Abstract
Off the coast of Victoria Land, Antarctica an area of open water—the Terra Nova Bay Polynya (TNBP)—persists throughout the austral winter. The development of this coastal polynya is driven by extreme katabatic winds blowing down the slopes of Transantarctic Mountains. The surface-atmosphere coupling and ABL transformation during the katabatic wind events between 18 and 25 September 2012 in Terra Nova Bay are studied, using observations from Aerosonde unmanned aircraft system (UAS), numerical modeling results and Antarctic Weather Station (AWS) measurements. First, we analyze how the persistence and strength of the katabatic winds relate to sea level pressure (SLP) changes in the region throughout the studied period. Secondly, the polynya extent variations are analysed in relation to wind speed changes. We conclude that the intensity of the flow, surface conditions in the bay and regional SLP fluctuations are all interconnected and contribute to polynya development. We also analyse the Antarctic Mesoscale Prediction System (AMPS) forecast for the studied period and find out that incorrect representation of vertical ABL properties over the TNBP might be caused by overestimated sea ice concentrations (SIC) used as model input. Altogether, this research provides a unique description of TNBP development and its interactions with the atmosphere and katabatic winds.
Highlights
Terra Nova Bay is located in the western Ross Sea, between Cape Washington in the North and the Drygalski Ice Tongue in the south, along the coast of Victoria Land, Antarctica (Figure 1)
Antarctic Mesoscale Prediction System (AMPS) is a real time mesoscale modelling system providing numerical forecasts for the Antarctic since 2000 [45]. It is run at the Mesoscale and Microscale Meteorology (MMM) Division of the National
The boundary conditions were assimilated by the Weather Research and Forecasting (WRF) Data Assimilation System (WRFDA) with a three dimensional variational data assimilation (3DVAR) approach from the output of NCEP Global Forecast System (GFS; [46])
Summary
Terra Nova Bay is located in the western Ross Sea, between Cape Washington in the North and the Drygalski Ice Tongue in the south, along the coast of Victoria Land, Antarctica (Figure 1). An ice-free stretch of sea persists there throughout the winter—the Terra Nova Bay Polynya (TNBP), forced by sea ice removal from the coast by strong offshore winds and maintained due to the presence of Drygalski Ice Tongue, which blocks the transport of ice from the south [1]. Turner et al [5] concludes that the enhancement of the strong wind events is dependent on the location of the storm offshore and Ebner et al [6] adds that when a cyclone moves from west to east along the Anatarctic coast it promotes the intensification of a downslope flow. The passage of a low pressure system in the Ross Sea or presence of a cyclone to the east of Terra Nova Bay is often accompanied by stronger and longer extreme winds events [7,8]. We acknowledge that they are rather a mix of katabatic, downslope and offshore flow
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