skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Occurrence Patterns of Magnetospherically Reflected (MR) and Specularly Reflected (SR) Whistlers Observed on Van Allen Probes
Title: Occurrence Patterns of Magnetospherically Reflected (MR) and Specularly Reflected (SR) Whistlers Observed on Van Allen Probes
The lightning energy from global thunderstorm activity plays an important role in the physics and dynamics of the inner magnetosphere. Lightning-generated whistlers, including magnetospherically reflected (MR) and recently discovered specularly reflected (SR) whistlers, have been observed on Van Allen Probes (Sonwalkar and Reddy, AGU Fall Meeting, 2021). MR whistlers propagate in nonducted mode and undergo reflections within the magnetosphere. SR whistlers propagate in nonducted mode, undergoing their first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergo magnetospheric reflections similar to an MR whistler. We inspected 31 days of RBSP-A and RBSP-B data during October-November 2012 period when 6-s continuous-burst data (~3400 6-s spectra on RBSP-A and ~6300 6-s spectra on RBSP-B) were available. Whistlers, either MR or SR, were detected on ~1430 spectra in the L-shell range ~1.1 to 5.0 at all near-equatorial geomagnetic latitudes covered by the Van Allen Probes. Whistlers were observed more frequently at nighttime (~1170, 82%) relative to daytime (~260, 18%), consistent with greater D-region losses at daytime. SR whistlers accompanied by MR whistlers were predominantly observed in the L-shell range of ~2 – 3, magnetic latitude λm of ~17° S to 15° N and MLT 0 – 3.6, and in the altitude range of ~ 6000-12,000 km. The MR and SR whistlers occurrence increased from L~2.0 to L~2.5 and then declined with increasing L-shell, a pattern consistent with reported observations of MR whistlers (Edgar, Ph.D. thesis, 1972) for which whistler occurrence increased with L from 2.0 to 2.4 and then declined with increasing L-shell. SR and MR whistlers were detected during geomagnetically quiet to moderately disturbed conditions. The maximum Kp index, 24 hours before detecting whistlers, ranged between 0.33-6.0. Our results indicate that SR whistlers are a common phenomenon, and their impact on the inner radiation belt should be similar to that of MR whistlers.  more » « less
Award ID(s):
2015765
PAR ID:
10516049
Author(s) / Creator(s):
;
Publisher / Repository:
American Geophysical Union
Date Published:
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, AGU Fall Meeting)
    The lightning energy from global thunderstorm activity plays an important role in the physics and dynamics of the inner magnetosphere. Lightning-generated whistlers, including magnetospherically reflected (MR) and recently discovered specularly reflected (SR) whistlers, have been observed on Van Allen Probes (Sonwalkar and Reddy, AGU Fall Meeting, 2021). MR whistlers propagate in nonducted mode and undergo reflections within the magnetosphere. SR whistlers propagate in nonducted mode, undergoing their first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergo magnetospheric reflections similar to an MR whistler. We inspected 31 days of RBSP-A and RBSP-B data during October-November 2012 period when 6-s continuous-burst data (~3400 6-s spectra on RBSP-A and ~6300 6-s spectra on RBSP-B) were available. Whistlers, either MR or SR, were detected on ~1430 spectra in the L-shell range ~1.1 to 5.0 at all near-equatorial geomagnetic latitudes covered by the Van Allen Probes. Whistlers were observed more frequently at nighttime (~1170, 82%) relative to daytime (~260, 18%), consistent with greater D-region losses at daytime. SR whistlers accompanied by MR whistlers were predominantly observed in the L-shell range of ~2 – 3, magnetic latitude λm of ~17° S to 15° N and MLT 0 – 3.6, and in the altitude range of ~ 6000-12,000 km. The MR and SR whistlers occurrence increased from L~2.0 to L~2.5 and then declined with increasing L-shell, a pattern consistent with reported observations of MR whistlers (Edgar, Ph.D. thesis, 1972) for which whistler occurrence increased with L from 2.0 to 2.4 and then declined with increasing L-shell. SR and MR whistlers were detected during geomagnetically quiet to moderately disturbed conditions. The maximum Kp index, 24 hours before detecting whistlers, ranged between 0.33-6.0. Our results indicate that SR whistlers are a common phenomenon, and their impact on the inner radiation belt should be similar to that of MR whistlers. 
