Responses of Ionospheric Radial Currents to Subauroral Polarization Streams During Quiet Periods

Using 4 years of ionospheric radial current (IRC) from Swarm and ion velocity from the Defense Meteorological Satellite Program, our work investigates the response of IRC to the subauroral polarization streams (SAPS) during the quiet time for the first time. Both noontime (magnetic local time, MLT 11-14) inward and duskside (MLT 18-19) outward IRC get strengthened in amplitude. The noontime inward Delta IRC is attributed to the penetration westward electric field at low-mid latitudes. It drives the poleward Hall currents and equatorward polarization electric field, which maps to the dip equator to form an inward Delta IRC at F layer. At dusk, the SAPS-poleward electric field could directly penetrate to the low-mid latitudes, mapping to the dip equator to drive the outward Delta IRC. The substorms-associated westward electric field is also critical in modulation of Delta IRC, resulting in a larger inward (weaker outward) Delta IRC under high auroral electrojet (AE) index than that under low AE around noon (dusk). Earth's ionosphere-thermosphere (I-T) system has a series of interesting phenomenon at different latitude bands, for instance, the ionospheric radial current (IRC) and subauroral polarization stream (SAPS). IRC is the radial current in the F-region over the dip equator, and SAPS is the fast westward plasma flow at subauroral latitudes. So far, whether IRC is modulated by SAPS remains unclear. This is the first observation of the response of IRC at dip equator to SAPS at mid-latitudes during quiet and substorm periods, which could help us further understand the I-T coupled system in the geospace. Noontime inward ionospheric radial current (IRC) are generated due to quiet time subauroral polarization streams (SAPS)Duskside outward IRC is developed due to quiet time SAPSSubstorm westward electric field facilitates (prevents) the formation of noon inward (dusk outward) IRC