Solar Radiation Storms and their Impact on Space Weather

1. Solar  Radiation  Storms  and  their  Impact  on  Space  Weather   Raúl Gómez-Herrero, Bernd  Heber, Robert F.  Wimmer-Schweingruber and Reinhold Müller-Mellin Institut  für  Experimentelle  und  Angewandte  Physik, Christian‐Albrechts‐Universität  Kiel, Kiel,  Germany Session 5, Nov 9, 2007 Planetary space weather

2. Space Weather • What is Space Weather?"Conditions on the Sun and in the solar wind, magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health." (U.S. National Space Weather plan) • What is the origin of the Space Weather?The ultimate origin of the space weather is (mainly) the magnetic variability of the Sun:  Eruptive phenomena (Solar flares, CMEs)   Effects in the interplanetary medium (Energetic particles, Shocks, IMF disturbances) Quiet Sun (High speed streams from Coronal Holes  CIRs) • Other sources (not solar, but affected by the Sun): Cosmic rays, interplanetary dust particles, debris, meteoroids, asteroids and comets

3. Consequences of Space Weather (in the Solar Wind) • Outside the magnetosphere, the most relevant Space Weather Effect are the Solar Radiation Storms (elevated levels of radiation that occur when the numbers of energetic particles increase) • Biological effects (ICRP, 1991) • Acute effects (Malfunctions of organs, eye cataracts, etc). Deterministic, threshold doses • Late effects (DNA damage, mutations, cancer) Stochastic, no threshold doses Accumulated dose from GCR is a serious problem for long voyage scenarios (Mars), even at solar maximum • Effects on technology (Valtonen 2005) • Surface charging (charge acc. by interaction with plasma, fields, or e.m. radiation) • Sputtering on surfaces • Contamination (e.g. by sputtering products) • Internal charging (by high energy electrons) • Single event effects (single particle strikes in spacecraft electronics) • Total ionizing damage (accumulated dose) • Displacement damage (displacement of atoms in the lattice) • Radiation induced interference and background

4. Consequences of Space Weather (in the Solar Wind) Jul 14, 2000 Nov 4, 2001 (Brekke et al, 2004)

5. Sources of energetic particles IGPP Univ. of California Riverside • Corotating Interaction Regions (CIRs) (only < 20 MeV/n ions) • Solar Energetic particle events (Flare and CME related) • Other populations of non solar origin, but strongly controlled by the large scale structure of the heliospheric magnetic field, and consequently by the solar cycle (modulation). • Galactic Cosmic Rays (GCR) • Anomalous Cosmic Rays (ACR) (only during solar minimum) • Jovian electrons These populations are also affected (locally) by transient phenomena like CMEs or CIRs (e.g. Forbush decreases)

6. Sources of energetic particles • During Solar quiet conditions, > 10 MeV proton flux is less than 1 (cm2 s sr)-1. In large SEP events it can exceed 104 (cm2 s sr)-1  severe radiation hazard to humans and onboard equipment • Composition is important because large abundances of heavy elements (Fe) can increase the dose significantly • Spectral contributions are variable but general characterization is possible: Mewaldt et al., 2001

7. Solar Energetic Particle Events • SEP events are the largest component of the interplanetary >10 MeV proton fluxes at radial distances  1 AU • Solar Energetic particle events • Impulsive (flare related) • Gradual (CME, shock related) • The separation scheme is not so clear (mixed contributions, hybrid events) • Impulsive events: • Frequently 3He andheavy elements • But, lower intensity, short duration, focused  Less severe

8. Gradual SEP Events Reames, 1999 Lopate, 2001 • Associated to fast CMEs driving IP shocks • P, He are more than 99% of the particle flux. • Composition, charge states similar to the ambient Corona • Energy spectra normally follow power laws with an exponential roll-over (Ellison and Ramaty,1985): I = I0 E exp (-E/E0) • The location of the “knee” is important for the dose: • 100 MeV protons require 10 g cm-2 shielding = 3.8 cm aluminium • 300 MeV protons require 66 g cm-2 shielding = 24 cm aluminium • Extreme events (Sept 1989) can produce doses ~4 cSv/h behind 10 g cm-2 of shielding  annual dose limit for astronauts (25 cSv) would be accumulated in 6-7 h  They are the most significant for Space Weather

9. Maximum Flux - Streaming limited intensities • “Streaming limit”: protons streaming away from a shock, generate Alfvén waves which scatter protons coming behind. (Reames and Ng, 1998) • Exact values depend on transport conditions. Some events do not follow the streaming limit

10. Intensity scaling for SEP events Vainio, 2006 • Characterization of the dependence of fluences and peak fluxes during SEP events with heliolongitude and radial distance are important for future missions • The angular separation between the observer footpoint and the source active region is a key parameter for the time profiles • Intensity dependence: exp (-k(-0)2), k[1.0,1.3] rad -2(Lario et al, 2006) • Asymmetric angular distribution shifted to the east (0<0) • Radial dependences weaker than R-2 within 1 AU

11. SEP Events - Forecasting • The occurrence rate is related to the solar cycle, but short term forecasting is difficult: • Occurrence of CMEs and flares are difficult to predict from precursor signatures (e.g. sigmoids and CMEs) • Prediction of the ICME/shock transit time to 1 AU and the importance of the possible ESP spike is also complicated • However, correlations between SEP intensities and CME properties can be found (e.g. power law dependence between peak flux and projected CME velocity from coronograph images, Reames, 2000) • SEP flux increases very quickly to high levels after the e.m. emissions from the flare/CME (minutes, hours) • New forecasting techniques using relativistic electrons as predictors for ion intensity profile (>20 min anticipation alert) Posner, 2007

