Engineering Models for Galactic Cosmic Rays and Solar Protons: Current Status

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1 Engineering Models for Galactic Cosmic Rays and Solar Protons: Current Status Stephen Gabriel Professor of Aeronautics and Astronautics School of Engineering Sciences University of Southampton England sbg2@soton.ac.uk

2 Outline Phenomenology : GCRs and Solar Energetic Particle Events(SEPEs) Requirements on engineering models Existing Models : GCRs SEPEs Issues and the future

3 Cosmic Rays: Origins and Acceleration Galactic Cosmic Rays Present consensus: Fermi acceleration by supernova shock- wave remnants Anomalous Cosmic Rays Thought to originate as neutral interstellar gas that drifts into the heliosphere, becomes singly-ionized near the sun and then convected to outer heliosphere where accelerated to higher energies

4 Cosmic Rays: Time Variations

5 Cosmic Rays: Propagation where

6 Cosmic Rays Energy Spectra Quiet-time energy spectra for the elements H, He, C, N and O measured at 1 AU over the solar minimum period from 1974 to 1978 (from Mewaldt et al., 1984). Note the anomalous enhancements in the lowenergy spectra of He, N and O. The data are from the Caltech and Chicago experiments on IMP-7 and IMP-8. (from Mewaldt, 1988)

7 Cosmic Rays Energy Spectra (contd)

8 Cosmic Rays - Composition

9 Solar Protons: Origins and Acceleration (1) Energetic Particle Events at the Sun Current view: Particle acceleration is caused by coronal mass ejection (CME) driven shocks in the corona and interplanetary medium

10 Solar Protons:Origins and Acceleration (2) X -ray events detected by GOES 7 spacecraft in geosynchronous orbit. The vertical lines are hour markers. The left-hand panel shows an impulsive event at about 9:00 UT (Universal Time) on May 3,1992. The right-hand panel shows a gradual event at about 15:45 UT on May 8, (From SolarGeophysical Data, Prompt Reports, Number 574-Part 1, June 1992, National Geophysical Data Center, Boulder CO.)

11 Solar Protons: Origins and Acceleration (3)

12 Solar Protons: Propagation (1) Propagation of solar energetic particles. Those propagating along the favorable path will be anisotropic at Earth. (From Shea, 1988)

13 Solar Protons: Propagation (2) Longitude distribution of propagation times of solar particles from the flare to the Earth. The various symbols indicate data from different studies. The line is added to guide the eye. (From Smart and Shea, 198,5, and Barouch et al., 1971)

14 Solar Protons: Time Variations Solar Cycle Solar cycle variation of yearly integrated fluences observed at 1 AU (From Feynman et al., 1990)

15 Solar Protons: Energy Spectra Exhibit large range both in fluence and peak flux spectra From R.A. Mewaldt et al, Solar Particle Energy Spectra during the Large Events of October-Novemeber 2003 qnd January 2005, 29th International Cosmic Ray Conference Pune (2005) 00,

16 Solar Protons: Time Variations Event Duration Proton fluxes from two major solar proton events (E > 60 MeV). Data from IMP 8 (T.P Armstrong, personal communication)

17 Solar Protons: Time Variations (cont) From R.A. Mewaldt et al, Solar Particle Energy Spectra during the Large Events of October-Novemeber 2003 qnd January 2005, 29th International Cosmic Ray Conference Pune (2005) 00,

18 Solar Protons: Composition Solar Energetic Particle Abundances From Reames, 1997

19 Annual Proton Fluence vs Sunspot Number

20 Engineering Models : Requirements For all high energy particle species(electrons, protons and heavy ions): Flux spectrum ( instantaneous) Fluence spectrum Directionality Spatial dependence At any time ( including solar cycle variations) High Velocity Coronal Mass Ejections(CMEs)

21 Important Parameters for Engineering Design Total Event Fluence Peak Flux Duration Hardness (Spectral Form) Heavy ion abundance Propagation Confidence Level/uncertainty (Design Margins)

22 GCR Models CREME 96 regarded as the most up-to-date and comprehensive model CREME96 is an update of the Cosmic Ray Effects on Micro-Electronics code, a widely-used suite of programs for creating numerical models of the ionizing-radiation environment in near-earth orbits and for evaluating radiation effects in spacecraft.

