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- Title
A Statistical Model of Vorticity in the Polar Ionosphere and Implications for Extreme Values.
- Authors
Chisham, G.; Freeman, M. P.
- Abstract
Measurements of vorticity in the Earth's ionosphere enable the characterization of turbulent structure in the ionospheric plasma flow and how it varies spatially in relation to large‐scale magnetic field‐aligned current (FAC) systems. We have determined the spatial variation of the probability density function (PDF) of ionospheric vorticity measurements made by the Super Dual Auroral Radar Network (SuperDARN) across the northern polar ionosphere for the 6‐year interval 2000–2005 inclusive. These PDFs are highly leptokurtic, with heavy tails, and are well‐modeled by Tsallis q‐exponential probability distributions. The parameters of the model q‐exponential distributions have been determined using maximum likelihood estimation, resulting in a statistical model of ionospheric vorticity that covers the polar ionosphere. The spatial variation of the model parameters is highly variable, with the shape and scale of the model distributions varying systematically in relation to the well‐known FAC regions, showing that FACs have a major influence on the character of ionospheric plasma vorticity. From the model distributions, we estimate the probability of observing extreme vorticity values with the SuperDARN radars (beyond thresholds of 5, 10, 20, and 40 mHz) across the northern polar ionosphere. Plain Language Summary: The term space weather defines the day‐to‐day variability of physical processes at the edges of the Earth's atmosphere and in the space environment. As with extreme meteorological weather in the lower atmosphere, it is important to understand the probability of occurrence of instances of extreme space weather. One way that this can be achieved is by using space weather observations to develop models of the probability of occurrence of space weather events of different intensity. Here, we specifically study the vorticity of the flow of ionized gases (plasma) in the Earth's ionosphere (located at an altitude of 250–400 km). Vorticity is a measure of how straight or curved this flow of plasma is at a given location, and its intensity is closely related to turbulence within the ionospheric environment. By making multiple measurements of vorticity across different locations in the high‐latitude ionosphere, we can model the probability distributions of vorticity at a range of locations. The probability of observing extreme values of vorticity can then be estimated from these model distributions, allowing us to quantify the likelihood of extreme space weather. Key Points: Measurements of ionospheric vorticity enable the study of ionospheric turbulenceProbability density functions (PDFs) of ionospheric vorticity are highly leptokurticModeling the PDFs of vorticity allows the estimation of the probability of extreme vorticity
- Subjects
VORTEX motion; POLAR ionosphere; EXTREME value theory; TURBULENCE; SPACE environment
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 11, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2021JA029307