Auroral pulsations and accompanying VLF emissions

Tagirov, V. R.; Ismagilov, V. S.; Титова, Е. Е.; Arinin, V. A.; Perlikov, A. M.; Manninen, J.; Turunen, T.; Kaila, K.

doi:10.1007/s00585-999-0066-9

Cited by 23 publications

(41 citation statements)

References 40 publications

(51 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Each dynamic spectrum shows successive rising-tone elements with an element duration and spacing of approximately 0.1-0.3 s, a duration of grouped elements of 2-3 s, and a spacing of each group of 20-30 s. These features observed in the chorus wave spectra are consistent with the values for pulsating auroral patches [Yamamoto, 1988;Samara and Michell, 2010]. Similar results from ground-based observations suggest that a wave-particle interaction may be the generating mechanism of pulsating aurora [Tsuruda et al, 1981;Hansen and Scourfield, 1990;Tagirov et al, 1999]. The first step toward estimating the location of the source region is to determine which auroral patch is spatially related to the observed chorus waves.…”

Section: Natural Vlf Waves and Optical Observationssupporting

confidence: 81%

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: A case study

et al. 2012

View full text Add to dashboard Cite

[1] A high correlation between a pulsating auroral patch and grouped chorus waves was observed on 17 April 2006 at Syowa Station in Antarctica. The spatial distribution of aurora-chorus correlation coefficients is evaluated in order to determine the source region. A pulsating patch at the highest-correlation pixel shows a one-to-one correspondence with the intensity variation of the grouped chorus waves, consisting of successive rising-tone elements with a duration and spacing of 2-3 s and 20-30 s, respectively. The generation region of the chorus waves is estimated from the latitude and longitude dependence of the equatorial electron gyrofrequencies using the IGRF geomagnetic field model. The extent of the estimated latitude and longitude is consistent with the spatial distribution of the high-correlation aurora-chorus region. The time difference between the chorus waves and the scattered electrons is also evaluated to discuss the validity of the source region. It shows that electrons reached the ionosphere sooner than the associated chorus waves by $1 s, consistent with the theoretical value for conjugate pulsating aurora generated at the equator. These results support the hypothesis that pulsating aurora is caused by pitch angle scattering of high-energy electrons by whistler mode chorus waves, via a cyclotron resonance at the equator. These results are the first ground-based observations of high correlations between a spatially extended aurora and chorus waves.

show abstract

Section: Natural Vlf Waves and Optical Observationssupporting

confidence: 81%

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: A case study

et al. 2012

View full text Add to dashboard Cite

show abstract

“…Deviations from other magnetic field models were investigated in our separate study [Nishimura et al, 2011]. The existence of multiple cores and the expanding and propagating features of patches are similar to the events reported by Tagirov et al [1999].…”

Section: Correlation Between Pulsating Aurora and Lower-band Chorussupporting

confidence: 64%

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

et al. 2011

View full text Add to dashboard Cite

[1] A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of ∼5000 km diameter for corresponding azimuthally elongated patches with ∼100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.Citation: Nishimura, Y., et al. (2011), Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions,

show abstract

“…Figure 6 magnifies the interval following the dipolarization, and relates the earthward bulk flow and the flux pileup to the electron temperature anisotropy, as discussed later in detail. The periodicity of the bursts is about 0.2 to 0.4 s, as observed previously for chorus waves (Helliwell, 1965;Tagirov et al, 1999). The fourth panel is the SCM wave burst interval starting at about 05:29:36.225 that falls between the dashed lines in the panel above.…”

Section: Discussionsupporting

confidence: 73%

“…A recent Time History of Events and Macroscale Interactions during Substorms (THEMIS) study of fast bursty bulk flows at L = 9 reveals that quasi-parallel whistler waves produced in the fast flows associated with dipolarization fronts are able to resonate with and scatter 2-26 keV electrons (Zhima et al, 2015). Tagirov et al (1999) observe VLF chorus emissions in concert with auroral pulsations in the morning sector during substorm activity, based on ground-based VLF recordings and optical measurements in Sodankylä, Finland. This is in contrast to other studies that found the waves were produced within the magnetic depressions Tsurutani et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Source of the Bursty Bulk Flow Diffuse Aurora: Electrostatic Cyclotron Harmonic and Whistler Waves in the Coupling of Bursty Bulk Flows to Auroral Precipitation

et al. 2019

View full text Add to dashboard Cite

Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant wave‐particle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L < 8. However, we find from Time History of Events and Macroscale (THEMIS) Interactions during Substorms observations of fast flows at L = 12 that oblique whistler chorus emissions play the dominant role in scattering electrons. Previous works have identified whistler‐mode waves within fast flows that are produced by an electron temperature anisotropy Te,⊥/Te,||> 1, consistent with electron betatron acceleration. Here, however, we find whistler chorus emissions throughout an interval of fast flows where Te,⊥/Te,||< 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigar‐shaped distributions are consistent with Fermi acceleration at dipolarizations in fast flows. We demonstrate that the scattering efficiency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast flows. The obliquity of the whistler waves permits efficient scattering of lower‐energy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important free‐energy source for the wave‐particle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions.

show abstract

Auroral pulsations and accompanying VLF emissions

Cited by 23 publications

References 40 publications

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: A case study

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: A case study

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

Source of the Bursty Bulk Flow Diffuse Aurora: Electrostatic Cyclotron Harmonic and Whistler Waves in the Coupling of Bursty Bulk Flows to Auroral Precipitation

Contact Info

Product

Resources

About