Assessment of ionospheric Joule heating by GUMICS-4 MHD simulation, AMIE, and satellite-based statistics: towards a synthesis

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 (Super-DARN) 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.Correspondence to: M. Palmroth (Minna.Palmroth@fmi.fi)

Numerical considerations in simulating the global magnetosphere

“…While there is an empirical understanding of the expected value of the actual CPCP as a function of interplanetary magnetic field (e.g., Rich and Hairston, 1994;Weimer, 1996;Ruohoniemi and Greenwald, 1996;Boyle et al, 1997;Siscoe et al, 2002;Ridley, 2005), there is not a very good understanding of what ideal MHD (with the allowance for numerical resistivity in the reconnection sites) should give. Some codes tend to give a very large CPCP (e.g., Fedder et al, 1998), while other codes give a value that is smaller than expected (e.g., Palmroth et al, 2005). In this paper, the values of the CPCP vary significantly as a function of many different parameters.…”

“…The Integrated Space Weather Prediction Model MHD code is similar to Winglee's code, but goes a step further -it models the magnetosphere and ionosphere as one system, using a spherical grid in the inner magnetosphere and ionosphere and a Cartesian grid in the outer magnetosphere (White et al, 1998;Sonnerup et al, 2001). The first-order Grand Unified Magnetosphere Ionosphere Coupling Simulation (GUMICS-4) code is similar to BATSRUS (described below) in some ways -namely it has a cell-based adaptive grid structure (while BATSRUS is block-based) and it uses a similar numerical scheme (e.g., Janhunen, 1996;Palmroth et al, 2001Palmroth et al, , 2003Palmroth et al, , 2005, and references within). The first-order nature of GUMICS-4 is compensated for by the ability to have higher resolutions in regions in which there are large gradients.…”

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

“…Palmroth et al (2005) argue that spatial anticorrelation of electric field and Pedersen conductance leads to the overestimation of Joule heating, if averaged measurements are used. On the other hand, if small-scale structures (e.g.…”

“…The median of the underestimation was about 20% and the upper value 65% in the case of hourly averaged electric field versus 6-min time resolution in their study. On the other hand, Palmroth et al (2005) argues that multiplying independent measurements of averaged electric fields and Pedersen conductances yields an overestimation of Joule heating. In this study, we use a temporal resolution of 2 min.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…The emphasis in this paper is on studies in which SuperDARN has been the major instrument used to deliver the science. However, it Surv Geophys (2007) 28:33-109 37 should be noted that there are a large number of significant satellite, data assimilation, and modelling-centric studies in which SuperDARN data have played an important supporting role (e.g., Lu et al 2001;Maynard et al 2003;Trattner et al 2003;Farrugia et al 2004;Trattner et al 2005;Palmroth et al 2005), which are not discussed here. The code name of each radar is highlighted in red close to the radar location.…”