Swarm in-situ neutral horizontal winds based on Swarm plasma and neutral density measurements

Abstract

In this presentation, we provide preliminary results of a new thermosphere neutral wind data product along the Swarm satellites. Thermosphere wind measurements are sparse in general, and in-situ measurements are nonexistent along Swarm. The neutral winds are key to understand the thermosphere-ionosphere dynamics. Thermospheric neutral winds mostly below 250 km in altitude have been observed by Fabry–Pérot interferometers during nighttime, and derived from incoherent scatter radar measurements for decades, but only at a few stations. In-situ measurements of neutral winds also exist covering various altitudes mostly below 400 km, but only for a limited period (e.g. GOCE and CHAMP satellites). Characterisation of the winds, for example, in terms of latitudinal, diurnal, seasonal, and solar cycle variations is a difficult task with these limited data. The literature, in general, also suggest disagreements between these data products not only by the technique used to derive the winds but also by the station. Unsurprisingly, the complex interconnectedness of neutral winds in upper atmospheric dynamics is not fully understood. Here, we use existing Swarm data products (neutral mass density, plasma density, and ion drift velocities) to derive the horizontal components of the in-situ neutral wind. We evaluate the new prototype data product against both empirical and physical models. We discuss the opportunity for a uniquely new data product with over 8 years (and continuing) of Swarm data to characterise neutral winds at all local times at its different altitudes, which start above 500 km.