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. Short-term upper atmosphere variations due tomagnetospheric forcing are very complex, and neither well understood norcapably modeled due to limited observations. In this paper, mass densityvariations from 10 years of GRACE observations (2003–2013) are isolated viathe parameterization of annual, local solar time (LST), and solar cyclefluctuations using a principal component analysis (PCA) technique. Theresulting residual disturbances are investigated in terms of magnetosphericdrivers. The magnitude of high-frequency (δ &lt; 10 d)disturbances reveals unexpected dependencies on the solar cycle, seasonal,and an asymmetric behavior with smaller amplitudes in June in the southpolar region (SPR). This seasonal modulation might be related to theRussell–McPherron (RM) effect. Meanwhile, we find a similar pattern, althoughless pronounced, in the northern and equatorial regions. A possible cause ofthis latitudinal asymmetry might be the irregular shape of the Earth'smagnetic field (with the north dip pole close to Earth's rotation axis, andthe south dip pole far from that axis). After accounting for the solar cycleand seasonal dependencies by regression analysis to the magnitude of thehigh-frequency perturbations, the parameterization in terms of the disturbancegeomagnetic storm-time index Dst shows the best correlation, whereas the geomagneticvariation Am index and merging electric field Em are the best predictors interms of time delay. We test several mass density models, including JB2008,NRLMSISE-00, and TIEGCM, and find that they are unable to completelyreproduce the seasonal and solar cycle trends found in this study, and showa clear overestimation of about 100 % during low solar activity periods.

Solar cycle, seasonal, and asymmetric dependencies of thermospheric mass density disturbances due to magnetospheric forcing