Mesospheric Joule Heating During the 2003 Halloween Superstorm

A large solar flare and coronal mass ejection produced an intense geomagnetic storm on 28-30 Oct 2003, referred to as the Halloween Storm. From 6 to 10 UT on 29 Oct 2003, the Sondrestrom incoherent scatter radar (ISR) observed enhanced high-latitude D-region electron densities and electric fields between 65 and 95 km. The observations indicate discrete enhancements of electron density associated with relativistic electron precipitation and diffuse enhancements, measuring 10x1011 m-3, due to proton precipitation. Diffuse enhancements were sustained for the four hour observing period. The large electron density, in combination with co-located electric fields observed to be in excess of 70 mV/m, leads to significant electron frictional heating. Using the TIME-GCM, it is shown that Joule heating rivals chemical and solar heating in the mesosphere during the observing period. We also demonstrate a sensitivity of mesospheric Joule heating to electron temperature, requiring the re- examination of the electron energy balance in the mesosphere.