Enhanced Electron Temperatures in the Polar D region

We demonstrate through modeling and measurement the occurrence of elevated electron temperatures in the polar D region. Geomagnetic storms are often accompanied by significant enhancements in high-latitude convection electric fields. Observations made by the Sondrestrom incoherent scatter radar (ISR) during the Halloween Storm of 2003 indicate a correlation between these enhanced electric fields and D-region electron temperature. A semi-empirical, physical model of electron momentum and energy in the D-region is developed to investigate this correlation. Results indicate electric field strengths exceeding 50 mV/m cause significant frictional heating of the D-region electron gas. Balanced by elastic and inelastic collisions with neutrals, frictional heating can heat the D-region electron gas up to three times the neutral temperature. A strong electron temperature dependency in the ISR total cross section is exploited to identify these electron temperature enhancements in the observed D-region radar backscattered power. This finding may help explain D-region ionosphere behavior that was previously not understood as electron temperature enhancements can affect polar D-region chemistry, conductivity and plasma diffusion. Although locally determined, the great spatial extent of strong electric fields caused by geomagnetic storms would lead to elevated D-region electron temperatures throughout the polar region.