Falk, Ulrike; Sala, Hernán (2015): Meteorological measurements from the Fourcade and Polar Club Glacier, Warszawa Icefield, King George Island, West Antarctica [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.848706,

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Supplement to: Falk, U; Sala, H (2015): Winter melt conditions of the inland ice cap on King George Island, Antarctic Peninsula. Erdkunde, 69(4), 341-363, https://doi.org/10.3112/erdkunde.2015.04.04

The South Shetland Islands are located at the northern tip of the AP which is among the fastest warming regions on Earth. The islands are especially vulnerable to climate change due to their exposure to transient low-pressure systems and their maritime climate. Surface air temperature increases (2.5K in 50 years) are concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. We have compiled a unique meteorological data set for the King George Island (KGI)/Isla 25 de Mayo, the largest of the South Shetland Islands. It comprises high-temporal resolution and spatially distributed observations of surface air temperature, wind directions and wind velocities, as well as glacier ice temperatures in profile with a fully equipped automatic weather station on the Warszawa Icefield, from November 2010 and ongoing. In combination with two long-term synoptic datasets (40 and 10 years, respectively) and NCEP/NCAR reanalysis data, we have looked at changes in the climatological drivers of the glacial melt processes, and the sensitivity of the inland ice cap with regard to winter melting periods and pressure anomalies. The analysis has revealed‚ a positive trend of 5K over four decades in minimum surface air temperatures for winter months, clearly exceeding the published annual mean statistics, associated to a decrease in mean monthly winter sea level pressure. This concurs with a positive trend in the Southern Annular Mode (SAM) index, which gives a measure for the strength and extension of the Antarctic vortex. We connect this trend with a higher frequency of low-pressure systems hitting the South Shetland Islands during austral winter, bringing warm and moist air masses from lower latitudes. Due to its exposure to the impact of transient synoptic weather systems, the ice cap of KGI is especially vulnerable to changes during winter glacial mass accumulation period. A revision of seasonal changes in adiabatic air temperature lapse rates and their dependency on exposure and elevation has shown a clear decoupling of atmospheric surface layers between coastal areas and the higher-elevation ice cap, showing the higher sensitivity to free atmospheric flow and synoptic changes. Observed surface air temperature lapse rates show a high variability during winter months (standard deviations up to ±1.0K/100 m), and a distinct spatial variability reflecting the impact of synoptic weather patterns. The observed advective conditions bringing warm, moist air with high temperatures and rain, lead to melt conditions on the ice cap, fixating surface air temperatures to the melting point.

This paper assesses the impact of large-scale atmospheric circulation variability and climatic changes on the atmospheric surface layer and glacier mass accumulation of the upper ice cap during winter season for the Warszawa Icefield on KGI.

In November 2010, we have installed an Automatic Weather Station (AWS) and an Eddy Covariance Station (ECS) at S 62° 14' 09.8'', W 58° 36' 48.7'' at 230m a.s.l. on the approximate divide of Fourcade and Polar Club glaciers, which are both part of Warszawa Icefield. The AWS is equipped with two heights wind anemometers and vanes (Alpine Wind Monitor), and air temperature and relative humidity sensors (HMP155A), five depths of snow and ice temperature measurements (107 Thermistor Probes) installed at depths of 10m, 5m, 1m, two snow temperature installed at the end of the summer. The AWS includes an NR01, a four-component radiation sensor for up- and down-welling long- and shortwave radiation fluxes, two narrow field infrared temperature sensors IR120 facing northwest and southeast at an angle of 40° to measure surface temperatures, and a SR50A Sonic Ranging Sensor installed at an initial height of 2m to measure surface elevation changes. For data acquisition and storage, a CR3000 Micrologger with extended temperature testing with a 2GB Compact Flash Card is used. The meteorological sensors were installed on a 3m tripod that was fixed at poles drilled into the ice. To ensure good quality of radiation measurements, all radiation sensors were mounted at a 3m boom extended from the tripod and fixed to additional 3m poles drilled into the ice. Levelling and adjustment of sensors were carried out at the beginning and ending of each summer campaign. In particular, at the end of the ablation season, the whole system needed to be lowered about 2 to 3m due to ablation at the station site. Power supply was realised with solar panels and a battery stack. Measurement rate was set to every 10 seconds with an averaging interval of 10 minutes. In the summer field campaign January – March 2012, an additional Automatic Weather Station (denoted ZAWS) was installed in the accumulation zone of the WI at S 62°12'5.7'', W 58°34'58.4'' and 434m a.s.l. The ZAWS measured wind speed and direction, air temperature, relative humidity and downward shortwave radiation (by means of Li190SB) for a period of two weeks. All sensors and AWS equipment were purchased from Campbell Scientific, Logan, Utah USA. Air temperature sensors were shielded and accuracy is given as ±0.1°C.