Physics – Space Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh53a1480k&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SH53A-1480
Physics
Space Physics
0654 Plasmas, 2134 Interplanetary Magnetic Fields, 2164 Solar Wind Plasma, 2447 Modeling And Forecasting, 7959 Models
Scientific paper
It is essential to know parameters of the Interplanetary Magnetic Field (IMF) and solar wind in the near Earth magnetosphere for research on the effects of the IMF in near-Earth space. Measurements of the IMF taken at the first Lagrange point (L_1) by the ACE space satellite, about 230 Earth Radii away, are typically used for estimation of IMF near the Earth. In many geophysical applications, it is assumed that we can use a simple kinematic approach to map the parameters measured at the satellite to the Earth by shifting them in time. The simple formula is to calculate the time delay as the distance from the Earth to the satellite divided by the velocity of the solar wind, projected along the Earth-Sun line. There are two important problems to be addressed with this simple kinematic approach. The first problem is that solar wind is not uniform and particles that hit the satellite often miss the Earth. Typically, the satellite is shifted by 30 or more Earth radii from the Earth-Sun straight line, and the Earth is also shifting from this line during the solar wind propagation time. IMF parameters may differ between the satellite and the Earth-Sun straight line. In this work, we address a second important problem: solar wind and IMF parameters may change during it's travel from the satellite towards the Earth. It is suggested here that a Magneto-Hydrodynamics approach can be used to deal with this problem. A simplified 1D solar wind propagation model was derived for this case using mass and momentum conservation laws and Maxwell equations. The model is simple and fast enough to use even in real-time applications, yet it takes into account real conservation laws of solar wind motion. To validate this model, comparisons of the IMF data and solar wind parameters were performed for the ACE and WIND satellites. Two different events were used. The first was from April 30, 1999, a day on which both satellites were approximately on the same line with the Sun. In that case, shifting differences of solar wind should not be important. The second was October 21, 1998, when both satellites were far away from the Earth-Sun line. Comparisons of these measurements and calculations shows an improvement of IMF calculations compared to the simple kinematic delay method. The suggested method can be effectively used instead of the kinematic delay algorithm in many space physics applications.
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