SuperDARN Evidence for Convection‐Driven Lagrangian Coherent Structures in the Polar Ionosphere

Abstract

Polar cap patches are large sporadic enhancements of plasma density on the scale of hundreds of kilometers, which can impact the performance of Global Navigation Satellite Systems. Lagrangian Coherent Structures (LCSs) are ridges that show areas of maximal separation in a time‐evolving flow. Previous work based on modeled ionospheric flow showed that LCSs exist in the ionosphere and are barriers governing patch formation. In this work, we identify the first data‐driven LCSs in the high‐latitude ionosphere using Super Dual Auroral Radar Network (SuperDARN) ion convection fields. The LCSs found using the Ionosphere‐Thermosphere Algorithm for LCSs are compared during geomagnetically quiet and active periods. The shape of the LCS is found to be dependent on the electric potential pattern. A consistent two‐cell pattern results in a W‐shaped LCS, but when the two‐cell pattern breaks down, the LCS loses this characteristic shape. The changes in the electric potential, and thus the LCS, are likely due to changes in the interplanetary magnetic field. A comparison between LCSs obtained from empirical models and data reveal that the data‐driven LCSs are poleward of and have a shorter longitudinal span than the model‐based LCSs. A comparison of the LCS location and the formation of a polar cap patch on 17 March 2015 showed that the center of the patch developed from plasma on the main LCS ridge, and this is confirmed with a separate polar cap patch event from 26 September 2011.

Alignment of High‐Latitude Ionospheric and Thermospheric Lagrangian Coherent Structures

“…(2017) found that a lower thermospheric LCS may have acted as the poleward barrier of space shuttle water vapor plume transport. The LCSs in modeled plasma drifts were found to be a necessary condition for the formation of the polar cap patch (Wang et al., 2018), then further supported by data‐assimilated ionospheric convection (Ramirez et al., 2019). Both T‐LCSs and I‐LCSs appear at middle‐to‐high latitudes and respond to geomagnetic disturbances by shifting equatorward and growing more complex.…”

Lower Thermospheric Material Transport via Lagrangian Coherent Structures

“…Interested readers may refer to Figure 1 of Ramirez et al. (2019) for an illustration of the terms in Equation 2. For a fluid element at , the amount of stretching it undergoes can be measured by the FTLE, the largest singular value of : …”

“…Interested readers may refer to Figure 1 of Ramirez et al (2019) for an illustration of the terms in Equation 2. For a fluid element at 0…”

High‐Latitude Electrodynamics Specified in SAMI3 Using AMPERE Field‐Aligned Currents

“…To validate convection maps, some authors have used ionospheric F-region electron density structures as a tracer of the ExB drift. Wang et al (2018) and Ramirez et al (2019) have used the observed motion of high-latitude electron density structures to assess the accuracy of Weimer's (2005) empirical model and Ruohoniemi and Baker's (1998) SuperDARN-driven high-latitude potentials. For this investigation, we will use in situ plasma drifts and GPS-derived total electron content (TEC) data to test the validity of high-latitude potential solutions.…”