Determining magnetotail reconnection location from polar rain energy dispersion

An improved algorithm was developed to estimate the polar rain electron path length from the magnetotail X-line to the polar ionosphere using the information of polar rain electron energy-latitude dispersion. Recent particle tracing simulations using APLOPM model (Applied Physics Laboratory - Open-field line particle Precipitation Model) (Wing et al., 2001;Wing and Zhang, 2015) indicate that an existing or traditional method underestimates the path length by at least 33%. A new method for estimating electron path length that introduces a new parameter (energy parameter) is proposed. The improved algorithm has been validated using the APLOPM simulation data. By applying the new algorithm to two real events measured by DMSP satellites, we found the polar rain electron path lengths of 67 and 114 RE, (X-lines estimated at X=−54 and −91 RE), respectively (assuming the distance from the X-line to the Earth is 80% of the electron path length). The associated IMF Bz were 1 and -11 nT, respectively for the two events. This is consistent with the expected stretched magnetotail configuration under a strongly southward IMF. The results are also consistent with statistical results of the X-line locations from Geotail measurements.