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2018WCRPspon col July2018 01 1

NChampollion- Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

Description

Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air-snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in-situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2-year long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to be a permanent process. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from Southwest (the prevailing direction) to Southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002 - 2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow-atmosphere interactions in Antarctica which deserves further quantification and modelling.

Authors:  Nicolas Champollion, Ghislain Picard, Laurent Arnaud, Eric Lefebvre, Michel Fily

ESA-CliC-EGU Conference on Earth Observation and Cryospheric Science, Frascati, Italy, November 13-16, 2012

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(Media / MBrogioni- Analysis of The Spatial and Temporal Features of The East-Antarctic Plateau by means of Multifrequency Microwave Emission Data)
Antarctica is the last mostly unexplored continent on Earth. The knowledge of its dynamics is very limited due to the impervious environment which makes almost impossible the human presence and thus the ground research activities. The largest region of Antarctica is represented by the...

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