[IGPP Everyone] NOW: Space Physics Seminar - Fri. Jan. 22nd - 3:30pm - Evidence of Alfvenic Poynting flux as the primary driver of auroral motion and O+ heating during an auroral substorm (S. Tian, U. Minn.)

[Emmanuel V. Masongsong]

SPACE PHYSICS SEMINAR 




DEPARTMENT OF EARTH, PLANETARY, AND SPACE SCIENCES 

DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES 

UNIVERSITY OF CALIFORNIA, LOS ANGELES 




ZOOM Link: https://ucla.zoom.us/j/94454128469?pwd=Qm9OSmZZekN5S0RoVTFITEs0N296QT09 

Meeting ID: 944 5412 8469 Passcode: 263337 



Evidence of Alfvenic Poynting flux as the primary driver of auroral motion and O+ heating during an auroral substorm 

Sheng Tian, Univ. of Minnesota 

Geomagnetic substorms are major energy transfer events where energy stored in the Earth’s magnetotail is released into the ionosphere. Substorm phenomena, including auroral activities, enhanced O+ outflow, earthward Poynting flux, magnetic field dipolarization, etc, have been extensively studied. However, the complex interplay among them is not fully understood. In a fortuitous event on June 07, 2013, the twin Van Allen Probes (separated by 0.4 hour in local time) observed bursts of earthward Alfvenic Poynting flux in the vicinity of the plasma sheet boundary layer (PSBL). The Poynting flux bursts correlate with enhancements of auroral brightness around the footpoints of both spacecraft. This indicates a temporal and spatial correlation between the auroral brightening and Poynting flux bursts, and that the auroral motion is tied to the perpendicular propagation of the Alfven wave. In addition, mono-energetic O+ outflows, seen as conics at the spacecraft, would have been perpendicularly heated around the altitude of the auroral acceleration region. These observations suggest that the Alfvenic Poynting flux is a primary driver for the auroral electron acceleration and O+ heating. Around the time of auroral brightening, a dipolarization was seen to propagate more than 4 hours in local time during a 20 min period. The azimuthal phase speed of this dipolarization (2 deg/min) is too small to explain the azimuthal motion of the aurora (13.6 deg/min), but the dipolarization could be related to the generation of the Alfvenic Poynting flux through phase mixing at strong density gradients like those in the PSBL. 



Friday, January 22, 2021 

3:30 - 5:00 PM 




In-Charge: Vassilis Angelopoulos 

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