An Evaluation of the Antarctic Mesoscale Prediction System using Unique New Data from the CONCORDIASI Field Program

The Antarctic Mesoscale Prediction System (AMPS, Polar WRF) is currently the only real-time, limited-area numerical weather prediction model (LAM) with a domain over the Antarctic continent and the surrounding region. AMPS simulations provide logistical support to numerous domestic and international interests in Antarctica including the United States Antarctic Program. Extreme conditions in the Antarctic region are associated with unique challenges to modelling efforts including the implementation of accurate physical parameterizations. Efforts to evaluate and improve the treatment of physical processes within AMPS have been hampered by the extreme and remote conditions in Antarctica which limit the spatial coverage of observations. Through a series of dropsonde launches from drifting stratospheric gondolas, the CONCORDIASI field project, in the fall of 2010, provided an unprecedented spatial coverage of around 640 upper air observations over a two-month period.

This study focuses on establishing and diagnosing the errors in AMPS by comparing the forecast soundings at different lead times against dropsonde observations made during CONCORDIASI. Interpolations to model eta coordinates and pressure levels provided a basis for analyzing the data through all levels of the troposphere as well as the lower stratosphere. A statistical analysis discovered substantial issues including consistent 1-2-K positive temperature biases and 3-4-K positive dew point biases at the surface during lead times ranging from 12-108 hours. Proposed causes of these errors include the radiation and snow parameterization schemes. An investigation using the Rapid Radiative Transfer Model is planned. In addition, vertical transport of moisture also appears to be an issue with large dew point biases of over 5 K and low correlations in the upper atmosphere. No substantial biases in the winds have been found. Further plans include a spatial analysis by surface characteristics and a comparison to the European Centre for Medium Range Weather Forecasting's operational global model to establish the benefit of LAM's in the Antarctic.