Equatorial ionospheric responses to high‐intensity long‐duration auroral electrojet activity (HILDCAA)

Abstract

The knowledge of the coupling processes between the magnetosphere and the equatorial ionosphere is of basic importance to the understanding of the near‐Earth space weather. This study focuses on observational results of such coupling processes based on data collected during the phenomenon defined as high‐intensity long‐duration continuous AE activity (HILDCAA) which occurs outside the main phase of geomagnetic storms. The fact that the responses of the equatorial/low‐latitude ionosphere to HILDCAA events have not been specifically focused so far is one of the motivations for this study. Ionosonde data on hmF2, h′F, and foF2 from three locations in Brazil (magnetic equatorial station São Luis (SL), subequatorial station Fortaleza (FZ), and low‐latitude station Cachoeira Paulista (CP)) are analyzed together with ACE satellite data on solar wind and interplanetary magnetic and electric fields during three HILDCAA events that occurred in the years 2000 and 2001. The results did not indicate any presence of penetrating electric field disturbance during these events. However, they provided clear evidence of disturbance dynamo electric field and disturbance thermospheric winds, through F layer height changes that were similar but generally less intense than those observed during a typical storm event. The foF2 presented no particular disturbances that can be clearly attributed to the HILDCAA event. Previous extensive studies carried out by the authors on ionospheric storm effects for these same three stations clearly illustrate the much more intense F layer storm disturbances compared with HILDCAA events disturbances.