Global ionospheric response to a periodic sequence of HSS/CIR events during the 2007-2008 solar minimum

TL;DR

This study analyzes the global ionospheric response to a series of high-speed solar wind streams during the 2007-2008 solar minimum, revealing complex nonlinear coupling and key parameters influencing ionospheric variability.

Contribution

It provides new insights into the nonlinear magnetosphere-ionosphere coupling and identifies the dominant solar wind parameters affecting ionospheric responses during HSS/CIR events.

Findings

NmF2 spectra show complex, nonlinear responses.

hmF2 correlates more closely with solar wind parameters.

Ionospheric response is more strongly linked to Bz and SYM-H.

Abstract

In this study, we investigate the global ionospheric impact of high-speed solar wind streams/corotating interaction regions (HSS/CIR). A series of ten such events are identified between December 1st 2007 and April 29th 2008, characterized in the frequency domain by the main spectral peaks corresponding to 27, 13.5, 9 and 6.75 days. The spectra of solar wind magnetic field, speed and proton density, as well as those of the geomagnetic indices AE and SYM-H are solely dominated by these features. By contrast, the ionospheric NmF2 and to a lesser extent the hmF2 spectra have a much more complex structure, with secondary peaks adding to or replacing the main ones. We argue that this is evidence of the nonlinear nature of the magnetosphere-ionosphere coupling, highlighted particularly in the NmF2 ionospheric response. Additionally, we show that hmF2 is more closely correlated than NmF2 to all parameters describing the solar wind and geomagnetic activity. Finally, the ionospheric response shows higher correlation with Bz than any other solar wind parameter, and higher with SYM-H than AE, indicating that for the low-frequency part of the spectrum, high-latitude Joule heating and particle precipitation play a secondary role to that of prompt penetration electric fields in dictating the ionospheric response to geomagnetic activity, in the case of this sequence of HSS/CIR events.