Small‐scale fluctuations in barium drifts at high latitudes and associated Joule heating effects

Abstract

AbstractMost previous estimates of Joule heating rates, especially the contribution of small‐scale structure in the high‐latitude ionosphere, have been based on incoherent scatter or coherent scatter radar measurements. An alternative estimate can be found from the plasma drifts obtained from ionized barium clouds released from sounding rockets. We have used barium drift data from three experiments to estimate Joule heating rates in the high‐latitude E region for different magnetic activity levels. In particular, we are interested in the contribution of small‐scale plasma drift fluctuations, corresponding to equivalent electric field fluctuations, to the local Joule heating rate on scales smaller than those typically resolved by radar or other measurements. Since Joule heating is a Lagrangian quantity, the inherently Lagrangian estimates provided by the chemical tracer measurements are a full description of the effects of electric field variance and neutral winds on the heating, differing from the Eulerian estimates of the type provided by ground‐based measurements. Results suggest that the small‐scale contributions to the heating can be more than a factor of 2 greater than the mean field contribution regardless of geomagnetic conditions, and at times the small‐scale contribution is even larger. The high‐resolution barium drift measurements, moreover, show that the fine structure in the electric field can be more variable than previous studies have reported for similar conditions. The neutral winds also affect the heating, altering the height‐integrated Joule heating rates by as much as 12%, for the cases studied here, and modifying the height distribution of the heating profile as well.