Localized thermosphere ionization events during the high-speed stream interval of 29 April to 5 May 2011

Abstract

We analyze localized ionospheric-thermospheric (IT) events in response to external driving by a high-speed stream (HSS) during the ascending phase of the Solar Cycle 24. The HSS event occurred from ∼ 29 April to 5 May, 2011. The HSS itself (and not the associated corotating interaction region) caused a moderate geomagnetic storm with peak SYM-H = -55 nT and prolonged auroral activity. We analyze TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) measurements of nitric oxide (NO) cooling emission during the interval as a measure of thermospheric response to auroral heating. We identify several local cooling emission (LCE) events in high to subauroral latitudes. Individual cooling emission profiles during these LCE events are enhanced at ionospheric E layer altitudes. For the first time, we present electron density profiles in the vicinity of the LCE events using collocated COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) radio occultation (RO) measurements. Measurements at local nighttime show the formation of an enhanced E layer (about 2.5 times increase over the undisturbed value) at ≥100 km altitude. Daytime electron density profiles show relatively smaller enhancements in the E layer. We suggest that the IT response is due to additional ionization caused by medium energy electron (>10 keV) precipitation into the subauroral to high-latitude atmosphere associated with geomagnetic activity during the HSS event.