Electric field variability associated with the Millstone Hill electric field model

Joule heating that is generated at high latitudes in the thermosphere becau se of the magnetospherically imposed electric potential is proportional to the average of the square of the electric field (E field). Most theoretical Joule heating computations use only average electric fields, resulting in heating that is proportional to the square of the average E field. The comp utation of the average of the square of the E field requires knowledge abou t the statistical characteristics of E field variability associated with th e average electric field model. In this paper we present the variability as sociated with the Millstone Hill bin-averaged empirical E held model [Foste r et al. 1986] and discuss the implications of variability as an upper atmo sphere energy source. We rebinned the radar plasma drift measurements from Millstone Hill, Massachusetts, in magnetic latitude and local time as a fun ction of auroral activity and calculated the average electric fields and th e variability associated with them as reflected in the bin standard deviati ons. We present the E held patterns and the associated variability for both quiet and disturbed geomagnetic conditions for the four seasons. We show t hat for an electric field model with a Gaussian distribution of small-scale variability around the mean, the average field and the variability have eq ual contributions to Joule heating generation.