Asymmetry in the tail neutral sheet rotation due to IMF By sign?

Abstract:

Evidence suggests that a non-zero dawn-dusk interplanetary magnetic field (IMF B_y) can cause a rotation of the cross-tail current sheet/neutral sheet around its axis aligned with the Sun-Earth line in the Earth’s magnetotail. We use Geotail, THEMIS and Cluster data to statistically investigate how the rotation depends on the sign and magnitude of IMF B_y. In our dataset, we find that at the tail range of -30 < XGSM < -15 R_E, the degree of the neutral sheet rotation is clearly smaller, there appears no rotation or even, the rotation is to an unexpected direction for negative IMF B_y compared to positive IMF B_y. Comparison to a model by Tsyganenko et al. (2015, doi:10.5194/angeo-33-1-2015) suggests that this asymmetry in the neutral sheet rotation between positive and negative IMF B_y conditions is too large to be explained only by the current known factors. The possible causes of the asymmetry and the potential limitations of our implemented analysis approach remain to be investigated.