    more » « less
  2. ; (, American Geophysical Union (AGU))
    The lightning energy from global thunderstorm activity plays an important role in the physics and dynamics of the inner magnetosphere. Lightning-generated whistlers, including magnetospherically reflected (MR) and recently discovered specularly reflected (SR) whistlers, have been observed on Van Allen Probes (Sonwalkar and Reddy, AGU Fall Meeting, 2021). MR whistlers propagate in nonducted mode and undergo reflections within the magnetosphere. SR whistlers propagate in nonducted mode, undergoing their first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergo magnetospheric reflections similar to an MR whistler. We inspected 31 days of RBSP-A and RBSP-B data during October-November 2012 period when 6-s continuous-burst data (~3400 6-s spectra on RBSP-A and ~6300 6-s spectra on RBSP-B) were available. Whistlers, either MR or SR, were detected on ~1430 spectra in the L-shell range ~1.1 to 5.0 at all near-equatorial geomagnetic latitudes covered by the Van Allen Probes. Whistlers were observed more frequently at nighttime (~1170, 82%) relative to daytime (~260, 18%), consistent with greater D-region losses at daytime. SR whistlers accompanied by MR whistlers were predominantly observed in the L-shell range of ~2 – 3, magnetic latitude λm of ~17° S to 15° N and MLT 0 – 3.6, and in the altitude range of ~ 6000-12,000 km. The MR and SR whistlers occurrence increased from L~2.0 to L~2.5 and then declined with increasing L-shell, a pattern consistent with reported observations of MR whistlers (Edgar, Ph.D. thesis, 1972) for which whistler occurrence increased with L from 2.0 to 2.4 and then declined with increasing L-shell. SR and MR whistlers were detected during geomagnetically quiet to moderately disturbed conditions. The maximum Kp index, 24 hours before detecting whistlers, ranged between 0.33-6.0. Our results indicate that SR whistlers are a common phenomenon, and their impact on the inner radiation belt should be similar to that of MR whistlers. 
    more » « less
  3. ; (, AGU Fall Meeting)
    The lightning energy from global thunderstorm activity plays an important role in the physics and dynamics of the inner magnetosphere. Lightning-generated whistlers, including magnetospherically reflected (MR) and recently discovered specularly reflected (SR) whistlers, have been observed on Van Allen Probes (Sonwalkar and Reddy, AGU Fall Meeting, 2021). MR whistlers propagate in nonducted mode and undergo reflections within the magnetosphere. SR whistlers propagate in nonducted mode, undergoing their first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergo magnetospheric reflections similar to an MR whistler. We inspected 31 days of RBSP-A and RBSP-B data during October-November 2012 period when 6-s continuous-burst data (~3400 6-s spectra on RBSP-A and ~6300 6-s spectra on RBSP-B) were available. Whistlers, either MR or SR, were detected on ~1430 spectra in the L-shell range ~1.1 to 5.0 at all near-equatorial geomagnetic latitudes covered by the Van Allen Probes. Whistlers were observed more frequently at nighttime (~1170, 82%) relative to daytime (~260, 18%), consistent with greater D-region losses at daytime. SR whistlers accompanied by MR whistlers were predominantly observed in the L-shell range of ~2 – 3, magnetic latitude λm of ~17° S to 15° N and MLT 0 – 3.6, and in the altitude range of ~ 6000-12,000 km. The MR and SR whistlers occurrence increased from L~2.0 to L~2.5 and then declined with increasing L-shell, a pattern consistent with reported observations of MR whistlers (Edgar, Ph.D. thesis, 1972) for which whistler occurrence increased with L from 2.0 to 2.4 and then declined with increasing L-shell. SR and MR whistlers were detected during geomagnetically quiet to moderately disturbed conditions. The maximum Kp index, 24 hours before detecting whistlers, ranged between 0.33-6.0. Our results indicate that SR whistlers are a common phenomenon, and their impact on the inner radiation belt should be similar to that of MR whistlers. 
