Alfvénic turbulence in high speed solar wind streams as a driver for auroral activity

Details Alfvénic turbulence in high speed solar wind streams as a driver for auroral activity Alfvénic turbulence in high speed solar wind streams as a driver for auroral activity

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jastp..71.1014d&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 71, Issue 10-11, p. 1014-1022.

Physics

Solar Wind, Mhd Turbulence, Auroral Activity

Scientific paper

The solar wind-magnetosphere interaction has been widely studied in the presence of intense perturbations in the solar wind, causing geomagnetic storms and substorms, by means of the so-called coupling parameters. However, remarkable variations in the geomagnetic field occur even in the absence of such perturbations. We suggest that, in these conditions, MHD turbulence might have a role. Recent results have shown that solar wind MHD turbulence can be described not only as a mixture of inward and outward stochastic Alfvénic fluctuations but includes also convected coherent structures, partially dominated by an excess of magnetic energy. The present study focuses on the relationship between solar wind MHD turbulence and auroral activity as measured by the AE index as a function of the solar cycle. We find that at solar minimum Alfvénic turbulence drives the auroral response. In addition, we present a preliminary statistical study on the intermittency of Bs (the southward z component of the interplanetary magnetic field) and AE, focusing in particular on their respective extreme events (those events that are located in the tails of the distribution and deviate from Gaussian statistics), for different phases of the solar cycle. In order to recognize the extreme events affecting our statistics, we use a technique, called local intermittency measure (LIM), based on wavelet decomposition. Once we have selected all the extreme events we can measure the elapsed time, or waiting time, between consecutive events and build the relative distribution. Our analysis shows that these distributions are characterized by well-defined power laws which would discard the possibility of uncorrelated events and would suggest the existence of long term correlations typical of turbulent processes. Moreover, we find that these distributions do not depend on the particular phase of the solar cycle considered.

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