HR: 1340h
AN: SH13A-1101    [Abstracts]
TI: Distinguishing non- stationarity from finite interval effects in the intermittent solar wind.
AU: * Kiyani, K H
EM: K.Kiyani@warwick.ac.uk
AF: Centre for Fusion, Space and Astrophysics, Physics Dept., Univ. of Warwick, Coventry, CV4 7AL, United Kingdom
AU: Chapman, S C
EM: S.C.Chapman@warwick.ac.uk
AF: Centre for Fusion, Space and Astrophysics, Physics Dept., Univ. of Warwick, Coventry, CV4 7AL, United Kingdom
AB: The solar wind flow has a magnetic Reynolds number estimated ~ 10⁵ and fluctuations in solar wind bulk plasma parameters typically show a clear region of power law scaling in the power spectrum with an exponent close to -5/3. Quantitative analysis of solar wind fluctuations are thus often performed in the context of intermittent turbulence and center around methods to quantify statistical scaling, such as generalized structure functions which assume a weakly stationary process. The solar wind exhibits large scale secular changes and so the question arises as to whether the timeseries of the fluctuations is non- stationary. One approach is to seek a local stationarity by restricting the time interval over which statistical analysis is performed. However multifractality implies that the scaling exponents are local in time. Computing scaling exponents over different intervals of a stationary multifractal process can thus potentially yield anomalously time varying values for the scaling exponents, suggestive of non stationarity. We investigate this using synthetic datasets generated from a (self affine) Levy flight and from a (multifractal) p- model. We are able to estimate the minimum interval (number of datapoints) needed to quantify the scaling exponents in a stationary multifractal process. With fewer datapoints the stationary timeseries becomes indistinguishable from a nonstationary process and we illustrate this with nonstationary synthetic datasets. Finally we apply these ideas to in- situ solar wind observations.
DE: 2159 Plasma waves and turbulence
DE: 2164 Solar wind plasma
DE: 3270 Time series analysis (1872, 4277, 4475)
DE: 4440 Fractals and multifractals
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting