falling throughout the day. The high correlation
between the Faraday total of precipitation days and ERA-40
MSLP over the ABS indicates that it can be used as a proxy of
surface pressure in this area.
The time series of the annual total of Faraday precipitation
days (Fig. 5) shows that this quantity increased at a
statistically significant rate from the early 1950s up to the
Fig. 8. The correlation of the January totals of precipitation days
from Faraday with the January mean values of MSLP from ERA-40.
Fig. 7. Maps showing the correlation of the annual totals of
precipitation days from Faraday (bottom) and the ERA-40 data at the
location of Faraday (top) with the annual mean values of MSLP from
ERA-40.
Turner and others: Positive trend in western Antarctic Peninsula precipitation 89
late 1970s and has been essentially unchanged since that
time. The trend varies considerably throughout the year, but
generally peaks during the first half of the year. The
essentially circular, or ‘annular’, nature of the precipita-
tion-day/MSLP correlation maps, along with the low-/high-
latitude out-of-phase relationship, points to the Southern
Annular Mode (SAM) playing a role. This is the principal
mode of variability in the atmospheric circulation of the
Southern Hemisphere extratropics and high latitudes, and
involves synchronous anomalies of opposite sign in Ant-
arctica and the mid-latitudes. Following Marshall (2003), the
SAM can be defined as:
SAM ¼P
40SP
65S,
where P
40Sand P
65Sare the normalized monthly zonal
MSLP at 408and 658S respectively.
In recent decades the SAM has entered a positive phase,
with decreasing pressures over the Antarctic and increasing
values in the mid-latitudes (Marshall, 2003). As shown in
Figure 9, the SAM has changed most during the first half of
the year. Clearly the trends in the SAM and the number of
precipitation days are not directly comparable, but the
annular form of the correlation maps and the large trends in
the SAM and precipitation data in the summer and autumn
both point to the SAM playing a role in the changing nature
of precipitation at Faraday.
It is interesting to consider how the changes in the SAM
could have resulted in more precipitation days on the
western side of the Antarctic Peninsula. The ABS is at the
latitude of the circumpolar trough, which is the belt of low
pressure around the continent between about 608and 708S.
It is present because of the large number of depressions in
this zone that have either developed just north of the
Antarctic or moved south from mid-latitudes. The fact that
pressures have decreased in the trough does not tell us
whether the number of depressions has increased or the
mean depth of the lows has decreased, with the number of
systems remaining constant. Either way, the ready supply of
moisture over the Southern Ocean coupled with lower
atmospheric pressures will result in greater dynamical lifting
and increased precipitation.
As discussed earlier, the temperature at Faraday has
increased most during the winter. Examination of the July
and August number of precipitation days for Faraday shows
that this quantity has increased since the 1950s, pointing to
lower pressures over the ABS. However, the SAM has
changed less in winter than in summer, suggesting that other
factors are responsible for the decrease in sea ice over the
ABS. During winter, the sea-ice edge is close to the latitude
of Faraday so that any changes in the depth or frequency of
synoptic-scale weather systems over the ABS will change the
northerly component of the wind, thus amplifying variations
in the air masses arriving at the station via the ice–
atmosphere feedback mechanism. However, further work,
especially using coupled atmosphere–ocean models, is
needed to fully explain the marked winter temperature
increase over the western Antarctic Peninsula.
It is difficult to compare the Faraday record of precipita-
tion days directly with glaciological measurements of
accumulation from the Antarctic Peninsula. Ice cores are a
powerful tool for investigating accumulation variability, but
must be collected from areas with no summer melt, and
there is considerable melt along the coastal strip of the
western Antarctic Peninsula where the stations are located.
However, ice cores collected in the southeastern part of the
peninsula and on James Ross Island near the tip of the
peninsula show accumulation increases over the second half
of the 20th century, reflecting the precipitation increase
suggested by the Faraday data.
CONCLUSIONS AND FURTHER WORK NEEDED
The time series of the number of precipitation days at
Faraday is a good proxy of the MSLP over the ABS and
suggests that pressures were higher over the ocean to the
west of the Antarctic Peninsula in the 1950s and 1960s. The
greatest increase in precipitation days has occurred during
the summer and autumn, and appears to be associated with
a change in the nature of the SAM. But the reasons for the
marked increase in winter near-surface temperature at
Faraday over the last 50 years are still not fully understood.
Further work is needed to understand why the SAM has
changed, and the results of this shift into a positive phase.
Automatic depression-tracking software needs to be run on
the ERA-40 fields to understand how the changes in the SAM
have altered the synoptic-scale weather systems in the area.
Has there been a change in the number of lows and/or in
their depth? And have there been changes in the ratio of
systems developing in the circumpolar trough and moving
south from mid-latitudes?
Model experiments also need to be carried out to
determine whether the small changes in the SAM during
winter could have influenced the depressions over the ABS
sufficiently to change the meridional component of the wind
to the point where the ice–atmosphere feedback mechanism
could have been responsible for the marked change in
surface temperature.
