An estimate of the global‐scale joule heating rates in the thermosphere due to time mean currents

Abstract

An estimate of the global‐scale joule heating rates in the thermosphere is made based on derived global equivalent overhead electric current systems in the dynamo region during geomagnetically quiet and disturbed periods. The total neutral gas heating rate due to joule dissipation is proportional to the Pedersen conductivity and the square of the total electric field perpendicular to the geomagnetic field line. The equivalent total electric field distribution is calculated from Ohm's law as applied to the dynamo region using the equivalent overhead currents estimated from geomagnetic data and the components of the two‐dimensional conductivity tensor determined from global empirical models of the electron and neutral gas number density distributions. The global‐scale joule heating rates are calculated for various monthly average periods in 1965. The calculated joule heating rates maximize at high latitudes in the early evening and postmidnight sectors. During geomagnetically quiet times the daytime joule heating rates are considerably lower than heating by solar EUV radiation. However, during geomagnetically disturbed periods the estimated joule heating rates increase by an order of magnitude and can locally exceed the solar EUV heating rates. The results show that joule heating is an important and at times the dominant energy source at high latitudes. However, the global mean joule heating rates calculated near solar minimum are generally small compared to the global mean solar EUV heating rates.