Auroral electrojets variations caused by recurrent high‐speed solar wind streams during the extreme solar minimum of 2008

Abstract

The IMAGE network magnetic measurements are used to investigate the response of the auroral electrojets to the recurrent high‐speed solar wind streams (HSSs) during the extreme solar minimum period of 2008. We first compare the global AU/AL indices with the corresponding IU/IL indices determined from the IMAGE magnetometer chain and find that the local IMAGE chain can better monitor the activity in MLT sectors 1230–2230 for IU and 2230–0630 for IL during 2008. In the optimal MLT sectors, the eastward and westward electrojets and their central latitude reveal clear 9‐day periodic variations associated with the recurrent HSSs. For the 9‐day perturbations, both the eastward and westward electrojet currents are better correlated with parallel electric field (EPAR) and electron hemispheric power (HPe) than with other forcing parameters. Interestingly, the eastward electrojet shows good correlations (r > 0.6) with EPAR and HPe only in part of its optimal MLT‐sector, roughly 1200–1800, while the westward electrojet shows good correlations (r < −0.6) with EPAR and HPe in its whole optimal MLT sector. The poor correlations between the eastward electrojet and EPAR and HPe in the MLT sector 1800–2200 might be attributed to the impact of other magnetosphere‐ionosphere coupling processes. The sensitivities of the eastward and westward electrojet currents to EPAR are close to 0.06 MA/(mV/m) and −0.12 MA/(mV/m), respectively, and the sensitivities of their central latitudes to EPAR are close to −2.83 Deg/(mV/m) and −2.14 Deg/(mV/m), respectively. The observed auroral electrojet response to the recurrent solar wind forcing provides new opportunities to study the physical processes governing the eastward and westward auroral electrojets.