Radial distribution of magnetic field in earth magnetotail current sheet

Knowing the magnetic field distribution in the magnetotail current sheet (CS) is essential for exploring magnetotail dynamics. In this study, using a joint dataset of Cluster/TC-1, the radial profile of the magnetic field in the magnetotail CS with radial distances covering 8 < r < 20R(E) under different geomagnetic activity states (i.e., AE <= 100 nT for quiet intervals while AE > 100 nT for active times) and solar wind parameters are statistically surveyed. Our new findings demonstrate that, independent of the activity state, the field strength and B-z component (GSM coordinates) start the monotonic increase prominently as r decreases down to similar to 11.5R(E), which means the dipole field starts to make a significant contribution from there. At least in the surveyed radial range, the B-z component is found to be weaker in the midnight and dusk sectors than that in the dawn sector, displaying a dawn-dusk asymmetry. The occurrence rate of negative B-z in active times also exhibits a similar asymmetric distribution, which implies active dynamics may occur more frequently at midnight and dusk flank. In comparison with that in quiet intervals, several features can be seen in active times: (1) a local B-z minimum between 10.5 < r < 12.5R(E) is found in the dusk region, (2) the B-z component around the midnight region is generally stronger and experiences larger fluctuations, and (3) a sharp positive/negative-excursion of the B-y component occurs at the dawn/dusk flank regions inside r < 10R(E). The response to solar wind parameters revealed that the B-z component is generally stronger under higher dynamic pressure (P-dy > 5 nPa), which may support the dawn-dusk squeezing effect as presented by Miyashita et al. (2010). The CS By is generally correlated with the interplanetary magnetic field (IMF) B-y component, and the correlation quality is found to be better with higher penetration coefficient (the ratio of CS B-y to IMF B-y) when IMF B-z is positive. The implications of the present results are discussed. (C) 2014 Elsevier Ltd. All rights reserved.