Observations of ion‐neutral coupling associated with strong electrodynamic disturbances during the 2015 St. Patrick's Day storm

Abstract

We use incoherent scatter radar observations at Millstone Hill (MHO) and Arecibo (AO) and topside ionosphere in situ Defense Meteorological Satellite Program (DMSP) observations during the great geomagnetic storm on 17–18 March 2015 to conduct a focused study on ion‐neutral coupling and storm time ionosphere and thermosphere dynamics. Some of these observations were made around the time of large ionospheric drifts within a subauroral polarization stream (SAPS). During the storm main phase, we identify multiple disturbance characteristics in the North American late afternoon and dusk sector. (1) Strong subauroral westward drifts occurred between 20 and 24 UT near MHO, accompanied by a storm enhanced density plume passage over MHO in the afternoon with a poleward/upward ion drift. The strongly westward flow reached 2000 m/s speed near the poleward plume edge. (2) Prompt penetration electric field signatures, appearing as poleward/upward ion drifts on the dayside over both MHO and AO, were consistent with DMSP vertical drift data and contributed to plume development. (3) Meridional wind equatorward surges occurred during daytime hours at MHO, followed by 2–3 h period oscillations at both MHO and AO. The zonal electric field at AO was strongly correlated with the wind oscillation. (4) Large ion temperature enhancements as well as 50+ m/s upward ion drifts throughout the E and F regions were observed during the SAPS period. These were presumably caused by strong frictional heating due to large plasma drifts. The heating effects appeared to drive significant atmospheric upwelling, and corresponding ion upflow was also observed briefly. This study highlights some of the important effects of fast plasma transport as well as other disturbance dynamics on ion‐neutral coupling during a single intensification period within a great geomagnetic storm.

Traveling Ionospheric Disturbances and Ionospheric Perturbations Associated With Solar Flares in September 2017

“…Rapid postflare responses in neutral density were also observed previously (Liu et al, ; Sutton et al, ). The intensity of the observed vertical drift enhancement is comparable to geospace storm induced large ionospheric up‐welling at subauroral latitudes (Zhang et al, ). F region heating effects caused by geomagnetic activity have also been noted previously (Deng et al, ; Heelis & Coley, ).…”

Electrodynamic disturbances in the Brazilian equatorial and low‐latitude ionosphere on St. Patrick's Day storm of 17 March 2015

“…This storm time disturbance neutral winds maximized to 100–250 m/s in westward and 200–300 m/s in equatorward [ Tulasi Ram et al ., , Figure 5]. Zhang et al [] have shown strong equatorward neutral wind surge (> 200 m/s) from the Millstone Hill radar in the dayside (American sector) consistently with nightside observations of Tulasi Ram et al []. Huang et al [] have also reported that there was a disturbance dynamo process initiated 3–4.7 h after the onset of the storm main phase and lasted for 31 h. Hence, it is expected that strong equatorward and westward neutral wind disturbance is also operating in the dayside Brazilian sector.…”

Effects of sudden commencement on the ionosphere: PFISR observations and global MHD simulation

“…Similar but persistent T i and V los increases due to frictional heating have also been observed during the main phase of the same storm but in the subauroral polarization stream (SAPS) region by the Millstone Hill radar [Zhang et al, 2017]. Significant and persistent frictional heating can also increase the neutral temperature and lead to neutral upwelling, as found in the SAPS region by Zhang et al [2017]. However, because the neutrals need much longer time (tens of minutes to days) to respond to frictional heating [Schunk and Nagy, 2009], it is unlikely to have such neutral upwelling formed within the first 5-10 min right after the onset of the strong horizontal flows due to the SC.…”

“…The T i increase occurred at the same time as the SC-related convection flow speed increase, and therefore, this increase is likely due to enhanced frictional heating. Similar but persistent T i and V los increases due to frictional heating have also been observed during the main phase of the same storm but in the subauroral polarization stream (SAPS) region by the Millstone Hill radar [Zhang et al, 2017]. Significant and persistent frictional heating can also increase the neutral temperature and lead to neutral upwelling, as found in the SAPS region by Zhang et al [2017].…”

“…Therefore, understanding the generation mechanisms of the initial ion upflow under various interplanetary and geomagnetic conditions is of great importance for understanding the ion outflow processes. Field‐aligned ion upflows have been observed by ground‐based ISRs in the dayside cusp region, in regions of fast ionospheric flows, as well as in regions of strong ionospheric flow shears [ Lühr et al , ; Moen et al , ; Liu and Lu , ; Zhang et al , ]. Statistical studies have shown that the ion upflow fluxes increase with increasing solar wind density and velocity [ Ogawa et al , ].…”