Neutral Wind Dynamics Preceding The Steve Occurrence And Their Possible Preconditioning Role In Steve Formation

Strong Thermal Emission Velocity Enhancement (STEVE) is a nightsky optical phenomenon of great research interest in recent years. Recent findings indicated that STEVE likely represents certain extremely intensified chemiluminescence airglow instead of traditional aurora. In this study, we investigate the patterns and variations of the neutral wind and temperature before the STEVE emergence using joint scanning Doppler imager (SDI 630 nm) and optical all-sky imager (ASI) observations, and make an initial effort to explore the potential preconditioning role of neutral winds in the STEVE production. Neutral winds enhance in westward and southward directions following substorm auroral intensification, and show an equatorward propagating trend from auroral latitudes. However, in STEVE events the enhanced equatorward winds feature a steep stop/reversal at certain subauroral latitude, and strong wind convergence is developed there. This pattern sustains for similar to 15-20 min, and then STEVE arises at about this stop latitude. The strength of the southward wind intensification and wind convergence is in general weaker or absent in nonSTEVE substorm events. We propose that enhanced equatorward winds may transport relevant neutrals species that are key to the STEVE airglow production to subauroral latitudes, and pile up at the stop latitude of the equatorward winds due to the strong convergence there. Such a transport/pileup effect led by the neutral winds may prepare a reservoir of neutral constituent which, when further aided by subauroral ion drift, leads to a dramatic increase of the airglow production and the STEVE occurrence.