REFERENCES
Bromwich, D.H. 1988. Snowfall in high southern latitudes. Rev.
Geophys., 26(1), 149–168.
Budd, W.F. and I. Simmonds. 1991. The impact of global warming
on the Antarctic mass balance and global sea level. In Weller,
G., C.L. Wilson and B.A.B. Severin, eds. International Con-
ference on the Role of the Polar Regions in Global Change:
proceedings of a conference held June 11–15, 1990 at the
University of Alaska Fairbanks. Fairbanks, AK, University of
Alaska. Geophysical Institute/Center for Global Change and
Arctic System Research, 489–494.
Fig. 9. The monthly trends in the SAM and the number of Faraday
precipitation reports, 1958–99.
Turner and others: Positive trend in western Antarctic Peninsula precipitation90
Doake, C.S.M. and D.G. Vaughan. 1991. Rapid disintegration of
the Wordie Ice Shelf in response to atmospheric warming.
Nature, 350(6316), 328–330.
Gibson, J.K., A. Hernandez, P. Ka
˚llberg, A. Nomura, E. Serrano and
S. Uppala. 1996. Current status of the ECMWF re-analysis project.
In Proceedings of the Seventh Conference on Global Change
Studies, Boston, MA, American Meteorological Society,112–115.
Kalnay, E. and 21 others. 1996. The NCEP/NCAR 40-year reanalysis
project. Bull. Am. Meteorol. Soc., 77(3), 437–471.
King, J.C. 1994. Recent climate variability in the vicinity of the
Antarctic Peninsula. Int. J. Climatol., 14(4), 357–369.
King, J.C., J. Turner, G.J. Marshall, W.M. Connolley and
T.A. Lachlan-Cope. 2003. Antarctic Peninsula climate variability
and its causes as revealed by analysis of instrumental records. In
Domack, E.W., A. Burnett, A. Leventer, P. Conley, M. Kirby and
R. Bindschadler, eds. Antarctic Peninsula climate variability:
a historical and paleoenvironmental perspective. Washington,
DC, American Geophysical Union, 17–30.
Marshall, G. J. 2003. Trends in the Southern Annular Mode from
observations and reanalyses. J. Climate, 16(24), 4134–4143.
Marshall, G.J. and J.C. King. 1998. Southern Hemisphere circula-
tion anomalies associated with extreme Antarctic Peninsula
winter temperatures. Geophys. Res. Lett., 25(13), 2437–2440.
Marshall, G.J., J. Turner and W.D. Miners. 1998. Interpreting recent
accumulation records through an understanding of the regional
synoptic climatology: an example from the southern Antarctic
Peninsula. Ann. Glaciol., 27, 610–616.
Physick, W.L. 1981. Winter depression tracks and climatological jet
streams in the Southern Hemisphere during the FGGE year. QJR
Meteorol. Soc., 107(454), 883–898.
Turner, J. and S.R. Colwell. 1995. Temporal variability of precipita-
tion over the western Antarctic Peninsula. In Proceedings of the
Fourth Conference on Polar Meteorology and Oceanography,15
January 1995. Boston, MA, American Meteorological Society,
113–116.
Turner, J., T.A. Lachlan-Cope, J.P. Thomas and S.R. Colwell. 1995.
The synoptic origins of precipitation over the Antarctic
Peninsula. Antarct. Sci., 7(3), 327–337.
Turner, J., W.M. Connolley, S. Leonard, G.J. Marshall and
D.G. Vaughan. 1999. Spatial and temporal variability of net
snow accumulation over the Antarctic from ECMWF re-analysis
project data. Int. J. Climatol., 19(7), 697–724.
Turner, J., T.A. Lachlan-Cope, G.J. Marshall, E.M. Morris,
R. Mulvaney and W. Winter. 2002. Spatial variability of
Antarctic Peninsula net surface mass balance. J. Geophys.
Res., 107(D13), 4173. (10.1029/2001JD000755.)
Van Lipzig, N.P.M., J.C. King, T. Lachlan-Cope and M.R. van
den Broeke. 2004. Precipitation, sublimation, and snow drift
in the Antarctic Peninsula region from a regional atmospheric
model. J. Geophys. Res., 109(D24), D24106. (10.1029/
2004JD004701.)
