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Title: The spatial and temporal distribution of foehn winds on the Larsen C ice shelf, Antarctica
Author: Turton, Jenny Victoria
ISNI:       0000 0004 6424 7117
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2017
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The Antarctic Peninsula (AP) was the fastest warming region on earth during the 20th century. The eastern side of the Peninsula is typically 5-10K colder than at equivalent latitudes on the western side. Despite this cooler climate, a number of ice shelves have collapsed in the last two decades. In 1995 Larsen A collapsed, shortly followed by Larsen B in 2002. Larsen C Ice Shelf (LCIS), the largest remaining ice shelf, is now showing evidence of potential destabilisation, including melt ponding and rift acceleration. The `hydrofracture mechanism’ suggests that percolation of melt water into crevasses allows them to deepen and extend to the ice shelf base, which leads to destabilisation. Advection of warm, dry air onto the ice shelf from foehn winds is partly responsible for the melt water. Investigating foehn winds over LCIS was one aim of the Orographic Flow and Climate of the Antarctic Peninsula (OFCAP) project. The aim of this research is to investigate the spatial distribution and frequency of the foehn winds, and assess their impact on the LCIS. To investigate this, near-surface observational data at six locations is combined with archived regional model output at 5km horizontal-resolution from the Antarctic Mesoscale Prediction System (AMPS). A novel semi-automatic algorithm has been developed to detect foehn winds from near-surface observations. A relatively new algorithm has been adapted for use over the AP, to detect foehn conditions from the AMPS output. Foehn characteristics over the ice shelf have been identified to create a mini-climatology of the location and occurrence of foehn winds from 2009 to 2012. Foehn conditions have been observed as far south as ~68S for the first time. Foehn events are most frequent in spring, when over 50% of days can experience the warm, dry winds. The average length of foehn events is approximately 12 hours, but they can occur in quick succession to have a longer-lasting effect. Some of the spatial features within the foehn flow were investigated further using high-resolution (1.5km) Weather Research and Forecasting (WRF) model. Foehn jets, hydraulic jumps and localised foehn enhancement were simulated by WRF in four case studies. The presence of a statically-stable cold pool over the ice shelf appears to reduce the propagation of foehn air, and interrupt the near-surface signal. When foehn winds occur in late spring they prompt earlier melt onset, increase the number of melt days and lengthen the melt season. Foehn-induced surface melting has been observed over 130km from the mountains. This research has highlighted the potential destabilising effect of foehn winds, which may provide an insight into the stability of the LCIS.
Supervisor: Ross, Andrew ; Kirchgaessner, Amelie ; King, John Sponsor: NERC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available