Response of Dayside Thermosphere to an Intense Geomagnetic Storm

Abstract

INCREASES in the density of the neutral thermosphere associated with geomagnetic activity were first noted by Jacchia¹. Although the thermosphere will not be in equilibrium, and acceleration by electrodynamic forces may be involved, on balance the increased density must reflect additional heating. Further studies^2–4 by orbital drag analysis from observations of artificial Earth satellites have led to a complex and somewhat confusing picture. The heating seems to be slightly greater^3,4 at high latitudes and, for larger disturbances, sometimes much greater^2,3. Also, the heating seems to be slightly greater^3,4 on the nightside, but possibly with the opposite trend³ for larger disturbances (K_p > 5). Jacchia et al.³ also found that the time delay between the peak of the storm, as measured by the planetary 3-h indices K_p or a_p, and the maximum response was a little shorter at high latitudes; on the other hand Roemer⁴ concluded that the time delay was independent of latitude, height or local time.