Space – based Observations Techniques, Instruments and Missions for the Sun-Earth System Len Culhane Mullard Space Scie

1. Space – based Observations Techniques, Instruments and Missions for the Sun-Earth System Len Culhane Mullard Space Science Laboratory University College London

2. Introduction • Following a brief discussion of photons and their interaction with Earth’s atmosphere, short wavelength optics and the role of CCDs are reviewed • The difficulties posed by operating in the Space environment are outlined • Several current space solar missions are described and results sumarised • The Sun-Earth connection is discussed including - solar eruptions - nature of magnetic clouds - instruments for in-situ plasma observations - solar wind and CME influence on the Earth’s Magnetosphere

3. Electromagnetic Spectrum Regions of the Spectrum Quantum nature of radiation: En = hn = hc/l • Radio/Microwave • (Frequency/Wavelength) • → THz, GHz, MHz, cm, m • Infra-red/Sub-mm (Wavelength) → mm, mm • Visible/UV/EUV (Wavelength) → Å, nm • X-ray, g-ray (Photon Energy) → eV 3

4. Radiation and Particle Interaction in the Earth’s Atmosphere Photon absorption by Earth’s atmosphere • X-rays - E > 50keV, penetrate to • ~30 km above Earth’s surface • - can measure from balloons • In practical terms need to go to • space for these wavelengths • Better observations even for the • optical band (400-1000 nm) • - avoid atmospheric turbulence

5. Telescope and Spectrometer Optical Design • Normal incidence optical systems used at IR, visible and near-UV wavelengths • EUV and X-ray photons are absorbed by trivial material thicknesses • - for normal incidence, reflectivity R ~ 10- 4 at l ~ 100 Å • - refractive index n ~ 0.995 for typical metals thus allowing Total External Reflection • - for n = 1 – d, the critical angle for external reflection is given by Cos qc=1 – d ~ √2d • - at EUV and X-ray wavelengths, qcis typically 1o to 3o → grazing incidence optics • For angles of glancing incidence, q ≤ qc, rays are reflected • Reflectivity of materials at soft X-ray/EUV wavelengths can be enhanced by the use of multilayer coatings - these operate in a similar manner to Bragg crystal diffraction 5

6. Optical Configurations for X-ray Reflection • q ≤ qCis a highly restrictive condition for optical designs • - small q value implies figuring and polishing large areas of substrate to achieve only small Aeff • For imaging, the Abbe sine condition must be obeyed • - needs at least two reflections to avoid severe coma for off-axis rays • Wolter Type I design uses successive reflections from confocal paraboloids and hyperboloids • Fields of view of ~ 1o with resolution ≥ 0.5 arc sec represent the present state of the art • Wolter II configuration involves external • reflection from the paraboloid and is used • to feed spectrometers e.g. SOHO CDS, • because of its lower beam divergence at • the focus

7. Grazing Incidence X-ray Optical System • To increase the small effective aperture at grazing incidenceWolter Type I telescopes are nested • Movie shows schematic operation of the Chandra X-ray Astronomy telescope • Radiation is absorbed at normal incidence but reflected at grazing incidence for q ≤ qc 7

8. High Z d Low Z Multilayer Coated Optics at Normal and Grazing Incidence • Multilayer coatings allow normal incidence reflectivities ≥ 30% for the range 10 nm < l < 50 nm • Multilayer operation is similar to that of a Bragg crystal spectrometer • - crystal atoms, plane spacing d, diffract X-rays (l) at glancing incidence q following Bragg’s law: nl = 2d sin q • Alternate layers of high and low Z material, with well controlled thickness, are deposited on an optical • substrate – mirror or grating, where d is the thickness of one layer pair • Photons are reflected from thin high Z layers while low Z – low absorption, layers separate the high-Z • layers by appropriate distances with much higher reflectivities possible than for a Bragg crystal • For layer boundaries, RMS roughness of0.6 nm limits • wavelengths at normal incidence to l ≥ 8 nm • At normal incidence, the bandwidth of the reflectance curve • is Dl ~ l/NLP where NLP is number of layer pairs • Increasing NLP reduces Dl and enhances Rpeak • - absorption in the layers sets an eventual limit

9. EUV Multilayer Instruments for Solar Physics SOHO EIT, TRACE, SDO AIA Hinode/EIS… EUV Imaging Spectrometer 9

10. Photon Response in Semiconductors - Charge Coupled Devices • Photon absorption with En > EBandGap will lift an electron into the conduction band and create an • electron-hole pair – intrinsic photoconduction • CCD operation uses a Metal Oxide Semiconductor (MOS) structure which acts like a capacitor • CCDs are photon detecting pixel arrays that use intrinsic photoconduction in Si • Response has been extended to En > 10 keV and they have revolutionised Astronomy • With +ve voltage on the p-type Si, majority carrier holes • are repelled and a depletion region, depth d, is swept • free of charge • Incoming photons produce electron-hole pairs and the • electrons are attracted to the insulator under the electrode + Electrode Ground Oxide Insulator e- Depletion Region d hn P-type Si • For backside illumination, physical device depth is etched • or thinned to be as close as possible to d = (2keomrsV)1/2 • For Si resistivity, r ~ 10 – 20 W cm gives d ~ 3 – 10 mm • - complex electrode structure defines pixels and enables charge transfer Ground

