A new comprehensive cloud–precipitation–meteorological observatory has been
established at Princess Elisabeth base, located in the escarpment zone of
Dronning Maud Land (DML), East Antarctica. The observatory consists of a set of
ground-based remote-sensing instruments (ceilometer, infrared pyrometer and
vertically profiling precipitation radar) combined with automatic weather
station measurements of near-surface meteorology, radiative fluxes, and snow
height. In this paper, the observatory is presented and the potential for
studying the evolution of clouds and precipitating systems is illustrated by
case studies. It is shown that the synergetic use of the set of instruments
allows for distinguishing ice, liquid-containing clouds and precipitating clouds,
including some information on their vertical extent. In addition, wind-driven
blowing snow events can be distinguished from deeper precipitating systems.
Cloud properties largely affect the surface radiative fluxes, with
liquid-containing clouds dominating the radiative impact. A statistical
analysis of all measurements (in total 14 months mainly during summer–beginning of winter)
indicates that these liquid-containing clouds occur during as much as 20 % of
the cloudy periods. The cloud occurrence shows a strong bimodal distribution
with clear-sky conditions 51 % of the time and complete overcast conditions
35 % of the time. Snowfall occurred during 17 % of the cloudy periods with a
predominance of light precipitation and only rare events with snowfall
Knowledge of the Antarctic hydrological cycle is essential in order to assess
potential future changes of the Antarctic surface mass balance (SMB), which
is one of the factors affecting global sea levels
The extreme environment and climate of the Antarctic ice sheet both lead to
unique cloud properties and poses significant difficulties in cloud and
precipitation observations. In polar latitudes, low temperatures
favour formation of thin ice clouds at all heights including near the surface
during the entire year as compared to their occurrence globally only in the
upper troposphere
Another important challenge in polar climate science is to understand complex
mechanisms controlling snow accumulation at different time and spatial scales
A new comprehensive observatory on cloud–precipitation–meteorological
interactions has been established in the escarpment zone of Dronning Maud Land (DML), East Antarctica, aiming to improve understanding of Antarctic cloud
properties and different components of the SMB. The observatory consists of a
set of basic and robust ground-based remote-sensing instruments, namely,
ceilometer, infrared pyrometer and vertically profiling precipitation radar
(presently the only precipitation radar over the Antarctic ice sheet). In
addition, an automatic weather station (AWS) provides hourly mean
near-surface meteorology, surface radiative fluxes, 1 m snow temperature
profile and snow accumulation
The specific combination of ground-based remote-sensing measurements is
intended to derive several key cloud and precipitation characteristics,
including the vertical structure of clouds and precipitation, cloud base height
and temperature, identification of ice-only and liquid-containing clouds, and
precipitation intensity. Further, the occurrence of ice virga (precipitation
not reaching the surface) and its association with liquid cloud layers can be
studied. The combination of the ground-based remote-sensing instruments with an
AWS allows for the study of cloud radiative forcing and attributing snow accumulation to precipitation with a potential to distinguish between local accumulation due
to snowfall or clear-sky drifting snow. The goal of collecting these data is
to perform detailed process-based model evaluation and improve cloud and
precipitation parameterisations, required for Antarctic climate simulations
The present paper demonstrates the potential of the observatory by providing
detailed case studies and presents statistics of cloud and precipitation
properties based on the available measurement periods during 2010–2013. In
addition, year-around radar snowfall measurements during 2012 are used for
snowfall analysis together with other SMB components. It gives insight about
the ice and liquid-containing cloud properties, precipitation intensity and
height, contribution of snowfall to SMB, and occurrence of strong blowing
snow events. The paper is structured as follows: historical background
related to cloud and precipitation measurements is given in
Sect.
