Observations of neutral composition and related ionospheric variations during a magnetic storm in February 1974

Abstract

The neutral atmosphere composition experiment on Atmosphere Explorer C measured N2, O, Ar, and He densities during a magnetic storm in February 1974 at altitudes down to about 160 km. At latitudes above 45øN, N2 and Ar densities generally increase during the storm, while He and O densities decrease. Below 45øN all densities tend to increase during the storm. The density increases at perigee indicate that density or temperature profile changes are taking place below 160 km. The return to prestorm conditions is very slow, demonstrating the integrating effect of the atmospheric response. A recent theoretical model incorporating thermospheric circulation and diffusion effects reproduces the longitudinally averaged data including latitude trends and the asymmetry about the storm maximum. Comparison with the mass spectrometer and incoherent scatter empirical model shows qualitative agreement with latitude trends but not with storm asymmetry, while the earlier J71 model based on total mass density is not in agreement with observed latitudinal trends. No significant correlation is found with the short-term variations of the ap index. At any fixed altitude and for latitudes above 45øN (perigee) the density variations are closely correlated with invariant (or magnetic) latitude, although invariant latitude alone is not adequate to order the data completely. A close correlation is found between in situ O/N• measurements and in situ and ground-based ionosonde measurements of electron density. 1, -40 LENINGRAD 60 ø N 30 ø E UPPSALA 59 ø N 17 ø E ß d• ß ß ßß ß ß •o ßß ß 41 42 43 44 45 46 47 DAY COUNT (1974)

Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

“…The largest variation of the extinction occurred at the heights 300-450 km (increase at 400 km by a factor of 1.7) which was probably produced by density enhancements in the ionosphere associated with magnetic disturbances during the storm (Hedin et al 1977). …”

A global model of the neutral thermosphere in magnetic coordinates based on AE‐C data

“…Direct use of these indices in modeling 4as, however, several problems. There is a time delay between the Joule heating and the 1 r^; winds and density perturbations and a further time delay before these affect densities at"lower latitudes, and this results in time delays and storage phenomena ('Wydra, 1975;Hedin et al, 1977c). Therefore the The same type of behavior was found in the recovery phase of another magnetic storm.…”

“…Taeusch and Hinton (1975) related N, density variations to _electradynamic and particle heating in the quiet polar thermosphere. Mass x spectrometer measurements of the 11` density from Ogo 6 were normalized to 450 km and then divided by the corresponding Og,o 6 model densities (Hedin #t et al, 1974) between measurements an-11-model estimates were the cusp area and the 0000 -0000 MT sector, Although the positiolc of the cusp was quito variable, it was usually located near 80 0 ILAT and 1200 ULT, In addition to large differences froze average values, the' densities in the cusp were.…”

Neutral Density Structures in the High Latitude Thermosphere

“…Mayr et al, 1973;Bums et al, 1991Bums et al, , 1995aFuller-Rowell et al, 1994, and others based on the AE and DE satellites (e.g. Hedin et al, 1977;Miller et al, 1990). Much of this work was summarized by Buonsanto (1999).…”

“…The variations in thermospheric temperature, density, and composition have been captured in empirical models such as Jacchia (1970;1974), in the Mass Spectrometer Incoherent Scatter Radar (MSIS) series of models of Hedin et al (1977Hedin et al ( , 1991Hedin et al ( , 1996, and most recently in the NRLMSISE-00 model (Picone et al, 2002).…”