Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm13b1804y&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM13B-1804
Physics
Plasma Physics
[2778] Magnetospheric Physics / Ring Current, [7845] Space Plasma Physics / Particle Acceleration, [7867] Space Plasma Physics / Wave/Particle Interactions
Scientific paper
The modulations of the outer ring current O+ ion fluxes by ULF Pc5 waves are investigated by multi-satellite observations during storm times. The O+ ions have energies up to tens of keV. We concentrate on the process in terms of drift-bounce resonance of O+ ions with ULF standing waves, to understand whether the ring current O+ ions could be accelerated/decelerated by ULF waves. Two case studies are performed, in which the Cluster satellites travel the outer ring current region in the morning sector with radial distances of about 5.5 RE. Distinct O+ ion flux oscillations are observed associated with fundamental mode ULF standing waves. On 25 Oct 2002, both satellites SC1 and SC4 observe strong poloidal and toroidal standing waves at approximately the same region one by one with a time lag of about 45 minutes. The O+ ion flux oscillations at ~20 keV are dominantly coherent with the poloidal standing wave at 3.4 mHz with cross phases of near 90°with respect to the magnetic field waves. The O+ phase space density spectra at around 10-25 keV, measured by both satellites, deviate the typical power-law distribution to higher levels. We suggest that the O+ ions at around 10-25 keV are accelerated due to drift-bounce resonance with the poloidal standing wave. On 04 Nov 2002, the satellite SC1 observes considerable poloidal and toroidal standing waves. The O+ ion flux oscillation at ~7 keV is well correlated with both the two wave modes at 3.7 mHz with cross phases of about 90° with respect to the magnetic field waves. The O+ spectra at 4-8 keV deviates the background power-law distribution to lower levels. Whereas, when the satellite SC4 encounters closely the same region 40 minutes later, the wave activities at 3.7 mHz are found to be rather weak and the O+ spectra is close to the background power-law distribution. We suggest that the spectra variation of SC1 is resulted from the deceleration of O+ ion at around 4-8 keV via drift-bounce resonances during the strong wave activities. The observations made in this study reveal the effective role of ULF standing waves in accelerating/decelerating the ring current O+ ions.
Fu Siqi
Korth Alex
Li Xiaoliang
Reme Henri
Yang Bokai
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