On a new process for cusp irregularity production

Abstract

Abstract. Two plasma instability mechanisms were thought until 2007 to dominate the formation of plasma irregularities in the F region high latitude and polar ionosphere; the gradient-drift driven instability, and the velocity-shear driven instability. The former mechanism was accepted as accounting for plasma structuring in polar cap patches, the latter for plasma structuring in polar cap sun aligned arcs. Recent work has established the need to replace this view of the past two decades with a new patch plasma structuring process (not a new mechanism), whereby shear-driven instabilities first rapidly structure the entering plasma, after which gradient drift instabilities build on these large "seed" irregularities. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process explains several previously unexplained characteristics of cusp and early polar cap patch irregularities. Here we introduce additional data, coincident in time and space, to extend that work to smaller irregularity scale sizes and relate it to the structured cusp current system.

Toward an integrated view of ionospheric plasma instabilities: 2. Three inertial modes of a cubic dispersion relation

“…Among other things, recent experimental studies of F region plasma waves have examined the observed irregularity formation times and compared them with those predicted by the F region instability theories including GDI and the Kelvin‐Helmholtz instability (KHI) [ Kintner and D'Angelo , ]. The results varied between being significantly faster than GDI predictions [ Moen et al , ; Carlson et al , , ] and being largely consistent with GDI [ Oksavik et al , ]. The first group of results is explained by invoking the KHI process.…”

Scintillation and irregularities from the nightside part of a Sun‐aligned polar cap arc

“…The velocity shear seen in the SuperDARN data (Figures i and j) could drive the Kelvin‐Helmholtz (KH) instability. The KH growth rate can be estimated by γ KH =0.2 Δ V / L where Δ V is the velocity difference and L is the scale length of the velocity difference [ Carlson et al , ]. Based on the velocity data shown in Figure j, the KH growth time can be estimated to ∼70 min, which indicates the KH instability is not effective.…”

GPS scintillation effects associated with polar cap patches and substorm auroral activity: direct comparison

“…However, although the GDI occurs initially on the trailing edge, the nonlinear development could penetrate through the entire patch (Gondarenko & Guzdar 2004). The plasma can also be structured throughout a patch upon its formation, formed either by a magnetic reconnection event which of itself introduces sheer driven instabilities (Carlson et al 2008), or by soft-electron precipitation (Kelley et al 1982). In addition, the patches may follow a nonuniform flow pattern which can be highly dynamic and pulsed.…”

“…Within the auroral zone there is a lot of free energy to drive various instabilities. Obviously, there may be velocity shears associated with auroral arcs that can rapidly develop small scale irregularities on large scale structures (auroral blobs) by the KelvinHelmholtz type, velocity shear Instability (KHI) (Kersley et al 1988;Keskinen et al 1988;Carlson et al 2008;Carlson 2012). The auroral precipitation interacting with the polar cap patches may give rise to plasma gradients on which the GDI can operate as has been documented in the dayside cusp (Moen et al 2012).…”