A foehn climatology of the McMurdo Dry Valleys of Antarctica using satellite remote sensing data
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This thesis investigates the McMurdo Dry Valley (MDV) foehn meteorology and its impact on the region's hydrology utilizing satellite remote sensing data and in-situ meteorological observations. It aims to establish Satellite Remote Sensing as a tool for studying the spatiotemporal variabilities in surface temperatures across MDV. The thesis utilizes Land Surface Temperature (LST) data from the MODIS sensor mounted atop Aqua and Terra satellites, along with the meteorological and stream discharge data from Automatic Weather Stations (AWS)s and stream gauges installed by Long Term Ecological Research (LTER) program. The research assesses the long-term (18 years: 2000-2017) summer meteorology recorded by the AWSs and investigates their inter and intra-valley variabilities across MDV. The thesis identifies the control of summer foehn-induced warming and incoming shortwave radiation (radiative warming) in influencing the valley floor temperatures along with the trends in the occurrence of strong foehn events that occur mostly during clear sky days. As the thesis works into understanding wider spatial scale changes in temperatures using satellite LST data, it checks the data for inconsistencies and evaluates its accuracy and sensitivity to register the day-to-day temperature changes in the valley floor. It recognizes satellite-derived LST to be a reliable dataset for studying the meteorology-induced temperature variations across the valleys.
Over-dependence of foehn's study on in-situ measurement had been a major obstacle in comprehending the meteorological variations that are associated with foehn winds over a wider spatial scale. The study, therefore, developed a methodology that can not only detect foehn in MDV without AWS support but also identify the various degree of warming each region experienced during a foehn event. The methodology developed detected foehn events in MDV using long-term satellite LST data for summer and winter periods individually. Due to the independence of the methodology in using AWS data, this technique can be utilized in the areas where there are no AWSs installed.
The thesis overcame the constraints of investigating temperature fluctuations in the valley floor due to foehn winds, using in-situ measurements from a single location by investigating satellite-derived LSTs' spatiotemporal changes across MDV. It examines the influence of terrain properties on the LST values across the region and later investigates the spatio-temporal changes in surface temperatures that occur during a major foehn event over the 2015-16 summer. The thesis later differentiates the spatial temperature signatures that are associated with foehn-induced warming (adiabatic warming) from that of radiative warming. Foehn events in MDV trigger higher and more uniform warming of the valley floor compared to radiative warming, which affects the differential warming of each location based on albedo.
To identify the varying foehn-induced warming across the valleys, the study delineates the areas in the regions based on their warming. The warming across the valley floor during foehn is categorized into low, moderate, and high category groups, and potential hotspots associated with each group are identified that have temperatures that are higher than the rest of the valley. It was found that the lower elevation areas in the valley floor experienced a greater number of days with a higher degree of warming in the region.
The meteorology associated with foehn events during summer is often responsible for high glacial melt and flooding of the streams in the region, as a result, the summer meteorology controls the regions’ hydrology and biodiversity. The thesis presents a broader study on the impact of valley floor temperature changes on the streams' hydrology using satellite LST datasets. It was able to identify the hotspots across the MDV floor that recorded a higher number of days with temperatures above melting point than the rest of the valley. The study recognizes the importance of incoming solar radiation in triggering high glacial melt over the summer. Austral summer ISWR can cause high glacial melt in large glacial sources like Brownworth despite fewer foehn hours. It was found that two seasons with high-frequency foehn events may have a different glacial melt due to differences in incoming solar radiation.
Lastly, the thesis is the first climatological study carried out on MDV using satellite remote sensing and delves into the wider spatial scale study of MDV foehn events and their effects on the region's temperature and hydrology.