@article {714, title = {An Opposite Response of the Low-Latitude Ionosphere at Asian and American Sectors During Storm Recovery Phases: Drivers From Below or Above}, journal = {Journal of Geophysical Research: Space Physics}, volume = {124}, year = {2019}, month = {07/2019}, pages = {6266 - 6280}, abstract = {

n this study, we focus on the recovery phase of a geomagnetic storm that happened on 6{\textendash}11 September 2017. The ground-based total electron content data, as well as the F region in situ electron density, measured by the Swarm satellites show an interesting feature, revealing at low and equatorial latitudes on the dayside ionosphere prominent positive and negative responses at the Asian and American longitudinal sectors, respectively. The global distribution of thermospheric O/N2 ratio measured by global ultraviolet imager on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite cannot well explain such longitudinally opposite response of the ionosphere. Comparison between the equatorial electrojet variations from stations at Huancayo in Peru and Davao in the Philippines suggests that the longitudinally opposite ionospheric response should be closely associated with the interplay of E region electrodynamics. By further applying nonmigrating tidal analysis to the ground-based total electron content data, we find that the diurnal tidal components, D0 and DW2, as well as the semidiurnal component SW1, are clearly enhanced over prestorm days and persist into the early recovery phase, indicating the possibility of lower atmospheric forcing contributing to the longitudinally opposite response of the ionosphere on 9{\textendash}11 September 2017.

}, issn = {2169-9380}, doi = {10.1029/2019JA026917}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2019JA026917}, author = {Xiong, Chao and L{\"u}hr, Hermann and Yamazaki, Yosuke} } @article {411, title = {Strong ionospheric field-aligned currents for radial interplanetary magnetic fields}, journal = {Journal of Geophysical Research: Space Physics}, volume = {119}, year = {2014}, month = {05/2014}, pages = {3979 - 3995}, abstract = {

The present work has investigated the configuration of field-aligned currents (FACs) during a long period of radial interplanetary magnetic field (IMF) on 19 May 2002 by using high-resolution and precise vector magnetic field measurements of CHAMP satellite. During the interest period IMF By and Bz are weakly positive and Bx keeps pointing to the Earth for almost 10 h. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average. The cross polar cap potential calculated from Assimilative Mapping of Ionospheric Electrodynamics and derived from DMSP observations have average values of 10{\textendash}20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the dayside and nightside. At the south pole FACs diminish in intensity to magnitudes of about 0.1 μA/m2, the plasma convection maintains two-cell flow pattern, and the thermospheric density is quite low. However, there are obvious activities in the northern cusp region. One pair of FACs with a downward leg toward the pole and upward leg on the equatorward side emerge in the northern cusp region, exhibiting opposite polarity to FACs typical for duskward IMF orientation. An obvious sunward plasma flow channel persists during the whole period. These ionospheric features might be manifestations of an efficient magnetic reconnection process occurring in the northern magnetospheric flanks at high latitude. The enhanced ionospheric current systems might deposit large amount of Joule heating into the thermosphere. The air densities in the cusp region get enhanced and subsequently propagate equatorward on the dayside. Although geomagnetic indices during the radial IMF indicate low-level activity, the present study demonstrates that there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the northern polar cusp region.

}, keywords = {air upwelling, field-aligned currents, radial interplanetary magnetic field}, doi = {10.1002/2014JA019951}, url = {http://doi.wiley.com/10.1002/2014JA019951}, author = {Wang, Hui and L{\"u}hr, Hermann and Shue, Jih-Hong and Frey, Harald. U. and Kervalishvili, Guram and Huang, Tao and Cao, Xue and Pi, Gilbert and Ridley, Aaron J.} } @book {436, title = {High-Latitude Thermospheric Density and Wind Dependence on Solar and Magnetic Activity}, year = {2013}, pages = {189 - 205}, publisher = {Springer Netherlands}, organization = {Springer Netherlands}, address = {Dordrecht}, abstract = {

Processes in the high-latitude thermosphere are strongly controlled by the activity of the sun and by the geomagnetic field geometry. The CHAMP satellite, with its sensitive tri-axial accelerometer, provided detailed information about thermospheric dynamics over its mission life-time (2000{\textendash}2010), thus contributing significantly to the CAWSES (Climate And Weather of the Sun-Earth System) programme. In this chapter, studies on thermospheric winds and density anomalies at high magnetic latitudes are presented. Thermospheric winds above the poles are directed predominantly from day to night side. Observations, however, reveal a distinct difference between winds on the dawn and dusk sides at auroral latitudes. While on the dawn side fast zonal winds towards night are prevailing, an anti-cyclonic vortex is formed on the dusk side. For the explanation of these local time dependent features various thermodynamic and electrodynamic influences have to be considered. As an example for mass density variation the cusp-related density anomaly is studied. The amplitude of this prominent local peak in mass density is influenced by the level of solar flux (F10.7) and by the solar wind input into the magnetosphere as quantified by the electric field caused by reconnection. A prerequisite for the appearance of density anomalies is the presence of soft-energy particle precipitation. By combining CHAMP and EISCAT measurements, it has been shown that Joule heating, fuelled predominantly by small-scale field-aligned currents (FACs), causes a strong increase in temperature at altitudes below 200 km. As a consequence molecular-rich air is up-welling. A density anomaly is recorded at 400 km altitude. Combining different observations and numerical model results provides a plausible chain of processes leading to the observed cusp-related density anomaly.

}, isbn = {978-94-007-4347-2}, issn = {2194-5217}, doi = {10.1007/978-94-007-4348-9_11}, url = {http://www.springerlink.com/index/10.1007/978-94-007-4348-9http://www.springerlink.com/index/pdf/10.1007/978-94-007-4348-9http://www.springerlink.com/index/10.1007/978-94-007-4348-9_11http://www.springerlink.com/index/pdf/10.1007/978-94-007-4348-9_11}, author = {L{\"u}hr, Hermann and Marker, Stefanie} }