Latitude-dependent delay in the responses of the equatorial electrojet and <i>S</i><sub><i>q</i></sub> currents to X-class solar flares

Abstract

Abstract. We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the S q and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of S q current outside the magnetic equator, in response to the flare radiation enhancement. The S q current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft Xrays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field.

Equatorial Ionospheric Electrodynamics Over Jicamarca During the 6–11 September 2017 Space Weather Event

“…The equatorial ionosphere is disturbed significantly during space weather events, including the solar flares and geomagnetic storms. When a solar flare erupts, the sudden enhancement in solar radiation increases the ionization in the E region and modifies the ionospheric electrodynamics (e.g., H. Liu et al, ; Nogueira et al, ; Xiong et al, ; Zhang, Liu, Le, & Chen, ). Solar flares often cause an impulsive increase in the dayside eastward EEJ (e.g., Manju et al, ; Rastogi et al, ; Xiong et al, ; Zhang, Liu, Le, & Chen, ) and also produce a westward increase under a counter electrojet condition (e.g., Rastogi et al, , ; Sripathi et al, ).…”

The Response of the D and E Regions of the Equatorial Ionosphere to Solar Flare Events

“…(2018), an equivalent current system of the geomagnetic crochets (SFE) during the 24 September 2011 flare event had a pattern similar to the background Sq current system at low and mid‐latitudes, and positive crochet was seen in the magnetometer measurements. However since the EEJ currents are weaker during the winter solstice period (Yamazaki & Maute, 2017, references there in), we can anticipate that any modifications in the conductivity can further modulate the electric field and hence the EEJ intensity (Nogueira et al., 2018; Qian et al., 2012; Richmond, 1973; Zhang et al., 2017). In fact, it has already been shown that compared to equinox and summer solstice, the magnitude of crochet is always small during the winter solstice period (Chakrabarty et al., 2013; Manju & Viswanathan, 2005).…”

“…Equation ). There are studies reporting variations in the Ex during solar flare events (Nogueira et al., 2018; Qian et al., 2012; Zhang et al., 2017). Any change in the conductivity or Ex can influence Ez as well.…”