2013 Radiation Belts Workshop: Comprehending, Specifying and Forecasting their Dynamics

Measurements of whistler-mode waves in the outer Van Allen belt: systematic analysis of 11 years of multicomponent data from the Cluster STAFF-SA instrument

3 Jul 2013, 10:20

20m

Island of Santorini, Greece (http://en.wikipedia.org/wiki/Santorini)

Oral Waves, Wave-Particle Interactions and Radiation Belt Dynamics Wave, Wave-Particle Interactions and RB Dynamics

Speaker

Ondrej Santolik (IAP Prague & Charles University in Prague)

Description

Whistler-mode waves in the Earth's inner magnetosphere significantly contribute to wave-particle interactions at different scales. Especially, whistler-mode chorus has been shown to play an important role in the dynamics of the outer Van Allen radiation belt. These waves are generated by nonlinear wave-particle interactions occurring in the region close to the geomagnetic equator. They are believed to transfer energy between different parts of the electron phase space distribution and thus contribute not only to the acceleration of radiation belt electrons to relativistic energies, but also to losses of electrons from the radiation belts by their precipitation into the high latitude ionosphere. Accurate description of propagation characteristics and nonlinear time-frequency structure of whistler-mode chorus is therefore important for successful modeling of the dynamics of the Van Allen radiation belts. For our analysis, we use an unprecedented database of measurements of the STAFF-SA instruments onboard the Cluster spacecraft. We separately analyze databases of all recorded data and a subset of this database including cases of banded whistler-mode emissions. We systematically determine the probability density functions of propagation characteristics of chorus. As the spacecraft orbits scan different regions of the Earth's inner magnetosphere, we build maps of these probability density functions. The results show that probability distributions of wave vector directions are often close to a Gaussian-shaped peak centered on the local magnetic field line. This result is especially significant for an important class of whistler-mode emissions of lower band chorus at higher latitudes, well outside their source region. This work receives EU support through the FP7-Space grant agreement no 284520 for the MAARBLE collaborative research project.