Modeled variations of the reconnection electric field at the dayside magnetopause during continued flux transfer event activity

摘要

Three periods of repeated flux transfer event (FTE) observations made by the Cluster satellites are investigated by a novel method for extracting from the observations the reconnection electric field E_(rec). On 21 January 2001, a series of FTEs is observed at the poleward edge of the cusp around 15 magnetic local time (MLT). Another series of FTEs is observed on 14 February 2001, at somewhat earlier MLTs at the high-latitude magnetopause at the equatorward edge of the cusp. In both cases, ground-based radar observations confirm that Cluster observations refer to transient reconnection. Additionally, we consider an event of several magnetosheath FTEs on 26 January 2001, during very steady interplanetary conditions. Here we apply a model based on time-dependent Petschek-type magnetic reconnection to the in situ magnetic field data to obtain the temporal variations of the reconnection electric field responsible for each FTE of the three series. On 14 February 2001 we find peak average values of E_(rec) = 2.1 ± 0.4 mV/m for the magnetospheric FTEs and peak average values E_(rec) = 0.9 ± 0.5 mV/m for the magnetosheath FTEs. The corresponding result for the four FTEs on 21 January 2001 is 3.7 ± 0.8 mV/m. Finally, the four FTEs observed on 26 January 2001 give a reconnection rate of 2.85 ± 1.68 mV/m. These results are discussed in the context of estimates of the reconnection electric field at the magnetopause obtained from diverse techniques.