Thermosphere and ionosphere response to subauroral polarization streams (SAPS): Model simulations

Abstract

[1] An empirical model of subauroral polarization streams (SAPS) has been incorporated into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). This SAPS driven TIEGCM is used to simulate the effect of SAPS on the global thermosphere and ionosphere during a moderate geomagnetically active period between day of year (DOY) 329 and 333 in 2008. Model results show: (1) SAPS caused an increase in global thermospheric temperature which became stronger with time. This neutral temperature increase was more significant in subauroral and auroral regions. Joule heating by the SAPS and the redistribution of this heat by dynamic processes were the primary mechanisms for the simulated global neutral temperature changes. (2) In the SAPS driven TIEGCM, the strong ion drag effect in the subauroral SAPS channel drove large changes in thermospheric winds. Zonal neutral winds had either an extra, separate channel of westward flow in the subauroral region in the afternoon-midnight sector or a broad westward wind jet that merged with the regular duskside auroral westward zonal neutral wind driven by the high latitude convection pattern. The exact latitudinal profile of the zonal winds depended on local time. (3) The response of neutral temperature and wind to SAPS was more significant at higher altitudes and exhibited seasonal/hemispheric asymmetry. (4) The heating to the thermosphere by SAPS also resulted in changes in thermospheric composition with upwelling of molecular rich air in subauroral and auroral regions and downwelling of atomic oxygen rich air at other latitudes. These changes in thermospheric composition contributed to the deeper and more extended ionospheric electron density depletions in subauroral middle latitude regions, as well as electron density increases along the equatorward edge of the SAPS channel in the afternoon sector.

Positive and negative ionospheric storms occurring during the 15 May 2005 geomagnetic superstorm

“…Another interesting feature is the signature of SED plume plasma shown by the Δ(O/N 2 ) polar plot as a local maximum (>0.02 and 0.01-0.02; indicated in red and pink, respectively) on the equatorward side of the trough and over the European sector (0-30°E). In good agreement with the results of Wang et al [2012], such Δ(O/N 2 ) increase is due to the downward surge of oxygen-rich air. Adding to their study, our results demonstrate that such surges can be associated with the downward flowing SED plume plasma.…”

“…Thus, this polar plot reveals that at trough latitudes there is a well-defined decrease in Δ(O/N 2 ) (ranging from À0.05 to À0.07; indicated in yellow, orange, and dark brown) that is due to the strong upward surges occurring in the trough region because of the intense frictional heating and thus transporting upward molecular-rich air from the lower thermosphere. These results are in good agreements with the Thermosphere Ionosphere Electrodynamics general circulation model (TIE-GCM) simulated results of Wang et al [2012] obtained for a moderately active (Kp = 4+) period. Another interesting feature is the signature of SED plume plasma shown by the Δ(O/N 2 ) polar plot as a local maximum (>0.02 and 0.01-0.02; indicated in red and pink, respectively) on the equatorward side of the trough and over the European sector (0-30°E).…”

“…But as the trough moved away from Chilton, the storm time F 2 layer height decreased from~200 km (at 0700 UT) tõ 140 km (at 1200 UT) compared to the nearly steady quiet time value of~260 km. Both the depletion of electron density and the lowering of F 2 layer during 0700-1200 UT (0700-1200 LT) over Chilton indicates downward surges of oxygen-rich air caused by convergent wind flows occurring away from the trough [Wang et al, 2012].…”

“…Meanwhile, away from the SAPS channel, some convergent downward plasma surges dominate [Wang et al, 2012]. These upward and downward plasma surges create also composition changes by decreasing the ratio of O and N 2 (indicated as O/N 2 ) in the auroral and trough regions and by increasing O/N 2 away from them, respectively [Cander and Mihajlovic, 2005;Wang et al, 2012]. TAD-related downward surges can also turn positive storms into negative storms [Vijaya Lekshmi et al, 2007].…”

“…As the midlatitude trough develops in the SAPS channel, the resultant SAPS-related upward plasma surges deepen the midlatitude trough and thus contribute to the development of negative storms at trough latitudes. Meanwhile, away from the SAPS channel, some convergent downward plasma surges dominate [Wang et al, 2012]. These upward and downward plasma surges create also composition changes by decreasing the ratio of O and N 2 (indicated as O/N 2 ) in the auroral and trough regions and by increasing O/N 2 away from them, respectively [Cander and Mihajlovic, 2005;Wang et al, 2012].…”