Geomagnetic storm effects in the low‐ to middle‐latitude upper thermosphere

Abstract

In this paper, we use data from the Dynamics Explorer 2 (DE 2) satellite and a theoretical simulation made by using the National Center for Atmospheric Research thermosphere/ionosphere general circulation model (NCAR‐TIGCM) to study storm‐induced changes in the structure of the upper thermosphere in the low‐ to middle‐latitude (20°‐40°N) region of the winter hemisphere. Our principal results are as follows: (1) The winds associated with the diurnal tide weaken during geomagnetic storms, causing primarily zonally oriented changes in the evening sector, few changes in the middle of the afternoon, a combination of zonal and meridional changes in the late morning region, and mainly meridional changes early in the morning. (2) Decreases in the magnitudes of the horizontal winds associated with the diurnal tide lead to a net downward tendency in the vertical winds blowing through a constant pressure surface. (3) Because of these changes in the vertical wind, there is an increase in compressional heating (or a decrease in cooling through expansion), and thus temperatures in the low‐ to middle‐latitudes of the winter hemisphere increase. (4) Densities of all neutral species increase on a constant height surface, but the pattern of changes in the O/N2 ratio is not well ordered on these surfaces. (5) The pattern of changes in the O/N2 ratio is better ordered on constant pressure surfaces. The increases in this ratio on constant pressure surfaces in the low‐ to middle‐latitude, winter hemisphere are caused by a more downward tendency in the vertical winds that blow through the constant pressure surfaces. Nitrogen‐poor air is then advected downward through the pressure surface, increasing the O/N2 ratio. (6) The daytime geographical distribution of the modeled increases in the O/N2 ratio on a constant pressure surface in the low‐ to middle‐latitudes of the winter hemisphere correspond very closely with those of increases in the modeled electron densities at the F2 peak.

Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model

“…10a, b). The same result is con®rmed by numerous satellite observations of thermospheric composition at low to middle latitudes (Hedin et al, 1977;ProÈ lss, 1982;Burrage et al, 1992;Burns and Killeen, 1992;Burns et al, 1995b) as well as closer examination of [O] density by ground-based incoherent scatter and Fabry±Perrot measurements (Burnside et al, 1991). They show that the thermospheric response to a geomagnetic storm at low to middle latitudes consists of a quite moderate density increase of all atmospheric constituents, while the ratio…”

“…Zuzic et al (1997) Burns et al (1995a) may not be a salient feature of the disturbed thermosphere. ProÈ lss et al (1998) repeated the magnetic storm modelling of December 8, 1992 (Burns et al, 1995b) using both the TIGCM and the CTIM. They compared both simulations with neutral gas measurements of the Dynamics Explorer 2 satellite and found that both models significantly overestimate the increase in the O/N 2 density ratio at mid and low latitudes (on a constant pressure surface).…”

Ionospheric Day-to-Day Variability Around the Whole Heliosphere Interval in 2008

“…The negative storm effects occurred often during the main and recovery phases of storms (Abdu, 1997;Cander and Mihajlovic, 2005). Negative storm effects at high and middle latitudes are caused primarily by neutral composition changes due to the upwelling of molecular-rich air to higher altitudes driven by storm-time enhanced Joule heating (Mayr, Harris, and Spencer, 1978;Burns et al, 1995;Fuller-Rowell et al, 1994). The negative storm effects around the geomagnetic Equator are more closely related to changes in transportation caused by penetration electric fields (Lei et al, 2008c;Wang et al, 2010), as well as changes in neutral composition at later times during strong storms (Prölss, 1995;Buonsanto, 1999).…”

Global O/N2 derived from DE 1 FUV dayglow data: Technique and examples from two storm periods

“…An extensive bibliography exists on the response of the global thermosphere to geomagnetic disturbances. Examples of recent papers on the subject are those by Burns et al [1991Burns et al [ , 1995, and Fuller-Rowe# et al [1994,1996], who base their findings on general circulation model results. Numerous references to past work may be found in these papers.…”