edu.ucar.opensky::articles:14564 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T03:19:36.885951 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d77s7pr1 Formation of the equatorial thermosphere anomaly trough: Local time and solar cycle variations 2014-12-01T00:00:00Z publication https://n2t.org/ark:/85065/d77s7pr1 https://doi.org/10.1002/2014JA020416 Hsu, V. author Thayer, J. author Lei, J. author Wang, Wenbin author UCAR/NCAR - Library publisher This paper evaluates the formation and behavior of the equatorial thermosphere anomaly (ETA) trough in neutral temperature and mass density using the National Center for Atmospheric Research thermosphere-ionosphere electrodynamics general circulation model under quiet geomagnetic activity and March equinox conditions. The driving mechanism for the generation of the ETA trough in the model is field-aligned ion drag. In our simulations, during the daytime, field-aligned ion drag on the north-south flanks of the magnetic equator causes a divergence in meridional winds, leading to an upward change in vertical winds, adiabatic cooling, and a reduction in neutral temperature of about 30 K over the magnetic equator near 400 km. This response closely links ETA behavior to variations in the equatorial ionosphere anomaly (EIA) associated with local time and solar cycle. As the EIA begins to disappear in the evening, the processes in the ETA mechanism recede, causing the ETA trough to subside. The ETA trough is not completely eliminated until about after 23:00 LT. In our simulations, the trough becomes more prominent as the solar cycle progresses from low (F10.7=80) to high (F10.7=180), in agreement with observations. The neutral-ion collision frequency (proportional to variations in electron density) controls ETA day-to-night and solar cycle variations, while plasma scale height and gradients in electron number density and plasma temperature produce a secondary structure in ETA local time behavior that varies with solar cycle levels. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2014 American Geophysical Union. None eng geoscientificInformation