Polar Ionospheric Large‐Scale Structures and Dynamics Revealed by TEC Keogram Extracted From TEC Maps

Abstract

A method named total electron content (TEC) keogram is introduced for surveying the large-scale irregularities continuously in the polar ionosphere. The TEC keogram is developed from a movie of TEC maps along various meridian lines from the dayside to the nightside across the magnetic pole, trying to identify and track several types of ionospheric structures. Through two examples, a clear train of polar cap patches are identified from TEC keogram and confirmed by SuperDARN radar observations. The motion speed of these patches estimated from this tool agrees with SuperDARN radar measurements. Then, the motions of patches relative to the background convection through the whole polar cap are statistically studied for the first time. Moreover, the occurrence dependence of fully tracked patches on months, UT hours, and interplanetary magnetic field conditions is generally consistent with previous reports. These results suggest that the TEC keogram offers a power tool for continuous monitoring and studying of large-scale plasma irregularities in the polar ionosphere.

Dependencies of GPS Scintillation Indices on the Ionospheric Plasma Drift and Rate of Change of TEC Around the Dawn Sector of the Polar Ionosphere

“…We have focused on the Canadian sector at where the CHAIN is located by selecting the time interval between 13:00 UT and 15:00 UT. Around this region, the plasma drift is probably the regular sunward return flow and/or the dawnside auroral polarization streams (DAPS) with high speeds (e.g., Liu et al., 2020; Wang et al., 2020; Zhang et al., 2013). The selected region is defined by the following criterions: (a) a number of GPS receivers around the selected region to provide plentiful ray paths; (b) high occurrence rate of high‐speed plasma flow in the selected region; (c) significant amount of back scatters from several SuperDARN radars to merge flow vectors in the selected region.…”

GPS Scintillations and TEC Variations in Association With a Polar Cap Arc

“…The density gradient effect on the trailing edge of the polar cap arc is consistent with the results that the scintillation activities appeared slightly after the intersection time of the GPS rays (Figure 3). 6h-6m), there is good backscatter near the polar cap arc (the black contour), strongly suggesting the presence of decameter-scale plasma irregularities (e.g., Greenwald et al, 1995;van der Meeren et al, 2016;Wang et al, 2020), which are likely related to scintillations. It is worth noting that the data gap in the velocity observations on the right-hand side of the arc contour is likely due to the observation altitude of the SuperDARN Inuvik radar being higher than the altitude where the arc or F layer irregularities often show up.…”

“…In the polar ionosphere, different types of large‐scale irregularities are often generated, such as the polar cap patch (e.g., Crowley, 1996; Hosokawa, Kashimoto, 2009; Hosokawa, St‐Maurice, et al., 2010; Hosokawa et al., 2019, Wang et al., 2020; Zhang et al., 2013), the tongue of ionization (e.g., Foster, 2005; Hosokawa, Tsugawa, et al., 2010), the polar cap arc (e.g., Hosokawa et al., 2011; Xing et al., 2018; Zhu et al., 1997), and so forth. From these large‐scale irregularities, a great number of smaller‐scale irregularities appear at their edges through multiple plasma instability processes, for example, the gradient‐drift instability and/or flow shear instability (or Kelvin‐Helmholtz instability) (e.g., Basu et al., 1998, 1990; Carlson, 2012; Moen et al., 2013; van der Meeren et al., 2014; Wang et al., 2016).…”