Abstract
Abstract. Numerical modelling of thermospheric temperature changes associated with periods of high geomagnetic activity are often inaccurate due to unrealistic representation of nitric oxide (NO) densities and associated 5.3-μm radiative cooling. In previous modelling studies, simplistic parameterisations of NO density and variability have often been implemented in order to constrain thermospheric temperature predictions and post storm recovery timescales during and following periods of high auroral activity. In this paper we use the University College London (UCL) 3-D Coupled Thermosphere and Middle Atmosphere (CMAT) General Circulation Model to simulate the 11-day period from 23 October to 3 November 2003, during which the Earth experienced some of the largest geomagnetic activity ever recorded; the so called "Halloween storm". This model has recently been updated to include a detailed self consistent calculation of NO production and transport. Temperatures predicted by the model compare well with those observed by the UCL Fabry Perot Interferometer at Kiruna, northern Sweden, when changes in solar and auroral activity are taken into account in the calculation of NO densities. The spatial distribution of predicted temperatures at approximately 250-km altitude is also discussed. Simulated NO densities at approximately 110 km are presented. Large quantities of NO are found to be present at to the equator, one to two days after the most intense period of geomagnetic activity. This is the first 3-D GCM simulation of NO production and transport over the 2003 Halloween storm period.
Highlights
A well established link between auroral energy input and thermospheric nitric oxide (NO) concentration has been demonstrated by numerous observational and modelling studies (e.g. Gerard and Barth, 1977; Barth, 1992; Solomon et al, 1999; Baker et al, 2001; Barth et al, 2003; Dobbin et al, 2006)
The very high temperatures measured by the FPI between 16:00 UT on 29 and 04:00 UT on 31 October are not reproduced by the “variable NO” Coupled Thermosphere and Middle Atmosphere (CMAT) simulation, which reaches a maximum of 1500 K on 29 October
The University College London (UCL) CMAT GCM has been used to simulate the period from 12:00 UT on 23 October to 12:00 UT on 3 November 2003, during which the Earth experienced extremely high levels of geomagnetic activity
Summary
A well established link between auroral energy input and thermospheric nitric oxide (NO) concentration has been demonstrated by numerous observational and modelling studies (e.g. Gerard and Barth, 1977; Barth, 1992; Solomon et al, 1999; Baker et al, 2001; Barth et al, 2003; Dobbin et al, 2006). The response of the thermosphere to this period of enhanced geomagnetic activity has been simulated using the CMAT model which has recently been updated to include a fully self-consistent calculation of odd nitrogen chemistry and transport (Dobbin et al, 2006; Dobbin, 2005). While there has been much speculation on the horizontal distribution of NO following high geomagnetic activity (Barth and Bailey, 2004; Marsh et al, 2004), no 3-D modelling simulations of a major storm event have been performed to date These results comprise the first predictions of the spatial and temporal distribution of NO over the “2003 Halloween storm”
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