Observations of clouds and precipitation in Antarctica can be dated back to
the first exploratory expeditions, most notably year-round regular
meteorological observations during Adrien de Gerlache's expedition on board RV
The Antarctic environment with its especially harsh conditions and difficult
accessibility calls for measurements using robust instruments requiring
minimal maintenance, but which still provide crucial information on cloud and
precipitation properties on a long term. The HYDRANT project (The
atmospheric branch of the hydrological cycle in Antarctica) tries to fulfil
this demand with its set of ground-based remote-sensing instruments providing
high vertical and temporal resolution of cloud and precipitation properties
on the long term combined with near-surface meteorological and snow-accumulation measurements. The base for our measurements is the Princess
Elisabeth (PE) station built on the Utsteinen Ridge, north of the Sør
Rondane mountain chain, in DML, in the escarpment zone
of the East Antarctic plateau (71
The measurement site is characterised by a relatively mild climate with a
rather high frequency of synoptic events under cyclonic influence and a lack
of katabatic drainage of cold air from the plateau due to mountain sheltering
The cloud–precipitation–meteorological observatory HYDRANT at the Princess Elisabeth base in East Antarctica. Shown on the figure are the ceilometer, the infrared pyrometer, the vertically profiling precipitation radar, the webcam with spotlight and the automatic weather station (right lower inset). The middle inset shows the location of the PE station on the Antarctic ice sheet (white square) together with the orography (metres above sea level).
An overall description of the HYDRANT instruments and their measurement
periods are given in Table
Cloud and precipitation measurements are combined with AWS measurements
providing hourly data on the near-surface air temperature and relative
humidity with respect to ice (RH
The project website (
All remote-sensing instruments are installed next to each other on the PE
base roof pointing vertically (Fig.
Overview of the HYDRANT instruments: raw measured data,
derived parameters, location and continuous measurement periods
used for analysis (with data gaps
Specifications of the HYDRANT ceilometer.
Specifications of the HYDRANT infrared pyrometer.
The ceilometer (Vaisala CL31), is a single wavelength lidar system without
polarisation with emitted laser pulse wavelength of 910 nm
(Table
Cloud/precipitation occurrence and base height are identified using the polar
threshold (PT) algorithm developed specifically for polar regions
The infrared radiation pyrometer (Heitronics KT15.82II) is a passive
radiometer measuring the downward radiance within the 8–14
For optically thick clouds the pyrometer temperature (
Specifications of the HYDRANT Micro Rain Radar.
The radar (METEK MRR-2) is a frequency-modulated continuous-wave vertically
profiling Doppler radar, transmitting at 24 GHz frequency
(
Photographs of the fallen snow crystals at PE in February 2010 and January
2011 revealed a maximum size of 0.5–0.8 mm, represented mostly by
dendrites, columns, capped columns and rosettes. This is comparable to the
snowfall particle shapes and sizes (0.03–0.6 mm) measured
at other Antarctic locations
In addition to snowfall, MRR can also detect ice virga, defined as streaks of
ice particles falling out of a cloud but evaporating before reaching the
earth's surface as precipitation
In order to compare with snow accumulation on the ground, we use
In order to demonstrate the complementary nature of HYDRANT measurements and
their utility for detailed process studies, this section presents analyses of
several cases representative for different cloud and precipitation types
(liquid-containing clouds, ice clouds, ice virga, and precipitation to the
surface) that occurred during the week of 6–13 February 2012. Using the
European Centre for Medium-Range Weather Forecasts Interim re-analysis data
(ERA-Interim)
Webcam sky images at specified day and UTC time (left) and maps of
corresponding daily mean sea level pressure (contours) and 10 m wind speed
and direction (arrows) from ERA-Interim re-analysis data (right) during
During the whole week of 6–13 February 2012, PE was under the influence of
passing cyclones with three distinct cases characterised by various cloud and
precipitation properties. Figure
On 6–7 February 2012, persistent liquid-containing stratocumulus clouds were
observed over PE for almost 30 h with an important impact on radiative
fluxes. Ceilometer measurements reveal a two-layer cloud structure
(Fig.