Zwally, H.J., J.C. Comiso, C.L. Parkinson, D.J. Cavalieri and
P. Gloersen. 2002. Variability of Antarctic sea ice 1979–1998.
J. Geophys. Res., 107(C5), 3041. (10.1029/2000JC000733.)
Turner and others: Positive trend in western Antarctic Peninsula precipitation 91
... The enhanced dynamic mass losses and the increased surface melt discussed so far do not necessarily imply a decrease in the overall mass balance, as they could be partly or totally 1.3 State of the art compensated by an increased accumulation rate. In fact, there is much evidence, mostly observational, indicating such an increase in the western coast of the AP: 1) the annual total of precipitation days at Faraday/Vernadsky station increased at a rate of +12.4 days/decade since the early 1950s, reaching a total number of 270-290 precipitation days per year during the last decade analyzed by Turner et al. (2005b); 2) Miles et al. (2008) have pointed out an increasing trend in winter (June, July, August) accumulation in the north-western AP, observed in ERA-40 reanalysis data; 3) ice cores from the northern (Aristarain et al., 2004), southern (Frey et al., 2006) and south-western (Thomas et al., 2008) parts of the AP, show that the accumulation rate increased during the second half of the 20th century. In particular, the Gomez ice core analyzed in Thomas et al. (2008) reveals a doubling of accumulation since the 1850s, with an increasing trend that began in the ∼1930s and accelerated in the mid-1970s, which is the largest increase observed across the region. ...
... Regarding the attribution of the observed increases in accumulation, Turner et al. (2005b) have associated the positive trends in precipitation on the western side of the Antarctic Peninsula with a deepening of the circumpolar pressure trough, which has improved the ascent of air masses and precipitation in the region. This is consistent with the evaluation of the relationships between the accumulation record from AP ice cores and the primary modes of atmospheric circulation variability. ...
... As a result, the net specific summer surface losses are nearly equal in both regions. In parallel with the decreased summer melting during the early 21st century, a slight accumulation increase was observed during this period and attributed to a deepening of the circumpolar pressure trough, bringing a larger amount of moisture to the western part of the AP (Turner et al., 2005b). ...
Thesis
Full-text available
The glaciers on the Antarctic Peninsula (AP) play an important role in ocean dynamics, global climate, and ecology. During recent decades, the AP has become an important contributor to sea-level rise. Despite this, the ice discharge, mass balance, and total volume of the region remain unclear. Furthermore, although the glaciers in the Antarctic periphery currently contribute modestly to sea-level rise, their contribution is projected to increase substantially until the end of the 21st century. This thesis aims to develop data processing and analysis methods that allow us to generate novel updated glacier data for the Antarctic Peninsula region. This is achieved using satellite remote sensing techniques such as radar and optical images, and also numerical models to infer the ice-thickness distribution of the Antarctic Peninsula Ice Sheet (APIS), with the goal of improving ice-discharge and total ice volume estimates for this region. The fundamentals of remote sensing are presented, including techniques such as synthetic aperture radar (SAR), InSAR, DInSAR, and offset-tracking. Optical imagery and Digital Elevation Model (DEM) techniques are also presented. We then focus on glacier flow modeling, describing the governing equations (mass and momentum conservation, rheology) and approximations such as shallow ice and perfect plasticity, used to infer the ice thickness of the Antarctic Peninsula Ice Sheet (APIS). The South Shetland Islands (SSI), located north of the Antarctic Peninsula, lack a geodetic mass balance calculation for the entire archipelago. Therefore, we estimate its geodetic mass balance over the period 2013-2017. Our estimation is based on remotely-sensed multispectral and interferometric SAR data covering 96% of the glacierized areas of the islands considered in our study and 73% of the total glacierized area of the SSI. Our results show a close to balance, slightly negative average specific mass balance for the whole area of −0.106 ± 0.007 m w.e. a⁻¹, and a mass change rate of −238 ± 12 Mt a⁻¹. These results are consistent with a wider scale geodetic mass balance estimation and with glaciological mass balance measurements at SSI locations for the same study period. They are also compatible with the cooling trend observed in the region between 1998 and the mid-2010s. We computed the ice discharge from the APIS north of 70ºS for the five most widely used ice-thickness reconstructions, using a common surface velocity field and a common set of flux gates. In this way, the differences in ice discharge can be solely attributed to the differences in ice thickness at the flux gates. The total volumetric ice discharge for 2015-2017 ranges within 45-141 km³ a⁻¹, depending on the ice-thickness model, with a mean of 87 ± 44 km³ a⁻¹. The substantial differences between the ice-discharge results and a multi-model normalized root-mean-squared deviation of 0.91 for the whole data set, reveal large differences and inconsistencies between the ice-thickness models. This makes evident the scarcity of appropriate ice-thickness measurements and the difficulty of the current models to reconstruct the ice-thickness distribution in this complex region. Motivated by this uncertainty about the ice-thickness distribution, we used a finite element method to infer the ice thickness in the APIS north of 70ºS applying a two-step approach. The first step uses two different assumptions, namely, the shallow ice approximation (SIA) and the perfect plasticity (PP). The second step then uses the mass conservation equation to estimate the thickness in fast-flowing regions, with the aim of overcoming the limitations of SIA and PP near the glacier termini. Manual adjustment of glacier outlines and new ways to deal with rheological parameters along the margins provided further improvements. The application of the model at our study site resulted in a total ice volume of 28.7 ± 6.8 103 km³ and an ice discharge of 95.0 ± 14.3 km³ a⁻¹.
