Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

M.Forster at al. These magnitude differences are generally smaller for the T96 and T01 models. In the case of the quiet geomagnetic conditions (left panels), the observed and modelled values practically coincide for the most part of the orbit. While approaching the perigee during the geomagnetically quiet orbit, all three models predict smaller field values with respect to the measured ones up to AB -15 nT. In the case of disturbed conditions (right panels), the differences between observed and modelled values are larger and the variations ДВ become more irregular. Near perigee at the end o f the disturbance orbit example, all three models show a sharp increase with differences up to AB-40-60 nT or almost 15% of the observed absolute values B(C1). Here, AB for T01 and T96 reverses sign, but for PM it keeps negative. The differences in the nature of variations might be caused by an insufficient treatment of the ring current field in the models. The root mean square values of the differences between the observed and modelled magnetic field magnitudes are shown in the lower panels o f Figure 1. During the quiet day they reached ~4.2 nT for T01 and up to ~9.5 nT for PM, while the T96 was in between with -5 .6 nT. The corresponding values gained -10.9 nT (T01), 16.0 nT (T96) and 18.8 nT (PM) during the geomagnetically disturbed day. The T01 model appears to be therefore the most reliable. 1 0 - 1 1 August 2 0 0 7 1 9 - 2 0 August 2 0 0 6 60 40 20 -20 -40 -6 0 -----18(d)! -IB(TO I)1 -----IB(cl)l-IB(T96)l .........IB(cl) I—1B(PM) I • ' /Л. , 'V4^ \ л/*' A = 4.16 A = 5.57 A = 9.46 75 50 25 0 -2 5 -5 0 -7 5 ---- IB(cl) I —IB(T01 )l Д = 10.SB ----IB(cl)t—IB(T96)I Д = 16.00 ....... IB(cl)l—IB(PM) I Д = 18.80 v i ; V i 23:00 04:16 09:36 14:55 20:15 UT 02:40 09:05 15:45 22:14 01:54 UT 20.43 19.12 16.73 13.00 7.03 R 19.40 17.81 14.94 10.24 4.10 -16.57 -14.77 -11.85 -7.54 -1.13 Xgsm -16.18 -13.29 -8.90 -2.60 3.67 -6.12 -5.77 -5.64 -2.31 2.58 Ygsm -4.31 -5.23 -3.17 1.90 1.72 -10.26 -10.67 -10.39 -10.33 -6.44 Zgsm -9.79 -10.65 -11.57 -9.72 -0.62 R Xgsm Ygsm Zgsm Figure 1: Variation of the FGM measurements along the Cluster C3 orbit, compared with the corresponding 1-min model values of T01, T96 and PM for the time interval August 10, 23 UT, till August 11, 2007, 20 UT (left) and August 19, 02 UT, till August 20, 2007, 02 UT (right). Top panels show the geomagnetic field magnitude | В |, and the bottom panels show the difference AB between the measured and model field magnitudes. The A numbers listed in the lower panels indicate the root mean square values of the differences AB. The Composition and Distribution Function analyser (CODIF) [Reme et al, 1997] on board Cluster measured the main magnetospheric ions (H+, He+, 0+ ) along the orbit within the energy range from -0 keV to -40 keV per charge with an angular resolution of 22.5°. This allowed to confirm that the spacecraft position on the night side magnetosphere was outside the plasma sheet along its orbital traces from 23 UT of August 10 to 20 UT of August 11, 2007 and from 02 UT of August 19 to 02 UT of August 20, 2007. We performed a study of the differences AB = B(Cl)-B(model) for 10 Cluster orbits of the years 2002+2008 with randomly selected data points along the satellite orbits at radial distances between 7.5 Re and 19 Re. TO1, T96 and PM model values were analysed. In the Table, we list the GSM coordinates o f the satellite, its radial distance R from the Earth's center, the magnetic field values of the FGM measurements on board Cluster together with the three 60