Abstract
Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.
Highlights
Some complex physical systems can establish a scale-free state known as self-organised criticality (SOC) (Bak et al, 1987; Frette et al, 1996)
The aim of this paper is to identify the characteristics of magnetospheric electric field fluctuations implied by Super Dual Auroral Radar Network (SuperDARN) observations of line-of-sight Doppler velocity, vLOS, in the noon and midnight sectors of the high-latitude ionosphere
Doppler spectral width tends to increase with the amplitude of velocity fluctuations which are expected to increase in proportion to the mean flow speed for turbulence, so it is not surprising that larger vLOS tended to be observed for Population B
Summary
Some complex physical systems can establish a scale-free state known as self-organised criticality (SOC) (Bak et al, 1987; Frette et al, 1996). These systems exhibit burstiness, intermittency, and self-similarity over many orders of spatial and temporal scale. Nivologists aim to incorporate the powerlaw behaviour of self-organised systems into routine predictions of avalanche risk for the European Alps (Palmer, 2003). This is an example of the way in which complexity science might contribute to the preservation of human life
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