The polarization of auroral radio emissions

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

doi:10.1029/97gl03160

Cited by 47 publications

(48 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The MF burst can be identified as broadband emissions covering from 1.9 to 2.6 MHz appearing only in the LH spectra. 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).…”

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

confidence: 81%

See 1 more Smart Citation

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

et al. 2008

View full text Add to dashboard Cite

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.

show abstract

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

confidence: 81%

“…MF burst shows a broadband impulsive feature with a bandwidth of 1-2 MHz in a frequency range of 0.8-4.5 MHz (LaBelle et al, 2005). The polarization character of 2 f ce roar and MF burst have been identified as left-handed polarized waves by Shepherd et al (1997), implying that they should propagate in the L-O mode in the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2008

View full text Add to dashboard Cite

show abstract

“…Because these frequency bands are considered to be close to the second and third harmonics of the electron cyclotron frequency in emission sources, each type of auroral roar is called 2f ce and 3f ce roars. The polarization character of 2f ce and 3f ce roars was identified as left-handed polarized waves by Shepherd et al [1997] and Sato et al [2008]. Both types are commonly attributed to mode conversion to the L-O mode of upper hybrid waves excited in the bottomside ionosphere by auroral electrons [e.g., LaBelle and Treumann, 2002].…”

Section: Introductionmentioning

confidence: 99%

First observations of 4f_ce auroral roar emissions

Sato

Ono

Sato

et al. 2012

Geophysical Research Letters

View full text Add to dashboard Cite

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.

show abstract

“…First reported by Weatherwax et al [1994], it is a bursty broadband emission between 1.3 and 4.5 MHz, observed for a few minutes around substorm onset, often coincident with auroral hiss, 2f ce and 3f ce auroral roar, and substorm-correlated absorption of AM broadcast band stations. LaBelle et al [1997] present 10 kHz bandwidth waveform measurements suggesting substructure with timescales as short as 100-300 ms. Shepherd et al [1997] determined that MFB is left-hand polarized. Using data from the South Pole Station, LaBelle et al [2005] demonstrated that MFBs are observed at ground level only during darkness and that their occurrence rate is primarily dictated by magnetic time, maximizing during premidnight hours, and that the frequency range of MFB varies characteristically with solar zenith angle.…”

Section: Introductionmentioning

confidence: 99%

Theoretical constraints on the generation mechanism of auroral medium frequency burst radio emissions

et al. 2011

View full text Add to dashboard Cite

[1] Auroral medium frequency (MF) burst is an impulsive auroral radio emission observed at ground level between ∼1.3 and 4.5 MHz for a few minutes at substorm onsets. Despite multiple suggested theories, the exact generation mechanism for MF burst remains unknown. The foremost theory suggests that MF burst originates from Langmuir or upper hybrid waves excited over a range of altitudes in the bottomside or topside F region, which linearly mode convert to the electromagnetic LO mode, gaining access to ground level. Analysis of plasmas with two electron components implies the existence of additional normal modes, commonly referred to as the electron acoustic (EA) and electron cyclotron sound (ECS) modes, which have been suggested to potentially play a role in the generation of MF burst. Analytical calculations using Waves in Homogeneous, Anisotropic Multicomponent Plasmas, or WHAMP, and other dispersion-solving calculations are applied to applicable ionospheric normal modes (RX, LO, Langmuir or upper hybrid, EA, and ECS), compared to previous results, and applied to MF burst and the auroral plasma environment. Computation of resonant parallel energies suggests that, in the presence of an auroral electron distribution, instability of EA, ECS, LX, and Langmuir or upper hybrid modes is possible. The same analysis suggests that LO and RX modes are unlikely to be directly excited. Excitation of the EA or ECS mode in the frequency range applicable to MF burst is found to be more favorable for higher ionospheric plasma densities ( f pe /f ce > 2.36) and higher secondary electron temperatures (T h ≈ 100s of eV). Growth rate calculations suggest that growth of the EA or ECS mode is excitable by the auroral electron beam with higher growth rates for the ECS mode.

show abstract

The polarization of auroral radio emissions

Abstract: Abstract. Ground level observations using two vertical loop antennas oriented at 900 to each other reveal the sense of polarization of several types of auroral radio emissions in the frequency range 30-5000 kHz. Auroral hiss is observed to be right elliptically polarized

Cited by 47 publications

References 11 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

Theoretical constraints on the generation mechanism of auroral medium frequency burst radio emissions

Contact Info

Product

Resources

About

The polarization of auroral radio emissions

Abstract: Abstract. Ground level observations using two vertical loop antennas oriented at 900 to each other reveal the sense of polarization of several types of auroral radio emissions in the frequency range 30-5000 kHz. Auroral hiss is observed to be right elliptically polarized

Cited by 47 publications

References 11 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

Theoretical constraints on the generation mechanism of auroral medium frequency burst radio emissions

Contact Info

Product

Resources

About

First observations of 4f_ce auroral roar emissions