Tidal signatures of the thermospheric mass density and zonal wind at midlatitude: CHAMP and GRACE observations

C Xiong,Y.-L Zhou,H Lühr,S.-Y Ma

doi:10.5194/angeo-33-185-2015

C Xiong, Y.-L Zhou + Show 2 more

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https://doi.org/10.5194/angeo-33-185-2015

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Abstract

Abstract. By using the accelerometer measurements from CHAMP and GRACE satellites, the tidal signatures of the thermospheric mass density and zonal wind at midlatitudes have been analyzed in this study. The results show that the mass density and zonal wind at southern midlatitudes are dominated by a longitudinal wave-1 pattern. The most prominent tidal components in mass density and zonal wind are the diurnal tides D0 and DW2 and the semidiurnal tides SW1 and SW3. This is consistent with the tidal signatures in the F region electron density at midlatitudes as reported by Xiong and Lühr (2014). These same tidal components are observed both in the thermospheric and ionospheric quantities, supporting a mechanism that the non-migrating tides in the upper atmosphere are excited in situ by ion–neutral interactions at midlatitudes, consistent with the modeling results of Jones Jr. et al. (2013). We regard the thermospheric dynamics as the main driver for the electron density tidal structures. An example is the in-phase variation of D0 between electron density and mass density in both hemispheres. Further research including coupled atmospheric models is probably needed for explaining the similarities and differences between thermospheric and ionospheric tidal signals at midlatitudes.

Highlights

The ionosphere–thermosphere (IT) system represents the transition region from Earth’s atmosphere to space
The purpose of the study is to compare the tidal effects on the thermospheric mass density and zonal wind with that of the electron density; the same method for deriving the tidal components has been used as described in Xiong and Lühr (2014)
In order to compare the tidal features of the topside ionosphere that are related to midlatitude summer nighttime anomaly (MSNA), as reported by Xiong and Lühr (2014), the same magnetic latitude (MLAT) range (±40 to ±60◦) has been selected for the thermospheric mass density and zonal wind measurements

Summary

Introduction

The ionosphere–thermosphere (IT) system represents the transition region from Earth’s atmosphere to space. Understanding ionosphere–thermosphere dynamics and electrodynamics is paramount when considering the necessity for more accurate space weather forecasts In recent years, both observational and theoretical studies have shown that a larger part of the variability in the global IT system is associated with lower atmospheric processes, especially the influence of various waves. Non-migrating tides are excited for instance by zonal asymmetries (e.g., topography, land-sea differences, longitude dependence of absorbing species) (Forbes et al, 2003) or by nonlinear interactions between the migrating diurnal tide and planetary waves (Hagan and Roble, 2001) or gravity waves (McLandress and Ward, 1994) Another important source for non-migrating tides is the latent heat release in the troposphere (Hagan and Forbes, 2002)

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