Observations of auroral medium frequency bursts

LaBelle, J.; Shepherd, Simon; Trimpi, M. L.

doi:10.1029/97ja01905

Cited by 27 publications

(56 citation statements)

References 15 publications

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“…The polarization character of this MF burst event is consistent with the result reported by Shepherd et al (1997). However, it is noted that the present event lasts for only a short time period (10 s), while the typical duration has been reported to occur for about several minutes (Weatherwax et al, 1995;LaBelle et al, 1997). Figure 8(c) shows a series of auroral images of 427.8 nm recorded by the Conjugate Auroral Imager (CAI) instrument, which was located in the Husafell station.…”

Section: Mf Burst (September 23 and October 28 2006)supporting

confidence: 74%

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

et al. 2008

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In order to study the generation and propagation processes of MF auroral radio emissions (referred to as auroral roar and MF burst) in the polar ionosphere, an Auroral Radio Spectrograph (ARS) system was installed at Husafell station in Iceland (invariant latitude: 65.3• ). Data analysis of man-made transmissions also provides useful information for the ionosphere study as well as an investigation of auroral radio emissions since the propagation character of MF radio waves changes depending on electron-neutral collisions in the bottomside ionosphere. Thus, ionospheric absorption is examined in comparison with the solar zenith angle and auroral phenomena. The results indicate that the ARS data can be used to detect ionization occurring at distant regions. In late 2006, the ARS detected one auroral roar and two MF bursts, which were identified as left-handed polarized waves. Results of data analysis, including other auroral data and particle spectra observed by the DMSP satellite, suggest that the MF bursts are generated by electrons with an average energy of several keV associated with auroral breakup. On the other hand, the auroral roar is generated as upper hybrid waves by relatively low-energy electrons over the observation site and propagates downward, being converted into L-O mode electromagnetic waves.

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Section: Mf Burst (September 23 and October 28 2006)supporting

confidence: 74%

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

et al. 2008

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“…But the narrowband auroral radio emission they detected was only 2f ce roar near 3 MHz. Subsequent measurements with sweeping receivers have been conducted below 5 MHz [e.g., Weatherwax et al, 1993;LaBelle et al, 1997;Sato et al, 2008]. The ARS-S observation, conducted for 24 hours every day, enables us to find a new frequency component of auroral roar near 5.5 MHz.…”

Section: Discussionmentioning

confidence: 99%

“…[10] The 4f ce roar did not accompany any other types of MF/HF auroral radio emissions (2f ce roar, 3f ce roar and MF burst), which are detected only during local darkness and are most common in the premidnight hours [e.g., Weatherwax et al, 1995;LaBelle et al, 1997;LaBelle and Weatherwax, 2002;LaBelle et al, 2005]. This difference is causallyrelated to dependence of ionospheric radio wave absorption on frequency: during daylight hours, photoionization enhances electron densities in the ionospheric D-and E-regions to increase radio wave absorption, which is severer for lower frequency waves.…”

Section: Discussionmentioning

confidence: 99%

First observations of 4f_ce auroral roar emissions

Sato

Ono

Sato

et al. 2012

Geophysical Research Letters

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This is a report on the first observations of auroral roar emissions near 4 times the ionospheric electron cyclotron frequency (fce) with a passive receiver installed in Svalbard, Norway. 4fce roar emissions were detected from 5.27 to 5.70 MHz during moderate geomagnetic disturbances in 22 days between May and September 2011 only from noon to evening, while no event occurred during the winter season. An analysis of a typical event shows that the electron density profile measured from EISCAT Svalbard dynasonde satisfies the condition that the upper frequency of the 4fce roar is nearly equal to both upper hybrid resonance frequency (fUH) and 4fce at 238‐km altitude. These observations support the idea expanded from the most commonly‐accepted generation mechanism of 2fce and 3fce roar: the origin of 4fce roar is upper hybrid waves favorably generated under the condition of fUH ∼ 4fce in the auroral F‐region ionosphere.

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“…Statistically, observed events tend to occur either above or below 2 f ce ≈ 2900 kHz [ Weatherwax et al , 1994, Figure 2]. LaBelle et al [1997] show case study evidence that MF burst events sometimes display a null near 2 f ce . MF burst occurrence rates show a broad peak around local midnight, with slightly more occurring premidnight than postmidnight, a local time‐dependence which closely echoes that of auroral hiss.…”

Section: Introductionmentioning

confidence: 99%

“…Auroral MF burst often coincides strikingly with impulsive auroral hiss, with impulsive features correlated down to timescales of seconds; at shorter timescales, the degree of correlation is not known. LaBelle et al [1997] show examples of fine structure of MF burst captured with a 10‐kHz bandwidth downconverting receiver, revealing that MF burst is sometimes composed of features with time durations as short as 100–300 μs. Shepherd et al [1997] show that MF burst at ground level is predominantly left‐hand polarized, suggesting it should be associated with LO mode in the ionosphere, in contrast to auroral hiss which is predominantly right‐hand polarized at ground level and associated with whistler mode in the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Statistical studies of auroral MF burst emissions observed at South Pole Station and at multiple sites in northern Canada

et al. 2005

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[1] Auroral MF burst is a broadband impulsive natural radio emission of auroral origin observed at ground level in the frequency range 0.8-4.5 MHz. Application of a semiautomated analysis method to data collected at South Pole Station, 74°magnetic latitude, results in a database of frequencies, amplitudes, and universal times of MF burst emissions observed during 1 January-31 December 2003. Besides confirming that MF burst emissions are observed at ground level only during darkness and that magnetic local time plays a significant role in controlling the MF burst occurrence rate, which maximizes in the pre-magnetic-midnight hours, these data reveal that the frequencies of MF burst emissions tend to be higher just after sunset and before sunrise than they are during midwinter. This observation supports a link between the emission frequency and the maximum plasma frequency in the ionosphere. South Pole data also show evidence for MF burst extending to frequencies well below the ionospheric gyrofrequency, which brings up the possibility that they are partly in the whistler mode. Analysis of optical and riometer data from one extra-low-frequency MF burst example suggests that MF burst is associated with a relatively high-energy (>10 keV) auroral electron beam. Data from multiple Canadian observatories during [1997][1998] show that the MF burst occurrence rate maximizes near 74°magnetic latitude. With observatories spaced by 260-585 km, about 10% of the MF burst events are observed at two or more stations. Among coincident events, about 3/4 occur first at the lower-latitude station and shift to the higher-latitude station. The average duration of the MF burst events detected at two or more observatories increases with latitude.

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Observations of auroral medium frequency bursts

Cited by 27 publications

References 15 publications

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

First observations of 4f_ce auroral roar emissions

Statistical studies of auroral MF burst emissions observed at South Pole Station and at multiple sites in northern Canada

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Observations of auroral medium frequency bursts

Cited by 27 publications

References 15 publications

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

First observations of 4fce auroral roar emissions

Statistical studies of auroral MF burst emissions observed at South Pole Station and at multiple sites in northern Canada

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First observations of 4f_ce auroral roar emissions