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Waves and Particles in the Radiation Belt
Kaiti Wang
PSSC/NCKU
March 17, 2009
Opportunity for Collaboration on ERG and SCOPE Missions & Community Input
An Important Question to Answer
Can chorus be a source for plasmaspheric hiss ?
Bortnik et al. (2008), The unexpected origin of plasmaspheric hiss from discrete chorus emissions, Nature, 452,doi:10.1038/nature06471
Observations of Plasmaspheric Hiss
[Dunckel and Helliwell, 1969]
OGO-1 satellite
f-t spectrogramsPrimary Observational Features:
1. Frequency < a few kHz2. Peak < 1kHz3. Ubiquitous everywhere within the plasmasphere4. Dependence on geomagnetic activities5. Dayside-Nightside asymmetry -> More intense at dayside6. Have been discovered for 40 years
Two Main Mechanisms Discussed
1. Local instability: In situ growth and amplification of background EM turbulence, driven by unstable energetic electron populations.
The calculated growth rate is too modest
[Church & Thorne, 1983] 2. Lightning flashes: The evolution of a spectrum of EM w
aves injected into the plasmasphere by terrestrial lightning strikes into the observed hiss band.
?
Distribution of hiss is not correlated with lightning flashes
[Meredith et al., 2006]
Land > Ocean
Hiss Intensity map back to Earth Surface
Almost stay in 2-D plane
[Draganov et al., 1992] CRRES data
Hiss intensity related to geomagnetic storms
Most intensive at recovery phase
-> but source from lightning cannot explain this feature
[Smith et al., 1974]
Histograms of peak spectral power from Ogo6 data
Observations of Chorus
[Chum et al., 2003]
[Sigsbee et al., 2008]L~6
Frequency Range:0.05 – 0.6 fce
Location:Outer radiation belt[Meredith et al, 2003]
fce~9kHz
since 1960’s
As L increases, the frequency range ofchorus emission would drop.
Chorus as a Source for Plasmaspheric Hiss
[Bortnik et al., 2008]
Nightside Hiss intensityis weaker
L=5 L=5
Cluster II CRRES
Traveling in whistler-mode
704Hz (0.1 fce)
[Wang et al., 2008]
Chorus can be a source for hiss in the extended Io torus of Jupiter
[Gunett et al., 1996]
Jovian hiss discovered since 1979
planet
planet
Chorussource
It takes 30 years!!
Hiss, Chorus & Electrons
Hiss can cause electron loss Resonant pitch angle scattering of energetic electrons by
plasmaspheric hiss largely accounts for the formation of the slot region that separates the inner (1.3 < L < 2) and outer (3 < L < 7) radiation belts. This mechanism remove the high-energy electrons that are trapped along the Earth’s magnetic field lines. [Meredith et al., 2007]
Chorus can accelerate electrons This process can energize electrons up to relativistic ener
gies through wave-particle interaction. Contribute to formation of high-energy electrons outside the plasmasphere. [Meredith et al., 2002]
References
Bortnik, J., R. M. Thorne, N. P. Meredith (2008), The unexpected origin of plasmaspheric hiss from discrete chorus emissions, Nature, 452,doi:10.1038/nature06471
Church S. R. and R. M. Thorne (1983), On the origin of plasmaspheric hiss: Ray path integrated amplification, J. Geophys. Res., 88, 7941.
Chum, J., F. Jiřiček, J. Šmilauer, and D. Shklyar (2003), Magion 5 observations of chorus-like emissions and their propagation features as inferred from ray-tracing simulation, Annales Geophysicae, 21:2293-2302.
Draganov, A. B., U. S. Inan, V. S. Sonwalkar, and T. f. Bell(1992), Magnetospherically reflected whistlers as a source of plasmaspheric hiss, Geophys. Res. Lett., 19, 233.
Dunckel N. and R. A. Helliwell, Whistler-mode emissions on the OGO-1 Gurnett, D. A., W. S. Kurth, A. Roux, S. G. Bolton, C. F. Kennel (1996), Galileo plamsa wave
observations in the Io plasma torus and near Io, Science, 274, 391. Meredith N. P, R. B. Horne, R. M. Thorne, R. R. Anderson (2003), Favored regions for chorus-
driven electron acceleration to relativistic energies in the Earth’s outer radiation belt, Geophys. Res. Lett., 30, 1871, doi:10.1029/2003GL017698.
Meredith, N. P., R. B. Horne, R. H. A. Iles, R. M. Thorne, D. Heynderickx, R. R. Anderson (2002), Outer zone relativistic electron acceleration associated with substorm-enhanced whistler mode chorus, J. Geophys. Res., 107,1114.
Meredith, N. P., R. B. Horne, M. A. Clilverd, D. Horsfall, R. M. Thorne, and R. R. Anderson (2006), Origins of plasmaspheric hiss, J. Geophys. Res., 111, A09217, doi:10.1029/2006JA011707.
Meredith, N. P., R. B. Horne, S. A. Glauert, R. R. Anderson (2007), Slot region electron loss timescales due to plasmaspheric hiss and lightning-generated whistlers, J. Geophys. Res., 112, A08214, doi10.1029/2007JA012413.
Sigsbee, K., J. D. Menietti, O. Santolík, J. B. Blake (2008), Polar PWI and CEPPAD observations of chorus emissions and radiation belt electron acceleration: Four case studies. J. Atmos. Solar-Terr. Phys., 70, doi:10.1016/j.jastp.2008.02.005.
Smith, E. J., A. M. A. Frandsen, B. T. Tsurutani, R. M. Thorne, K. W. Chan (1974), Plasmaspheric hiss intensity variations during magnetic storms, J. Geophys. Res., 79, 2507.
Wang, K., R. M. Thorne, R. B. Horne (2008), Origin of Jovian Hiss in the extended Io torus, Geophys. Res., Lett., 35, L16105, doi:10.1029/2008GL034636.
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