Cloud-drift and Water VaporWinds in the Polar Regions from MODIS

Tropospheric winds play an important role in the energy and mass balances of thepolar regions. Mid- and upper-level winds control the horizontal flow of heat and moisture to, from, and within the Arctic and Antarctic. However, no routine measurements of winds are made over the Arctic Ocean and most of the Antarctic continent. While geostationary satellites provide useful wind information in the low and midlatitudes, they are of limited use at high latitudes. Can polar-orbiting satellites be used to obtain wind information in the polar regions? An examination of orbital characteristics shows that equatorward of 60 degrees latitude the temporal sampling provided by two satellites is too sparse to obtain meaningful wind estimates. However, poleward of about 70 degrees the coverage is such that useful wind information can be obtained throughout the course of a day.

Here we present preliminary results from a project to estimate winds in the polar regions by tracking clouds and water vapor in MODerate-resolution Imaging Spectroradiometer (MODIS) data. The automated procedure that is currently used for geostationary satellite cloud-drift winds has been modified for use with MODIS, taking advantage of MODIS' high spatial resolution and its advanced capabilities for surface/cloud discrimination and cloud height determination. Estimates of wind speed, direction, and altitude will be shown for case studies in both polar regions. Ultimately we expect that the assimilation of these satellite-derived wind estimates in regional and global models will improve forecasts. Samples of other high-latitude products will also be shown.