High-latitude cloud-drift winds from MODIS

Tropospheric winds play an important role in the energy and mass balances of sea ice and the ice sheets. Mid- and upper-level winds control the horizontal flow of heat and moisture to, from, and within the polar regions. 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 little use at high latitudes due to poor spatial resolution.

In this paper we present results from a new project to estimate winds in the polar regions by tracking clouds and water vapor in MODIS imagery. The automated procedure currently used for geostationary satellite cloud-drift winds has been modified for use with MODIS, taking advantage of MODIS' advanced surface/cloud discrimination, high spatial resolution (1 km). It will be shown that equatorward of 60 degrees latitude the temporal sampling of the Terra and future Aqua polar-orbiting satellites is too sparse to obtain meaningful wind estimates, but poleward of about 75 degrees the coverage is such that useful wind information can be obtained throughout the course of a day. Estimates of wind speed, direction, and altitude will be shown for a number of case studies in both polar regions. The feasibility of tracking water vapor in clear sky areas will also be discussed. Ultimately, we expect that the assimilation of these satellite-derived wind estimates in coupled ice-atmosphere models will improve our ability to predict changes in the surface energy balance and ice mass.