Abstract
Abstract. The aim of this paper is to advance the current understanding of the spectral width parameter observed by coherent high frequency (HF) radars. In particular, we address the relationship of a frequently observed gradient, between low ( < 200 m/s) and high ( > 200 m/s) spectral width, to magnetospheric boundaries. Previous work has linked this gradient in the spectral width, in the nightside sector of magnetic local time, to the Polar Cap Boundary (PCB), and also to the boundary between the Central Plasma Sheet (CPS) and the Plasma Sheet Boundary Layer (PSBL). The present case study investigates the former by comparison with the 630.0 nm optical emission. No suitable data were available to test the second of the two hypotheses. It is found that during the interval in question the spectral width gradient is within the region of the 630.0 nm optical emission. A comparison of coherent and incoherent scatter radar data is also conducted, which indicates that values of high spectral width are typically collocated with elevated F-region electron temperatures. We conclude that the high spectral width region in the interval under study is associated with particle precipitation and also that the spectral width gradient is not a reliable method for locating the PCB.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities)
Highlights
The magnetosphere is dynamic and the locations of different plasma regimes within it evolve continually
Blanchard and co-workers used DMSP satellite data to show that a well-defined step in the intensity of the 630.0 nm emission at its poleward edge locates the polar cap boundary (PCB) to an accuracy of ±0.9◦ invariant latitude in the pre-midnight sector
A previous case study in the pre-midnight sector (Lester et al, 2001) concluded that the well-defined gradient between low (< 200 m/s) and high (> 200 m/s) spectral width can be used, with caution, as an ionospheric proxy for the PCB. This conclusion was based on the fact that the gradient would, at times, follow the poleward edge of the 630.0 nm optical emission, which has been proposed as a proxy for the PCB (Blanchard et al, 1995)
Summary
The magnetosphere is dynamic and the locations of different plasma regimes within it evolve continually. Many of the processes that occur in the magnetosphere leave signatures in the ionosphere that can be observed either from the ground or from space. Of particular interest in the magnetosphere is the open/closed field line boundary (OCFLB). Blanchard and co-workers used DMSP satellite data to show that a well-defined step in the intensity of the 630.0 nm emission at its poleward edge locates the PCB to an accuracy of ±0.9◦ invariant latitude in the pre-midnight sector. This step indicates the change from high-energy precipitation on closed field lines to the low energy, diffuse polar rain observed within the polar cap itself
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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.
