Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm33b1572m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM33B-1572
Physics
[2744] Magnetospheric Physics / Magnetotail, [2768] Magnetospheric Physics / Plasmasphere, [2794] Magnetospheric Physics / Instruments And Techniques
Scientific paper
Electron density is a key physical quantity to characterize any plasma medium. Its measurement is thus essential to understand the various physical processes occurring in the environment of a magnetized planet. However, any magnetosphere of the solar system is far from being an homogeneous medium with a constant electron density and temperature. For instance, the Earth’s magnetosphere is composed of a variety of regions with densities and temperatures spanning over at least 6 decades of magnitude. For this reason, different types of scientific instruments are usually carried onboard a magnetospheric spacecraft to estimate in situ the electron density of the various plasma regions crossed by different means. In the case of the European Space Agency Cluster mission, five different instruments on each of its four identical spacecraft can be used to estimate it: two particle instruments, a DC electric field instrument, a relaxation sounder and a high-time resolution passive wave receiver. Each of these instruments has its pros and cons depending on the plasma conditions. The focus of this study is the accurate estimation of the electron density in cold plasma regions of the magnetosphere including the magnetotail lobes (Ne ≤ 0.01 e-/cc, Te ~ 100 eV) and the plasmasphere (Ne> 10 e-/cc, Te <10 eV). In these regions, particle instruments can be blind to low energy ions outflowing from the ionosphere or measuring only a portion of the energy range of the particles due to photoelectrons. This often results in an under estimation of the bulk density. Measurements from a relaxation sounder enables accurate estimation of the bulk electron density above a fraction of 1 e-/cc but requires careful calibration of the resonances and/or the cutoffs detected. On Cluster, active soundings enable to derive precise density estimates between 0.2 and 80 e-/cc every minute or two. Spacecraft-to-probe difference potential measurements from a double probe electric field experiment can be calibrated against the above mentionned types of measurements to derive bulk electron densities with a time resolution below 1 s. Such an in-flight calibration procedure has been performed successfully on past magnetospheric missions such as GEOS, ISEE-1, Viking, Geotail, CRRES or FAST. We will first present the outcome of this calibration procedure for the Cluster mission for plasma conditions encountered in the plasmasphere, the magnetotail lobes and the polar caps. This study is based on the use of the Cluster Active Archive (CAA) for data collected in the plasmasphere. CAA offers the unique possibility to easily access the best calibrated data collected by all experiments on the Cluster satellites over their several years in orbit. This has enabled in particular to take into account the impact of the solar activity in the calibration procedure. Recent science nuggets based on these calibrated data will then be presented showing in particular the outcome of the three dimensional (3D) electron density mapping of the magnetotail lobes over several years.
Escoubet Christophe P.
Laakso H. E.
Masson Andre
Pedersen Andreas
Taylor M. G.
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