Case studies of drivers of ionospheric upwellings

<p dir="ltr">Electron precipitation is a phenomenon that occurs when highly energetic electrons are ‘‘rained’’ into the<br>ionosphere through electromagnetic waves energisation, and as a result, ambipolar electric field is set up to accelerate<br>particles such as O? to higher energy in order to cause an upwelling. Similarly, Joule heating, which points to neutral<br>atmosphere heating, can also cause the neutral gas to upwell and as a result, pull up ions along the field lines. Analysis of<br>the EISCAT Svalbard Radar (ESR) data in this work indicates periods when (i) ambipolar electric field is set up to drive ion<br>upflow, (ii) Joule heating is responsible to the upwelling ions, and (iii) when both drivers combined to cause the ener-<br>gisation of the ion for upflow. The peak upwelling during the March 15, 2007 ambipolar-electric-field-driven event<br>indicates enhanced ion flux of up to 1:0 ? 10 14 m?2 s?1 , covering up to the upper E-region. However, the September 11,<br>2007 event is Joule-heating-driven, and the heating is most effective in the F-region altitude, modifying the plasma<br>pressure gradient and resulting in field-aligned ion acceleration. When strong electric field drives ion population through<br>the neutral gas, friction heating occurs and an elevation of the plasma pressure gradient as a result. This is observed in the<br>September 29, 2007 event, where both ambipolar electric field and the Joule heating are co-drivers, making the upwellings<br>to cover long duration of up to 5 h. Data from Cooperative UK Twin Located Auroral Sounding System (CUTLASS)<br>indicates cusp signature for the dayside events.</p>