Statistical survey of quasi-periodic VLF emissions observed in the inner magnetosphere conjugated with geomagnetic field fluctuations measured on the ground

0473456 - ÚFA 2017 FR eng A - Abstrakt
Hájoš, Mychajlo - Santolík, Ondřej - Němec, F. - Demekhov, A. - Parrot, M. - Raita, T.
Statistical survey of quasi-periodic VLF emissions observed in the inner magnetosphere conjugated with geomagnetic field fluctuations measured on the ground.
4th Cluster and THEMIS workshop: Book of abstracts. Paris: European Space Agency (ESA), 2017. s. 58.
[Cluster-THEMIS Workshop /4./. 07.11.2016-12.11.2016, Palm Springs]
Institucionální podpora: RVO:68378289
Klíčová slova: quasiperiodic ELF/VLF emissions * DEMETER spacecraf * magnetosphere
Kód oboru RIV: BL - Fyzika plazmatu a výboje v plynech
http://themis.igpp.ucla.edu/events/CLUSTER_THEMIS_2016/Workshop_abstracts_v3.pdf

We present a comparison between properties of quasiperiodic (QP) ELF/VLF
emissions observed by the low-altitude DEMETER spacecraft and ULF geomagnetic
field pulsations measured on the ground by the THEMIS/CARISMA (Canadian Array
for Realtime Investigations of Magnetic Activity) system of flux-gate magnetometers
and by the Sodankyla Geophysical Observatory (SGO) magnetometer. We have
selected for analysis about 400 QP DEMETER events which were conjugated with
ground-based stations. The analyzed QP events have modulation periods larger than
10 s and frequency bandwidths higher than 200 Hz.
A good agreement between modulation periods of QP emissions and frequencies of
the most intense fluctuations of ULF pulsations has been found for QP events with
modulation periods larger than 40 s. Such QP emissions which appear to be closely
associated with coincident geomagnetic pulsations are called QP1, representing
about 18 percents of the total number of analyzed QP events. No corresponding
geomagnetic pulsations were identified in the remaining 82 percents of QP events,
and these events are classified as QP2. The maximum spectral intensity of QP1
events does not seem to depend on the intensity of geomagnetic field fluctuations
while QP2 events intensity is increasing with integral intensity of the geomagnetic
field fluctuations at frequencies 10 - 500 mHz. The intensity of geomagnetic field
disturbances gradually increases with invariant geomagnetic latitudes during QP
emissions of both types. However, in the case of QP2 type, a rapid rise of
geomagnetic field fluctuations was observed in the latitude range of 60 to 65
degrees.
Based on the observed association between QP emissions and geomagnetic field
disturbances, we attempt to estimate the spatial extent of the QP emissions and we
discuss the effect of ULF pulsations of different origin on QP1 emissions in the
magnetosphere.
Trvalý link: http://hdl.handle.net/11104/0270574