Imaging riometer observations on energetic electron precipitation at SANAE IV, Antarctica

Abstract

[1] The expansion phase of a substorm on the evening of 1 May 1997 was studied from recordings of all-sky optical aurora and a 64-beam imaging riometer at the Antarctic base SANAE IV (L = 4.1). Digitized all-sky, low-level white light images of auroral optical emissions were mapped onto the angular directivity functions of the 64-beam imaging riometer. During the period of investigation, several optical arcs appeared and disappeared, while a persistent absorption structure appeared in the south (poleward). This and new structures changed only slowly in time. The differences in morphologies of optical emissions and absorption regions, together with temporal differences, imply that there are two categories of energetic auroral electrons: the softer electrons (<10 keV) causing optical emissions in the E and F regions of the ionosphere and the harder (>10 keV) electrons ionizing down into the D region for cosmic radio noise absorption (CRNA). Optical emissions tend to lead the appearance of cosmic radio noise absorptions by 0-60 s in a specific region of ionospheric space. Furthermore, in the all-sky optical data, westward traveling surges (WTS) were observed coincident with a CRNA WTS and leading the CRNA WTS by $30-50 s. In the CRNA data the WTS was ribbon-like, traveling westward at a speed of 2.3 km s À1 . These observations suggest that the softer electrons, causing E and F region optical emissions, may be injected onto drift paths closer to Earth than the more energetic electrons, ionizing down into the D region for cosmic radio noise absorption. The harder electrons could have been accelerated by, for instance, an increasing dawn-to-dusk electric field for later precipitation.

A Case Study of Energy Deposition and Absorption by Magnetic Cloud Electrons and Protons over the High Latitude Stations: Effects on the Mesosphere and Lower Thermosphere

“…To study the reaction of MCs with the atmosphere over the region of interest, we used the imaging riometer data (Hargreaves 1969;Browne et al 1995;Wilson and Stoker 2002). The riometer data employed in this study was obtained from two locations, Halley in the Southern Hemisphere and stations belonging to the Finnish chain which is at the vicinity of the Halley magnetic conjugate in the Northern Hemisphere.…”

Extracting gravity wave parameters during the September 2002 Southern Hemisphere major sudden stratospheric warming using a SANAE imaging riometer

“…Similar to the imaging riometer at Halley, the riometer at SANAE operates on 38.2 MHz and samples a region of over 200 km × 200 km at 90 km altitude with 49 means every second (Detrick and Rosenberg, 1990). The details of the imaging riometer at SANAE are well explained by Wilson (2000). The projection of the riometer beams at 90 km altitude as defined by 3 dB beam projections is shown in Fig.…”

“…There have been no studies of short-period GWs using the South Africa National Antarctic Expedition (SANAE, 72 • S, 3 • W) imaging riometer before. Some of the studies which employed this instrument include the observation of energetic electron precipitation at SANAE IV, Antarctica, by Wilson and Stoker (2002), and spatial structures in enhanced ionization of the ionosphere observed by absorption of cosmic radio waves by Wilson et al (2001).…”

Evidence of Polar Mesosphere Summer Echoes Observed by SuperDARN SANAE HF Radar in Antarctica

“…Riometers respond to the integrated absorption of cosmic ray noise through the ionosphere (Wilson and Stoker 2002;Hargreaves and Friedrich 2003), usually around 90 km altitude (Ogunjobi et al 2014b). The E-region irregularities due to geomagnetic disturbances can result in aurora (Greenwald et al 1995;Liu et al 2013;Zhang et al 2013).…”