... Although nest flooding occurs across a range of ecosystems (Scarton & Valle, 2020;Windhoffer et al., 2017), for polar species, the occurrence of precipitation in the form of rain is uncommon (Robinson et al., 2020) outside of the Western Antarctic peninsula (Chapman et al., 2011;Thompson et al., 1994;Turner et al., 2005), but can occur from water run-off after snow melt. Historically, precipitation is thought to be responsible for major seabird population changes at other sites in Antarctica (Gao et al., 2018) and is known to affect the breeding success and phenology of Adélie penguins (Boersma, 2008;Hinke et al., 2012). ...
Article
Full-text available
Reproductive success is an important demographic parameter that can be driven by environmental and behavioural factors operating on various spatio‐temporal scales. As seabirds breed on land and forage in the ocean, processes occurring in both environments can influence their reproductive success. At various locations around East Antarctica, Adélie penguins' ( Pygoscelis adeliae ) reproductive success has been negatively linked to extensive sea‐ice. In contrast, our study site in the Windmill Islands has limited fast ice present during the breeding season, allowing us to examine drivers of reproductive success under vastly different marine environmental conditions. Here, we examined the reproductive success of 450 Adélie penguin nests over a 10‐year period using images obtained from remotely operated cameras. We analysed nest survival in relation to marine and climatic factors, environmental conditions at the camera site and immediately around the nest, and behavioural attributes reflecting parental investment and phenological timing. Our key result was a strong positive association between nest structure and chick survival, particularly when ground moisture and snow cover around the nest were high. Earlier nesting birds were more likely to build bigger nests, although it is unclear whether this is due to more time available to build nests or whether early arrival and high‐quality nests are complementary traits. This intrinsic activity is likely to become more important if future predictions of increased snowfall in this region manifest.
... Some extreme precipitation daily totals could reach 40-60% of the annual amount (Turner et al., 2019;Wille et al., 2021). Turner et al. (2005) applied observational and ERA-40 data for the last several decades over the western Antarctic Peninsula and showed precipitation to increase in duration during summer and ISSN 1727ISSN -7485. Óêðà¿íñüêèé àíòàðêòè÷íèé aeóðíàë, 2023ISSN , Ò. 21, ¹ 2, https://doi.org/10.33275/1727ISSN ...
Article
Full-text available
Changes in precipitation extremes over West Antarctica and the Antarctic Peninsula belong to the observed consequences of current climate change. We discuss the spatio-temporal patterns of extreme precipitation and their relationships with the Amundsen Sea Low (ASL) parameters. Based on the ERA5 reanalysis data, the 95th percentile of daily precipitation totals was estimated and linked to the ASL parameters over the main glacier basins in the region. The 95th percentile of precipitation varied from 5 mm to over 40 mm over the region, showing higher values along the coastline and reaching the maximum over the west coast of the Antarctic Peninsula. The tendencies of extreme precipitation vary from –3 to 4 mm per decade and enhance the observed spatial distribution differences. On average, extreme precipitation events covered 4.7–4.9% of the basins’ area. All dependencies had a well-detected seasonality. Both total and extreme precipitation varied under the ASL fluctuations, showing significant average-to-strong correlations. The ASL shifts to the west caused a decrease in precipitation over the Amundsen Sea and an increase over the Antarctic Peninsula. The ASL deepening (lower atmospheric pressure of the system) resulted in a precipitation decrease over the Getz Ice Shelf and a precipitation increase over the western part of the Antarctic Peninsula. There are two regions with opposite responses of precipitation to the ASL changes: the western part over the Getz Ice Shelf with nearby marine areas, and the eastern part covering the Antarctic Peninsula, Pine Island glaciers, the Abbot Ice Shelf, and the Bellingshausen Sea. The obtained results are crucial for our understanding of extreme precipitation occurrences over West Antarctica in recent decades under climate change.
... Gentoo penguins (Pygoscelis papua), another historically sub-Antarctic distributed species, have increased in population size and are expanding their range south along the Western Antarctic Peninsula (WAP) (Herman et al., 2020;Lynch et al., 2012), where declines in sea ice and increases in precipitation have been linked to a suite of oceanographic and ecological changes over the last 40 years (Lin et al., 2021;Meredith et al., 2017;Turner et al., 2005Turner et al., , 2013. ...
Article
Many species are shifting their ranges in response to climate‐driven environmental changes, particularly in high‐latitude regions. However, the patterns of dispersal and colonization during range shifting events are not always clear. Understanding how populations are connected through space and time can reveal how species navigate a changing environment. Here, we present a fine‐scale population genomics study of gentoo penguins ( Pygoscelis papua ), a presumed site‐faithful colonial nesting species that has increased in population size and expanded its range south along the Western Antarctic Peninsula. Using whole genome sequencing, we analysed 129 gentoo penguin individuals across 12 colonies located at or near the southern range edge. Through a detailed examination of fine‐scale population structure, admixture, and population divergence, we inferred that gentoo penguins historically dispersed rapidly in a stepping‐stone pattern from the South Shetland Islands leading to the colonization of Anvers Island, and then the adjacent mainland Western Antarctica Peninsula. Recent southward expansion along the Western Antarctic Peninsula also followed a stepping‐stone dispersal pattern coupled with limited post‐divergence gene flow from colonies on Anvers Island. Genetic diversity appeared to be maintained across colonies during the historical dispersal process, and range‐edge populations are still growing. This suggests large numbers of migrants may provide a buffer against founder effects at the beginning of colonization events to maintain genetic diversity similar to that of the source populations before migration ceases post‐divergence. These results coupled with a continued increase in effective population size since approximately 500–800 years ago distinguish gentoo penguins as a robust species that is highly adaptable and resilient to changing climate.
