Source of the dayside cusp aurora

Autor: Harald U. Frey, Vassilis Angelopoulos, Stephen B. Mende
Rok vydání: 2016
Předmět:
Zdroj: Journal of geophysical research. Space physics, vol 121, iss 8
Journal of Geophysical Research. Space Physics
ISSN: 2169-9402
2169-9380
DOI: 10.1002/2016ja022657
Popis: Monochromatic all‐sky imagers at South Pole and other Antarctic stations of the Automatic Geophysical Observatory chain recorded the aurora in the region where the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites crossed the dayside magnetopause. In several cases the magnetic field lines threading the satellites when mapped to the atmosphere were inside the imagers' field of view. From the THEMIS magnetic field and the plasma density measurements, we were able to locate the position of the magnetopause crossings and map it to the ionosphere using the Tsyganenko‐96 field model. Field line mapping is reasonably accurate on the dayside subsolar region where the field is strong, almost dipolar even though compressed. From these coordinated observations, we were able to prove that the dayside cusp aurora of high 630 nm brightness is on open field lines, and it is therefore direct precipitation from the magnetosheath. The cusp aurora contained significant highly structured N2 + 427.8 nm emission. The THEMIS measurements of the magnetosheath particle energy and density taken just outside the magnetopause compared to the intensity of the structured N2 + 427.8 nm emissions showed that the precipitating magnetosheath particles had to be accelerated. The most likely electron acceleration mechanism is by dispersive Alfvén waves propagating along the field line. Wave‐accelerated suprathermal electrons were seen by FAST and DMSP. The 427.8 nm wavelength channel also shows the presence of a lower latitude hard‐electron precipitation zone originating inside the magnetosphere.
Key Points Comparison between THEMIS satellite data and ground‐based optical auroral data proves that cusp auroras are on open field linesThe source of the dayside cusp auroral particles is the magnetosheathThe soft cusp auroras contain significant N2 + intensity to imply that acceleration of the magnetosheath particles takes place
Databáze: OpenAIRE
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