Science of NASA’s Radiation Belt Storm Probes

1. Science of NASA’s Radiation Belt Storm Probes Mona Kessel, NASA HQ Contributions by Jacob Bortnik, Seth Claudepierre, Nicola Fox, Shri Kanekal, Kris Kersten, Craig Kletzing, Lou Lanzerotti, Tony Lui, Barry Mauk, Joe Mazur, Robyn Millan, Geoff Reeves, David Sibeck, Sasha Ukhorskiy, John Wygant

2. Outline • Short description of RBSP • Mission • Instruments • Early Science Endeavors of RBSP • EMFISIS • EFW • ECT • RBSPICE • RPS • Coordinated Science • BARREL • THEMIS • Theory & Modeling

3. The broad objectives of RBSP Provide understanding,ideally to the point of predictability,of how populations of relativistic electrons and penetrating ions in space form or change in response to variable inputs of energy from the Sun. • Which Physical Processes Produce Radiation Belt Enhancement Events? • What Are the Dominant Mechanisms for Relativistic Electron Loss? • How do Ring Current and other geomagnetic processes affect Radiation Belt Behavior? The instruments on the two RBSP spacecraft will measure the properties of charged particles that comprise the Earth’s radiation belts and the plasma waves that interact with them, the large-scale electric fields that transport them, and the magnetic field that guides them.

4. Sun Two spacecraft will target key radiation belt regions with variable spacing • 2 identically-instrumented spacecraft for space/time separation. • Lapping rates (4-5 laps/year) for simultaneous observations over a range of s/c separations. • 600 km perigee to 5.8 RE geocentric apogee for full radiation belts sampling. • Orbitalcadences faster than relevant magnetic storm time scales. • 2-year mission for precession to all local time positions and interaction regions. • Low inclination (10) to access allmagnetically trapped particles • Sunward spin axis for full particle pitch angle and dawn-dusk electric field sampling. • Space weather broadcast Space Weather & the White House

5. Radiation Belt Storm Probes

6. Comprehensive Particle Measurements electrons protons ion composition 1GeV 1MeV 1eV 1keV Energy Plasmasphere Ring current Radiation belts

7. Comprehensive E and B Field Measurements DC Magnetic EMFISIS FGM AC Magnetic EMFISIS SCM DC Electric EFW Perp 2D AC Electric EFW Par 1D 1kHz 1MHz Frequency 1Hz ~DC 1mHz 10Hz EFW E-fld Spectra EMIC Whistler mode Background ULF magnetosonic

8. RBSP First Science Endeavors • What issues can be resolved about whistler mode interactions and their roles in electron energization and loss in the first 3 months? • What issues can be resolved about the large scale dynamics and structure with just the first few major geomagnetic storms? • What issues can be resolved about the source, structure, and dynamics of the inner (L<2) ion and electron belts in the first 3 months?

9. Question 1 EMFISIS Science Understand correlations between various wave modes using varying separations between the two satellites. By start of normal operations (~60 days after launch) the satellites should be well separated. • What wave modes happen at both satellites as a function of separation and location? What is the spatial coherence of chorus for small separation? • What is the relationships between Chorus and hiss. Is chorus the parent wave for hiss? • Are micro-bursts on SAMPEX and BARREL correlated to chorus or other wave modes? • Does Chorus modulate with density changes? (ECT/HOPE) Contribution by Craig Kletzing Shprits et al., 2006

10. Plasmaspheric Hiss 100Hz  few kHz • Confined primarily to high density regions: plasmasphere, dayside drainage plumes. • Generation mechanism not yet understood. • At high frequency (>1kHz) and low L source could be lightning • At typical frequencies (few 100 Hz) source is likely magnetospheric Shprits et al., 2006

11. Plasmaspheric Hiss 100Hz  few kHz • Confined primarily to high density regions: plasmasphere, dayside drainage plumes. • Generation mechanism not yet understood. • At high frequency (>1kHz) and low L source could be lightning • At typical frequencies (few 100 Hz) source is likely magnetospheric Why do we care? Hiss depletes the slot region by pitch angle scattering. Shprits et al., 2006