... Rock glacier velocity is hence a good proxy for the effects of climate change on permafrost, and its significance [5,6] is leading to its possible integration as an Since the 1950s, the western Antarctic Peninsula has suffered one of the highest maximum mean annual air temperature (MAAT) increases of the Antarctic, with as much as 3.4 • C, or about 0.5 • C/decade based on the Faraday/Vernadsky station record [17], placing the region as one of the world's climate warming hotspots [18][19][20]. Higher temperatures have been accompanied by increased precipitation [21,22] and higher snow accumulation, particularly in the western Antarctic Peninsula [23]. However, a regional cooling has been reported for the northwest Antarctica Peninsula from 1999 to 2015. ...
Article
Full-text available
In the second half of the 20th century, the western Antarctic Peninsula recorded the highest mean annual air temperature rise in the Antarctic. The South Shetland Islands are located about 100 km northwest of the Antarctic Peninsula. The mean annual air temperature at sea level in this Maritime Antarctic region is close to −2 °C and, therefore, very sensitive to permafrost degradation following atmospheric warming. Among geomorphological indicators of permafrost are rock glaciers found below steep slopes as a consequence of permafrost creep, but with surficial movement also gen-erated by solifluction and shallow landslides of rock debris and finer sediments. Rock glacier surface velocity is a new essential climate variable parameter by the Global Climate Observing System, and its historical analysis allows insight into past permafrost behavior. Recovery of 1950s aerial image stereo-pairs and structure-from-motion processing, together with the analysis of QuickBird 2007 and Pleiades 2019 high-resolution satellite imagery, allowed inferring displacements of the Hurd rock glacier using compression ridge-and-furrow morphology analysis over 60 years. Displacements measured on the rock glacier surface from 1956 until 2019 were from 7.5 m to 22.5 m and surface velocity of 12 cm/year to 36 cm/year, measured on orthographic images, with combined deviation root-mean-square of 2.5 m and 2.4 m in easting and northing. The inferred surface velocity also provides a baseline reference to assess today’s displacements. The results show patterns of the Hurd rock glacier displacement velocity, which are analogous to those reported within the last decade, without being possible to assess any displacement acceleration.
Article
Few studies have assessed a comprehensive understanding of how the seasonal and interannual variability and trends of the surface mass balance (SMB), including the influence of atmospheric river (ARs), are governed by the climate on the South Shetland Islands (SSI) glaciers located in the northerly Antarctic Peninsula (AP). To address this gap, we comprehensively analyzed the correlations and regressions between seasonal and annual SMB with regional to global climate indices and a state-of-the-art AR tracking database from 1980 to 2019. The daily and monthly SMB was obtained from two physical glaciological models, which was verified against 19 years of annual and seasonal glacier-wide SMB observations available in three glaciers (Johnsons, Hurd, and Bellingshausen), showing a good ability to capture interannual and seasonal variability. Results indicate a low dependence of the SMB on main atmospheric modes of variability (e.g., El Niño-Southern Oscillation and the Southern Annular Mode), and a moderate dependence on regional climate indices based on atmospheric pressure anomalies and sea surface temperature anomalies over the Drake Passage. Furthermore, our findings reveal that ARs have different effects on the SMB depending on the season. For example, winter ARs tend to boost accumulation due to increased snowfall, while summer ARs tend to intensify surface melting due to increased sensible heat flux. Our study highlights the Drake Passage as a key region that has the potential to influence the interannual and seasonal variability of the SMB and other climate variables, such as air temperature and snowfall over the SSI. We suggest that future work should consider this region to better understand the past, present and future climate changes on the SSI and surrounding areas.
