Extreme Events In The Earth’s Electron Radiation Belts Sarah A. Glauert Richard B. Horne, Nigel P. Meredith British Antarctic Survey, Cambridge, UK ESWW 14, Ostend, Belgium 29 November 2017 Image: NASA

Outline Background on the model Demonstration for an large storm Extreme CME Extreme period of fast solar wind Comparison of results with extreme event analysis

EU-FP7 project April 2014 – March 2017 Aim: To model severe space weather events and mitigate their effects on satellites by developing better mitigation guidelines, forecasting, and by experimental testing of new materials and methodologies to reduce vulnerability The research leading to these results funded in part by the European Union Seventh Framework Programme (FP7) under grant agreement No 606716 SPACESTORM

Electron Radiation Belts High energy electrons trapped by Earth’s magnetic field Two torus shaped regions: Inner belt Between 1.2 and 2 Earth radii Fairly stable Outer belt Between 3 and 7 Earth radii Highly dynamic Slot region between the two belts Flux is usually low but can be significant during strong storms The Earth’s radiation belts are regions in space where high energy electrons are trapped by the Earth’s magnetic field. Generally, under quiet conditions two belts are formed. The inner belt lies between about 1.2 and 2 Earth radii at the equator and is relatively stable. The outer belt, between about 3.5 and 7 Earth radii at the equator, is very dynamic. Between these two belt lies the slot region which is often described as having much lower electron fluxes. This is true during quiet conditions but the flux here can be significant during more active periods.

BAS Radiation Belt Model Diffusion equation for the drift averaged phase-space density Includes: Radial transport Wave-particle interactions Chorus, EMIC waves, plasmaspheric hiss, lightning-generated whistlers Loss to atmosphere and magnetopause Drivers Kp sequence Diffusion rates Solar wind pressure and IMF Bz Magnetopause location [Shue et al, 1998] We model the behaviour of the radiation belts using the BAS-RBM. This is a state-of-the-art model that has been developed at BAS over the last 5 years or so. It is based around solving a diffusion equation for the electron phase-space density. The equation is shown on the right. If equations aren’t your thing then feel free to ignore it – and I promise there won’t be any more! I’ve just put it here to illustrate the processes we include in the model. We have a term to determine the radial transport of the electrons, terms that deal with the interactions between the electrons and various electromagnetic waves that are present in space and we also account for loss of electrons to the atmosphere and magnetopause. There are many types of wave present in space; we include the effects of plasmaspheric hiss, lightning-generated whistlers, whistler mode chorus waves and electro-magnetic ion cyclotron waves. Glauert et al. [2014a, 2014b], Horne et al. [2013], Kersten et al. [2014]

Diffusion coefficients Radial diffusion Ozeke et al., [2014] Chorus Don’t have enough data for extreme conditions Used extreme value analysis Thanks to Ianto Cannon

Model boundaries 0o to 90o in pitch-angle (α) Between L*=1.5 and L*= 8 Minimum and maximum energy Energy range varies with L* Emin=100 keV, Emax = 30 MeV at L*=8 Need a boundary condition on each boundary And an initial state for the whole grid

Boundary conditions α = 0o, α = 90o ∂f/∂α = 0 Emax(L) f = 0 Outer L* boundary At L*=8 ∂f/∂L=0 Minimum energy Emin = 100 keV at L*=8 Use POES data Technique developed by Hayley Allison

20 Nov. 2003 After Halloween storm Dst = -422 nT L* >800 keV Kp >2 MeV >4MeV GOES flux (cm-1s-1sr-1) Bz Vsw (nT) (km s-1) Psw Dst (nPa) (nT) Kp Baker et al., 2004

