Weather and Climate Systems

Concordiasi Dropsondes: Improved Characterization of Errors in the Antarctic Mesoscale Prediction System

James Russell
OU School of Meteorology

16 April 2014, 3:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The Antarctic Mesoscale Prediction System (AMPS) is a real-time, limited-area numerical weather prediction model with domains covering the Antarctic and its surrounding regions. AMPS simulations provide logistical support to the United States Antarctic Program and numerous other international interests in Antarctica. Extreme conditions in the region are associated with unique challenges to modelling efforts including the implementation of accurate physical parameterizations. Efforts to evaluate and improve AMPS have been hampered by the limited spatial coverage of observations. During the fall of 2010, special dropsonde observations were obtained in an intensive observation period during the Concordiasi field program, providing a unique opportunity to evaluate both upper- and lower-level model performance in an otherwise data-sparse region of the globe.
In this study, we discuss differences between AMPS forecasts and Concordiasi dropsondes. Results indicate that model bias characteristics largely fall into four subsets: those over the Antarctic continent land areas, those over ocean areas, and to a lesser extent, during the day and during the night. Over land, the surface inversion is much weaker in AMPS, resulting in an elevated cold bias of approximately 3 K. Also over land, boundary-layer temperature, relative humidity, and wind speed biases are 4 K, -20%, and -2 m/s, respectively. Over ocean, warm and dry biases are centred below the 700-hPa level. Since these biases grow with forecast lead-time it is proposed that they are the result of physical parameterizations. It is hypothesised that the latter biases are a result of an under-predictions of clouds.

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