Abstract
Abstract. Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the Northern Hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigation Satellite System (GNSS) receivers. Steep electron density gradients have been associated with phase scintillation in previous studies; however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It is concluded that both significant electron density gradients and plasma density levels above a certain threshold are required for scintillation to occur.
Highlights
The F-region ionosphere is a weakly ionised plasma in the Earth’s atmosphere extending from an altitude of ∼ 150 to ∼ 500 km, above which it merges with Earth’s plasmasphere
Several mechanisms have been proposed to break a tongue of ionisation” (TOI) into a series of patches, including variations in the high-latitude convection pattern moving flux tubes in and out of sunlight (Anderson et al, 1988), expansion and contraction of the high-latitude convection pattern in response to transient bursts of reconnection drawing in plasma from different latitudes (Cowley and Lockwood, 1992; Lockwood and Carlson, 1992; Carlson et al, 2002, 2004, 2006), variations in the y component of the interplanetary magnetic field (IMF) drawing in plasma from different magnetic local times (MLT; Sojka et al, 1993), variation in Published by Copernicus Publications on behalf of the European Geosciences Union
At 18:00 UT and 21:00 UT larger electron densities can be observed crossing the polar cap in a two-cell convection pattern, with values of ∼ 15 TECu, indicating that plasma produced by photoionisation on the dayside is being drawn into the polar cap
Summary
The F-region ionosphere is a weakly ionised plasma in the Earth’s atmosphere extending from an altitude of ∼ 150 to ∼ 500 km, above which it merges with Earth’s plasmasphere. One type of structure commonly observed are polar cap patches, referred to as patches, which are enhancements of plasma density with at least twice the background value and a horizontal spatial extent of 100 km or more (Crowley, 1996). Buchau et al (1983) observed such patches of enhanced ionisation drifting anti-sunward with the background plasma flow in the central region of the polar cap at Thule, Greenland: 77.5◦ N, 69.2◦ W; 85.4◦ MLAT (magnetic latitude), 32.4◦ MLON (magnetic longitude). A comparison of average maps of the electron density and the high-latitude convection pattern suggested that solar-produced plasma was drawn into the polar cap as a continuous density enhancement known as the “tongue of ionisation” (TOI; Foster, 1984). Several mechanisms have been proposed to break a TOI into a series of patches, including variations in the high-latitude convection pattern moving flux tubes in and out of sunlight (Anderson et al, 1988), expansion and contraction of the high-latitude convection pattern in response to transient bursts of reconnection drawing in plasma from different latitudes (Cowley and Lockwood, 1992; Lockwood and Carlson, 1992; Carlson et al, 2002, 2004, 2006), variations in the y component of the interplanetary magnetic field (IMF) drawing in plasma from different magnetic local times (MLT; Sojka et al, 1993), variation in Published by Copernicus Publications on behalf of the European Geosciences Union
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