An extreme CME What is extreme? Realistic extreme - July 2012 Magnetic field Solar wind speed Number density Dst Kp What is extreme? Realistic extreme - July 2012 Very large CME missed Earth Observed by STEREO-A Baker et al. [2013] Dst ~-470 nT Vsw > 2000 km/s Kp from Peter Wintoft (Lund) Storm phase dependent low energy boundary from POES data How would the radiation belts have responded? The other application of the model that I’m going to talk about is calculating the effects of an extreme CME. The first issue is defining the event. The Carrington event is the largest recorded event, but we don’t have enough information from the event to simulate it accurately. However, in July 2012 a very large CME left the sun. It missed the Earth but was observed by STEREO-A and those observations have been used to reproduce the solar wind and other parameters that would have been seen at Earth, had the CME come our way. Dan Baker estimated that Dst would be about -470 nT and the solar wind speed was over 2000 km/s. The panel shows the various parameters, the dotted lines are their best estimates after applying corrections. The question is, what would have happened had this CME hit the Earth?

July 2012 CME Dropout to L*=~3 L*<3 – rapid increase Recovery GEO L* Dropout to L*=~3 Magnetopause L*=~4.5 L*<3 – rapid increase Recovery Initially L*~3, later L*~4 L*<3 – slow decay

Range of results Baker et al. only has 1 day after storm Have to decide what happens next These choices affect peak fluxes MEO more at risk than GEO

Very High Speed Solar Wind Stream Super-posed epoch analysis Meredith et al., [2011] No density – No MP

Extreme case? Epoch-1 to epoch+7 days Upper quartile 2 MeV flux at GEO <103cm-1 sr-1 s-1 keV-1 0 2 4 6 Days from epoch Days from epoch

Extreme case? Maximum values Epoch-1 to epoch+7 days Upper quartile Peak flux ~ L* = 3 High flux at GEO 2 MeV flux >102 cm-2 sr-1 s-1 keV-1 Significant flux in the slot region 2 MeV flux >104 cm-2 sr-1 s-1 keV-1 Flux at GEO sensitive to MP location Activity determines decay Low activity => low wave power => slow decay Another HSS may enhance the belts Epoch-1 to epoch+7 days Upper quartile Not extreme 0 2 4 6 Days from epoch

Comparison with Meredith et al.   1 in 100 year event [Meredith et al., 2017] HSS Maximum flux CME maximum flux Energy 2.05 MeV 2 MeV L* = 4.5 5.8x102 1.4x102 - 5.8x102 5.2x102 - 9.7x102 L* = 6.0 1.6x102 5.3x10-1 - 1.8x103 19.0 - 29.0 788 keV 800 keV 9.3x103 8.1x103 - 1.3x104 7.9x103 - 1.4x104 3.0x103 1.0x102 - 3.0x103 ~1.1x103 Flux units are cm-1 sr-1 s-1 keV-1 CME Activity following storm has greatest influence on flux at GEO HSS Magnetopause location has greatest influence

Flux in MEO Good agreement between maximum model flux and extreme value analysis 800 keV flux similar for both HSS and CME CME associated with higher 2 MeV flux HSS CME

Flux near GEO CME Large dropout HSS Large variation in maximum flux depending on magnetopause location At GEO, HSS may lead to higher fluxes than a CME HSS CME

Conclusions Extreme CME Initially extreme fluxes at low L*, not at GEO Outer belt (L*>~3 )flux drop-out Slot region (L*<~3) flux increases rapidly by several orders of magnitude Peak flux at GEO depends on activity following the CME Extreme HSS Flux at GEO can be orders of magnitude higher than extreme CME Peak flux is around L* = 3 (L*=4 for CME) Slot region fluxes are again raised by several orders of magnitude Harder spectrum than CME Timescale for decay depends on geomagnetic activity Results are consistent with an extreme value analysis [Meredith et al., 2017]

Thank you

Low energy boundary Don’t have POES data for the extreme event POES data for November 2003 event Divide 2003 event into 4 phases: Pre-storm 00:00 16/11 - 00:00 20/11 Drop-out 10:30 20/11 - 23:30 20/11 Recovery 12:00 23/11 - 00:00 26/11 Post storm 00:00 28/11 - 14:00 28/11 Calculate average flux for each phase Identify corresponding phases in July 2012 event Use average flux for the phase as boundary condition