Journal article
Observational study of generation conditions of substorm-associated low-frequency AKR emissions
Annales geophysicae (1988), Vol.22(10), pp.3571-3582
2004
DOI: 10.5194/angeo-22-3571-2004
Abstract
It has lately been shown that low-frequency bursts of auroral kilometric radiation (AKR) are nearly exclusively associated with substorm expansion phases. Here we study low-frequency AKR using Polar PWI and Interball POLRAD instruments to constrain its possible generation mechanisms. We find that there are more low-frequency AKR emission events during wintertime and equinoxes than during summertime. The dot-AKR emission radial distance range coincides well with the region where the deepest density cavities are seen statistically during Kp>2. We suggest that the dot-AKR emissions originate in the deepest density cavities during substorm onsets. The mechanism for generating dot-AKR is possibly strong Alfvén waves entering the cavity from the magnetosphere and changing their character to more inertial, which causes the Alfvén wave associated parallel electric field to increase. This field may locally accelerate electrons inside the cavity enough to produce low-frequency AKR emission. We use Interball IESP low-frequency wave data to verify that in about half of the cases the dot-AKR is accompanied by low-frequency wave activity containing a magnetic component, i.e. probably inertial Alfvén waves. Because of the observational geometry, this result is consistent with the idea that inertial Alfvén waves might always be present in the source region when dot-AKR is generated. The paper illustrates once more the importance of radio emissions as a powerful remote diagnostic tool of auroral processes, which is not only relevant for the Earth's magnetosphere but may be relevant in the future in studying extrasolar planets.
Details
- Title: Subtitle
- Observational study of generation conditions of substorm-associated low-frequency AKR emissions
- Creators
- A. Olsson - Swedish Institute of Space PhysicsP. Janhunen - Finnish Meteorological InstituteJ. Hanasz - Centrum Badań KosmicznychM. Mogilevsky - Space Research InstituteS. Perraut - Université de Versailles Saint-Quentin-en-YvelinesJ. D. Menietti - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Annales geophysicae (1988), Vol.22(10), pp.3571-3582
- Publisher
- European Geosciences Union
- DOI
- 10.5194/angeo-22-3571-2004
- ISSN
- 0992-7689
- eISSN
- 1432-0576
- Language
- English
- Date published
- 2004
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984627182502771
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