23 CREME 96 Has many significant features, including (1) improved models of the galactic cosmic ray, anomalous cosmic ray, and solar energetic particle components of the near-earth environment; (2) improved geomagnetic transmission calculations; (3) improved nuclear transport routines; (4) improved single-event upset (SEU) calculation techniques, for both proton-induced and direct-ionizationinduced SEUs; and (5) an easy-to-use graphical interface, with extensive online tutorial information.

24 Cosmic Rays: Solar Cycle Modulation CREME 96

25 SEPE models All current models are statistical/probabilistic in nature 3 most recent proton models : JPL 91 Xapsos et al Nymmik(MSU) Heavy Ion Model : Tylka : PROBABILITY DISTRIBUTIONS OF HIGH-ENERGY SOLAR- HEAVY-ION FLUXES FROM IMP-8: IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 44, NO. 6, DECEMBER 1997

26 Comparison of 3 Models Nymmik assumes that the mean event frequency is proportional to the average sunspot number while others assume that there are 7 active years of a solar cycle JPL models assume a log normal distribution, Nymmik model assumes a power law, Xapsos determines the distribution using maximum entropy ( truncated power law) JPL model only goes up to >60MeV, MSU model up to 100s of MeV

27 Comparison of 3 Models JPL model is for fluences only while MSU and Xapsos have peak flux models too Event definition appears to be different between JPL and MSU models Different data sets for all three models

28 ESP and JPL-91 comparison Sample spectra of the ESP models for a seven year mission in solar maximum conditions and confidence level 90%: total fluence model; worst case event fluence model; JPL model for the same conditions.

29 Fluence Probability Curve (1)

30 Distribution of Solar Event Fluences (1)

31 Sensitivity of fluence model to the size of the event data set Rosenqvist and Hilgers1 have shown that the current size of the event data set ( ~ 200 events) can lead to significant errors in the prediction of the fluence probability distribution function 1 Rosenqvist, L. and Hilgers, A. Sensitivity of a statistical solar proton fluence model to the size of the event data set, Geophysical Research Letters, 30, 1865, 2003

32 Geomagnetic Shielding: Simple Theory During quiet periods, Stormer Theory can be used : Assumes Earth's magnetic field is dipolar Gives cut-off rigidity, RC (minimum momentum per unit charge) for a particle arriving from a given direction to reach a given location at the Earth Useful approximation for lowest value, RCW, which is from magnetic west, is RCW = [CScos4 ] / {r2[1+ (1+ cos3 )1/2]2} earth where CS a constant, r is distance from dipole centre in radii and is magnetic latitude

33 Geomagnetic Shielding: Störmer Theory (2) Cut-off rigidity in the dipole approximation of the Earth's magnetic field for west, east, and vertical direction as a function of magnetic latitude (from Klecker, 1996)

34 Geomagnetic Shielding: Simple Theory

35 Conclusions Concentrated on existing engineering models and their inadequacies,ideally what is needed and some of the basic physics Models : Cosmic Rays: CREME 96: Uses Nymmik's semi-empirical model for solar cycle modulation based on Wolf sunspot number (includes large-scale structure of heliospheric magnetic field) Incorporates multiply-charged ACR component (above ~ 20 MeV/nucleon), from Sampex results ~ 25% error on average for solar modulation and spectra, compared to data

36 Conclusions (contd.) Geomagnetic Shielding More data analysis/modelling during active periods to understand cut-off depression/predict transmission (CRÈME 96 combined IGRF and extended Tsyganenko model) Importance of partially-ionised heavy ions (mean-ionic charge ~14 rather than 26)

37 Conclusions (contd.) Solar Protons Importance of CMEs and CME-driven shocks Currently,most generally accepted statistical models are JPL-91 ( The JPL proton fluence model : an update, Feynman et al, Journal of Atmospheric and Solar-Terrestrial Physics) and ESP(Xapsos) models.

38 Conclusions (contd.) Solar Protons New ESA model under development: Data driven models Must address user needs Better Radial Scaling needed for missions like Bepi Colombo, Solar Orbiter, Solar Dynamic Observer, Heliospheric Sentinels, STEREO, Mars missions, etc