HR: 08:45h
AN: NG21A-04    [Abstracts]
TI: Scaling and a Fokker-Planck model for AU and AL- Solar Cycle Dependence.
AU: Hnat, B
EM: hnat@astro.warwick.ac.uk
AF: Space and Astrophysics, University of Warwick, Coventry, CV4 7AL United Kingdom
AU: * Chapman, S C
EM: sandrac@astro.warwick.ac.uk
AF: Space and Astrophysics, University of Warwick, Coventry, CV4 7AL United Kingdom
AU: Rowlands, G
EM: G.Rowlands@warwick.ac.uk
AF: Space and Astrophysics, University of Warwick, Coventry, CV4 7AL United Kingdom
AU: Watkins, N W
EM: nww@bas.ac.uk
AF: Physical Sciences Division, British Antarctic Survey, Cambridge, CB3 0ET United Kingdom
AB: Scaling and a departure from Gaussian statistics has been identified as a key property of magnetospheric energy release in the form of bursty bulk flows in the magnetotail, ``blobs" in the aurora, non-Gaussian fluctuations in geomagnetic indices and in single station magnetometer data. Models include Self-Organized Criticality (SOC) and multi-fractal models related to those of turbulence. We study scaling in fluctuations of the AU and AL geomagnetic indices that provide a measure of magnetospheric activity, and of the epsilon parameter which is a measure of the solar wind driver. We perform analyses that provide quantitative measures within the framework of models for turbulence and for critical phenomena; that is, we find the exponent that captures the self-similarity in the time series, and the functional form of the non-Gaussian Probability Density Function (PDF) that expresses its intermittency. Generalized structure function analysis is accompanied by PDF rescaling. Fluctuations in all quantities are found to exhibit self-similar statistics for up to 1-2 hours for fluctuation size up to 10 standard deviations. We divide the data into intervals of solar maximum and minimum and find that whereas fluctuations in epsilon and AU change their properties with the solar cycle, fluctuations in AL do not. This places strong statistical constraints on the propagation of information from these below-substorm scale fluctuations from the solar wind to the magnetosphere as seen by the indices. Having established scaling in AU and AL we then develop a Fokker-Planck model for their timeseries which we test against the PDF of the fluctuation timeseries. This provides a Langevin (stochastic dynamical) equation for the fluctuations in the indices.
DE: 2159 Plasma waves and turbulence
DE: 2722 Forecasting
DE: 3210 Modeling
DE: 3250 Fractals and multifractals
SC: Nonlinear Geophysics [NG]
MN: 2004 AGU Fall Meeting