Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

Abstract

Abstract. Data from HF-radars are used to make the ®rst simultaneous conjugate measurements of the dayside reconnection electric ®eld. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic ®eld (IMF) was southward whilst the eastward component (By) was variable. The¯ow patterns derived from the radar data show the expected conjugate asymmetries associated with IMF jByj > 0. High-time resolution data (50 and 100 s) enable the¯ow of plasma across the open/closed ®eld line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical dierence of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s A1 ) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively ®ts that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be signi®cantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat¯ow occurs is dierent in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric ®eld values are largest when the radar's meridian is in the throat ow or early afternoon¯ow regions. In the morning or afternoon convection cells, the reconnection electric ®eld tends to zero away from the throat¯ow region. The reconnection electric ®eld observed in the throat¯ow region is bursty in nature.

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…They combined these with measurements of the SWB to estimate the reconnection rate across an extended longitudinal region. Following this, Pinnock et al (1999) determined the temporal variation of the reconnection rate at conjugate meridians, using the Goose Bay radar in the northern hemisphere, and the Halley radar in the southern hemisphere. They showed that the dayside reconnection rate values were largest when the radar's meridian was in the throat flow or early afternoon flow regions, and that the reconnection rate in the throat flow region was bursty in nature.…”

Measuring the dayside reconnection rate during an interval of due northward interplanetary magnetic field

“…The dayside reconnection electric field has been measured extensively in this way under southward IMF conditions (Baker et al, 1997;Pinnock et al, 1999;Blanchard et al, 2001;Milan et al, 2003;Pinnock et al, 2003), but measurements under northward IMF conditions have been generally confined to determinations of the cross-polar cap potential from low-altitude spacecraft overflights or from model convection patterns (Cumnock et al, 1995;Weimer, 1995;Ruohoniemi and Greenwald, 1996). Cumnock et al (1995) measured a potential drop of ∼10-20 kV between the centres of the reverse convection cells during intervals of northward IMF.…”

Simultaneous optical and radar signatures of poleward-moving auroral forms

“…6 (beam 9) shows the lowlatitude limit of large spectral width (larger than 150 m/s) in radar data. This limit between narrow and wide HF spectra has been shown to indicate the position of the separatrix between closed and opened ®eld lines in the cusp (Baker et al, 1997;Pinnock et al, 1999). This limit correlates closely with the low-latitude boundary of the red line emissions at the level of 3 kR (shown by the dotted line), after the initial period of equatorward drift of the auroral emission.…”