Abstract
Abstract. The temporal scaling properties of F-region velocity fluctuations, δvlos, were characterised over 17 octaves of temporal scale from τ=1 s to <1 day using a new data base of 1-s time resolution SuperDARN radar measurements. After quality control, 2.9 (1.9) million fluctuations were recorded during 31.5 (40.4) days of discretionary mode soundings using the Tasmanian (New Zealand) radars. If the fluctuations were statistically self-similar, the probability density functions (PDFs) of δvlos would collapse onto the same PDF using the scaling Ps (δvs, τ)=ταP (δvlos, τ) and δvs=δvlosτ−α where α is the scaling exponent. The variations in scaling exponents α and multi-fractal behaviour were estimated using peak scaling and generalised structure function (GSF) analyses, and a new method based upon minimising the differences between re-scaled probability density functions (PDFs). The efficiency of this method enabled calculation of "α spectra", the temporal spectra of scaling exponents from τ=1 s to ~2048 s. The large number of samples enabled calculation of α spectra for data separated into 2-h bins of MLT as well as two main physical regimes: Population A echoes with Doppler spectral width <75 m s−1 concentrated on closed field lines, and Population B echoes with spectral width >150 m s−1 concentrated on open field lines. For all data there was a scaling break at τ~10 s and the similarity of the fluctuations beneath this scale may be related to the large spatial averaging (~100 km×45 km) employed by SuperDARN radars. For Tasmania Population B, the velocity fluctuations exhibited approximately mono fractal power law scaling between τ~8 s and 2048 s (34 min), and probably up to several hours. The scaling exponents were generally less than that expected for basic MHD turbulence (α=0.25), except close to magnetic dusk where they peaked towards the basic MHD value. For Population A, the scaling exponents were larger than for Population B, having values generally in the range expected for basic MHD and Kolmogorov turbulence (α=0.25–0.33). The α spectra exhibited complicated variations with MLT and τ which must be related to different physical processes exerting more or less influence.
Highlights
In accordance with scientific method, the space physics community has adopted simple homogenous models of the ionosphere, yet accepted more complicated dynamics and morphology when compelled to do so by new observations
Consider an early, basic model of high-latitude ionospheric convection (Volland, 1975), the greater detail contained in more recent statistical models (e.g. Papitashvili and Rich, 2002), and the real time variability observed by DMSP spacecraft and the Super Dual Auroral Radar Network (SuperDARN) (Greenwald et al, 1995; Chisham et al, 2007)
The power law scaling exponent for fluctuations equatorward of the open-closed boundary (OCB) was estimated to be α=0.39 (0.31). They suggested the scaling exponent poleward of the OCB was related to spatial structure in the solar wind, whereas the scaling exponent equatorward of the OCB was related to internal dynamics of the magnetosphereionosphere system
Summary
In accordance with scientific method, the space physics community has adopted simple homogenous models of the ionosphere, yet accepted more complicated dynamics and morphology when compelled to do so by new observations. Chapman et al, 2005; Kiyani et al, 2006) to characterise the temporal scaling of electric field fluctuations in the high-latitude ionosphere inferred using SuperDARN observations of F-region Doppler velocity made at 1-s time resolution. Parkinson (2006) used SuperDARN radar measurements to estimate temporal scaling exponents of zonal electric field fluctuations in the high-latitude ionosphere. The power law scaling exponent for fluctuations equatorward (poleward) of the open-closed boundary (OCB) was estimated to be α=0.39 (0.31) They suggested the scaling exponent poleward of the OCB was related to spatial structure in the solar wind, whereas the scaling exponent equatorward of the OCB was related to internal dynamics of the magnetosphereionosphere system. This paper extends the results of these earlier studies by analysing a data base of experimental radar measurements made at 1-s resolution This represents a 60-fold decrease in the minimum temporal scale used to characterise the fluctuations. Parkinson: Scaling of velocity fluctuations in the high-latitude F-region ionosphere scaling exponents with temporal scale due to multi-fractal behaviour
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