Global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from CHAMP accelerometer data

Abstract

[1] Measurements of atmospheric density near 410 km from the STAR accelerometer on the CHAMP satellite are used to illustrate the spatial-temporal dependence of the thermospheric response to the severe solar storms occurring during 29 October to 1 November 2003. This interval includes periods of elevated magnetic activity with K P values of 5-9, as well as undisturbed intervals that serve to define quiet time baseline densities. Measurements are available from À87°to +87°latitude during both day and night at local times near 1300 and 0100 hours, respectively. During times of maximum geomagnetic activity for this study, density measurements exhibit enhancements of 200-300%. Northern Hemisphere daytime responses are much larger than in the Southern Hemisphere; the origins of this effect are unknown. Nighttime density disturbances more readily propagate to equatorial latitudes, possibly facilitated by the predominant equatorward flow in both hemispheres due to the diurnal tides driven by in situ EUV heating. The CHAMP density measurements are compared with density predictions from the NRL-MSISe00 empirical density model and demonstrate some model shortcomings. Measurements of cross-track accelerations provide the opportunity to estimate zonal winds from the equator to about ±60°latitude, transitioning to a measure of purely meridional winds at the turning point of the orbit near ±87°latitude. A periodic variation in cross-track winds with an apparent period of 24 hours appears at high latitudes and exhibits similar amplitudes and temporallatitudinal structures to the empirical HWM-93 wind model when projected into the cross-track direction. This periodicity is due to the displacement of geomagnetic and geographic coordinates. At low latitudes, CHAMP and HWM-93 both yield westward winds of order 100 ms À1 during midday under quiet magnetic conditions; however, during severely disturbed periods the HWM-93 winds generally show a greater westward intensification (to 250 ms À1 ) than the CHAMP measurements. At night, CHAMP winds are near zero under quiet conditions whereas HWM-93 indicates eastward winds of order 50-100 ms À1 . Under disturbed conditions the CHAMP winds shift to westward values of order 200 to 250 ms À1 , while HMW-93 values do not exceed about 50 ms À1 in the westward direction. The physical origins of the observed effects are difficult to isolate, and unequivocal interpretation will require sophisticated numerical modeling taking into account self-consistent interactions between the neutral winds, drifts, and ionization densities.

Thermospheric atomic oxygen density estimates using the EISCAT Svalbard Radar

“…We have also considered geomagnetic activity prior to the CHAMP pass [cf. Aruliah et al, 1999], which can influence the thermospheric density [e.g., Sutton et al, 2005;Zhou et al, 2009] andcomposition [e.g., Crowley et al, 2006]. While the Kp ≤ 2 criterion was satisfied during and within the 3 h interval prior to the CHAMP pass, in both the cases where the ESR estimate was below that of the CHAMP measurement (cases 4 and 8), the Kp index had been raised to levels > 2 in the 24 h prior to the interval of the CHAMP measurement.…”

“…The reader is referred to Sutton et al [2005] and Sutton [2009] where descriptions of the force model used in the STAR accelerometer data processing and estimations of the total mass density can be found. The time resolution of the CHAMP data used was 10 s, which corresponds to a spatial separation of approximately 80 km between consecutive measurements along the satellite track.…”

“…[3] Global satellite drag measurements at middle and high latitudes have shown that large geomagnetic storms can result in dramatic enhancements of the atomic oxygen density of several hundred percent at altitudes near 400 km [Sutton et al, 2005;Zhou et al, 2009]. On occasions the enhancement can reach up to almost an order of magnitude [Bruinsma et al, 2006;Liu and Lühr, 2005].…”

“…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]. Zhou et al [2009] addressed this issue by developing a method that used the dependence of the mass density changes on Joule heating power and Sym-H indices to correct the NRLMSISE-00 model [Picone et al, 2002] estimates during disturbed conditions.…”

Predicting global average thermospheric temperature changes resulting from auroral heating

“…[9] Sutton et al [2005] reported the following observations from CHAMP measurements: During the first stage of geomagnetic activity on 29 October 2003, on the dayside elevated density levels of the order of 300% could be seen at northern latitudes. On the nightside density enhancements last longer than on the dayside and can be seen to travel toward the equator.…”