Föhn winds on South Georgia and their impact on regional climate

Abstract

South Georgia is a small and mountainous island, located in the remote Southern Ocean. The island's subantarctic climate is controlled by its location and steep orography; with 19 peaks over 2000m and situated within a belt of strong westerly winds South Georgia acts as an effective barrier to the winds that impinge upon it.Since the 1920s, average summer temperatures have risen by ~1 o C on South Georgia.Coupled with this has been an increase in the rate of glacial retreat throughout the last century, with glaciers on the northeast leeside of the island retreating at a faster rate than those on the southwest side. These asymmetrical changes are thought to be linked with the strengthening of the westerlies. If the strength of the westerlies is sufficient, downslope winds can develop on the leeside of the island causing significant temperature increases as the descending air warms adiabatically; this is known as the föhn effect. Therefore, the aim of this thesis is to investigate whether the observed asymmetric pattern of regional warming and glacier retreat are caused by the föhn warming process.To explore the link between the föhn effect and its impact on the regional climate of

The characteristics and temporal variability of föhn winds at King Edward Point, South Georgia

“…WRF is a fully compressible, nonhydrostatic regional atmospheric model that uses a terrain‐following pressure coordinate in the vertical (Skamarock et al ., ), making it a suitable tool for studying atmospheric flow over complex terrain at high resolution. For the case study presented here, we use WRF version 3.8.1 along with the model configuration as described in detail in Bannister (). Table provides a summary of the WRF model setup and the parametrizations used.…”

“…Unlike criterion (1), we did not set specific thresholds for criteria (2) and (3) because the signals in near‐surface wind speed and relative humidity were often more muted, variable, or inconsistent compared to the temperature signal. Wind speed was not given a specific threshold because it is strongly controlled by the local complex topography of King Edward Cove and can easily obscure föhn onset and cessation, while relative humidity was similarly not given a specific threshold because it was found that the warming conditions often remained established despite an increase in relative humidity compared to its pre‐föhn value (see Bannister, , for examples and further details). Additional limitations in data availability and missing data (e.g., relative humidity data was only available from March 2006 onwards, Table ) also restricted thresholding.…”

“…Approximately, 56% of the total land surface of the island is covered by permanent snow and ice. However, the regional climate of South Georgia is spatially heterogeneous (Bannister, ). Although the island is typically less than 30 km wide along its approximately 150 km length, its mountainous spine (Figure ) forms an effective physical barrier to the prevailing westerly winds of the lower troposphere (Figure b).…”

“…The World Meteorological Organization () defines föhn as a warm, dry, downslope wind, descending on the leeside of a mountain range as a result of synoptic‐scale, cross‐barrier flow. South Georgia's central mountain chain lies across the track of prevailing westerly winds, making the island's northeast coastal region susceptible to föhn (Bannister, ). Föhn has been identified as an important driver of extreme high temperatures and enhanced glacial melt at several Antarctic and subantarctic locations, including the McMurdo Dry Valleys (Speirs et al ., ), the Antarctic Peninsula (Cape et al ., ), and the South Orkney Islands (King et al ., ).…”

Estimación del efecto <em>Venturi</em> como factor desencadenante de la pluviometría en la Sierra de Grazalema

“…Su orientación y altitud determina que los vientos procedentes del Atlántico, cargados de humedad, estén obligados a ascender por las laderas a barlovento, lo que provoca su condensación y descarga pluvial en dicha exposición. Por otra parte, a sotavento, no se recibe precipitación alguna, conociéndose este efecto como föhn, altamente estudiado en numerosas áreas de montaña y regiones polares (Bannister & King, 2015;Nastos et al, 2017).…”