Incoherent scatter radar identification of the dayside magnetic separatrix and measurement of magnetic reconnection

Abstract

Abstract. Incoherent scatter (IS) radar measurements of the ionospheric electron density are analyzed for the signature of the magnetic separatrix in the dayside ionosphere by comparison with separatrix locations determined using precipitating electron data from DMSP spacecraft within 1.5 hours in magnetic local time (MLT) of the Sondrestrom radar. A model of photoionization is used to remove its effects from the measured electron density to study the ionization by precipitating particles. The altitude of peak ionization and the peak ionization rate are used to determine whether a magnetic field line is open or closed. We observe that on closed field lines the peak ionization rate is high (> 2200 cm '3 s 'l) or the peak is lower than 140 km in altitude, and on open field lines the peak ionization is low (< 900 cm "• s -•) or the peak is h!gher than 140 km. These rules are used to identify the separatrix with an accuracy of 0.36 ø and a precision of +0.39 ø. This signature of the separatrix is only apparent in the prenoon and noon sectors (0600 to 1300 MLT). In the postnoon sector (1630-1800 MLT) the altitude of peak ionization and the peak ionization rate do not show any systematic difference between the open and closed field line regions. Finally, an example is presented in which the data on the location and motion of the separatrix and IS radar measurements of F region plasma velocity are used to measure the magnetic reconnection rate as a function of the interplanetary magnetic field clock angle.

Space- and ground-based investigations of solar wind–magnetosphere–ionosphere coupling

“…Other techniques for identifying the OCB include detection of the ionospheric electron density enhancement produced by precipitating trapped particles, for instance with an incoherent scatter radar (e.g. de la Beaujardiere et al, 1991;Blanchard et al, 2001), and identification of the spectral width boundary observed by coherent radars (e.g. Chisham and Freeman, 2003).…”

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.…”

The location and rate of dayside reconnection during an interval of southward interplanetary magnetic field

“…To achieve this measurement is difficult, as it usually requires a conjunction of at least two observing instruments; one to determine the footprint of the X-line and a second to measure the plasma flow. Blanchard et al (2001) have shown how a single incoherent scatter radar can be used to measure the reconnection rate at a single meridian. Studies by Baker et al (1997) and Pinnock et al (1999) demonstrated the ability of the radars of the Super Dual Auroral Radar Network (SuperDARN) to perform the measurement, the greater field of view of a single Super-DARN radar extending the coverage to ∼2 h of MLT.…”