HL-TWiM empirical model of high-latitude upper thermospheric winds

HL-TWiM represents the large-scale neutral wind circulation, in geomagnetic coordinates, for the given input conditions. The model synthesizes the most extensive collection to date of historical high-latitude wind measurements; it is based on statistical analyses of several decades of F region thermospheric wind measurements from 21 ground-based stations (Fabry-Perot Interferometers and Scanning Doppler Imaging Fabry-Perot Interferometers) located at various northern and southern high latitudes and two space-based instruments (UARS WINDII and GOCE).

The geomagnetic latitude and local time dependences in HL-TWiM are represented using vector spherical harmonics, day of year and longitude variations are represented using simple harmonic functions, and the geomagnetic activity dependence is represented using quadratic B splines. In this paper, we describe the HL-TWiM formulation and fitting procedures, and we verify the model against the neutral wind databases used in its formulation.