SM51F-03
Equatorial Noise Emissions and Their Quasi-Periodic Modulation
Friday, 18 December 2015: 08:27
2018 (Moscone West)
Frantisek Nemec, Charles University, Prague, Czech Republic, Ondrej Santolik, Institute of Atmospheric Physics ACSR, Praha 4, Czech Republic, Zuzana Hrbackova, Charles University in Prague, Prague 8, Czech Republic, Jolene S Pickett, University of Iowa, Iowa City, IA, United States, Nicole Cornilleau-Wehrlin, LPPP/CNRS - Ecole Polytechnique, Palaiseau, France, Michel Parrot, CNRS - LPCE, Orleans, France and Mykhaylo Hayosh, Institute of Atmospheric Physics ACSR, Praha 4, 141, Czech Republic
Abstract:
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. Finally, we demonstrate that EN
emissions with QP modulation of the wave intensity can propagate down to
altitudes as low as 700 km.
