Yiu, HI; (2014) High latitude thermosphere meso-scale studies and long-term database investigations with the new Scanning Doppler Imager and Fabry-Perot Interferometers. Doctoral thesis , UCL (University College London).

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Abstract

The SCANning Doppler Imager, SCANDI, is a new all-sky development on the network of UCL Fabry Perot Interferometers, FPI, in the Arctic region. It is able to provide high temporal and spatial resolution measurements on the upper atmosphere, in scales of minutes and tens of kilometres. This is a step change from the single look direction provided by a standard FPI. SCANDI’s mechanics, control-software, data analysis and calibration methods are presented. This includes details on techniques that are specific to the instrument’s all-sky capability. The meso-scale data are of particular interest to developments in atmospheric models, which look for increasingly small-scale structures. An ionospheric cusp study utilising SCANDI is able to provide direct neutral measurements at high spatial resolution. It indicates Joule heating is likely to be one of the main sources which contributes to atmospheric cusp density upwelling. The neutral cusp results also complement the CHAMP satellite density data and are able to demonstrate the neutral thermosphere has a considerable meso-scale structure reflecting its response to the cusp dynamics. The temperature variation over the recent solar-cycle in years 1999-2009 is analysed, which covers the extended solar minimum of cycle 23/24. It is also the longest continual period of FPI observation from a single site that has been analysed. The dataset demonstrates that the polar cap neutral temperature is unaffected by the unusually low solar activity, possibly because of high latitude geomagnetic contributions. The difference between measurements and MSIS model results are explored, which demonstrate MSIS unexpectedly over-estimated the neutral temperature by 200 K at this solar maximum. It indicates MSIS is unable to recreate the low temperatures in this unusually weak solar cycle. A new technique was also developed for the study of FPI long term neutral temperature by modelling the red and green-line emission profiles. It is demonstrated that the FPI-measured temperature can be lowered by ∼50K because of variations in the width of the emission height profile and peak altitude. This needs to be considered in long-term temperature trend analysis, especially where looking for trends of as small as a few Kelvin.

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