A Statistical Study of Bz-dips in Front of Magnetotail Dipolarization Fronts

Abstract:

Dipolarization fronts (DF) are a key ingredient of magnetic flux transport in the magnetotail towards Earth. They are accompanied by fast flows, also called bursty bulk flows (BBFs), and a sharp increase in the magnetic field Z-component perpendicular to the current sheet in the tail. This increase in Bz is typically preceded by a decrease, a Bz-dip, which sometimes even turns negative.

We present a study on the depth of the Bz-dips with respect to DF-characteristics, -geometry and location in the tail. For our study, we use the ECLAT DF-list introduced in Schmid et al. [J. Geophys. Res., 120, 1096 (2015)], which is based on 9 years (2001-2009) of Cluster magnetotail observations. Relative to the Bz change across the DF, we find the Bz-dip depth to be independent of the distance to the centre of the neutral sheet and/or the azimuthal and polar direction where Cluster crossed the DF. We relate these results to the current systems and density distribution on and in the vicinity of DFs.