Cloud and precipitation properties derived from ground-based remote-sensing instruments during the case studies period 6–13 February 2012:
A strong impact on surface radiative fluxes and consequently on surface and
air temperature is one of the important characteristics of liquid-containing
clouds over the Antarctic ice sheet. The increase in the surface incoming LW flux (LW
Hourly meteorological parameters during the case studies period
6–13 February 2012:
From 8 to 11 February 2012, ceilometer and MRR profiles
(Fig.
The
The observed cloud and precipitation properties cause a large variability of
LW
The case on 12–14 February 2012 highlights the role of liquid-containing
clouds in precipitation formation and radiative forcing. Similarly to case 2,
ceilometer and MRR profiles (Figs.
In the morning of 13 February, radar
The hydrometeor layer after 18:00 UTC on 13 February contains precipitating ice
crystals as indicated by the high radar
Changing cloud properties exhibit a strong influence on LW
Cloud-free blowing snow event on 8 April 2013 (case 4):
A special case on 8 April 2013 shows a strong blowing snow event occurring
during cloudless conditions, which is a rare and extreme event at PE, where
katabatic winds are usually rather weak being sheltered by the mountain range
Figure
The MRR detects no signal during this day, confirming that the blowing snow
is limited to a shallow layer near the surface (
In addition to case studies, we provide a compilation of basic cloud and
precipitation statistics derived from the remote-sensing instruments based on
the available measurement periods during 2010–2013 (14 months of cloud
measurements mainly during summer through beginning of
winter and 26 months of snowfall measurements
including an entire year; see Table
Figure
Number of occurrences by height on 1 min temporal scale for
The frequency by height diagram for ceilometer
As shown by
Using collocated 1 min
Total frequency relative to the measurement period (%) of hourly
mean cloud occurrence frequency (COF; unitless fraction from 0 to 1) for all
clouds and precipitation. The column corresponding to COF
Further, the overcast conditions are divided among liquid-containing clouds
(7 % of the total measurement period or 20 % of the overcast periods),
snowfall (6 % of the total period or 17 % of the overcast) and ice clouds or
weak precipitation not detected by MRR (22 % of the total period or 63 % of
the overcast). Thus, while ice clouds occur most frequently, the
liquid-containing clouds are also observed during a significant period of
time. Low SOF, compared to cloudy periods, combined with precipitation
intensity statistics (Fig.
Further, we show the role of the snowfall-driven high-accumulation events in
the local SMB. The PE site is characterised by high interannual variability
in local SMB (230, 23, 227 and 52 mm w.e. during 2009, 2010, 2011
and 2012, respectively), which is in accordance with high interannual
variability in a much larger region: yearly total accumulation averaged over
the 180 km long stake line from PE to the coast is 606, 157, and 598 mm w.e.
for 2009, 2010, and 2011, respectively. This stake line was installed within
the GLACIOCLIM project
We analyse in detail daily mean snow height changes and snowfall rates during
2 years (2011–2012), which are characterised by very different yearly snow
accumulation (Fig.
Using radar measurements, we attributed all of these high-accumulation events
to snowfall of various intensity (blue diamonds in Fig.
Daily snow height (with respect to 1 January 2011) and snowfall rate
(
At the same time, small and medium accumulation events could be both due to
snowfall and wind-driven deposition (Fig.
Snowfall measurements were available almost continuously during 2012
(Fig.
The other SMB components are estimated as following. SU
Radar-derived snowfall rate summed over the year 2012 is
Figure
Removal by the wind (ER
Cumulative daily surface mass balance (SMB) components during 2012:
snowfall (
In this paper we present a new cloud–precipitation–meteorological observatory
established in the escarpment zone of eastern DML, East
Antarctica. Cloud and precipitation properties at high vertical and temporal
resolution are derived from a set of ground-based remote-sensing instruments
(910 nm ceilometer, 8–14
The paper demonstrates the value of this set of instruments via detailed case
studies and presents basic cloud and precipitation properties based on the
available measurement periods during 2010–2013. Case studies show the ability
of the observatory to capture complex and constantly evolving cloud and
precipitation properties, as well as to measure intense wind-driven blowing
snow events. In particular, we have demonstrated the potential of the
observatory to be used for investigating the following relationships:
distinguish between ice clouds (including weak precipitation), virga (precipitation not reaching the surface), liquid-containing clouds and snowfall; study the effect of changing cloud base heights and temperatures on surface radiative fluxes; assess the vertical extent and radiative forcing of thin ice clouds; assure that radar-derived snowfall (limited to 400 m a.g.l.) is observed all the way to the surface; identify intense ( distinguish snow accumulation due to snowfall from wind-driven deposition; quantify the SMB components and study their relation to meteorological conditions.
