Ionosphere-thermosphere response to high-speed solar streams during 2018-2019 as observed by Swarm-C, GNSS TEC and modeled by SD/WACCM-X

Abstract:

In the declining phase of the solar cycle the polar coronal holes expand and form non-axisymmetric extensions toward the solar equator. These extensions enhance the occurrence of high-speed solar wind streams (HSS) and related co-rotating interaction regions (CIR) in the low-latitude heliosphere, and cause moderate, recurrent geomagnetic activity affecting the ionosphere and thermosphere (IT). A combination of dawn and dusk total mass density observations from the Swarm-C satellite near 460 km, GNSS total electron content (TEC), and output from the Specified-Dynamics (SD) Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) are used to investigate the IT response to quasi 9-day recurrent geomagnetic activity driven by three sequences of HSS/CIR events observed during November 2018 - April 2019. Both observations and model indicate a significant global-scale response in thermospheric neutral density and ionospheric TEC, F2-layer peak electron density (NmF2), and height maximum of the F2-layer (HmF2) associated with these HSS/CIR events. The SD/WACCM-X low- to mid-latitude temporal variability associated with these HSS/CIR events is found in general agreement with the Swarm-C and TEC observations, with some latitudinal dependency in the correlation functions. Model and observations demonstrate that the maximum neutral density and TEC amplitude response to these events can persist for several days after the onset of the activity. These results suggest that CIR/HSS events can have significant effects on the IT for several days after the CIR has ended, with effects that during solar minimum are comparable to those of coronal mass ejections (CME) events, at least in thermospheric neutral densities.