Representation of the neutral wind in height-integrated, high-altitude ionosphere-thermosphere electrodynamics

Many studies of electrodynamics of the coupled ionosphere-thermosphere (IT) system at high latitudes represent the ionosphere as a two-dimensional spherical shell, and rely on the height-integrated ionospheric Ohm's law to understand IT electrodynamic coupling. Thermospheric winds play a central role in IT electrodynamics, but they are generally ignored in existing empirical models and assimilative methods. A main issue is the lack of comprehensive wind measurements, but there is also a gap in the literature on how to represent the thermospheric winds in a height-integrated description of high-latitude IT electrodynamics, and what the associated sources of error might be. Here we summarize a handful of results from previous and ongoing studies, including: (1) There is in general no single suitable definition of the neutral wind term in the height-integrated ionospheric Ohm's law; (2) When an appropriate estimate of the neutral wind is included in calculations of quantities such as height-integrated Joule heating or the height-integrated current density, estimates of these height-integrated quantities lie within ~20% of their true values. (3) When the neutral wind is ignored (i.e., assumed to be zero in Earth's corotating frame of reference) estimates differ from their true values by as much as 100%. These results are based on altitude profiles of winds, currents, and conductivities derived from rocket measurements, including chemical release experiments for estimating the neutral wind, as well as Poker Flat Incoherent Scatter Radar (PFISR) measurements.