Statistical analysis using ceilometer and MRR measurements during austral summer to beginning of winter 2010–2013 reveals cloud and precipitation properties, many of which are derived for the first time over the Antarctic ice sheet. Ice cloud layers and weak precipitation are most frequently found from near the surface up to 3–3.5 km a.g.l., while the lowest observed liquid-containing cloud layers are confined to 1–3 km a.g.l.
Clouds at PE show a clear bimodal distribution with either clear sky or
overcast most of the time. While ice-only clouds (including virga) occur most
frequently (63 % of cloudy periods), liquid-containing clouds are also
observed during a significant period of time (20 % of all cloudy overcast
cases). Snowfall rates derived from radar measurements show high frequency of
low intensity precipitation with rare occasional moderate intensity snowfalls
of
Another long-standing question, which can be addressed using the observatory
data, is attribution of accumulation to snowfall in contrast to the
wind-driven deposition. Despite the naturally large uncertainty in the
derived snowfall intensity due to the large range of possible
In contrast to the large accumulation events, medium to low accumulation
occur both due to snowfall and wind-driven deposition. Also not every
snowfall results in significant snow accumulation, and wind erosion (together
with sublimation) can entirely remove locally precipitated snow mass.
Combining radar-derived snowfall rates during 2012 with sublimation
estimates based on the AWS measurements, allowed us to isolate the
wind-driven erosion term and compare it to other SMB components.
The radar-derived snowfall rate summed over the year 2012 is
Application of the observatory extends beyond clouds and precipitation, and
can be used to capture intense wind-driven blowing snow events (in the
absence of snowfall from clouds) up to several hundred meters above the
ground, associated with strong near-surface winds. Measurements from the
ceilometer installed at PE and also lidars and ceilometers found at other
locations around Antarctica
The goal of the observatory is to evaluate clouds and precipitation simulated
by climate models allowing both a detailed look into processes and statistical
comparisons. It can also be used in synergy with satellite cloud and
precipitation data. Collocating profiles from ground-based and satellite
lidars can offer better representation of the cloud vertical structure.
Similarly, collocation of MRR precipitation measurements with satellite-based
radar provides additional information on precipitation occurrence and
properties close to the surface offering a solution to the disturbance of
satellite radars due to ground clutter
This project has been successful thanks to the continuous support of many people,
companies and institutions. We are grateful to the Belgian Federal Science
Policy (BELSPO) for the financial support of the HYDRANT project
(EA/01/04AB). We thank International Polar Foundation (IPF) and all staff at
Princess Elisabeth base for providing the infrastructure, technical and
logistical support, and particularly Erik Verhagen and Karel Moerman (IPF)
for help with on-site instrument maintenance. Special thanks for continuous
technical support of the KU Leuven engineers Jos Meersmans and Valentijn Tuts,
and all companies who provided the remote-sensing instruments and
technical support – Vaisala (Finland), Heitronics/MeraBenelux
(Germany/the Netherlands), Metek (Germany), and Mobotix (Germany). Many thanks to
Johan Boon and Hilde Vandenhoeck (KU Leuven) for computer and website
support. We are grateful to Michiel van den Broeke, Carleen Reijmer and Wim Boot (Institute for
Marine and Atmospheric research Utrecht, the Netherlands) for scientific discussions, the
AWS development, support and raw data processing. We are grateful to Roland Meister
(Institute for Snow and Avalanche Research – SLF, Switzerland) for providing
the equipment and training for snow pit measurements. We thank the French
Glacioclim-SAMBA project
(