| Autor: |
Walker, S.N., Demekhov, A.G., Boardsen, S.A., Ganushkina, N.Y., Sibeck, D.G., Balikhin, M.A. |
| Jazyk: |
angličtina |
| Rok vydání: |
2016 |
| Předmět: |
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| ISSN: |
2169-9402 |
| Popis: |
Equatorial magnetosonic waves are normally observed as temporally\ud continuous sets of emissions lasting from minutes to hours. Recent\ud observations, however, have shown that this is not always the case. Using\ud Cluster data, this study identifies two distinct forms of these non-temporallycontinuous\ud emissions. The first, referred to as rising tone emissions, are characterised\ud by the systematic onset of wave activity at increasing proton gyroharmonic\ud frequencies. Sets of harmonic emissions (emission elements) are\ud observed to occur periodically in the region ±10◦ off the geomagnetic equator.\ud The sweep rate of these emissions maximises at the geomagnetic equator.\ud In addition, the ellipticity and propagation direction also change systematically\ud as Cluster crosses the geomagnetic equator. It is shown that the\ud observed frequency sweep rate is unlikely to result from the sideband instability\ud related to nonlinear trapping of suprathermal protons in the wave field.\ud The second form of emissions is characterised by the simultaneous onset of\ud activity across a range of harmonic frequencies. These waves are observed\ud at irregular intervals. Their occurrence correlates with changes in the spacecraft\ud potential, a measurement that is used as a proxy for electron density |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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