TY - JOUR

T1 - Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

AU - Billett, Daniel

AU - Wild, Jim

AU - Grocott, Adrian

AU - Aruliah, Anasuya

AU - Ronksley, Amy

AU - Walach, Maria

AU - Lester, Mark

N1 - Accepted for publication in Journal of Geophysical Research: Space Physics. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted.

PY - 2019/8/30

Y1 - 2019/8/30

N2 - It has previously been shown that in the high-latitude thermosphere, sudden changes in plasma velocity (such as those due to changes in interplanetary magnetic field) are not immediately propagated into the neutral gas via the ion-drag force. This is due to the neutral particles (O, O 2, and N 2) constituting the bulk mass of the thermospheric altitude range and thus holding on to residual inertia from a previous level of geomagnetic forcing. This means that consistent forcing (or dragging) from the ionospheric plasma is required, over a period of time, long enough for the neutrals to reach an equilibrium with regard to ion drag. Furthermore, mesoscale variations in the plasma convection morphology, solar pressure gradients, and other forces indicate that the thermosphere-ionosphere coupling mechanism will also vary in strength across small spatial scales. Using data from the Super Dual Auroral Radar Network and a Scanning Doppler Imager, a geomagnetically active event was identified, which showed plasma flows clearly imparting momentum to the neutrals. A cross-correlation analysis determined that the average time for the neutral winds to accelerate fully into the direction of ion drag was 75 min, but crucially, this time varied by up to 30 min (between 67 and 97 min) within a 1,000-km field of view at an altitude of around 250 km. It is clear from this that the mesoscale structure of both the plasma and neutrals has a significant effect on ion-neutral coupling strength and thus energy transfer in the thermosphere.

AB - It has previously been shown that in the high-latitude thermosphere, sudden changes in plasma velocity (such as those due to changes in interplanetary magnetic field) are not immediately propagated into the neutral gas via the ion-drag force. This is due to the neutral particles (O, O 2, and N 2) constituting the bulk mass of the thermospheric altitude range and thus holding on to residual inertia from a previous level of geomagnetic forcing. This means that consistent forcing (or dragging) from the ionospheric plasma is required, over a period of time, long enough for the neutrals to reach an equilibrium with regard to ion drag. Furthermore, mesoscale variations in the plasma convection morphology, solar pressure gradients, and other forces indicate that the thermosphere-ionosphere coupling mechanism will also vary in strength across small spatial scales. Using data from the Super Dual Auroral Radar Network and a Scanning Doppler Imager, a geomagnetically active event was identified, which showed plasma flows clearly imparting momentum to the neutrals. A cross-correlation analysis determined that the average time for the neutral winds to accelerate fully into the direction of ion drag was 75 min, but crucially, this time varied by up to 30 min (between 67 and 97 min) within a 1,000-km field of view at an altitude of around 250 km. It is clear from this that the mesoscale structure of both the plasma and neutrals has a significant effect on ion-neutral coupling strength and thus energy transfer in the thermosphere.

KW - ionosphere

KW - thermosphere

KW - coupling

KW - magnetosphere

KW - neutrals

KW - plasma

U2 - 10.1029/2019JA026627

DO - 10.1029/2019JA026627

M3 - Journal article

VL - 124

SP - 6950

EP - 6960

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9402

IS - 8

ER -