RBSP observations: Poloidal ULF waves and drift-resonance wave particle interaction

Lei Dai, Kazue Takahashi, John Wygant, EFW team. EMFISIS and ECT(MagEIS) team.

EFW/BARREL Science team meeting, June, 2014 Minnesota

Poloidal ULF waves with intense azimuthal electric fields near equator

Large azimuthal electric fieldsnear equator: symmetric poloidal mode/fundamental mode

RBSP observations: Excitations of poloidal ULF waves through drift-resonance wave-particle interaction

Dai et al., 2013 GRL, selected by AGU as a ‘Research spotlight’.

RBSP Data

Oscillations of ion fluxes. Phase is energy dependent.

Azimuthal electric field ~10mv/m. Radial magnetic field ~3-4nT

88keV ions is in-phase and has a high coherence with the azimuthal electric fields, direct evidence of drift-resonanceAt 88keV.

Drift-resonance

N=0, drift-resonance with a symmetric (fundamental) mode

Existence of the fundamental mode are hinted from ground observations of Giant Pulsations before. [Green, 1979; Thompson and Kivelson, 2001]

Only recently have observations started to identify the fundamental (symmetric) mode of poloidal waves in space [Takahashi et al., 2011;Takahashi et al., 2013] and reveal their correspondence to Giant Pulsations on the ground [Glassmeier et al., 1999;Takahashi et al., 2011]

Identification of the fundamental mode poloidal waves

Model results of the fundamental mode poloidal mode [Cummings et al., 1969] with realistic ionosphere boundary condition.

courtesy of Kazue Takahashi

Fundamental poloidal mode

Free energy source for the wave generation

Resonant ions~ 11-12 meV/G

Particles lose energy to waves when drifting outward.

Free energy for waves=more ions “closer” than “farther out”.

What’s next

• Fundamental mode Poloidal waves as the source of Giant Pulsations on the ground.

• The occurrence rate and location dependence of Poloidal waves produced by drift/drift-bounce resonance in the inner magnetosphere.

• Drift-bounce resonance instability may accelerate relativistic-energy electrons.

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Intense poloidal ULF waves when thedst index increased at rate faster thannormal.

Resonance interaction with~ 100-200keV ions. However, This is not the core population Of ring current.

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Intense azimuthal wave electric field and radial wave magnetic fields, with some mixture of compression magnetic field component .

Resonance interaction with~ 100-200keV ions