Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation

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.

Dynasonde Observations of Ionospheric Polar Holes Under Quiet Geomagnetic Conditions at Jang Bogo Station, Antarctica

“…The disappearance of a smooth transition in JVD data should appear longer than 1 hour below the NmF2 value of ∼4.0 × 10 10 m −3 . This threshold value for a polar hole is comparable to that in previous studies (e.g., Jenner et al., 2020; Makarevich et al., 2015). Finally, in order to ensure that the polar hole events are associated with quiet conditions, the maximum Kp was ≤1+ for the two 3‐hr Kp values (6 hr) prior to the polar hole event.…”

“…Similar characteristics of polar holes, including occurrence location, horizontal scale size, duration time, and geomagnetic conditions for the polar hole formation, have been reported using observations in space and on the ground (Benson & Grebowsky, 2001;Bjoland et al, 2021;Brinton et al, 1978;Crowley et al, 1993;Forsythe et al, 2021;Hoegy & Grebowsky, 1991;Jenner et al, 2020). However, we believe that our analyses are the first to report the relationship between antisunward plasma convection speed and exponential electron density depletion prior to the polar hole formation.…”

“…(e.g., Jenner et al, 2020;Makarevich et al, 2015). Finally, in order to ensure that the polar hole events are associated with quiet conditions, the maximum Kp was ≤1+ for the two 3-hr Kp values (6 hr) prior to the polar hole event.…”

“…Under quiet geomagnetic conditions, depleted plasma density structures in the polar cap ionosphere, known as ionospheric polar holes, have been reported using observations in low-altitude orbits and on the ground (Benson & Grebowsky, 2001;Bjoland et al, 2021;Brinton et al, 1978;Crowley et al, 1993;Forsythe et al, 2021;Hoegy & Grebowsky, 1991;Jenner et al, 2020) and performing numerical study (Sojka et al, 1981a, 1981b, Sojka et al, 1981b. Polar holes were first observed by Brinton et al (1978) using winter F-region data acquired by low-altitude (∼300 km) satellite in the southern hemisphere.…”

Electron Density Depletion Region Observed in the Polar Cap Ionosphere

“…They occur on the nightside between 70° and 80° magnetic latitude, co‐located with the auroral cavities (e.g., Benson & Grebowsky, 2001). During quiet geomagnetic conditions, polar holes form as a result of slow anti‐sunward convection across the dark polar cap or circulation in perpetual darkness (Brinton et al., 1978; Jenner et al., 2020; Sojka et al., 1981). Circulation in perpetual darkness can occur during low geomagnetic activity when the polar cap is contracted, or in lobe cells when the interplanetary magnetic field (IMF) is northward.…”