Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh13a1101k&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH13A-1101
Physics
2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma, 3270 Time Series Analysis (1872, 4277, 4475), 4440 Fractals And Multifractals, 4475 Scaling: Spatial And Temporal (1872, 3270, 4277)
Scientific paper
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.
Chapman Sandra C.
Kiyani K. H.
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