Article
Full-text available
The west side of the Antarctic Peninsula (AP) has shown great variability since the middle of the last century characterized by warming mainly because of the oceanic and atmospheric effects such as the disintegration of floating ice and the strength of westerly winds. Here, we used two climatic databases (reanalysis from 1979 to 2020 and surface stations from 1947 to 2020) to investigate trends in extreme air temperatures and wind components in the oceanic region between 55° S and 70° S in the west (75° W) and in the east sector (45° W) and over the AP (60° W). Non-parametric statistical trend tests and extreme value approaches are used. A set of annual, monthly, and seasonal series are fitted. The extremal index is applied to measure the degree of independence of monthly excesses over a threshold considered extreme events. Increasing trends are verified in the annual and monthly temperature and wind series. The greatest trends are observed for seasonal series from reanalysis without change-point in summer and winter. Decreasing trends are observed for maximum temperature in summer and positive trends mainly for the westerly winds over the AP. But in winter, the maximum temperature shows an increasing trend also over the AP. Most of reanalysis seasonal minimum temperature and wind components as well as maximum and minimum temperatures from stations present increasing trends with change-point but tend to stability after the breakpoints. The generalized distribution (GEV) is used to fit temperatures and westerly wind between South America (SA) and north of the AP. The 100-year return levels exceed the maximum value of the maximum temperature in Esperanza and maximum westerly winds at several grid points. Pareto and Poison distributions are applied for the maximum temperatures from stations and the 100-year return levels are not exceeded. Our findings show significant positive trends for monthly wind components near the SA in the region of the westerly winds whose changes in position influence directly the SAM, which modifies the atmospheric patterns in the South Hemisphere (SH). A predominance of seasonal warming is identified, which may impact the climate with consequences not only locally but also in other regions.
Article
Full-text available
We analyze the internal structure of two polythermal glaciers, Hurd and Johnsons, located on Livingston Island, Antarctica, using 200 and 750 MHz GPR data collected in 2003/04, 2008/09 and 2016/17 field campaigns. Based on the different permittivities of snow and ice, we determined the thickness distribution of the end-of winter snow cover and of the cold ice layer. Their knowledge is fundamental for mass balance and glacier dynamics studies due to the different densities and rheological properties of such media. The average measured thicknesses for the snow and cold ice layers (the latter including the snow layer) were of 1.44 ± 0.09 and 29.1 ± 1.5 m, and their corresponding maxima were of 2.45 ± 0.21 and 80.8 ± 2.5 m. GPR snow profiling allowed for extension of the coverage of the snow thickness survey, but added little information to that supplied by snow pits, stake readings and manual snow probing, because of the multiplicity of reflections within the seasonal snowpack caused by internal ice layers and lenses. The polythermal structure determined for Hurd Glacier fits into the so-called Scandinavian type, seldom reported for the Antarctic region.
Article
Full-text available
This study investigates the transient snowline (TSL) altitude for summer 2020, as well as glacial area loss in King George Island Icefields since 1988 using Sentinel-1 and 2 and Landsat Thematic Mapper (TM) imagery. Trends and anomalies in atmospheric temperature, U-wind, and V-wind were examined using ERA5 solutions. Results show the wet-snow zone corresponds to values of ≤ -13dB, and 44.3% of the glacial area is located above the TSL (≥ 300 m). Glacial area for 2020 is 999.95 km², and losses in the period represent 104.9 km² (error <1%) - a retreat of 3.17 km² / year. Glaciers in Keller Peninsula and Bellingshausen Dome lost the most area (28% and 17%, respectively) and did not have a TSL in 2020; followed by Warszawa (15%), Kraków (13%), and Eastern (10%), where the TSL was verified. Percentage area loss values increased with decreases in dimensions, area above TSL, and maximum elevation. Calving glaciers with ice-flow toward deeper and steeper submarine sectors (Bransfield Strait) exhibited greater glacier variations. The trend in warming atmospheric temperature was greater in the Bransfield Strait than in the Drake Passage. TSL and retreat difference between glaciers were influenced by climatic and ocean input, as well as multiple environmental factors.
Article
Full-text available
The Antarctic Peninsula Ice Sheet (APIS) has become a significant contributor to sea-level rise over recent decades. Accurately estimating the ice discharge from the outlet glaciers of the APIS is crucial to quantify the mass balance of the Antarctic Peninsula. We here compute the ice discharge from the outlet glaciers of the APIS north of 70 {^\circ } S for the five most widely used ice-thickness reconstructions, using a common surface velocity field and a common set of flux gates, so the differences in ice discharge can be solely attributed to the differences in ice thickness at the flux gates. The total volumetric ice discharge for 2015–2017 ranges within 45–141 km ³ a ⁻¹ , depending on the ice-thickness model, with a mean of 87 ± 44 km ³ a ⁻¹ . The substantial differences between the ice-discharge results, and a multi-model normalized root-mean-squared deviation of 0.91 for the whole data set, reveal large differences and inconsistencies between the ice-thickness models, giving an indication of the large uncertainty in the current ice-discharge estimates for the APIS. This manifests a fundamental problem of the region: the scarcity of appropriate ice-thickness measurements and the difficulty of the current models to reconstruct the ice-thickness distribution in this complex region.
Article
Full-text available
A regional atmospheric model, with a horizontal grid spacing (Δx) of 14 km, is used to study the surface mass balance components (precipitation, sublimation, and snow drift) in the region of the Antarctic Peninsula (AP). An integration is performed for the 7-year period 1987-1993, using a realistic forcing at the lateral model boundaries and at the sea surface. Output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the AP, where the upward motion in the atmosphere is largest. Uplift occurs upstream of the barrier, affecting the precipitation distribution over sea. The effect of the barrier on the precipitation distribution over the Bellingshausen Sea might have important implications for the ocean circulation in this region. The mean precipitation over the grounded ice of the AP (1.20 m water eq yr-1) is 6 times larger than the mean value over all the grounded ice of Antarctica. Our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9% and 6 ± 1% of the precipitation, respectively. In situ data of the wind distribution at three coastal sites located on the northern, eastern, and western sides of the AP are used to evaluate the modeled wind field, which is important for the snow drift calculations. For two of the three sites considered, the prevailing wind direction and bimodal wind distribution are correctly represented by the model. The calculated distribution of accumulation and ablation due to snow drift shows a complex pattern. The wind removes snow from the spine of the AP, where the near-surface flow field diverges, whereas deposition occurs mainly on the eastern slopes, where the near-surface flow field converges. An intercomparison between two 7-year integrations at different horizontal resolution (Δx = 14 km and Δx = 55 km) shows that the precipitation on the northwestern slope is very sensitive to the model resolution: In the Δx = 14 km integration, precipitation on the northwestern slope is higher than in Δx = 55 km because of higher vertical velocities, resulting in a 35% increase in average precipitation over the grounded ice of the AP.
Article
Full-text available
Precipitation over Antarctica is an important climatic variable whose study has been limited by the frequent inability to discriminate between actual snow precipitation and drifting snow. For broad-scale studies in the continental interior net snow accumulation closely approximates precipitation. Annual precipitation is relatively high over the marginal ice slopes in relation to amounts in the interior. This meridional distribution is due to the orographic lifting of moist air by the ice sheet. Zonal precipitation variations are related to the quasi-stationary cyclones in the circumpolar low-pressure trough. Most precipitation falls in winter, when the average moisture content of the air is low. The intensity of cyclonic activity is the key factor governing the amount of precipitation and its variations. Precipitation generation in coastal regions is strongly influenced by the fact that poleward moving, moist maritime air masses are deflected by the steep marginal ice slopes to blow parallel to the terrain contours. Direct orographic lifting with accompanying adiabatic cooling is the dominant precipitation formation mechanism inland of the 1-km elevation contour. -from Author
Article
Full-text available
In this study we correlate temporal features within the electrical con-ductivity (acidity) traces offour shallow firn cores obtained from the southern Antarctic Peninsula to synoptic-scale variations in the regional climate, as depicted by a numerical weather prediction model. It is demonstrated that the three high-acidity features present within the 1992-93 accumulation correspond to periods of significant precipitation, a hypothesis supported by the association of these events with strong onshore winds, ideal for transporting the biogenically derived sources of precipitation acidity to the core sites. The longitudinal location o[ depressions within the Bellingshausen Sea is shown to be the principal factor governing the volume of precipitation that they give over the western Peninsula. Annual accumulation in the model is rv25% lower than revealed by the cores; although there are too many uncertainties to provide a definite reason for the deviation, the smoothed model orography and inaccurate land-sea mask are believed to be signifi-cant factors. It is postulated that the acidity pattern within southern Peninsula cores may reveal an El Nifio-Southern Oscillation signal.
Article
Full-text available
Measurements from ice cores and snow pits collected over the last 50 years are used to examine how net surface mass balance varies across the Antarctic Peninsula to give the first detailed map of mass balance for the region. A total of 211 reliable mass balance measurements were available for the preparation of the map, but some areas were found to be very data sparse. The analysis suggests that the largest values of mass balance are found along the spine of the northern part of the peninsula, where over 2.5 m yr-1 water equivalent (WE) has been measured. A secondary peak of more than 2.0 m yr-1 WE is determined along the mountains of eastern Alexander Island. Precipitation minus evaporation (P-E) fields from the European Centre for Medium-Range Weather Forecasts reanalysis project are compared with our analysis of in situ data. The model fields are found to have peak values of P-E of only half the amounts found from the measurements; the greatest model values are located on the western side of the peninsula. Areas where a high density of in situ data is available, including King George VI Sound and the high south central plateau part of the peninsula, show a high spatial variability of net surface mass balance, suggesting that local orographic features play a major part in dictating the mass balance.
Chapter
Climate observations made since the mid twentieth century reveal that the Antarctic Peninsula is a region of extreme climate variability and change. The pattern of change is, however, both seasonally and spatially inhomogeneous. Limited data from the east (Weddell Sea) coast indicate that surface air temperatures here are rising at around 0.03 degreesC per year in all seasons. On the west (Bellingshausen Sea) coast, summer temperature trends are similar to those prevailing on the east coast but, in winter, warming trends of over 0.1 degreesC per year are observed, making this the most rapidly warming part of the Southern Hemisphere. Rapid warming is confined to the very lowest levels of the atmosphere and warming of the free troposphere over the Peninsula is not statistically significantly different from the Southern Hemisphere average. Interannual variations in winter temperatures on the west coast are strongly correlated with variations in atmospheric circulation and sea ice extent, suggesting that both atmospheric and ice/ocean processes may be contributing to the long-term warming. However, there is little observational evidence to support long-term atmospheric circulation changes. Coupled atmosphere-ocean general circulation model (AOGCM) experiments, forced with observed greenhouse gas increase, fail to reproduce the observed pattern of warming around the Peninsula. However, current AOGCMs may not be sophisticated enough or of high enough resolution to represent all of the processes that control climate on a regional scale around the Antarctic Peninsula.
