Aruliah, A;
(2012)
The role of neutral atmospheric dynamics in cusp density and ionospheric patch formation.
Defense Technical Information Center: London, UK.
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Abstract
One of the most highly cited papers over the last 10 years in upper atmospheric physics literature is that describing the CHAMP satellite observation of a persistent and large density bulge over the magnetic cusp regions, which are around the north and south magnetic poles (Lühr et al., 2004). It has since been a serious challenge to atmospheric modellers to reproduce this observation. Unrealistically large quantities of heating and complicated mechanisms involving atmospheric gravity waves have been invoked. A phenomenon such as this density bulge affects satellite drag, and so has a commercial as well as scientific interest. Carlson et al (2012) proposed a simple mechanism, whereby depositing energy at a higher altitude by soft particle precipitation would produce a doubling of atmospheric density without requiring excessive energy. The experimental field trip funded by the EOARD grant number FA8655-11-1-3038 of $24,000 has produced observational data that has confirmed this mechanism, though with an important limitation detailed in the report. The collaboration between Dr Carlson and the UCL team has allowed the Carlson mechanism to be properly modelled using the UCL Coupled Middle Atmosphere (CMAT2) model in order to complete the Carlson et al (2012) paper, and the observational results to be presented in a paper in preparation (Aruliah et al, 2012). In addition to supporting the Carlson mechanism, the latter paper presents the first observations of a rapid response of the thermosphere to heating, and very large (up to 200m/s), sustained (nearly 4 hours) vertical winds using co-located radars and Fabry-Perot Interferometers. What is particularly interesting about this result is that it goes against convention. The common expectation was that energetic/hard particle precipitation (>keV) would be required to produce the large energies to lift the thermosphere and increase densities at satellite altitudes. Instead it turns out that energetic particles penetrate too deeply into the atmosphere (near altitudes of 100-120km), resulting in non-dissipative Hall currents, and, furthermore, it is highly difficult to lift the long column of air that lies above. Meanwhile soft particle precipitation (~hundreds eV) that penetrates only a short distance to altitudes of 160-200km, result in Pedersen currents, and hence Joule heating, and have only to lift a short column of rarefied gas. The soft precipitation deposits relatively little energy, yet will have a dramatic effect on satellite orbits through upwelling and the consequently density perturbation. The probability of occurrence of moderately energetic particles is higher than of energetic particles, which increases the likelihood of these density perturbations. All these considerations need to be taken into account for realistic high latitude atmospheric modelling and orbit prediction.
| Type: | Report |
|---|---|
| Title: | The role of neutral atmospheric dynamics in cusp density and ionospheric patch formation |
| Open access status: | An open access version is available from UCL Discovery |
| Publisher version: | https://apps.dtic.mil/sti/citations/ADA569768 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10140106 |
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