12. SEP Events - Forecasting • Long term fluences forecasting for mission planning is based on probabilistic models (e.g. Feynman et al, 1993, Xapsos et al, 1998, Nymmik 2004) • Better understanding of the physical processes governing particle acceleration and propagation during SEP events is essential to improve forecasting quality: • Acceleration and Injection processes near the Sun • Timing: particle onset times vs. flare onset and CME lift-off times • SEP Interplanetary transport (diffusive models) • Interplanetary propagation of disturbances (ICMEs and shocks)

13. Conclusions • Outside the Magnetosphere the most important contribution to Space Weather is the energetic particle radiation • During the last years a numerous spacecraft fleet offered accurate In-situ and remote-sensing measurements of plasma, fields, particles and e.m. emissions. The SEP events of solar cycle 23 were the best observed in history • The most severe Solar Radiation Storms are caused by large streaming-limited Gradual SEP events showing also ESP spikes. They are the main contribution to the total fluence • The ICME-shock geometry organizes the spatial distribution of intensities during the events • Forecasting models and tools become progressively more reliable. However, better knowledge about Physics behind Space Weather is needed (acceleration, propagation). CMEs and flares can not be predicted yet. • More observation points and new technologies are required to attain a wider spatial coverage and better data quality (resolution, time cadence, background,…) • New missions will help to achieve these goals (SDO, Sentinels, Solar Orbiter, IBEX, Solar Probe, Swarm, Geostorm,…)

14. Conclusions • Outside the Magnetosphere the most important contribution to Space Weather is the energetic particle radiation • During the last years a numerous spacecraft fleet offered accurate In-situ and remote-sensing measurements of plasma, fields, particles and e.m. emissions. The SEP events of solar cycle 23 were the best observed in history • The most severe Solar Radiation Storms are caused by large streaming-limited Gradual SEP events showing also ESP spikes. They are the main contribution to the total fluence • The ICME-shock geometry organizes the spatial distribution of intensities during the events • Forecasting models and tools become progressively more reliable. However, better knowledge about Physics behind Space Weather is needed (acceleration, propagation). CMEs and flares can not be predicted yet. • More observation points and new technologies are required to attain a wider spatial coverage and better data quality (resolution, time cadence, background,…) • New missions will help to achieve these goals (SDO, Sentinels, Solar Orbiter, IBEX, Solar Probe, Swarm, Geostorm,…) 'My God, space is radioactive!' Ernie Ray, 1958 (member of Van Allen's Explorer I team)

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17. SEP Events

18. Intensity scaling for SEP events • The dominant parameter is the longitudinal distance between the magnetic footpoint of the spacecraft and the site of the associated solar flare, rather than the heliocentric radial distance of the observer (Lario et al, 2006): • The decrease of peak intensities and fluences with the angular distance between the flare site and the observer’s magnetic footpoint can be approx. by: exp (-k(-0)2), with k[1.0,1.3] rad -2 • Angular distributions of peak intensities and fluences are not symmetric around the longitude of the observer’s footpoint but shifted toward eastern longitudes • Radial dependences Rn are weaker than those usually recommended (R-2) to extrapolate particle intensities to distances R < 1 AU  The use of the previously suggested radial dependences may overestimate the values extrapolated from near-Earth observations to distances R <1 AU

19. Space storms (NOAA Space Weather Scales) • Radio blackouts (soft X-ray flux) • direct effect of flares on the diurnal side of the ionosphere • HF Radio: HF radio communication blackout • Navigation: Outages of low-frequency navigation signals • Geomagnetic storms (Kp index) • large dynamical changes in the geomagnetic field leading, e.g., to intensified manetospheric electron fluxes • Spacecraft operations: extensive surface charging, problems with orientation, uplink/downlink and tracking satellites • Power systems: voltage control and protective system problems, grid systems collapses or blackouts. Transformer damage. • Other systems: induced pipeline currents, HF radio propagation sporadic, satellite navigation degraded, aurora seen at low latitudes • Solar radiation storms (>10-MeV proton flux) • radiation effects due to solar energetic particle events • Biological: unavoidable radiation hazard to astronauts on EVA; passengers and crew in high-flying aircraft at high latitudes exposed to radiation risk • Satellite operations: memory device problems, noise on imaging systems; star-tracker problems; solar panel efficiency degraded • Ionization effects: blackout of HF radio communications possible • (Vainio, SWW3 2006)

20. NOAA Space Weather Scale for Radiation Storms

21. Multi-spacecraft observations • A numerous fleet of spacecraft offers better observational coverage than ever before: ACE, Cluster, Fast, Geotail, Hinode, Polar, RHESSI, SOHO, STEREO, THEMIS, TIMED, TRACE, Ulysses, Voyager, Wind (Up to recently also: SAMPEX, IMP-8, Yohkoh,…) • In-situ and remote-sensing instruments onboard these spacecraft offer accurate measurements of plasma, fields, particles and e.m. emissions. The SEP events of solar cycle 23 were the best observed in history • But more observation points are required to attain a wider spatial coverage (in radial distance, heliolongitude and heliolatitude). • New technologies will improve also the data quality (resolution, time cadence, background,…), allowing better knowledge of the physics behind SEP events in different temporal and spatial scales. • These goals will be achieved by new missions during the upcoming years: SDO, Sentinels, Solar Orbiter, IBEX, Solar Probe, Swarm, BepiColombo, Geostorm,…