scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Storm-time dayside ULF activity: CIR and CME driven storms comparison
Kozyreva Olga , Kleimenova Natalia
Institute of Physics of the Earth, RAS
The dayside ULF-pulsation activity has been analyzed during the
selected succession of 10 recurrent magnetic storms (CIR-driven storms),
which repeated with the periodicity of about 27 days in 2006. The ULF-index,
as a measure of the wave level activity in the frequency range of 2-7 mHz, was
calculated according to the ground-based 1-min observations at the morning
(03-12 MLT) and afternoon (12-18 MLT) sectors for auroral (60-70º) and polar
(70-90º) latitudes. It was found that in all phases of the magnetic storms under
consideration, the enhanced ULF-activity was found at the auroral as well as at
the polar latitudes. In the studied CIR-driven storms, the value of the solar wind
velocity was very large (more 600 km/c) providing the Kelvin-Helmholz
instability progression and, correspondingly, the ULF wave generation. The
daytime polar zone ULF intensity was of the same order or even higher then at
the auroral zone. The ULF-index, calculated for the fluctuations in the
Interplanetary Magnetic Field (IMF), indicated the enhancement of the strong
ULF waves in the initial and main phases of the analyzed magnetic storms. We
assume that some of these fluctuations could penetrate into the open polar cap
and provide an enhancement of the dayside ULF geomagnetic pulsations at the
high latitudes. The ULF-index, based on the geostationary GOES data,
demonstrated increasing of the intense ULF pulsations in the magnetosphere in
the storm main and recovery phases, but not in the storm initial phase. The
comparison of the ULF-activity during the CIR-driven storms (typical for the
solar activity minimum) and CME-driven storms (typical for the solar activity
maximum) showed that the ULF-activity associated with the CIR-driven storms
was observed at the higher latitudes then in the CME-driven storm.