12. Whistler mode Chorus 100Hz  5 kHz • Outside plasmasphere primarily on dawn side near equator. • Generated by electron cyclotron instability near equator in association with injected plasmasheet electrons. • Increased intensity during substorms and recovery. • Associated with microburst precipitation. Why do we care? Capable of emptying the outer belt in a day or less. Major potential mechanism for electron acceleration. Shprits et al., 2006

13. Question 1 EFW Science Explore the connection between large amplitude whistler waves and microburst precipitation. Contribution by John Wygant, Kris Kersten

14. Large Amplitude Whistler • Santolik, et al. (2003) - first report of large amplitude chorus elements • Lower band chorus (<0.5fce) wave electric fields approaching 30mV/m • Brief (<1s) increases in the flux of precipitating MeV electrons, first satellite observations by Imhof, et al. (1992). • Usually observed near dawn, but may extend from near midnight past dawn. • Most commonly observed from L~4–6. Contribution by John Wygant, Kris Kersten

15. Question 1 EFW Science Explore the connection between large amplitude whistler waves and microburst precipitation. Microburst precipitation occurrence Large Amplitude Whistler Occurrence Lorentzen et al., 2001 Cully et al., 2008 Statistically the connection is strong. Contribution by John Wygant, Kris Kersten

16. Question 2 ECT Science Why do the radiation belts respond so differently to different storms? Some geomagnetic storms can: (a) Cause dramatic radiation belt enhancement; (b) Deplete radiation belt fluxes; (c) Cause no substantial effect of flux distributions; (b) (a) (c) [Reeves et al., 2003] Contribution by Geoff Reeves

17. Question 2 ECT Science Identify the processes responsible for the precipitation and loss of relativistic and near relativistic particles, determine when and where these processes occur, and determine their relative significance. Expected Electron Distributions Quick Science Study: Comparison of theory and observations for characteristic signatures of EMIC waves Compare PSD as a function of E and PA during a dropout. 2D Energy-pitch angle diffusion model at fixed L Do observations show expected signatures? Contribution by Geoff Reeves Li et al., 2007

18. Question 2 RBSPICE Science If we have some geomagnetic storms during the first few months of RBSP operation, then we can address the following question. • How is current density from protons, helium ions, and oxygen ions compared during weak and strong geomagnetic storms? Energy density of oxygen ions can dominate that of protons during intense geomagnetic storms H+ O+ Hamilton et al., 1988 Contribution by Tony Lui

19. Question 3 RPS Science Discovery: What is the energy spectrum of the inner belt protons? Few satellites have spent significant time near the magnetic equator and at the peak intensities of the inner belt. Example of the wide variation in modeled inner belt spectra The dominant source for protons above ~50 MeV in the inner belt is the decay of albedo neutrons from galactic cosmic ray protons that collide with nuclei in the atmosphere and ionosphere (Cosmic Ray Albedo Neutron Decay, or CRAND). • Ion energy spectrum is known to extend beyond 1 GeV, but the spectral details are not well established: shape, maximum energy, time dependence • Electron spectrum unknown. How do electrons get to the inner belt? AP8 MIN: Sayer & Vette 1976; AD2005: Selesnick, Looper, & Mewaldt 2007 Contribution by Joe Mazur

20. BARREL Mission The proposed investigation will address the RBSP goal of, "differentiating among competing processes affecting precipitation and loss of radiation particles" by directly measuring precipitation during the RBSP mission. • Launch 20 balloons each in January 2013 and January 2014 from Antarctica. • BARREL will simultaneously measure precipitation over 8-10 hours of magnetic local time. • Combine the measurements of precipitation with the RBSP spacecraft measurements of waves and energetic particles. Contribution by Robyn Millan

