Deriving dynamics from GPS radio occultation: Three-dimensional wind fields for monitoring the climate

Global Positioning System (GPS) radio occultation (RO) measurements are proven highly useful for observing the thermal structure of the troposphere and stratosphere. Here we use RO data for the first time to derive climatological wind fields from sampling error-corrected geopotential height fields on isobaric surfaces from about 800 hPa to 3 hPa. We find monthly mean RO geostrophic wind and gradient wind fields (2007 to 2012, about 500 km horizontal resolution, outside tropics) to clearly capture all main wind features, with differences to atmospheric analysis winds being, in general, smaller than 2 m/s. Larger differences (up to 10 m/s) occur close to the subtropical jet where RO winds underestimate actual winds. Such biases are caused by the geostrophic and gradient wind approximations, while RO retrieval errors introduce negligible effect. These results demonstrate that RO wind fields are of high quality and can provide new information on troposphere-stratosphere dynamics, for the benefit of monitoring the climate from weekly to decadal scales.