Equatorial Noise Emissions and Their Quasi-Periodic Modulation

0453191 - ÚFA 2016 US eng A - Abstrakt
Němec, F. - Santolík, Ondřej - Hrbáčková, Zuzana - Pickett, J. - Cornilleau-Wehrlin, N. - Parrot, M. - Hayosh, Mykhaylo
Equatorial Noise Emissions and Their Quasi-Periodic Modulation.
AGU Fall Meeting. San Francisco: American Geophysical Union, 2015. SM51F-03.
[AGU Fall Meeting 2015. 14.12.2015-18.12.2015, San Francisco]
Institucionální podpora: RVO:68378289
Klíčová slova: equatorial noise * magnetosonic waves * quasiperiodic modulation
Kód oboru RIV: BL - Fyzika plazmatu a výboje v plynech
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/59251

Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic structure related to the ion cyclotron frequency in the source region. We analyze more than 2000 EN events observed by the wave instruments on board the Cluster spacecraft, and we find that about 5% of EN events are not continuous in time, but exhibit a quasi-periodic (QP) modulation of the wave intensity. Typical modulation periods are on the order of minutes. The events predominantly occur in the noon-to-dawn local time sector, and their occurrence is related to the periods of increased geomagnetic activity and higher solar wind speeds. We suggest that the QP modulation of EN events may be due to compressional ULF pulsations, which periodically modulate the wave growth in the source region. These compressional ULF pulsations were identified in about half of the events. EN emissions with QP modulation of the wave intensity can propagate down to altitudes as low as 700 km.
Trvalý link: http://hdl.handle.net/11104/0254055