Thermosphere density variations due to the 15–24 April 2002 solar events from CHAMP/STAR accelerometer measurements

Abstract

[1] Thermosphere densities near 410 km altitude between ±87°latitude and near 0430 and 1530 local time from the accelerometer experiment on the CHAMP satellite are used to elucidate the response to three coronal mass ejections occurring on 17, 19, and 21 April 2002. Comparisons of the global responses with the NRLMSISE00 empirical model and the NCAR TIEGCM are performed and interpreted. An enhanced daytime response in comparison to TIEGCM on 17 April is found that is suggestive of preconditioning of the atmosphere due to enhanced solar EUV fluxes maximizing on 13 April. Out of several solar wind parameters and geophysical indices that were examined, the highest correlation with thermosphere densities occurred with respect to the magnitude of the interplanetary magnetic field as measured by the ACE spacecraft. Wave-like structures with scales ranging from 100s to 1000s of kilometers are also revealed in the CHAMP data. These structures are primarily a nighttime phenomena, and the associated total variance is correlated with magnetic activity throughout the 15-24 April 2002 period. The NCAR TIEGCM was utilized to provide the basis for interpreting the equatorward propagation of large-scale traveling atmospheric disturbance (TADs). Following a sudden increase in magnetic activity and high-latitude heating, TADs were launched from both hemispheres, traveled toward the equator with phase speeds of order 800 m s À1 , constructively interfered near the equator to produce a total density perturbation of $20%, and then passed through each other and into the opposite hemisphere. Perspectives on future applications of CHAMP accelerometer data to elucidate magnetic storm-related perturbations of the thermosphere are outlined.

A new method for studying the thermospheric density variability derived from CHAMP/STAR accelerometer data for magnetically active conditions

“…The large scale spatial variations in the density, mostly related to altitude/latitude variations are captured by the first singular vector; time variations are captured by the associated projection coefficient, down to time scale on the order of one orbital period. Smaller scale spatial and time variations typically correspond to the variations induced by gravity waves generated by Joule heating as the one discussed by Forbes et al (2006) and Bruinsma et al (2006). Their morphology along each orbit segment is captured by the residual, i.e.…”

“…In this latitude range, this error may reach 10% during large storms, which is small compared to the 200% or larger observed density enhancements during such large magnetic storms (Sutton et al, 2005;Forbes et al, 2006;Bruinsma et al, 2006).…”

“…Bruinsma et al (2004) showed that the density determination error due to winds is always less than 5% when geomagnetic activity is low or moderate (K p ≤3 or am≤40 nT). Forbes et al (2006) found that these errors may be 30% or even more at high latitudes during magnetically disturbed periods, but at latitudes below 50 • , density errors are evaluated not to be larger than 10% and not to vary so much with magnetic activity. In what follows, we therefore limit our analysis to low latitudes between 50 N and 50 S.…”

“…The high precision and stability of the STAR accelerometer installed within one mm of its centre of mass, and the high precision of GPS tracking, allowed significant progress in the precision of thermospheric density retrieval to be made. The resulting accuracy of thermospheric density values derived from STAR accelerometer measurements makes it possible to study the statistical properties of the thermospheric density global distribution (Bruinsma et al, 2004;Liu et al, 2005), or its response to the geomagnetic activity forcing, in particular during severe geomagnetic storms (Sutton et al, 2005;Forbes et al, 2006;Bruinsma et al, 2006).…”

Thermospheric atomic oxygen density estimates using the EISCAT Svalbard Radar

“…The statistical nature of MSIS dictates that accurate predictions hold only during quiet and steady state conditions. Several studies have shown that significant differences exist between in situ measurements and MSIS-modeled thermospheric mass densities during geomagnetic disturbances [e.g., Bruinsma et al, 2006;Burke et al, 2007;Forbes et al, 2005]. The severity of underestimation by MSIS can range from a factor 2 [e.g., Sutton et al, 2005] up to as much as 5 when expressed in terms of the enhancement above the prestorm densities [Liu and Lühr, 2005].…”