Storm-dependent Radiation Belt Dynamics

Mei-Ching FokNASA Goddard Space Flight Center, USA

Richard Horne, Nigel Meredith, Sarah GlauertBritish Antarctic Survey, UK

AOGS 5th Annual General Meeting16-20 June 2008

Busan, Korea

ST03-A008

Motivation

Taken from Reeves et al., 2003

Outline

Model the radiation belt enhancements during the storms in October 2002

Two-step acceleration processes –– What causes post-storm enhancement in the outer belt?

Real-time running of the RBE model at NASA Goddard

The Radiation Belt Environment (RBE) model Model logic Model formulation Model input/output

The Radiation Belt Environment (RBE) Model

Solar Wind, Dst, Kp data

Radiation Belt Environment Model

Energetic Electron Flux(10 keV – 6 MeV)

Magnetic Field and Electric Field Models

Plasmasphere Model

WaveDiffusion Model

Plasma Sheet Model

Radiation Belt Environment Model: The Equation

€

fs = f s t,λ i,φi,M,K( )

€

λi

: phase space density of electrons

: magnetic latitude at the ionosphere

€

φi : magnetic local time at the ionosphere

M : magnetic moment

K : longitudinal invariant

€

˙ λ i , ˙ φ i : drift velocities (convection + magnetic drift + corotation)

€

∂fs

∂t+ ˙ λ i

∂fs

∂λ i

+ ˙ φ i∂fs

∂φi

=1

E + Eo( ) E E − 2Eo( )

∂

∂EE + Eo( ) E E − 2Eo( )DEE

∂fs

∂E

⎛

⎝ ⎜

⎞

⎠ ⎟

+1

T(α o)sin2α o

∂

∂α o

T(α o)sin2α oDα oα o

∂fs

∂α o

⎛

⎝ ⎜

⎞

⎠ ⎟−

fs

0.5τ b

⎛

⎝ ⎜

⎞

⎠ ⎟losscone

€

T(α o) =1

2Ro

ds

cosαsm

sm*

∫

b: bounce period

Radial diffusion is included implicitly in the time-varying magnetic and electric fields.

Radiation Belt Environment Model: The Input

Dst, Kp: Kyoto University Geomagnetic Data Service

Shifted solar wind data: ACE or WIND satellite

Magnetic field model: T96 or T04 model

Electric field model: Weimer model

Plasmasphere model: Ober and Gallagher model

Diffusion coefficients: Horne’s PADIE code

Distribution at the outer boundary (10 RE): kappa distribution Nps(t) = [(0.02 Nsw(t-2hr) + 0.316)] sqrt(amu) cm^-3Eo(t) = 0.016 Vsw(t-2hr) - 2.4 keV

The PADIE Code: Pitch Angle and Energy Diffusion of Ions and Electrons

Electron diffusion rates for whistler mode chorus waves (wave amplitude = 100 pT)

Taken from Horne et al., 2006

CRRES Lower-band Chorus Wave Data

Provided by N. Meredith

Radiation Belt Environment Model: The Output

RBE Output: 3-dimensional Electron Flux from 10 keV to 6 MeV at all pitch angles

800 keV electrons

Magnetic Storm on 23 - 27 October 2002

RBE Simulation of the Storm on 23 - 27 October 2002

Pre-storm

Early recovery

RBE Simulation of the Storm on 23 - 27 October 2002

Pre-storm

Storm on Oct 23-27, 2002: RBE Simulations versus LANL-SOPA Data

Storm on Oct 23-27, 2002: RBE Simulations versus SAMPEX Data

SAMPEX: electrons: 2 – 6 MeV RBE–T04 with WP interactions

Storm on Oct 23-27, 2002: RBE Simulations versus SAMPEX Data

SAMPEX: electrons: 2 – 6 MeV RBE–T04 with WP interactions RBE–T04 without WP interactions

Storm on Oct 23-27, 2002: RBE Simulations versus SAMPEX Data

SAMPEX: electrons: 2 – 6 MeV RBE–T04 with WP interactions RBE–T96 with WP interactions

Two-Step Acceleration of the Outer Belt

No WP interactions With WP interactions

RBE with T04

RBE with T96

The RBE Model Running in Real Time

Real-time ACE data:Nsw, Vsw, IMF (NOAA)

Real-time Dst (Kyoto U.) and Kp (NOAA)

Radiation Belt Environment (RBE) Model

Energetic Electron Flux(updated every 15 minutes)

Real-time GOES-11(E > 0.6 MeV)

Real-time GOES-12(E > 0.6 MeV)

http://mcf.gsfc.nasa.gov/RB_nowcast/

Summary

A data-driven physical model of the radiation belt (RBE model) has been developed to understand the radiation belt dynamics and provide prediction of the radiation belt environment.

Storm on 23-27 October 2002 was simulated. We found a two-step acceleration in the outer belt:

1. Particle injection and radial transport form a seed population

2. Further energization by interacting with waves

Storms that are not able to produce seed population or wave excitation have no radiation belt enhancement.

The RBE model is running in real-time at NASA Goddard and compared with GOES data:

http://mcf.gsfc.nasa.gov/RB_nowcast