TY - JOUR

T1 - Thermospheric density perturbations in response to substorms

AU - Clausen, L. B. N.

AU - Milan, S. E.

AU - Grocott, Adrian

N1 - ©2014. American Geophysical Union. All Rights Reserved.

PY - 2014/6

Y1 - 2014/6

N2 - We use 5 years (2001–2005) of CHAMP (Challenging Minisatellite Payload) satellite data to study average spatial and temporal mass density perturbations caused by magnetospheric substorms in the thermosphere. Using statistics from 2306 substorms to construct superposed epoch time series, we find that the largest average increase in mass density of about 6% occurs about 90 min after substorm expansion phase onset about 3 h of magnetic local time east of the onset region. Averaged over the entire polar auroral region, a mass density increase of about 4% is observed. Using a simple model to estimate the mass density increase at the satellite altitude, we find that an energy deposition rate of 30 GW applied for half an hour predominantly at an altitude of 110 km is able to produce mass density enhancements of the same magnitude. When taking into account previous work that has shown that 80% of the total energy input is due to Joule heating, i.e., enhanced electric fields, whereas 20% is due to precipitation of mainly electrons, our results suggest that the average substorm deposits about 6 GW in the polar thermosphere through particle precipitation. Our result is in good agreement with simultaneous measurements of the NOAA Polar-orbiting Operational Environmental Satellite (POES) Hemispheric Power Index; however, it is about 1 order of magnitude less than reported previously.

AB - We use 5 years (2001–2005) of CHAMP (Challenging Minisatellite Payload) satellite data to study average spatial and temporal mass density perturbations caused by magnetospheric substorms in the thermosphere. Using statistics from 2306 substorms to construct superposed epoch time series, we find that the largest average increase in mass density of about 6% occurs about 90 min after substorm expansion phase onset about 3 h of magnetic local time east of the onset region. Averaged over the entire polar auroral region, a mass density increase of about 4% is observed. Using a simple model to estimate the mass density increase at the satellite altitude, we find that an energy deposition rate of 30 GW applied for half an hour predominantly at an altitude of 110 km is able to produce mass density enhancements of the same magnitude. When taking into account previous work that has shown that 80% of the total energy input is due to Joule heating, i.e., enhanced electric fields, whereas 20% is due to precipitation of mainly electrons, our results suggest that the average substorm deposits about 6 GW in the polar thermosphere through particle precipitation. Our result is in good agreement with simultaneous measurements of the NOAA Polar-orbiting Operational Environmental Satellite (POES) Hemispheric Power Index; however, it is about 1 order of magnitude less than reported previously.

KW - thermosphere

KW - substorm

KW - energy input

U2 - 10.1002/2014JA019837

DO - 10.1002/2014JA019837

M3 - Journal article

VL - 119

SP - 4441

EP - 4455

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9402

IS - 6

ER -