Article
The Southern Hemisphere reveals markedly different circulation patterns associated with extreme warm and cold Antarctic Peninsula (AP) winter temperatures. Warm winters are associated with negative 500 hPa height anomalies in the Amundsen Sea-Bellingshausen Sea (AS-BS) and positive anomalies in the South Pacific (SP) and Scotia Sea with opposing anomalies existent in cold winters. Furthermore, a switch in the relative strength of the two arms of the New Zealand split jet, the subtropical jet (STJ) and polar front jet (PFJ), occurs with the PFJ (STJ) strengthened and the STJ (PFJ) weakened in warm (cold) years leading to increased cyclonic activity in the AS-BS (SP) and a corresponding decrease in the SP (AS-BS). These hemispheric anomaly patterns bear a strong resemblance to those associated with El Niño-Southern Oscillation (ENSO) events, and their origins can be ascribed to tropical sea surface temperatures (SST) changes. However, the correspondence between warm (cold) ENSO events and cold (warm) winters is not perfect. Potential contributors to this non-linearity include intraseasonal tropical SST variations (not necessarily represented in the usual filtered ENSO indices) and the persistence of local sea ice anomalies west of the Peninsula.
Article
The principal characteristics of the variability of Antarctic sea ice cover as previously described from satellite passive microwave observations are also evident in a systematically calibrated and analyzed data set for 20.2 years (1979-1998). The total Antarctic sea ice extent (concentration >15%) increased by 11,180 +/- 4190 km2 yr-1 (0.98 +/- 0.37% (decade)-1). The increase in the area of sea ice within the extent boundary is similar (10,860 +/- 3720 km2 yr-1 and 1.26 +/- 0.43% (decade)-1). Regionally, the trends in extent are positive in the Weddel Sea (1.4 +/- 0.9% (decade)-1), Pacific Ocean (2.0 +/- 1.4% (decade)-1), and Ross (6.7 +/- 1.1% (decade)-1) sectors, slightly negative in the Indian Ocean (-1.0 +/- 1.0% (decade)-1), and strongly negative in the Bellingshausen-Amundsen Seas sector (-9.7 +/- 1.5% (decade)-1)). For the entire ice pack, ice increases occur in all seasons, with the largest increase during fall. On a regional basis the trends differ season to season. During summer and fall the trends are positive or near zero in all sectors except the Bellingshausen-Amundsen Seas sector. During winter and spring the trends are negative or near zero in all sectors except the Ross Sea, which has positive trends in all seasons. Components of interannual variability with periods of about 3-5 years are regionally large but tend to counterbalance each other in the total ice pack. The interannual variability of the annual mean sea ice extent is only 1.6% overall, compared to 6-9% in each of five regional sectors. Analysis of the relation between regional sea ice extents and spatially averaged surface temperatures over the ice pack gives an overall sensitivity between winter ice cover and temperature of -0.7% change in sea ice extent per degree Kelvin. For summer some regional ice extents vary positively with temperature, and others vary negatively. The observed increase in Antarctic sea ice cover is counter to the observed decreases in the Arctic. It is also qualitatively consistent with the counterintuitive prediction of a global atmospheric-ocean model of increasing sea ice around Antarctica with climate warming due to the stabilizing effects of increased snowfall on the Southern Ocean.
Article
The onset of global warming from increasing greenhouse gases in the atmosphere can have a number of important different impacts on the Antarctic ice sheet. These include increasing basal melt of ice shelves, faster flow of the grounded ice, increased surface ablation in coastal regions, and increased precipitation over the interior. An analysis of these separate terms by ice sheet modeling indicates that the impact of increasing ice sheet flow rates on sea level does not become a dominant factor until 100--200 years after the realization of the warming. For the time period of the next 100 years the most important impact on sea level from the Antarctic mass balance can be expected to result from increasing precipitation minus evaporation balance over the grounded ice. The present Antarctic net accumulation and coastal ice flux each amount to about 2000 km3 yr-1, both of which on their own would equate to approximately 6 mm yr-1 of sea level change. The present rate of sea level rise of about 1.2 mm yr-1 is therefore equivalent to about 20% imbalance in the Antarctic mass fluxes. The magnitude of the changes to the Antarctic precipitation and evaporation have been studied by a series of General Circulation Model experiments, using a model which gives a reasonable simulation of the present Antarctic climate, including precipitation and evaporation.