In Situ Observational Evidence of the Polar Cap Arc at 1500 MLT (15MLT-PCA) Associated With the Lobe Reconnection

The polar cap arc at 1500 MLT (15MLT-PCA) has been considered as an auroral signature of the cusp's duskside boundary and been speculated to be caused by lobe reconnection. However, no observational evidence has been provided to support this speculation. Here we report a 15MLT-PCA event occurred on 29 November 2017 using multi-instrument observations. During the DMSP observed the 15MLT-PCA, Cluster, with its footprints at the root of the 15MLT-PCA, identified two FTEs in the southern hemisphere's lobe region, accompanied by an increase in electron and ion energy from hundreds of eVs to several keVs. AMPERE observed an increase in upward field-aligned currents associated with the 15MLT-PCA. SuperDARN observed a single cell convection with an enhancement of sunward plasma flow near the root of 15MLT-PCA. We suggest that these observations provide the in-situ observational evidence that the 15MLT-PCA is generated by a lobe reconnection at the cusp's duskside boundary.