Presentation on theme: "Waves and Particles in the Radiation Belt Kaiti Wang PSSC/NCKU March 17, 2009 Opportunity for Collaboration on ERG and SCOPE Missions & Community Input."— Presentation transcript:
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: /nature06471
Observations of Plasmaspheric Hiss [Dunckel and Helliwell, 1969] OGO-1 satellite f-t spectrograms Primary Observational Features: 1. Frequency < a few kHz 2. Peak < 1kHz 3. Ubiquitous everywhere within the plasmasphere 4. Dependence on geomagnetic activities 5. Dayside-Nightside asymmetry -> More intense at dayside 6. 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 waves 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 f ce Location: Outer radiation belt [Meredith et al, 2003] fce~9kHz since 1960’s As L increases, the frequency range of chorus emission would drop.
Chorus as a Source for Plasmaspheric Hiss [Bortnik et al., 2008] Nightside Hiss intensity is weaker L=5 Cluster II CRRES Traveling in whistler-mode 704Hz (0.1 f ce )
Illustration Earth Hiss Lightning? Local instability? Chorus It takes 40 years!!
[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 Chorus source 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 energies 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: /nature06471 Church S. R. and R. M. Thorne (1983), On the origin of plasmaspheric hiss: Ray path integrated amplification, J. Geophys. Res., 88, 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: 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: /2003GL
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: /2006JA 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, doi /2007JA 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: /j.jastp 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, Wang, K., R. M. Thorne, R. B. Horne (2008), Origin of Jovian Hiss in the extended Io torus, Geophys. Res., Lett., 35, L16105, doi: /2008GL