Polar patches observed by ESR and their possible origin in the cusp region

Abstract

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma¯ow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.

Swarm in situ observations of F region polar cap patches created by cusp precipitation

“…This time history also shows that electron density features that are closer to the region of particle impact ionization are more structured than those farther along track, which are evolving into the classic asymmetric and flat‐topped shape of a polar cap patch. The time history of patch morphology created by this technique provides more context and can resolve shorter timescale changes than previous in situ observations [e.g., Smith et al , ].…”

“…These are the first in situ observations of a series of patches, entrained in the polar cap flow, traveling from their source in the cusp to the nightside auroral oval. The observations contrast the classical view of polar cap patch formation that solar EUV‐ionized patches are chopped off from the tongue of ionization and structure is added by the GDI acting on the trailing edge [ Gondarenko and Guzdar , ]. Instead, we observe cusp precipitation that produces large plasma density structures [e.g., Kelley et al , ; Walker et al , ; Smith et al , ] near noon that convect across the polar cap and smooth into classical polar cap patches. We conclude that the resulting kilometer‐scale structures are the product of particle impact ionization in the cusp.…”

Drifting airglow patches in relation to tail reconnection

“…There are several proposed methods on how the TOI is restructured into patches, such as the IMF controlled alterations in the cusp inflow region [c.f. Sojka et al , 1993; Smith et al , 2000], convection jets (also known as flow‐channel events) [ Rodger et al , 1994], convection vortices [ Schunk et al , 1994; Valladares et al , 1996; Decker et al , 1994], polar cap expansion and contraction [ Anderson et al , 1988], and linked to the latter, an expansion of the polar cap convection driven by pulsed reconnection [ Lockwood and Carlson , 1992].…”

Comparison of observed and predicted MUF(3000)F2 in the polar cap region

“…VOACAP and ICEPAC modeled values do not reproduce the daytime variations observed in the CADI measurements. One of the most discussed features in the polar ionosphere are the polar patches: enhancements of electron density caused by different mechanisms [ Smith et al , ; Carlson et al , ; Lockwood et al , ; Oksavik et al , ]. MacDougall and Jayachandran [] not only observed a higher patch activity in winter than in summer but also noted that the seasonal variation depends on the patch definition used.…”