Publication:

Figure 1: Global maps of differential GPS TEC (left panels) and CMIT simulated TEC (right panels) between the disturbed day (December 15, 2004) and quiet day (December 13, 2004) from 1600 to 2200 UT.

(1) Ionospheric response to the initial phase of geomagnetic storms: 1. Common features: Wenbin Wang , Jiuhou Lei , Alan G. Burns , Stanley C. Solomon , Michael Wiltberger , Jiyao Xu, Yongliang Zhang, Larry Paxton, and Anthea Coster (Submitted to J. Geophys. Res, 2009)

Ionospheric responses to the initial phases of three geomagnetic storms: April 2–5, 2004; November 7–9, 2004, and December 13–16, 2006, were compared using both ground-based GPS total-electron-content (TEC) data and Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model simulations. The onset times for these storms all occurred at local daytime in the North American sector. This similarity of onset times and other factors resulted in some common features in their ionospheric response. These common features include: 1) Enhanced TEC (positive response) at low and middle latitudes in the daytime; 2) Depleted TEC (negative response) around the geomagnetic equator in the daytime; 3) A north-south asymmetry in the positive response as the northern hemispheric response appeared to be more pronounced; and 4) Negative response at high latitudes as the storms progressed. The CMIT model reproduced these features reasonably well (Figure 1). Analysis of model results showed that storm-time enhancements in the daytime eastward electric field were the primary cause of the observed positive storm effects at low and middle latitudes as well as the negative response around the geomagnetic equator in the daytime. These eastward electric field enhancements were caused by the penetration of high latitude electric fields to low latitudes during southward interplanetary-magnetic-field (IMF) periods, when IMF Bz oscillated between southward and northward direction in the initial, shock phase of the storms. Consequently, the ionosphere was lifted up at low and middle latitudes to heights where recombination was weak, allowing the plasma to exist for a long period and resulting in higher densities. In addition, the CMIT model showed that high-latitude negative storm responses were related to the enhancements in molecular nitrogen seen in TIMED/GUVI observations, whereas the negative storm effects around the geomagnetic equator were not associated with thermospheric composition changes, but were rather the result of plasma transport process.