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Data Presentation

The PSFR, described in detail elsewhere [e.g., Weatherwax, 1994], operates in a standard mode which sweeps each 2 s from 30 kHz to 5 MHz with 10-kHz resolution and operates for 20 hours each day centered on local midnight. The PSFR has a dynamic range of ~70 dB and an instrument sensitivity of a few nV m$^{-1}$ Hz$^{-1/2}$, though in practice the noise floor at the Sondrestrom site is significantly higher than this level. The non resonant dipole antenna used in this system is sensitive to electromagnetic wave fluctuations emanating from a large portion of the sky; for example, the antenna sensitivity to a radio wave propagating from an azimuthal angle of 45$^\circ$ (~300 km ground range) is at worst half that compared to a wave propagating from directly overhead. Radio wave observations from ground stations located in Canada and separated by ~275 km suggest that auroral roar often originate from nearly overhead.

Kelly et al. [1995] present a recent description of the capabilities of the Sondrestrom radar and ancillary ground-based instruments. During the auroral roar observations presented below, the Sondrestrom ISR operated in one of three modes, performing elevation or composite scans and providing several degrees of latitudinal coverage of plasma parameters. The horizontal resolution of each experiment mode will be discussed later. The transmitter pulse length for these experiments was 320 $\mu$s, and thus autocorrelation functions were formed with a range resolution of 48 km.

To identify study intervals, the survey spectrograms of the PSFR data were first systematically searched for occurrences of auroral roar. By comparing these occurrences with the radar operation schedule, a subset of these events was identified for which the ISR was in an appropriate mode to measure the two-dimensional electron density distribution in the F region ionosphere. Six such days including 18 individual radar scans are the focus of this study. The small number of coincidences during 1995 to 1997 is in part due to radio frequency interference from equipment in the radar facility which obscures many auroral radio emissions. The PSFR antenna has recently been moved further away from noise sources, an improvement which should increase opportunities for joint PSFR/ISR observations during future auroral roar observations.


\begin{plate*}
% latex2html id marker 66\figbox*{\hsize}{}{\epsfig{file=figs/p...
...he
observation of 2$f_{ce}$\ and 3$f_{ce}$\ auroral roar emissions.}\end{plate*}


\begin{plate*}
% latex2html id marker 72\figbox*{\hsize}{}{\epsfig{file=figs/p...
...avity, strong $N_e$\ gradients,
and adequate upper hybrid matching.}\end{plate*}


\begin{plate*}
% latex2html id marker 78\figbox*{\hsize}{}{\epsfig{file=figs/p...
...een in Plate \ref{ev05}c immediately poleward of the $E$region arc.}\end{plate*}


\begin{plate*}
% latex2html id marker 85\figbox*{\hsize}{}{\epsfig{file=figs/p...
...h the
entire frequency range of the observed auroral roar emission.}\end{plate*}


\begin{plate*}
% latex2html id marker 91\figbox*{\hsize}{}{\epsfig{file=figs/p...
...ans show the screening of the source region by the
$E$\ region arc.}\end{plate*}


\begin{plate*}
% latex2html id marker 98\figbox*{\hsize}{}{\epsfig{file=figs/p...
...ome regions where the upper hybrid matching condition is
satisfied.}\end{plate*}



Subsections
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Next: Ionospheric Structure Up: Ionospheric structure and the Previous: Introduction