Power law probability distributions of multiscale auroral dynamics from ground‐based TV observations

Abstract

[1] Some of the most significant observational indications of self-organized critical (SOC) behavior in the magnetosphere are the scale-free statistical distributions of nighttime auroral emission regions as depicted by the Ultraviolet Imager (UVI) onboard the POLAR spacecraft [Uritsky et al., 2002]. Here, we report the results from a similar study of ground-based optical observations. Individual active auroral regions have been detected and analyzed using a spatiotemporal technique and statistical methods appropriate for quantifying critical behavior in SOC models. Probability distributions of the lifetime, maximum and integrated size, maximum power, and integrated energy output for auroral emission regions are shown to follow power law relations over wide ranges of scales. The powerlaw exponents that we obtained are consistent with the UVI image exponents, extending the range of observed scale-free auroral SOC dynamics by several orders of magnitude to smaller spatial and temporal scales.

Data‐derived spatiotemporal resolution constraints for global auroral imagers

“…The analysis we present here is the first attempt to quantify this tendency on a rigorous empirical basis using extended image databases from previous auroral imaging missions. The auroral images are processed using the event detection methodology presented in previous publications [Uritsky et al, 2002[Uritsky et al, , 2003Kozelov et al, 2004;Uritsky et al, 2006]. We show the existence of a nontrivial scaling relation between the relaxation time and the size of auroral emission events.…”

“…reported by Kozelov et al [2004], and then to derive b from POLAR and IMAGE data. The results will be extrapolated to small spatial and temporal scales based on the convergence of ground-based and satellite-based statistics [Kozelov et al, 2004].…”

“…The results will be extrapolated to small spatial and temporal scales based on the convergence of ground-based and satellite-based statistics [Kozelov et al, 2004]. We will also use image data to get the average velocity of auroral features at all relevant scales.…”

“…The reported results are based on an extensive set of images from two previously flown instruments, POLAR UVI and IMAGE WIC, processed using the event detection methodology developed by Uritsky et al (2002Uritsky et al ( , 2003Uritsky et al ( , 2006. We use the cross-scale analysis of ground-based and spacecraft observations of auroral emission regions by Kozelov et al (2004) to derive the power law exponent relating spatial and temporal scales of auroral precipitation events, and estimate the normalization factor entering this relation using the satellite data. Our results show the existence of a nontrivial scaling relation between the relaxation time and the spatial dimension of auroral emission events.…”

Investigating turbulent structure of ionospheric plasma velocity using the Halley SuperDARN radar

“…a measure of fluctuations with no characteristic scales (power law), over a wide range of scales. Examples include (a) power spectra of ground magnetic fields (Cambell, 1976;Francia et al, 1995;Consolini et al, 1998;Weatherwax et al, 2000;Abel and Freeman, 2002), and ionospheric electric fields (Kintner, 1976;Weimer et al, 1985;Bering et al, 1995;Buchert et al, 1999;Abel and Freeman, 2002;Golovchanskaya et al, 2006), (b) probability density functions (PDFs) of durations between threshold crossings of the auroral electrojet indices AU and AL (Freeman et al, 2000), (c) PDFs of durations, areas, and other quantities of auroral bright patches (Lui et al, 2000;Uritsky et al, 2002;Kozelov et al, 2004) and (d) structure functions of the auroral electrojet indices AU, AL and AE, the polar cap index PC (Takalo et al, 1993;Takalo and Timonen, 1998;Hnat et al, 2002), ground magnetic fields (Pulkkinen et al, 2006) and ionospheric convection (Parkinson, 2006;Abel et al, 2006).…”