Frequency dependence of VLF chorus Poynting flux in the source region: THEMIS observations and a model

0477983 - ÚFA 2018 BE eng A - Abstrakt
Demekhov, A. G. - Taubenschuss, Ulrich - Santolík, Ondřej
Frequency dependence of VLF chorus Poynting flux in the source region: THEMIS observations and a model.
Papers from URSI: XXXIInd General Assembly and Scientific Symposium (URSI GASS). Ghent: URSI, 2017. G36-2, HJ34-3.
[URSI General Assembly and Scientific Symposium (URSI GASS) 2017 /32./. 19.08.2017-26.08.2017, Montreal]
Institucionální podpora: RVO:68378289
Klíčová slova: VLF chorus emissions * THEMIS spacecraft * wave-particle interaction
Kód oboru RIV: BL - Fyzika plazmatu a výboje v plynech

We present the results of observations of VLF chorus emissions based on several events detected by THEMIS spacecraft within the chorus generation region. Using the THEMIS multicomponent wave data of parallel propagating chorus elements detected at some distance from the magnetic field minimum, we have found that the elementspropagatingequatorwardhadslightlybutsystematicallyhigherfrequenciesandsmalleramplitudescomparedwithsimultaneouslyobservedelementspropagatingawayfromtheequator. Theexponentialgrowthratesof the elements propagating in both directions had close or equal values.
We propose an explanation of the observed feature on the basis of spatio-temporal evolution of the energetic electron distribution function in the course of VLF wave generation. The motion of electrons from the equator is accompaniedbyadecreaseintheirparallelvelocityduetoboth,adiabaticmirrorforceandnonlinearwave-particle interaction,whichcausesanadditionalincreaseinthewavefrequencyofequatorwardpropagatingchoruselements generatedbysuchelectrons. Theelementspropagatingintheoppositedirection, i.e., fromtheequator, areformed by electrons whose parallel velocities are larger due to the adiabatic mirror force. Correspondingly, such electrons generate waves with lower frequencies. We present the results of numerical simulations confirming the proposed mechanism.
Trvalý link: http://hdl.handle.net/11104/0274213