Polar Wind retrievals using the Advanced Microwave Sounding Unit

Satellite-derived wind measurements are most valuable over the oceanic regions where fewer conventional observations exist. This lack of observational data extends over all latitudes, from the tropics to the polar regions. Recent results have shown that horizontal winds in polar regions estimated from satellite data have the capability to increase the accuracy of numerical model forecasts, illustrating the need for improved wind observations in these data sparse regions.

A satellite-based method for estimating the winds in tropical cyclones has been adapted for use at high latitudes. In this method, temperature profiles are calculated from radiances from the Advanced Microwave Sounding Unit (AMSU) which flies aboard NOAA's most recent polar-orbiting satellite series. Using the hydrostatic assumption and a 100-hPa height field from the GFS model as a boundary condition, the temperature profile is used to compute the height field as a function of pressure. A nonlinear balance equation is then solved for the streamfunction, from which the u and v components of the nondivergent wind may be calculated.

AMSU data were acquired over the Arctic north of 60oN from 2ƒ{17 December 2004, providing 81 swaths of data. Radiosonde profiles from 20 stations were also collected during this same time period. Comparisons of the satellite-retrieved temperature and wind profiles with collocated radiosondes are given.

Future work will focus on increasing the validation dataset and comparing this wind retrieval technique with other satellite-based methods, such as feature-tracked winds from GOES. In addition, NESDIS' operational polar-orbiting satellite retrievals, ATOVS, which uses both the HIRS and the AMSU instrument, will replace the current AMSU-only retrieval technique. The possibility of developing a multi-platform wind retrieval method will also be investigated.