A Comparative Study of Magnetic Storm Effects on the Ionosphere in Polar Cap and Auroal Oval —F‐Region Negative Storm

Abstract

AbstractWith coordinated EISCAT and ESR radar data, ionospheric storm in both the dayside polar cap and the auroral oval during the major magnetic storm of May 15, 1997 is studied, focusing on the F‐region negative storm. It is found that in both the polar cap and the auroral zone a F1‐like peak of ionization appeared at 190km height during the main and recovery phase of the storm, while the normal F2 peak disappeared and great depletions of electron density occurred. In contrast, variations of ion temperature are very different in the two regions, with little change in polar cap while strong enhancement in auroral oval, implying a difference in key mechanisms for the negative storms in the two regions. The increased O+ ion loss rate through chemical reaction due to Joule heating and ion temperature enhancement, which are resulted from strong electric field, played a crucial role in the auroral zone. The plasma transport process, however, especially the long‐lasting large ion upflow, is of great importance in the polar cap. In addition, large F‐region electron density depletion associated with null Joule heating and ion temperature enhancement is observed by EISCAT radar in the transient region of the two cells of plasma convection, which is caused by strong field‐aligned O+ ion outflow when the radar passing through probably under the polar cleft ion fountain region.