Abstract

Abstract. We performed a statistical analysis of the occurrence distribution of Doppler spectral width around the day-side high-latitude ionosphere using data from the conjugate radar pair composed of the CUTLASS Iceland-East radar in the Northern Hemisphere and the SENSU Syowa-East radar in the Southern Hemisphere. Three types of spectral width distribution were identified: (1) an exponential-like distribution in the lower magnetic latitudes (below 72°), (2) a Gaussian-like distribution around a few degrees magnetic latitude, centered on 78°, and (3) another type of distribution in the higher magnetic latitudes (above 80°). The first two are considered to represent the geophysical regimes such as the LLBL and the cusp, respectively, because they are similar to the spectral width distributions within the LLBL and the cusp, as classified by Baker et al. (1995). The distribution found above 80° magnetic latitude has been clarified for the first time in this study. This distribution has similarities to the exponential-like distribution in the lower latitude part, although clear differences also exist in their characteristics. These three spectral width distributions are commonly identified in conjugate hemispheres. The latitudinal transition from one distribution to another exhibits basically the same trend between two hemispheres. There is, however, an interhemispheric difference in the form of the distribution around the cusp latitudes, such that spectral width values obtained from Syowa-East are larger than those from Iceland-East. On the basis of the spectral width characteristics, the average locations of the cusp and the open/closed field line boundary are estimated statistically.Key words. Ionosphere (ionosphere-magnetosphere inter-actions; plasma convection) – Magnetospheric physics (magnetopause, cusp, and boundary layers)

Highlights

  • Determining the open/closed field line boundary (OCFLB) around the dayside ionosphere enables us to estimate several geophysical parameters such as (1) the rate of reconnection at the magnetopause, (2) the size of polar cap, and (3) the creation and destruction of open magnetic flux associated with the dayside and nightside reconnection

  • Intersection of the two summary point arrays ranges from 70◦ to 81◦ in magnetic latitude, which lies from the average position of the LLBL to the polar cap, through the OCFLB and the cusp in the radar observation around the dayside ionosphere

  • Characteristics of the spectral width distribution were investigated using the conjugate radar pair composed of Coordinated UK Twin-Located Auroral Sounding System (CUTLASS) Iceland-East in the Northern Hemisphere and SENSU Syowa-East in the Southern Hemisphere

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Summary

Introduction

Determining the open/closed field line boundary (OCFLB) around the dayside ionosphere enables us to estimate several geophysical parameters such as (1) the rate of reconnection at the magnetopause, (2) the size of polar cap, and (3) the creation and destruction of open magnetic flux associated with the dayside and nightside reconnection. A relationship between the magnetospheric cusp particle precipitation into the ionosphere and the HF radar backscatter from the ionospheric F region has been reported by a number of authors (Baker et al, 1990, 1995; Rodger et al, 1995; Yeoman et al, 1997). Baker et al (1995) analyzed the HF radar data for eight cusp events and eight low-latitude boundary layer (LLBL) events which were identified by the DMSP satellite They reported that the distribution of observed spectral widths in the cusp is significantly different from that observed in the LLBL. There have been only a few simultaneous observations of the cusp and the OCFLB using the data from magnetic conjugate radars (Pinnock et al, 1999; Milan and Lester, 2001). Significant interhemispheric differences in the characteristics of spectral width distribution are found and the statistical locations of the cusp and the OCFLB were determined in both hemispheres

Statistics database
Geophysical bias
Latitudinal variation of the spectral width distribution
Longitudinal variation of the spectral width distribution
Form of the spectral width distribution
Generation mechanisms of broad spectral width
Interhemispheric differences in spectral width values
Findings
Comparison with the other observations
Summary and conclusion
Full Text
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