The Spatial Variation of Large‐ and Meso‐Scale Plasma Flow Vorticity Statistics in the High‐Latitude Ionosphere and Implications for Ionospheric Plasma Flow Models.

The ability to understand and model ionospheric plasma flow on all spatial scales has important implications for operational space weather models. This study exploits a recently developed method to statistically separate large‐scale and meso‐scale contributions to probability density functions (PDFs) of ionospheric flow vorticity measured by the Super Dual Auroral Radar Network (SuperDARN). The SuperDARN vorticity data are first sub‐divided depending on the Interplanetary Magnetic Field (IMF) direction, and the separation method is applied to PDFs of vorticity compiled in spatial regions of size 1° of geomagnetic latitude by 1 hr of magnetic local time, covering much of the high‐latitude ionosphere in the northern hemisphere. The resulting PDFs are fit by model functions using maximum likelihood estimation (MLE) and the spatial variations of the MLE estimators for both the large‐scale and meso‐scale components are presented. The spatial variations of the large‐scale vorticity estimators are ordered by the average ionospheric convection flow, which is highly dependent on the IMF direction. The spatial variations of the meso‐scale vorticity estimators appear independent of the senses of vorticity and IMF direction, but have a different character in the polar cap, the cusp, the auroral region, and the sub‐auroral region. The paper concludes by discussing the sources of the vorticity components in the different regions, and the consequences for the fidelity of ionospheric plasma flow models. Plain Language Summary: The ability to accurately model the flow of ionized gases (plasma) in the Earth's ionosphere (the ionized region of the Earth's upper atmosphere) has important implications for operational space weather models. Large‐scale variations in this plasma flow are modeled well, but fluctuations on the meso‐scale and small scale are typically ignored in these models. This study uses measurements from a high‐latitude ground‐based radar network to measure the ionospheric plasma flow in terms of its vorticity (how straight or curved the flow is). The measured vorticity is separated into components related to both the large and meso‐scale fluctuations. The paper discusses the origins of the meso‐scale component, and what needs to be done before it can be confidently added to ionospheric plasma flow models. Key Points: The spatial variation of meso‐scale ionospheric flow vorticity is independent of the prevailing IMF By directionMeso‐scale ionospheric flow vorticity is strongest in the cusp and the auroral regionMeso‐scale ionospheric flow vorticity is most intermittent in the polar cap and the sub‐auroral region [ABSTRACT FROM AUTHOR]