Nowcasted low energy electron fluxes for the calculations of the satellite surface charging N. Yu. Ganushkina (1, 2), O. A. Amariutei (1) (1) Finnish Meteorological Institute, Helsinki, Finland (2) University of Michigan, Ann Arbor MI, USA Special thanks for Dave Pitchford (SES) for AMC 12 CEASE electron data Special acknowledgement for the use of LANL spacecraft data to M. Thomsen and R. Friedel (LANL) Ninth European Space Weather Week, November 5 - 9, 2012, Brussels, Belgium

2 Low energy electrons in the inner magnetosphere The distribution of low energy electrons, the seed population (10 to few hundreds of keV), is critically important for radiation belt dynamics. Surface charging by electrons with < 100 keV can lead to discharges within and on the surface of the outer spacecraft layers that can cause significant damage and spacecraft anomalies. Satellite measurements cannot provide continuous measurements. With the development of the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) for low energy particles in the inner magnetosphere [Ganushkina et al., 2005, 2006, 2012], the computational view on the low energy electron fluxes important for radiation belts at L=2-10 is now feasible. This research has funding from Seventh Framework Programme of the European Union, Collaborative Project SPA , SPACECAST: “Protecting space assets from high energy particles by developing European dynamic modeling and forecasting capabilities”

3 Inner Magnetosphere Particle Transport and Acceleration Model The inner magnetosphere particle transport and acceleration model: - follows distributions of ions and electrons with arbitrary pitch angles - from the plasma sheet to the inner L-shell regions - with energies reaching up to hundreds of keVs - in time-dependent magnetic and electric fields. - distribution of particles is traced in the guiding center, or drift, approximation (motion of a charged particle as displacements of its guiding center, or the center of the circular Larmor orbit of a moving particle) In order to follow the evolution of the particle distribution function f and particle fluxes in the inner magnetosphere dependent on the position, time, energy, and pitch angle, it is necessary to specify: (1) particle distribution at initial time at the model boundary; (2) magnetic and electric fields everywhere dependent on time; (3) drift velocities; (3) all sources and losses of particles.

Electrons’ energy density initial main recovery

Time series of storm-time electron fluxes in noon-midnight meridianal plane

Page 6 16 November 2010 NSS-803 / 806 CPA Observations – Post CEASE Activation – 2 – A Less Quiet Day

Modelled event Magnetic field model: T96 (Dst, Psw, IMF By and Bz) Electric field model: Boyle (Vsw, IMF B, By, Bz) Boundary conditions: Tsyganenko and Mukai (Vsw, IMF Bz, Nsw)

daytime Event is rather quiet Flux increases are related to AE index peaks only AE peaks are low (less than 200 nT) small, isolated substorms The lower the energy, the large the flux increase First peak at midnight seen for energies starting from 11 keV No flux increases when satellite on dayside

No significant variations in models’ parameters – no changes in modeled electron fluxes

Changes in model fluxes as observed, when IMF and SW parameters vary

Energetic particle injections are important manifestations of substorm expansion phase (Arnoldy and Chan, 1969; Belian et al., 1978, 1984; Reeves et al., 1991). Electric field behaviour is important to understand how particle injections are formed: - Intense (a few mV/m) electric fields with a strong pulsed component have been detected deep in the inner magnetosphere during substorms (Sheperd et al., 1980; Aggson et al., 1983; Maynard et al., 1983, 1996; Rowland and Wygant, 1998; Tu et al., 2000); - Simulations (Birn et al., 1997; Li et al., 1998; Ganushkina et al., 2005) suggested these fields to be driving force of particle injections. Models to explain the particle injections (Li et al., 1998; Sarris et al., 2002). An earthward propagating pulse with constant velocity of westward E and corr. B. Impulsive electric fields in the Earth’s inner magnetosphere: Observations and models

Electric field pulse model Time varying fields associated with dipolarization in magnetotail, modeled as an electromagnetic pulse (Li et al., 1998; Sarris et al., 2002):  Perturbed fields propagate from tail toward the Earth;  Time-dependent Gaussian pulse with azimuthal E;  E propagates radially inward at a decreasing velocity;  decreases away from midnight. Time-dependent B from the pulse is calculated by Faraday’s law.

IMPTAM model for low energy electrons in the inner Earth’s magnetosphere Modelling of low energy electrons in the Earth’s magnetosphere: Transport of electrons from the plasma sheet to the inner regions is due to combination of large-scale convection and substorm-associated fields. To be able to model, nowcast, forecast low energy electrons introducing of substorm influence is needed. This study was done for rather quiet event. Disturbed events require accurate boundary conditions. Low energy electrons are important as seed population for electron radiation belts and spacecraft charging effects. Summary

17 Inner Magnetosphere Particle Transport and Acceleration Model (2) -Changes in distribution function f and flux calculations for ions and electrons with arbitrary pitch angles using Liouville’s theorem taking into account loss processes. - Boundary distribution: at any location from 6.6 to 10 Re - Transport of particles: -Drifts with velocities, radial and longitudinal, as sum of ExB and magnetic drifts, 1st and 2nd inv = const in time-dependent magnetic and electric fields with self-consistent magnetic field

18 Losses for ions: - charge exchange with Hydrogen from geocorona; - Coulomb interaction in dense thermal plasmas (plasmasphere); - convection outflow, particle intersects the magnetopause and flows away along magnetosheath magnetic field lines. Losses for electrons: - Coulomb collisions and loss to the atmosphere; - convection outflow, particle intersects the magnetopause and flows away along magnetosheath magnetic field lines; - scattering into the loss cone due to pitch angle diffusion. Inner Magnetosphere Particle Transport and Acceleration Model (3)

19 Next Radial diffusion is applied (Schulz and Lanzerotti, 1974) with diffusion coefficients D LL (Brautigam and Albert, 2000) And Pitch- angle diffusion by introducing electron lifetimes 1. by Chen et al. (2005) for strong diffusion and Shprits et al. (2007) for weak diffusion 2. By Gu et al. (2012) ”Parameterized lifetime of radiation belt electrons interacting with lower-band and upper-band oblique chorus waves”, submitted Inner Magnetosphere Particle Transport and Acceleration Model: Diffusion

Inner Magnetosphere Particle Transport and Acceleration Model: Electrons’ Lifetimes (1) Strong diffusion: p is the particle momentum, γ is the ratio of relativistic mass to rest mass, Bh is the magnetic field at either foot point of field line, Ψ is the magnetic flux tube volume, η =0.25 backscatter coefficient (25% of electrons that will mirror at or below 0.02 Re are scattered back to flux tube instead of precipitating into atmosphere) Weak diffusion: Bw is the local wave amplitude, E is kinetic energy in MeV