Abstract
Abstract. Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial for making accurate measurements of magnetic reconnection. This study compares the latitudes of spectral width boundaries (SWBs) measured by different beams of the Goose Bay radar of the Super Dual Auroral Radar Network (SuperDARN), with the latitudes of OCBs determined using the low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the accuracy of the SWB as a proxy for the ionospheric projection of the OCB depends on the line-of-sight direction of the radar beam. The latitudes of SWBs and OCBs were identified using automated algorithms applied to 5 years (1997–2001) of data measured in the 1000–1400 magnetic local time (MLT) range. Six different Goose Bay radar beams were used, ranging from those aligned in the geomagnetic meridional direction to those aligned in an almost zonal direction. The results show that the SWB is a good proxy for the OCB in near-meridionally-aligned beams but becomes progressively more unreliable for beams greater than 4 beams away from the meridional direction. We propose that SWBs are identified at latitudes lower than the OCB in the off-meridional beams due to the presence of high spectral width values that result from changes in the orientation of the beams with respect to the gradient in the large-scale ionospheric convection pattern. Keywords. Ionosphere (Instruments and techniques; Plasma convection) – Magnetospheric physics (Magnetopause, cusp and boundary layers)
Highlights
Many large-scale processes in the magnetosphere are best measured remotely from the ionosphere
We have chosen the 1000–1400 magnetic local time (MLT) region for this analysis as the spectral width boundaries (SWBs) on meridional beams has been shown to be a good Open-Closed field line Boundary (OCB) proxy here, there is good overlap in coverage between the Goose Bay SWBs and the Defense Meteorological Satellite Program (DMSP) OCBs in this region (Chisham et al, 2005), and because the SWB is well defined in this region and has a minimal dependence on the spectral width threshold used
We propose that the high spectral width values that occur equatorward of the OCB in off-meridional beams are a result of geometrical effects associated with the radar beam orientation with respect to the global-scale ionospheric convection pattern, as suggested by Villain et al (2002), and are not due to structure on scales less than the radar sampling scales, as is thought to be the case with large spectral width values poleward of the OCB
Summary
Many large-scale processes in the magnetosphere are best measured remotely from the ionosphere. Reconnection analyses typically require accurate measurements of the boundary between closed geomagnetic field lines with both foot points on the Earth, and open geomagnetic field lines with one end connected to the Interplanetary Magnetic Field (IMF) This boundary is known as the Open-Closed field line Boundary (OCB), its ionospheric projection is known as the polar cap boundary. The SWB is a latitudinal transition between radar backscatter with high and variable Doppler spectral width values, typically observed at high latitudes, and that with low Doppler spectral width values, typically observed at low latitudes (Chisham et al, 2001) This SWB is readily observed at all magnetic local times, during all geomagnetic conditions (Chisham and Freeman, 2004), and can be identified using objective automated algorithms (Chisham and Freeman, 2003)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
