A Statistical Study of Dayside Magnetosphere Erosion Based on Wind and GOES Measurements in 1996-1999.

Details A Statistical Study of Dayside Magnetosphere Erosion Based on Wind and GOES Measurements in 1996-1999. A Statistical Study of Dayside Magnetosphere Erosion Based on Wind and GOES Measurements in 1996-1999.

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm31a..05m&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SM31A-05

Other

2708 Current Systems (2409), 2730 Magnetosphere: Inner, 2784 Solar Wind/Magnetosphere Interactions, 7835 Magnetic Reconnection

Scientific paper

We carry out a statistical investigation relating the depression of the geostationary magnetic field near noon to the strength of the southward component of the IMF (Bz). We use measurements made by GOES, WIND and ground-based magnetograms. The period studied is 1996-1999. In search of extreme Bz events, we also include some data close to solar maximum (2000-2001). We select intervals with (1) a steady dynamic pressure, Pdyn; (2) a steady and negative IMF Bz; (3) when one of the GOES spacecraft was within 2 hours of local noon; and (4) during substorm growth phase (as ascertained by readings from nightside ground magnetometers). We explore two approaches. In one approach, raw values of the total geostationary field, Btot are corrected first for the compression due to Pdyn. To do this, we chose a number of ``reference" days encompassing a wide range of Pdyn values when the IMF was strongly northward (clock angle < 45o), and fitted Btot to the functional form Btot = a + b Pdyn1/2 passing through the dipolar value for zero Pdyn. We then do a linear fit of the corrected Δ Btot values to IMF Bz in the range (0, -16) nT. We find Δ Btot=-6.27 + 1.69 Bz [nT]. In the second approach, we carry out a bivariate analysis of Btot as a function of (Pdyn1/2, Bz), and obtain Btot=100.71 + 19.55√ {Pdyn}+1.78 Bz [nT]. Both methods are in good agreement with each other. This work extends the pioneering investigation of Sibeck (JGR, 99, 8513, 1994) by the more extensive, negative Bz dynamic range employed here. The limiting case of very low Pdyn, which was discussed earlier with a different approach (Farrugia et al. (JGR, 106, 25,517, 2001), is shown to agree well our more extensive statistical results. Ackowledgements This work is supported by NASA WIND Grant NAG5-2834, NASA Living with a Star Grant NAG 5-10883, by INTAS ESA 12077-99, the Austrian Fonds zur F=Foerderung der Wissenschaftlichen Forschung under Project P13804-TPH, and by ``Buero fuer Auslandsbeziehungen'' of the Austian Academy of Sciences.

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