Forecasting the high-energy electron fluxthroughout the radiation belts

Sarah Glauert

British Antarctic Survey, Cambridge, UK

SPACECAST stakeholders meeting, BAS, 7 February 2014

Electron Radiation Belts

• High energy electrons (E>500 keV) are trapped by Earth’s magnetic field

• Form two torus shaped regions around earth– Inner belt 1.2 < L < 2 Fairly stable– Outer belt 3 < L < 7 Highly dynamic

• Slot region lies between the two belts– During active conditions the flux in this region can be significant

(>103 cm-2 s-1 sr-1 keV-1 for 1 MeV electrons)

Motion of trapped electrons

An electron’s motion is constrained by the magnetic field

3 parts:• Orbiting round the field line• Bouncing along the field line • Drifting between field lines

Modelling uses a coordinate system related to magnetic field:• L (L*) is the distance from the centre of the Earth to the equatorial crossing of

the field line measured in Earth radii

A few minutes in the life of an MeV electron

ChorusHiss

EMIC

Electron drift path

Magnetopause

Magnetic field fluctuations driven by ULF waves

Loss and acceleration

Loss

Loss

Loss

Everything is location, geomagnetic activity and energy dependent

chorus waves

plasmapause

• Chorus - outside the plasmapause

Chorus and HissFr

eque

ncy

(kH

z)

Time

hiss

• Hiss – inside the plasmapause

Radiation Belt Models

• SPACECAST has 2 radiation belt models:• BAS Radiation Belt Model• Salammbô – ONERA

• Developed independently• Calculate the high-energy electron flux throughout radiation belt

• Include the effects of • Radial transport• Interactions between electrons and electromagnetic waves• Collisions between electrons and the atmosphere

• Models have been adapted for use in forecasting • Models have been improved during the project

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Ef

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LEE

Radiation Belt Models

Equation used in modelling (don’t panic!):

• Includes the physical processes present in the radiation belts• Many parameters describe the different processes

– Using correct values for these parameters is crucial

ELJ

LL fDg

gLf

LD

LL

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12

2

Describing the waves• A good description of the interaction between the waves and the

electrons is vital for accurate modelling• Build global maps of the wave properties• Use these to determine parameters in the models

Intensity of the waves

Increasing geomagnetic activity

Earth

CRRES data

Just radial transport

Radial transport and hiss

Radial transport, hiss and chorus

Role of the different processes

510 keV electrons

Simulation with radial diffusion, hiss and chorus

GPS Galileo

Slot region

CRRES data Data

Model

High-energy electron forecasts - 1

• Detailed forecast of flux– Simulation of last 24 hours– Forecast of next 3 hours

• Various energies available– 300, 800, 2000 keV– >100, >300, >800, >2000 keV

• Solar wind parameters and magnetic indices also shown

High-energy electron forecasts - 2

• 24 hour fluence >2MeV electrons• Related to internal charging• Produced for GEO, MEO and slot region

Validation• GOES flux for >800 keV and >2MeV electrons

– Comparison with GOES data shown for each forecast– Geostationary orbit only

• CRRES data– Data from across whole outer radiation belt– See what the models would have predicted and compare– Less than 2 years data from 1990-1991

• Galileo data (SREM instrument on Giove-B)– Counts not flux so comparison is difficult

• Van Allen Probes– Great data set for future work

We need more data

Summary of developments in SPACECAST

• Research models have been developed into forecasting models– Forecast 3 hours ahead every

hour

• Forecasts available on the web www.fp7-spacecast.eu– Variety of formats

• Models have improved but there is still more work to do

Questions

1. What information would be useful that we don’t currently provide?

2. We show flux at geo because we have GOES data for comparisona) We can calculate flux along other orbits – which?b) Would the flux, fluence or risk at particular satellites be useful?

3. Risk indicesa) Are these useful? b) Are we using the right measurement and thresholds?c) Would you be interested in customising these?

4. We can simulate periods in the past and calculate the flux/fluence encountered by a satellitea) Would anyone use this for post-event analysis?

High-energy electron risk index

Based on the 24 hour electron fluence (F) for >2MeV electrons Electron fluence: electron flux integrated over 24 hours (cm-2 sr-1)

The risk index is set according to :High F > 5x108 electrons cm-2 sr-1

Medium 5x107 ≤ F ≤ 5x108 electrons cm-2 sr-1

 Low F < 5x107 electrons cm-2 sr-1

 Threshold values above which internal charging occurred on particular satellites at geosynchronous orbit [Wrenn et al., 2002].

Wrenn, G. L., D. J. Rodgers, and K. A. Ryden (2002), A solar cycle of spacecraft anomalies due to internal charging, Ann Geophys., 20, 953–956.

 

High-energy electron forecasts - 2

• 24 hour fluence >2MeV electrons

• Related to internal charging

• Produced for GEO, MEO and slot region

Still too much information?

High risk

Low risk

High-energy electron forecasts - 3

Based on the 24 hour electron fluence (F) for >2MeV electrons: High F > 5x108 electrons cm-2 sr-1

Medium 5x107 ≤ F ≤ 5x108 electrons cm-2 sr-1

  Low F < 5x107 electrons cm-2 sr-1

 [Wrenn et al., 2002].

High-energy electron radiation belt forecast models

(Work package 401)

• Background• Physical processes in the radiation belts• Radiation Belt models• Forecasting the high-energy electron radiation belts• Validation• Progress made in SPACECAST