    more » « less
  4. ; (, American Geophysical Union (AGU))
    Nu whistlers are a special case of magnetospherically reflected (MR) whistlers in which, on a spectrogram, 2- and 2+ whistlers are joined at their lower cutoff frequency, fmin. An MR whistler is labeled 2- if the lightning energy has crossed the equator twice before reaching the satellite, and it is labeled 2+ if the lightning energy after crossing the equator twice has undergone a magnetospheric reflection before reaching the satellite (Smith and Angerami, JGR, 73, 1-20, 1968). A magnetospheric reflection occurs when the local lower hybrid frequency is close to the wave frequency (Kimura, Radio Science, 269, 1966). Nu whistlers are, therefore, observed when the satellite is at a location where flh ~ fmin, so both 2- and 2+ MR whistlers have almost identical propagation paths, hence the identical time delay. In addition to conventional Nu whistlers described above, some of the OGO-1 observations contain a second set of Nu whistler-type traces, which, according to previous authors (Smith and Angerami, JGR, 73, 1-20, 1968; Edgar, Ph.D. thesis, 1972), resulted from multipath propagation, possibly due to large scale irregularities in the magnetosphere. Recent whistler observations from the Van Allen probe have led to the discovery of a new kind of whistler - the specularly reflected (SR) whistler (Sonwalkar and Reddy, AGU Fall Meeting 2021, SM43C-02). An SR whistler propagates in nonducted mode, undergoing its first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergoing magnetospheric reflections similar to that of an MR whistler. Using ray tracing analysis, we show that the second set of Nu whistlers are Nu specularly reflected whistlers. Our research implies that there are two types of Nu whistlers: Nu MR whistler and Nu SR whistler. Nu whistlers potentially provide a new method to determine the ion composition at the satellite location. 
    more » « less
  5. ; (, AGU Fall Meeting)
    Nu whistlers are a special case of magnetospherically reflected (MR) whistlers in which, on a spectrogram, 2- and 2+ whistlers are joined at their lower cutoff frequency, fmin. An MR whistler is labeled 2- if the lightning energy has crossed the equator twice before reaching the satellite, and it is labeled 2+ if the lightning energy after crossing the equator twice has undergone a magnetospheric reflection before reaching the satellite (Smith and Angerami, JGR, 73, 1-20, 1968). A magnetospheric reflection occurs when the local lower hybrid frequency is close to the wave frequency (Kimura, Radio Science, 269, 1966). Nu whistlers are, therefore, observed when the satellite is at a location where flh ~ fmin, so both 2- and 2+ MR whistlers have almost identical propagation paths, hence the identical time delay. In addition to conventional Nu whistlers described above, some of the OGO-1 observations contain a second set of Nu whistler-type traces, which, according to previous authors (Smith and Angerami, JGR, 73, 1-20, 1968; Edgar, Ph.D. thesis, 1972), resulted from multipath propagation, possibly due to large scale irregularities in the magnetosphere. Recent whistler observations from the Van Allen probe have led to the discovery of a new kind of whistler - the specularly reflected (SR) whistler (Sonwalkar and Reddy, AGU Fall Meeting 2021, SM43C-02). An SR whistler propagates in nonducted mode, undergoing its first reflection (specular) at the Earth-ionosphere boundary (~90 km) in the conjugate hemisphere and subsequently undergoing magnetospheric reflections similar to that of an MR whistler. Using ray tracing analysis, we show that the second set of Nu whistlers are Nu specularly reflected whistlers. Our research implies that there are two types of Nu whistlers: Nu MR whistler and Nu SR whistler. Nu whistlers potentially provide a new method to determine the ion composition at the satellite location. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email