Diurnal and seasonal variation of electron heat flux measured with the Poker Flat Incoherent-Scatter Radar

Abstract

[1] Measurements made with the Advanced Modular Incoherent Scatter Radar were used to calculate the average diurnal electron temperature and corresponding vertical heat flux above Poker Flat, Alaska. Our results show that both the electron heat flux and temperature exhibited seasonal variation during 12 consecutive months in 2009 and 2010, a period of exceptionally quiet solar and geomagnetic activity. Both the electron temperature and heat flux varied diurnally, with larger magnitudes observed during the day than night. Contrary to midlatitude measurements from the late 1960s, the downward heat fluxes above Poker Flat were found to vary significantly with season and were typically greater during summer than winter. The time-dependent topside electron heat flux is an important parameter describing magnetosphere-ionosphere coupling and it also drives boundary conditions in physics-based ionosphere models. Parameterizations of the average electron thermal flux and temperature sufficient for use in ionosphere models are provided. A physics-based high-latitude ionosphere model is used to demonstrate that a constant heat flux boundary condition leads to an electron temperature increase near local midnight that is not observed in the radar measurements. The resulting inaccuracy in electron temperature calculations leads to more than a 15% overestimate of daytime peak electron number density. Applying a time-varying heat flux boundary condition brings the model electron temperature and peak density to good agreement with measurements.