Low-altitude Satellite Data Research Articles

Study of plasma pressure distribution in the inner magnetosphere using the low altitude satellite data and its relevance for magnetospheric dynamics

Plasma pressure distribution in the inner magnetosphere is one of the key parameters for understanding the main magnetospheric processes including geomagnetic storms and substorms. However, the pressure profiles obtained from in-situ particle measurements by the high-altitude satellites inside the plasma sheet do not allow tracking the pressure variations related to the magnetospheric dynamics, because time interval needed to do this generally exceeds the characteristic times of the main magnetospheric processes. On the contrary, fast movement of low-altitude satellites makes it possible to restore quasi-instantaneous profiles of plasma pressure along the satellite trajectory, using the precipitating particle flux data in the regions of isotropic plasma pressure. It was found that during quiet geomagnetic conditions profiles obtained from low-altitude and high-altitude satellites coincide. Nevertheless, the plasma pressure profiles change significantly during the development of storms and substorms, that indicates possibility of the interchange (storm) or modified interchange (substorm) instability development.

Radial distribution of the inner magnetosphere plasma pressure using low-altitude satellite data during geomagnetic storm: The March 1–8, 1982 event

Plasma pressure distribution in the inner magnetosphere is one of the key parameters for understanding the main magnetospheric processes including geomagnetic storms and substorms. However, the pressure profiles obtained from in-situ particle measurements by the high-altitude satellites inside the plasma sheet and other regions of the magnetosphere do not allow tracking the pressure variations related to the storms and substorms, because a time interval needed to do this generally exceeds the characteristic times of them. On the contrary, fast movement of low-altitude satellites makes it possible to retrieve quasi-instantaneous radial or azimuthal profiles of plasma pressure along the satellite trajectory, using the precipitating particle flux data in the regions of isotropic plasma pressure. For this study, we used the low-altitude polar-orbiting Aureol-3 satellite data for plasma pressure estimation, and the IGRF, Tsyganenko 2001 and Tsyganenko 2004 storm time geomagnetic field models for the pressure mapping into the equatorial plane, and for the evaluation the corresponding volume of the magnetic flux tube. It was found that during quiet geomagnetic condition the radial pressure profiles obtained coincide with the profiles, obtained previously from the high-altitude measurements. On the contrary, the plasma pressure profiles change significantly during the development of storms and substorms. Nevertheless, three geomagnetic field models gave significantly different geomagnetic field profiles, those points out the necessity to develop a magnetically self-consistent model for description of the inner magnetosphere geomagnetic field. However, the common features observed for all models are: during geomagnetic storm the plasma pressure profiles became sharper; the position of the maximum of plasma pressure corresponds to expected one for given D st minimum; the maximum value of inner magnetosphere static pressure correlates with the solar wind dynamic pressure. Increase in the plasma pressure profiles indicates the possibility to consider the interchange instability as one of important factors for the development of the main phase of geomagnetic storm.

Satellite and rocket studies of relativistic electrons and their influence on the middle atmosphere

Magnetospheric electrons from hundreds of keV to over 10MeV in energy have been systematically measured at geostationary altitude (6.6 R E) for well over a decade. We find evidence of significant diurnal, solar-rotational (27-day), annual, and solar-cycle (11-yr) variations in the fluxes of the relativistic electron component. We have also used low-altitude satellite data and sounding rocket measurements to characterize the location and strength of the relativistic electron precipitation into the atmosphere. We conclude that the magnetospheric electrons, when dumped into the middle atmosphere, represent a very significant ionization source which affects the pattern of conductivity, electric fields, and atmospheric chemistry. These measurements—when combined with global atmospheric modeling—suggest that relativistic electrons provide a robust coupling mechanism to impose long-term solar wind and magnetospheric variability onto the Earth's deep atmospheric regions. A strong 11-yr cycle of relativistic electron effects is found in available atmospheric data sets.

The use of low altitude satellite data bases for modeling of core and crustal fields and the separation of external and internal fields

The near-Earth geomagnetic field is a complex combination of fields from a variety of sources within and external to the Earth. These fields have a complex characterization in space and time such that if the field were known at all times and positions external to the Earth's surface it would be possible to separate the measured field into its component parts except for the low degree field from the crust and the high degree field from the core. In practice the measurements come far short of such a space-time characterization. Because of this it is useful to keep in mind several principles when working with these data. These principles are: (1) know the enemy, i.e., understand as much as possible about all the sources, (2) don't expect a boy to do a man's job, i.e., recognize the limitations of the data, (3) use some common sense, and, (4) recognize personal prejudice. Examples are given from published and unpublished results to illustrate how these principles have been, and ought to be, applied. At the same time, suggestions are made as to how future analyses might proceed. These examples are drawn first of all from the way the main field and near-Earth magnetospheric fields are modeled, then from analyses of residuals from such models resulting from ionospheric and crustal fields.