Abstract
Abstract. We investigate the Northern Hemisphere Joule heating from several observational and computational sources with the purpose of calibrating a previously identified functional dependence between solar wind parameters and ionospheric total energy consumption computed from a global magnetohydrodynamic (MHD) simulation (Grand Unified Magnetosphere Ionosphere Coupling Simulation, GUMICS-4). In this paper, the calibration focuses on determining the amount and temporal characteristics of Northern Hemisphere Joule heating. Joule heating during a substorm is estimated from global observations, including electric fields provided by Super Dual Auroral Network (SuperDARN) and Pedersen conductances given by the ultraviolet (UV) and X-ray imagers on board the Polar satellite. Furthermore, Joule heating is assessed from several activity index proxies, large statistical surveys, assimilative data methods (AMIE), and the global MHD simulation GUMICS-4. We show that the temporal and spatial variation of the Joule heating computed from the GUMICS-4 simulation is consistent with observational and statistical methods. However, the different observational methods do not give a consistent estimate for the magnitude of the global Joule heating. We suggest that multiplying the GUMICS-4 total Joule heating by a factor of 10 approximates the observed Joule heating reasonably well. The lesser amount of Joule heating in GUMICS-4 is essentially caused by weaker Region 2 currents and polar cap potentials. We also show by theoretical arguments that multiplying independent measurements of averaged electric fields and Pedersen conductances yields an overestimation of Joule heating. Keywords. Ionosphere (Auroral ionosphere; Modeling and forecasting; Electric fields and currents)
Highlights
Joule heating, calculated as the scalar product of the current and electric field, is a term used to describe the Ohmic production of heat that occurs as the charged particles drifting in the direction of the electric field collide with the neutral particles of the resistive medium
In this paper we have estimated the Northern Hemisphere Joule heating with various techniques during a substorm event of 28–29 March 1998, aiming to quantitatively estimate the ability of GUMICS-4 global MHD simulation to predict ionospheric Joule heating
Since in the simulation both the Joule heating and precipitation were in temporal agreement with the Atmospheric Explorer (AE) index, it was argued that the right-hand side of Eq (2) could roughly predict the temporal behavior of ionospheric power dissipation as determined by the AE-proxies
Summary
Joule heating, calculated as the scalar product of the current and electric field, is a term used to describe the Ohmic production of heat that occurs as the charged particles drifting in the direction of the electric field collide with the neutral particles of the resistive medium. Palmroth et al (2004a), using a global MHD simulation, computed the amount of Joule heating along with the energy associated with the particle precipitation in the ionosphere. Palmroth et al (2004a) used the GUMICS-4 MHD simulation (Janhunen, 1996) to estimate the total storm-time and substorm-time ionospheric energy consumption including the two largest ionospheric energy sinks: the Joule heating and particle precipitation. In one case study, we compare the Joule heating in the GUMICS-4 global MHD simulation with the results of large statistical surveys (Foster et al, 1983; Olsson et al, 2004), commonly used proxies by Ahn et al (1983), the AMIE procedure, and data from SuperDARN radars and and the UV and X-ray imagers on board the Polar satellite. We discuss the most important factors that affect the accuracy of the Joule heat estimates in the various methods
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