21. Question 1 BARREL/RBSP Coordinated Science What is the loss rate due to precipitation versus magnetopause losses? Motivation: Recent results of Turner et al., 2012 (magnetopause shadowing) vs earlier results from e.g., Selesnick 2006, O’Brien 2004 (precipitation). Measurements • RBSP: measure changes in in-situ trapped electron intensity • BARREL: quantify precipitation at range of local times • THEMIS: magnetopause losses THEMIS RBSP Contribution by Robyn Millan Figure courtesy of A. Ukhorskiy

22. Question 2 THEMIS/RBSP Coordinated Science First Planned Science Campaign Science Objectives: • What are the cause(s) of dawn-dusk differences in ion fluxes during geomagnetic storms? • What role does the Kelvin-Helmholtz instability play in particle energization, transport, and loss? • What are the relative roles of EMIC waves in the dusk magnetosphere, chorus waves in the dawn magnetosphere, and hiss deep within the magnetosphere? THEMIS has 4-8-12 hours separation of the 3 satellites along the orbit. Contribution by David Sibeck

23. Question 1 Theory & Simulation/RBSP Coordinated Science Coincident observation of chorus and hiss on THEMIS • 1 inside plasmasphere, 1 outside plasmasphere • Plasma wave instruments, recording simultaneously • High resolution, correct frequency range • Correct spatial regions, day side, ~equator • Geomagnetic activity October 4th, 2008 Contribution by Jacob Bortnik

24. Chorus - Hiss Bortnik et al. [2009] • THEMIS-E: discrete chorus, 600 Hz- 3 kHz, 0.2-0.5 f/fce, y=30-60 • THEMIS-D: incoherent hiss, <2 kHz • Average spectral time-series, 1.2 – 1.6 kHz, high correlation! Wave burst mode, 64-bin FFT, 20 Hz-4 kHz, every 1s Contribution by Jacob Bortnik

25. Numerical Ray tracing Bortnik et al. [2008] • Ray trace all rays in allowable wave normal angles, Y • Y ~ -50 to -45, L=6 waves reflect toward lower L and propagate into plasmasphere • Timescale Y = -48 : • 1 s, enter plasmasphere, • 2 s, 1st EQ crossing • 3.2 s, magnetospheric reflection • 7.7 s, second EQ crossing • 20 s completely damped Contribution by Jacob Bortnik

26. Question 2 Theory & Simulation/RBSP Coordinated Science Effect of ULF waves on radiation belt electrons Measurements • ECT: measure changes in in-situ trapped electron intensity • EMFISIS: measure magnetic field (FFT to generate ULF wave power) Simulation • Global MHD (LFM) : simulate magnetospheric ULF waves driven by dynamic pressure fluctuations Theory & Modeling • Radial Diffusion : transport elecrons across drift shells Contributions by Seth Claudepierre & Sasha Ukhorskiy

27. Pressure fluctuations In High Speed Stream excite magnetosphere (Pc 5 frequency range) Kessel, 2007 Contribution by Mona Kessel

28. LFM Simulation Driving frequency 10 mHz Solar wind dynamic pressure fluctuations can drive compressional ULF waves on the dayside SW that can excite toroidal mode FLRs. Eigenfrequency Profiles Contribution by Seth Claudepierre Claudepierre, 2010

29. Non-diffusive Transport Solar Wind driven ULF waves lead to non-diffusive transport Radial transport in MHD field model dominated by drift resonant interactions, each producing large coherent displacement of the distribution. Radial transport across the outer belt can be driven by a variety of ULF waves induced by SW and ring current instabilities. Transport exhibits large deviations from radial diffusion, which may account for the observed nonlinear response of electron fluxes to geomagnetic activity: even similar storms can produce vastly different radiation levels across the belt . Contribution by Sasha Ukhorskiy Ukhorskiy 2009

30. RBSP launch Aug 23, 2012 RBSP team and the science community ready to get the data and *change* the theories.