Meridional winds derived from COSMIC radio occultation measurements

Abstract

Meridional winds at the magnetic meridian in the upper thermosphere are derived from the peak height and density of the ionospheric F2 layer as retrieved by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites for 4 months from November 2006 to February 2007. These winds (referred to as COSMIC winds) are first validated by comparison at multiple locations with winds obtained from ground‐based incoherent scatter radar (ISR) and Fabry‐Perot interferometer (FPI) measurements. Then longitudinal variations of these winds are investigated and compared with simulations by the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR TIE‐GCM). The results show generally good agreement between COSMIC winds, ground‐based measurements, and the simulations. Significant longitudinal variations are presented in the COSMIC winds. At 40°N (local winter), around midnight the COSMIC winds exhibit stronger and longer‐duration equatorward velocities within 110°W–20°W (large negative magnetic declination sector) than those in other longitudes; during late morning hours the poleward winds show similar longitudinal variations. At 40°S (local summer), during the daytime the poleward winds are stronger within 120°E–110°W (large positive magnetic declination sector) than in 60°W–90°E (large negative magnetic declination sector), while during the nighttime the maximum equatorward winds shifts about 2 h later in 60°W–90°E than in 120°E–110°W. Analysis of the TIE‐GCM simulations suggests that the longitudinal variation of meridional winds is mainly induced by magnetic declination due to the contribution of geographic zonal wind.