EISCAT Svalbard Radar data, obtained during the IPY-ESR 2007 campaign at a period of deep solar minimum, has been examined to study ionospheric upflow events with fluxes exceeding 10¹³m⁻²s⁻¹. Ion upflow newly categorized, classifies the upflow events into low, medium and high flux upflows, and the incidence and seasonal distribution of these different classes are discussed. Over 300,000 field-aligned profiles have been considered and analysed. It is observed that, while high upflow fluxes are comparatively rare, low flux upflow events are a frequent phenomenon. Analysis of the ESR data shows that the occurrence frequency of the upward flux maximizes around local noon for all levels of upflow, with occurrence peaks of 31%, 16% and 2% being observed for low, medium and high upflow fluxes respectively during geomagnetically disturbed periods. Analysis of the seasonal distribution reveals that while high-flux upflow has its peak around local noon in the summer, with its occurrence being driven predominantly by high geomagnetic disturbance, the occurrence of low-flux upflow is broadly distributed across all seasons, geomagnetic activity conditions and times of day. The ambipolar electric force drives upflows about seven times more frequently as the Joule heating mechanism. This study finds that, though rare, Poynting flux leads to substantial upflow flux of 4.67×1013 m−2 s−1 even in the absence of precipitating flux. Upflow occurrence was found to correlate better with solar wind density than speed, and fits better with number density and dynamic pressure below about 20 cm−3 and 5 nPa respectively. Moreover, it was found that occurrence maximizes when the IMF clock angle is southward however, analysis showed a preference for duskward asymmetry of the cusp in comparison to dawnward’s. Analysis shows that reconnection is not compulsory for upflow flux, but only enhances its occurrence.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:727439 |
| Date | January 2017 |
| Creators | David, Timothy Wemimo |
| Contributors | Wright, Darren ; Milan, Steve |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/40448 |
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