The Impact of Satellite-Derived Polar Winds on Lower-Latitude Forecasts

Abstract

The use of atmospheric motion vectors (AMVs) in NWP models continues to be an important source of information in data-sparse regions. These AMVs are derived from a time sequence of images from geostationary and polar-orbiting satellites. NWP centers have documented positive impact on model forecasts not only in regions where the AMVs are measured, but elsewhere as well. One example is the effect of the Moderate Resolution Imaging Spectroradiometer (MODIS) polar winds on forecasts in the middle and lower latitudes. Using a preoperational version of NCEP?s Global Forecast System (GFS), an experiment was run during August and September 2004, with and without the MODIS polar winds. Several cases within this period were analyzed to determine how winds poleward of 70° latitude affect the height and wind fields into lower latitudes. From the five cases examined, it was determined that the addition of the polar winds modifies the mass balance in synoptic-scale waves near the polar jet streams. This change in mass balance is evident in differences in the ageostrophic wind, which has an effect on the speed and amplitude of baroclinic waves that extends from the jet stream into lower latitudes in later forecast times. These results reveal the substantial impact that polar-only observations may have on the predictability of global weather systems.