Auroral and related emissions

File

Size

Description

663 KB

Pure auroral whistlers recorded in Alaska with a WR-3E hand-held ELF/VLF receiver connected to a 1m long whip antenna tuned between 0.1 and 11 kHz. Recorded on Sep 9, 1995 at 0930 UTC. Additional information can be found on Stephen P. McGreevy's website. Document McGreevy

684 KB

Second part of Sept 9, 1995 event. Document McGreevy

663 KB

Auroral chorus during a magnetic storm. Recorded on Vancouver island on Feb 21, 1994 at 1045 UTC using a WR-3E hand-held ELF/VLF receiver connected to a 3m long vertical antenna. Document McGreevy

668 KB

Auroral chorus recorded in Alberta on Sept 26, 1993 at 1110 UTC. When the "sliding tone" emission occured the aurora became brighter. Document McGreevy

453 KB

Second part of Sept 26, 1993 event. Recorded at 1115 UTC. Document McGreevy

340 KB

Auroral chorus and "nose whistlers" recorded in Saskatchewan on Sept 25, 1993 at 0930 UTC. Document McGreevy

217 KB

Recording of a very intense aurora disturbing VHF bands. Source and instrument unknown.

297 KB

Magnetosphere saucer recorded on March 27, 1996 at 2005 UTC by Don Gurnett, principal Polar Plasma Wave Investigator at U.Iowa. Saucer emissions are found near the low-latitude boundary of the auroral precipitation region. Saucers are electromagnetic whistler-mode emissions characterized by a V-shaped or saucer-shaped signature on high resolution frequency-time spectrograms.

Saucers are upward-propagating emissions that usually last only seconds. The short time duration of the saucers is the most significant spectral difference between these emissions and the broadband auroral hiss found in the same region. 

On the audio tape, the saucers have distinct falling and rising tones. The V-shaped saucer is centered on 20:05:42 UTC and extends in frequency up to 5 kHz. The dish-shaped saucer is centered on 20:05:47 UTC and extends in frequency up to 2.5 kHz. Both saucers are found on dayside auroral field lines near the poleward edge of the auroral zone. For this pass, the wideband receiver was connected to an electric Eu antenna.

273 KB

Magnetosphere hiss recorded on May 28, 1996 at 2148 UTC by Don Gurnett from U.Iowa.

Auroral hiss emissions are broad, intense electromagnetic emissions which occur in a narrow latitudinal band, typically only 5-10° wide, centered on the auroral zone. 

Auroral hiss is emitted in a beam around an auroral magnetic field line at altitudes of 2-4 RE. The beam width increases with increasing frequency. At high altitudes, the auroral hiss often has a sharp high frequency cutoff due of either the electron plasma frequency or the electron cyclotron frequency.

Typically above 10,000 km, the emissions are propagating upward and at low altitudes. Below 1000 km, the radiation is usually propagating downward. Downward propagating auroral hiss emissions are closely correlated with intense, downgoing 100 eV to 1 keV inverted-V electron beams. Upward propagating auroral hiss is correlated with upgoing ~50 eV electron beams.

Because the auroral hiss emissions appear as a uni-directional signal to the spacecraft antennas, the continuous, featureless spectrum of the hiss emissions is strongly spin-modulated when observed on high- resolution wideband spectrograms. Well-defined nulls in the signal occur every half-spin when the electric antennas are aligned perpendicular to wave propagation direction. The resulting tones on the audio tape are strongly modulated hiss-like tones.

The recording was taken from a nightside auroral zone pass in the northern hemisphere. The wideband receiver was connected to an electric Eu antenna during this pass. The strongly spin-modulated hiss signal is found below 3 kHz.

297 KB

Magnetosphere hiss recorded on June 11, 1996 at 0144 UTC by Don Gurnett from U.Iowa. Same as previous. The strongly spin-modulated hiss signal is found below 1 kHz.

377 KB

Magnetosphere Auroral Kilometric Radiation (AKR) recorded on May 10, 1996 at 1638 UTC by Don Gurnett from U.Iowa. Recording taken from a pass through the nightside auroral zone in the southern hemisphere. The wideband receiver was configured to obtain data in the frequency range of 250-340 kHz and is connected to the electric Eu antenna. The multiple discrete spectral features are predominantly rising tones of varying frequency dispersions between 270 kHz and 340 kHz.

AKR is an intense radio emission escaping outward from the Earth's auroral regions at frequencies above the local electron plasma frequency. AKR usually consists of a very intense band of emission in the frequency range of about 50-500 kHz. The AKR intensity is usually highly variable, often changing by as much as 60-80 dB on time scales of ten minutes or less. The periods of high intensity tend to occur in storms lasting from a fraction of an hour to days and are closely correlated with global auroral displays, particularly with discrete auroral arcs in the evening sector. The occurrence of intense bursts of AKR is closely associated with the occurrence of inverted-V electron precipitation events. 

Direction-finding measurements have shown that the most intense bursts of AKR come from a source region on the nightside auroral field lines at radial distances ranging from 2-4 RE. Dayside sources are also observed and are associated with the dayside cusp region. These dayside sources are typically less intense than the nightside sources. AKR is observed in both hemispheres and has been found to propagate in both the right- and left-hand polarization R-X and L-O free space modes.

552 KB

Earth Auroral Kilometric radiation (AKR). Document U.Iowa

367 KB

Dawn or aurora chorus recorded between 0-100 Hz (infrasound) by Altaïr