Abstract
Abstract. It is now a common practice to employ ground-based radars in an attempt to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed magnetic field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromsø, Norway (66° N geomagnetic). On this occasion, a number of equatorward excursions of the SWB in the radar backscatter are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band as the SWB passes overhead. Thus, these observations support the possibility that high-frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the nightside ionosphere. Key words. Ionosphere (auroral ionosphere) – Magnetospheric physics (MHD waves and instabilities) – Radio science (ionospheric physics)
Highlights
The use of ground-based radars for making observations of the terrestrial ionosphere and the subsequent diagnosis of dynamic magnetospheric regions and processes is well founded
It has been proposed that the boundary between high and low spectral widths, the latter usually occurring at lower latitudes, might be a good way of identifying the open-closed field line boundary (OCFLB)
The observed radar spectral widths associated with a series of dusk-sector equatorward-propagating transient features are compared with dynamic spectral measurements of the Pc1-2 wave band from a newly deployed induction coil magnetometer located in Tromsø, Norway
Summary
The use of ground-based radars for making observations of the terrestrial ionosphere and the subsequent diagnosis of dynamic magnetospheric regions and processes is well founded. This paper discusses an interval of HF radar data where features exhibiting large spectral widths are observed simultaneously with broad-band high-frequency wave activity and which appear to be related to substorm and pseudobreakup occurrence. In their standard mode of operation auto-correlation functions (ACFs) are formed every 100 ms and this could sample the electric fields associated with waves in the Pc1–2 band without a loss of temporal resolution. In an attempt to reduce cross-range noise the radar data are subsequently integrated to provide one measurement every 3 or 7 s, and this reduction in temporal resolution will lead to a loss of spectral information associated with individual waves which will act to broaden individual spectra
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