10/2/2015 - Polar Cap Precursor of Nightside Meso-scale Auroral Enhancements


3:30 PM - 4:50 PM
Geology 6704

Presented By:
Ying Zou - UCLA AOS


Understanding the occurrence of meso-scale enhanced auroras is critical for forecasting ionospheric scintillation and remote-sensing magnetospheric disturbances. One important nightside meso-scale aurora is poleward boundary intensifications (PBIs), which are intensifications along the poleward boundary of the nightside auroral oval and are produced by magnetotail reconnection. By combining white light and multi-spectral all-sky imagers (ASIs) with radars, we try to understand when and where PBIs and the associated magnetotail reconnection occur, spontaneously or driven by external forcing. We found that in radar measurements polar cap convection is structured and the embedded narrow fast flows highly (90%) correlate with PBI occurrence at the same longitude. Although radar field-of-view is limited, a polar cap multi-spectral ASI substantially expand our observing area by enabling flow tracing over long distance using airglow patches and polar cap arcs. It shows localized fast flows commonly occur deep in the polar cap, propagate at ~600 m/s as channels elongated in the noon-midnight meridian, and significantly contribute to magnetic flux convection across the polar cap. The mosaic images further show that as these fast flow propagate equatorward from the magnetic pole and impinge on the nightside auroral poleward boundary, they are followed by oval intensifications that are spatially connected to them and initiate within a few minutes delay. Such intensifications are major disturbances that do not occur until the impingement of polar cap flows, suggesting the intensifications to be triggered by these flows. Our results suggest that locally enhanced nightside auroras can be preceded by, and developed around, localized flow enhancements arriving at the auroral poleward boundary from the polar cap. This preceding signature is essential to understand the development of magnetotail reconnection, and gives the potential of forecasting the specific time and location of disturbances in the magnetosphere and ionosphere.

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