On the MLT distribution of F region polar cap patches at night

Abstract

[1] Eight years of meridian scanning photometer data from Ny-Å lesund, Svalbard have been analyzed to study the occurrence of F region polar cap patches at night. In total 333 patches in 43 days were observed to hit the poleward boundary of nighttime auroras which is a unique signature of ongoing tail reconnection. The MLT distribution of patches is smooth and exhibit a bell shaped function symmetric around 23:25 MLT. The symmetry of the patch distribution about midnight indicates that patches populate the morning cell and the dusk cell of polar cap convection at the same probability. About 60% of the patches exit the polar cap from 22-01 MLT, but the entire distribution span from 18:30-04:50 MLT, i.e., nearly the full MLT span where tail reconnection may occur. The patch occurrence statistics presented here is an important new result of relevance to phenomena related to the presence and transport of patches. Citation: Moen, J., N.

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

“…Mitchell et al (2005) found phase and amplitude scintillations to be colocated with strong gradients in the Total Electron Content (TEC) at the edges of the high electron density streams. Furthermore, scintillation climatology studies by Spogli et al (2009) demonstrated enhanced scintillation levels around magnetic midnight, which were consistent with the Magnetic Local Time (MLT) distribution of polar cap patches at night (Moen et al 2007). By comparing the GPS data with radio instruments, Prikryl et al (2010) claimed that the polar cap patches are the main contributors to scintillation-causing irregularities in the polar cap.…”

“…To conclude, the worst situation in the European Arctic sector can occur when polar cap patches are further structured by the substorm auroral arc dynamics, i.e., signal interferences with the auroral blob phenomenon around magnetic midnight. This can explain the scintillation climatology study by Spogli et al (2009) who attributed the scintillation peak around magnetic midnight to the statistical distribution of polar cap patches exiting the polar cap around magnetic midnight (Moen et al 2007). However, there is a need to carry out a statistical study to see if this is always true.…”

“…From around 18:30 UT to 23:00 UT, we find a sequence of six inverted integral signs in the keogram (denoted by A-F in Fig. 1a), which is a feature of polar cap patches travelling across the FOV from north to south (Lorentzen et al 2004;Moen et al 2007). From 20:00 UT to 22:00 UT, the auroral boundary moved poleward, stopped and retreated equatorward several times, which is an auroral signature of transient tail reconnection followed by boundary relaxation (Lorentzen et al 2004;Cowley & Lockwood 1992;Moen et al 2007).…”

“…1a), which is a feature of polar cap patches travelling across the FOV from north to south (Lorentzen et al 2004;Moen et al 2007). From 20:00 UT to 22:00 UT, the auroral boundary moved poleward, stopped and retreated equatorward several times, which is an auroral signature of transient tail reconnection followed by boundary relaxation (Lorentzen et al 2004;Cowley & Lockwood 1992;Moen et al 2007). Several polar cap patches crossed the open/closed magnetic field line boundary and exited into the nightside auroral oval, where they changed their status to auroral blobs (Crowley et al 2000).…”

Airglow and Aurorae from Dome A, Antarctica

“…Two subsets of discrete polar aurora include polar cap arcs and polar cap patches. Polar cap arcs occur during quiet magnetic activity and northward IMF (Zhu et al 1997) and are 4 times more common in magnetic dawn than dusk (Hosokawa et al 2011), while polar cap patches exhibit a maximum at 23 hr MLT with intensities several times that of airglow (typically 1 kR; McEwen & Harrington 1991;Moen et al 2007).…”