Impact of Magnetosphere Forcing and Model Resolution on Joule Heating Estimates in WACCM-X During the 24 August 2005 Storm

Kurzfassung

We investigate the high-latitude Joule heating in a recently developed high-resolution configuration of the WACCM-X whole-atmosphere model coupled to the MAGE model. Model resolution and geomagnetic forcing effects during the severe geomagnetic storm on 24 August 2005 are analyzed, distinguishing storm peak and recovery conditions. The Joule heating energy in MAGE-coupled runs is 71.7%-121.7% higher compared to Heelis- and Weimer-driven WACCM-X runs, due to stronger convection electric fields. Due to the higher Joule heating, the column-integrated ratio is significantly lower in MAGE-coupled runs, potentially correcting a previously observed overestimation of the WACCM-X model. The distribution of modeled Joule heating rates with geomagnetic latitude is affected by the coupling to MAGE as well. The high-resolution model shows distinctly different thermospheric dynamics in response to the geomagnetic storm, leading to a lower neutral particle density over the polar region during storm recovery compared to the coarse-resolution model. The altered thermospheric dynamics causes a 50% higher Joule heating up to about 120 km and lower Joule heating at F region altitudes, in turn affecting the thermospheric neutral density. Despite the overall lower Joule heating rates in the high-resolution model run, the neutral gas heating rate is higher compared to the coarse-resolution run, leading to slightly lower ratios. The electron density is affected on meso-scales, especially in the area of the auroral oval, by the increase in model resolution, which causes strong local variations of Joule heating estimates between the high- and coarse-resolution model runs.