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

Abstract

Understanding the complex dynamics of neutral winds in the upper atmosphere is crucial for understanding thermosphere-ionosphere interactions. However, the limited availability of measurements and data coverage has hindered the comprehensive characterisation of these winds. This feasibility study explores the potential of using existing data from the Swarm satellites to develop a reliable neutral horizontal wind product and improve our understanding of the upper atmosphere. Historically, observations of thermospheric neutral winds have relied on techniques such as Fabry-Pérot interferometers and incoherent scatter radar measurements, providing fragmented data from a few selected stations. Remote and satellite in-situ measurements, while covering a range of altitudes, mostly below 400 km, have also been limited in duration. These limitations have made it difficult to study the complex variations of the neutral winds in terms of latitude, diurnal, seasonal and solar cycle patterns. With over seven years of data, the Swarm satellites provide a unique and comprehensive resource for characterising neutral winds at different orbital altitudes and all local times. The feasibility study uses several Swarm data products in the horizontal momentum equation to solve for the neutral winds. Overall, this study highlights the complexity and uncertainties involved in obtaining reliable wind fields from Swarm data and emphasises the need for further research and validation in data processing and parameter determination to improve the understanding of neutral winds.