The impact of satellite-derived polar winds in global forecast models

The use of Atmospheric Motion Vectors (AMVs) in Numerical Weather Prediction (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 subtropical latitudes.

Feature-tracked winds derived from a time-sequence of MODIS satellite imagery over the polar regions are routinely input into many operational global numerical models. These NWP centers report that the winds have a positive impact on forecasts not only in the polar regions, but also into mid- and lower-latitudes, especially in 3 to 5 day forecasts. However, the impact differs for different models.

Side-by-side experiments were run, with and without MODIS polar winds, using the National Centers for Environmental Prediction's (NCEP) Global Forecast System (GFS) and the Navy's Operational Global Atmospheric Prediction System (NOGAPS) models. Output from these experiments was analyzed by using a combination of model analyses and forecasts, with sophisticated visualization techniques, to determine the impact to global model fields. The differences in these model fields between the GFS and NOGAPS due to the inclusion of the MODIS winds are explained by data thinning, weighting of the wind observations, and characteristics of their respective assimilation systems.