Abstrakt
We investigate the influence of interplanetary (IP) shocks on the intensity of extremely and very low frequency (ELF/VLF) waves measured by the French DEMETER spacecraft between 2004 and 2010. DEMETER is particularly useful for this kind of analysis, because it had a Sun-synchronous orbit (local time 10:30 and 22:30), operated at a low altitude (700 km) with 14 orbits per day, which allows a fast sampling of a given portion of the magnetosphere.
Altogether, 225 IP shocks were detected in the Wind spacecraft data (close to L1 point) during the duration of the DEMETER mission (more than 6 years). Among these, there were 87 fast forward (FF), 31 fast reverse (FR), 59 slow forward (SF), and 48 slow reverse (SR) shocks.
The analysis was performed using one component of power spectral density of electric field fluctuations measured in the frequency range up to 20 kHz. The overall geomagnetic activity around the times of the shocks increases after the time of the shock arrival.
However, the variation of the measured wave intensity (along with the observed time delay) depends on the type of the shock. The most significant effect was observed for FF shocks.
These results were also verified by the principal component analysis, which allows us to conveniently characterize the measured wave intensity and its variations.