Modeled IMF By Effects on the Polar Ionosphere and Thermosphere Coupling

摘要

There is still an inadequate understanding of how the interplanetary magnetic field (IMF) east-west component (B_y) affects thermospheric composition, and other ionospheric and thermospheric fields in a systematic way. Utilizing the state-of-art first-principles Coupled Magnetosphere Ionosphere Thermosphere (CMIT) modeling and TIMED/Global Ultraviolet Imager (GUVI)-observed ΣO/N_2 covering an entire solar cycle (year 2002-2016), as well as a neutral parcel trajectory tracing technique, we emphasize that not only the direction of B_y, but also its strength relative to the IMF north-south component (B_z) that has important effects on high latitude convection, Joule heating, electron density, neutral winds, and neutral composition patterns in the upper thermosphere. The Northern Hemisphere convection pattern becomes more twisted for positive B_y cases than negative cases: the dusk cell becomes more rounded compared with the dawn cell. Consequently, equatorward neutral winds are stronger during postmidnight hours in negative B_y cases than in positive B_y cases, creating a favorable condition for neutral composition disturbances (characterized by low ΣO/N_2) to expand to lower latitudes. This may lead to a more elongated ΣO/N_2 depletion area along the morning-premidnight direction for negative B_y conditions compared with the positive B_y conditions. Backward neutral parcel trajectories indicate that a lower ΣO/N_2 parcel in negative B_y cases comes from lower altitudes, as compared with that for positive B_y cases, leading to larger enhancements of N_2 in the former case.