Observations of storm time midlatitude ion‐neutral coupling using SuperDARN radars and NATION Fabry‐Perot interferometers

Abstract

Ion drag is known to play an important role in driving neutral thermosphere circulation at auroral latitudes, especially during the main phase of geomagnetic storms. During the recovery phase, the neutrals are known to drive the ions and generate ionospheric electric fields and currents via the disturbance dynamo mechanism. At midlatitudes, the precise interplay between ions and neutrals is less understood largely because of the paucity of measurements that have been available. In this work, we investigate ion‐neutral coupling at middle latitudes using colocated ion drift velocity measurements obtained from Super Dual Auroral Radar Network radars and neutral wind velocity and temperature measurements obtained from the North American Thermosphere Ionosphere Observing Network (NATION) Fabry‐Perot interferometers. We examine one recent storm period on 2–3 October 2013 during both the main phase and late recovery phase. By using ion‐neutral momentum exchange theory and a time‐lagged correlation analysis, we analyze the coupling time scales and dominant driving mechanisms. We observe that during the main phase the neutrals respond to the ion convection on a time scale of ∼84 min which is significantly faster than what would be expected from local ion drag momentum forcing alone. This suggests that other storm time influences are important for driving the neutrals during the main phase, such as Joule heating. During the late recovery phase, the neutrals are observed to drive the ion convection without any significant time delay, consistent with the so‐called “neutral fly wheel effect” or disturbance dynamo persisting well into the late recovery phase.

Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

“…This result is consistent with studies by Joshi et al (2015) and Heelis et al (2002) while falling within the range of lags calculated by other studies (Baron & Wand, 1983;Killeen et al, 1984;Kosch et al, 2001). This result is consistent with studies by Joshi et al (2015) and Heelis et al (2002) while falling within the range of lags calculated by other studies (Baron & Wand, 1983;Killeen et al, 1984;Kosch et al, 2001).…”

“…Studies using this method on individual events, however, produce a wide range of e-folding times due to typically rapid variations in plasma measurements. Joshi et al (2015) also presented a different method for determining neutral lag time. More recently, Joshi et al (2015) used midlatitude Super Dual Auroral Radar Network (SuperDARN) radars and FPI instruments to calculate with values falling in the range of 10 to 360 min, also varying rapidly from measurement to measurement.…”

“…For instance, Kosch et al (2001) used coincident EISCAT incoherent scatter radar ion measurements and Fabry-Perot Interferometer (FPI) neutral measurements over a near 7-hr time interval to calculate , which was found to vary between 30 and 300 min. More recently, Joshi et al (2015) used midlatitude Super Dual Auroral Radar Network (SuperDARN) radars and FPI instruments to calculate with values falling in the range of 10 to 360 min, also varying rapidly from measurement to measurement. This makes clear an issue when trying to determine a neutral wind lag time from plasma or neutrals with high temporal variability; sudden increases or decreases in plasma velocity which are not sustained will mean that the neutrals do not have enough time to respond and thus never fully accelerate or decelerate to some equilibrium state.…”

“…This makes clear an issue when trying to determine a neutral wind lag time from plasma or neutrals with high temporal variability; sudden increases or decreases in plasma velocity which are not sustained will mean that the neutrals do not have enough time to respond and thus never fully accelerate or decelerate to some equilibrium state. Joshi et al (2015) also presented a different method for determining neutral lag time. This comprised a relatively simple cross-correlation analysis whereby a time series of neutral measurements was lagged back at constant time steps to the beginning of the plasma measurements, with a correlation coefficient calculated at each lag.…”

Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars

“…Several studies have attempted to identify the efficiency of these interactions and the time scales on which they operate. Joshi et al (2015) investigated mid-latitude ion-neutral coupling during the geomagnetic storm of 2-3 October 2013 using co-located measurements of ionospheric convection from North American mid-latitude SuperDARN radars and neutral winds from Fabry-Perot interferometers (FPIs). The time scales on which the coupling operates were analyzed using momentum exchange theory and (Killeen et al 1984) but significantly faster than what is expected from local ion-drag momentum forcing alone.…”