Aruliah, A; (2013) The role of neutral atmospheric dynamics in cusp density and ionospheric patch formation – 2nd campaign. The European Office of Aerospace Research and Development: London, UK.

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Abstract

This report will present observations from three field trips on Svalbard which were undertaken to test a mechanism that explains unexpected density enhancements seen by the CHAMP satellite. The CHAMP satellite observed up to double the surrounding atmospheric density in the region of the magnetic cusp at altitudes of 400km (Lühr et al., 2004). This is a significant enough perturbation to be included in satellite drag models, and consequently inspired several modelling studies. The proposed mechanism by Carlson et al. (2012) requires that soft particle precipitation increases the conductivity at 150‐200km altitude and simultaneously there should be bursts of fast plasma convection to provide strong frictional heating. Heating at this high altitude means that it requires little energy to lift the rarefied gas above, and thereby bring denser air from below into the region passed through by CHAMP (~400km). The atmospheric drag increases at altitudes where satellites orbit as a consequence of upwelling, The EOARD grant FA8655-13-1-3012 funded a field trip in January 2013 to Svalbard for a joint optical and radar experiment. This provided two case studies that test and augment the first case study from January 2012. The optical observations were provided by two University College London (UCL) Fabry-Perot Interferometers (FPIs) measuring the neutral (non-ionised) component of the upper atmosphere. Independent measurements of the ionosphere were made using the European Incoherent SCATter (EISCAT) Svalbard Radar (ESR). The radar time was won by competitive peer review from radar time awarded to the UK as part of its membership of the EISCAT consortium. Svalbard is currently the only site that passes under the magnetic cusp that is equipped with radar, optical and other suitable observational instrumentation. Further data have been sought out from the University of Oslo Meridian Scanning Photometer (MSP) and the SuperDARN coherent scatter radars and all are currently being analysed and interpreted, to be written up in a paper for submittal to the Journal of Geophysical Research (JGR). Our aim is to determine what are the conditions that caused upwelling on the nights of 22nd Jan 2012 (the first cusp upwelling experiment, reported in Aruliah et al., 2014) and on the 14th January 2013; but not on the 12th January 2013. The first experiment appeared to confirm the Carlson et al. (2012) mechanism. The second and third experiments will be a test that we have correctly identified the mechanism. The second and third experiments also have the advantage of the radar beam scanning, which was not possible for the first owing to a broken driver motor. During the period of this award, a paper by Aruliah et al. (submitted in 2013) reported the first cusp upwelling experiment in January 2012, also funded by an earlier EOARD grant. The paper is currently undergoing the refereeing process. The results of the 2012 and 2013 cusp upwelling experiments were used as part of a 3 year grant proposal to the UK Natural Environment Research Council (NERC) for a modelling and experimental study to improve the modelling of the lower thermosphere. This proposal went through to the final selection, but we heard recently that it was not funded. Over the last few years it has been realized by the atmospheric community that the middle atmosphere plays a valuable role in coupling the lower atmosphere, where weather and climate are, with the upper atmosphere, which is strongly influenced by solar variability and the solar wind, i.e. Space Weather. Investigating the cusp upwelling mechanism was one of the coupling mechanisms used in our NERC proposal and is a motivation in addition to improving satellite drag modelling.

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