Separating Contributions to Plasma Vorticity in the High-Latitude Ionosphere From Large-Scale Convection and Meso-Scale Turbulence

摘要

Measurements of ionospheric flow vorticity can be used for studying ionospheric plasma transport processes, such as convection and turbulence, over a wide range of spatial scales. Here, we analyze probability density functions (PDFs) of ionospheric vorticity for selected regions of the northern hemisphere high-latitude ionosphere as measured by the Super Dual Auroral Radar Network over a 6-year interval (2000-2005 inclusive). Subdividing these PDFs for opposite polarities of the By component of the prevailing interplanetary magnetic field allows the separation into two distinct components: (a) A single-sided Weibull distribution which relates to the large-scale convection driven by magnetic reconnection; (b) A double-sided and symmetric q-exponential distribution which arises from meso-scale plasma flow related to processes such as turbulence. This study investigates the processes that contribute to the vorticity of the flow of ionized gases (plasma) in the Earth's ionosphere (at an altitude of SIM;250-400 km). Vorticity is a measure of how straight or curved this flow of plasma is at a particular location. We show that the measured probability distributions of ionospheric vorticity at high-latitude locations can be explained as a combination of vorticity inherent in the large-scale ionospheric plasma flow pattern driven by variations in the solar wind (plasma and magnetic field ejected by the Sun), and vorticity resulting from meso-scale fluid processes such as turbulence. Being able to model ionospheric vorticity in this way helps to improve models of the ionospheric flow process, which are often key components of larger operational space weather models.