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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A11205, doi:10.1029/2007JA012483, 2007

Solar wind control of Pc5 pulsation power at geosynchronous orbit

Kazue Takahashi

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


Aleksandr Y. Ukhorskiy

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


Abstract

We statistically study the solar wind control of Pc5 magnetic pulsations at geosynchronous orbit. Solar wind conditions are quantified with the use of proton measurements at L1 from the ACE spacecraft that are propagated to the bow shock nose. In addition to the solar wind velocity, V sw , density, N sw , and dynamic pressure, P sw , we also consider the dynamic pressure variance in the Pc5 band, VarP sw. Pc5 pulsation parameters are derived from the GOES 8 magnetic field measurements at geosynchronous orbit at ∼10° magnetic latitude. The pulsations are quantified by three parameters: S y , total power of the azimuthal magnetic field component in the 1.6- to 6.7-mHz Pc5 band; S z , total power of the field-aligned (compressional) component in the same band; and S tor, the azimuthal power of narrow-band Pc5 oscillations attributed to the fundamental toroidal standing Alfvén waves. All parameters are computed in non-overlapping 1-h time windows and then used in linear correlation analysis. We find that all pulsation parameters are positively correlated with P sw and VarP sw with a correlation coefficient of up to ∼0.7 on the dayside. While the correlation of pulsation parameters with the solar wind velocity and density is also positive, the correlation coefficients are smaller. We discuss three mechanisms relevant to the observed P sw and VarP sw control of pulsation power: (1) solar wind-forcing of magnetic pulsations (breathing mode); (2) P sw control of the magnetopause-satellite distance, which results in the P sw dependence of the amplitude of surface waves observed at the satellite; and (3) coupling of impulsively excited fast mode waves to toroidal standing Alfvén waves.

Received 18 April 2007; accepted 10 September 2007; published 10 November 2007.

Keywords: Pc5 pulsations; solar wind; GOES satellite.

Index Terms: 2752 Magnetospheric Physics: MHD waves and instabilities (2149, 6050, 7836); 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2730 Magnetospheric Physics: Magnetosphere: inner; 2724 Magnetospheric Physics: Magnetopause and boundary layers; 2774 Magnetospheric Physics: Radiation belts.

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Citation: Takahashi, K., and A. Y. Ukhorskiy (2007), Solar wind control of Pc5 pulsation power at geosynchronous orbit, J. Geophys. Res., 112, A11205, doi:10.1029/2007JA012483.