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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L10103, doi:10.1029/2004GL022151, 2005

Rapid evolution of magnetic decreases (MDs) and discontinuities in the solar wind: ACE and Cluster

Bruce T. Tsurutani

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA


Fernando L. Guarnieri

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Brazilian Institute for Space Research, Sao Jose dos Campos, Sao Paolo, Brazil


Gurbax S. Lakhina

Indian Institute of Geomagnetism, Mumbai, India
Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan


Tohru Hada

Department of Earth Science and Technology, Kyushu University, Fukuoka, Japan


Abstract

An experiment was conducted to identify and measure the same magnetic decreases (MDs) and interplanetary discontinuities at two different points in space separated by ∼0.01 AU along the radial distance from the sun. The ACE and Cluster satellite data were used in this study. Solar wind speeds measured at Cluster were used to calculate the approximate (earlier) times of arrival at ACE. The field component changes at both spacecraft were intercompared to ensure that the same discontinuities were detected. Out of 7 MDs/discontinuities selected, 6 were identified at ACE. The MDs/discontinuities were identified within 7 s to 35 s of the convection times. The MD thicknesses at Cluster were substantially smaller than at ACE. The ratio of thicknesses varied from 0.21 to 0.045. One possible interpretation of this observation is that the Alfvén wave front (rotational discontinuity) is steepening by a factor of greater than 15 per wavelength propagated. This may have important consequences for the generation of high frequency turbulence in interplanetary space. It is noted that the 6 discontinuities transited the ∼0.01 AU distance from ACE to Cluster with essentially the solar wind convection speed. A possible mechanism contributing to this feature is discussed.

Received 3 December 2004; accepted 31 March 2005; published 27 May 2005.

Index Terms: 2109 Interplanetary Physics: Discontinuities (7811); 2159 Interplanetary Physics: Plasma waves and turbulence; 4490 Nonlinear Geophysics: Turbulence (3379, 4568, 7863); 7836 Space Plasma Physics: MHD waves and instabilities (2149, 2752, 6050).

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Citation: Tsurutani, B. T., F. L. Guarnieri, G. S. Lakhina, and T. Hada (2005), Rapid evolution of magnetic decreases (MDs) and discontinuities in the solar wind: ACE and Cluster, Geophys. Res. Lett., 32, L10103, doi:10.1029/2004GL022151.