11. Charge Coupled Devices (CCDs) as Photon Detectors • Quantum efficiency: - percentage of photons actually detected is the Quantum Efficiency (QE) of the CCD • Wavelength range: - CCDs have a wide wavelength response from ~ 1 Å (X-ray) to ~ 10,000 Å (Infra- red) with a peak sensitivity at around 7000 Å - use of back-thinning is necessary to extend the CCD wavelength response to shorter wavelengths e.g. EUV and X-ray or l ≤ 500 Å - note that 1 Å = 10 nm and E (keV) = 12.38/l (Å) • Dynamic range: - CCD dynamic range describes the minimum and maximum number of electrons that can be imaged - with more photons incident on the CCD, more electrons are collected in the MOS potential well - when no more electrons can be accommodated in the well, the pixel is saturated. 11

12. Environmental Challenges in Orbit • Vacuum of Space - contaminants can move from one part of an instrument to another - will preferentially deposit on cold surfaces - can cause serious degradation of optical surfaces particularly at EUV wavelengths - high voltage discharge can occur if instrument is not fully evacuated • Thermal Environment - spacecraft illuminated by Sun on one side (T~6000K) and Earth (T~300K) or space (T~4K) on the other - temperature must be controlled to ~ 10 ± 5 deg C to maintain e.g. optical alignments • Ionizing radiation - electronic components susceptible to radiation damage - radiation-hard devices must be used particularly in high dose orbits - photon and particle detectors can suffer high backgrounds 12

13. Spacecraft - Solar Array Radiation Damage

14. Rocket Launching • Chemical rocket motors (liquid or solid fuel) generally employed - electrical (ion) propulsion being developed for interplanetary missions • Primary cost driver for a launch is the payload e.g. spacecraft, mass • Cost or vehicle performance envelopes will restrict spacecraft size • Instruments will suffer severe vibration and acoustic energy inputs from the rocket motors - pre-flight vibration testing is mandatory • Mechanical shocks will also be present - caused by e.g. first stage separation, rocket motor restarts 14

15. Telemetry – Spacecraft Data Transmission to Earth • Downlink data rate can be a crucial constraint for solar space observations, - limits the cadence of imaging instruments - reduces the quantity of spectral information • Initial SOHO/EIT telemetry allocation was 1 kilobits/s (1 kbps) - allowed only 6 full-disk images/day but can now operate with ~ 12 minute cadence - SOHO has a standard science telemetry rate of 40 kbs • TRACE employs several different multilayer passbands - has an on-board mass memory of 700 Gbits capacity - manage memory use to achieve partial Sun image cadence of ~30 seconds • SDO has eight multilayer image channels - uses a dedicated ground station at White Sands and transmits at 150 Mbits/s - acquires and transmits eight full-sun images every 10 seconds 15

16. Choice of Orbit • Low Earth Orbit (LEO) - 200-1200km above Earth with orbital period of 90-100 m - orbit between atmosphere and Van-Allen radiation belts - minimizes the damaging effect of high energy particles • Sun Synchronous Orbit (SSO) - special LEO case at ~ 800km with Sun always in view e.g. TRACE, Hinode • High Earth Orbit (HEO) - above the radiation belts e.g. XMM-Newton, with apogee > 30,000km - more energy and cost to launch • Geosynchronous Orbit (SSO) - same orbital period as the sidereal period of the Earth at an altitude of 42,164 km - full time contact e.g. IUE 16

17. Sun-Earth Lagrange Points • Quasi-stable orbits can be maintained around the Lagrange points with minimum energy use • L2, on the anti-sun side of earth and • at a distance of 1.5 x 106 km, allows • a spacecraft to run cold (T ~ 50 K) • and to have a relatively unconstrained • view of the Universe • L1, L4 and L5 are suitable for sun-viewing • spacecraft while L2 is useful for Astronomy • L3 is difficult due to communication problems

18. Space Missionsfor Solar Observations

19. Solar Remote Sensing • The Sun in X-rays and white light - X-ray emission from the corona is associated with photospheric activity • Access to space is essential for remote sensing observations - atmosphere absorbs X-ray and EUV emission - seeing limits visible spatial resolution to ≥ 1 arc sec for long duration observations • Spaceis also essential for long term observations of • coronal variability • Movie shows SOHO/EIT 195Å images of the corona • for the interval 10 – 23 December, 1999 • - coronal structures vary on timescales of minutes through hours to • months

20. Sun-Earth Observations • Solar phenomena influencing the near-Earth environment • - Solar Flares • - Coronal Mass Ejections (CMEs) • - Solar Wind • In a flare an unstable magnetic field relaxes to • a lower energy state with released energy • - accelerating particles • - heating plasma • - often causing a filament eruption and a CME • Accelerated high energy particles from the flare can • reach the Earth • CMEs are large outbursts of material detected by • coronagraphs with ~ 1015 g lost from the Sun • In-situ instruments sample the particles and • ejected plasma near the Earth

21. Solar Minimum pass – 1992/97 Comparison with Solar maximum pass – 1998/2003 Solar Wind Results from Ulysses Spacecraft orbit, established by gravity assist from Jupiter, allowed the first sampling of the Heliosphere out of the ecliptic plane • Near Minimum → • Average wind speed at: • high latitude ~ 700 km/s • (Polar Coronal Holes) • equator ~ 350 km/s • (Equatorial Streamers) • Abrupt transition from low to high speed ← Through Maximum Highly variable flows are observed at all heliolatitudes. Flows arise from a mixture of sources including extended polar holes, streamers, CMEs, small low latitude coronal holes

22. Advanced Composition Explorer (ACE) NASA mission to study Solar Wind and CMEs • This spacecraft is located at the Lagrange L1 point between Earth and Sun • Includes a set of nine instruments to sample the arriving Solar Wind and CME • plasma close to Earth. It measures in-situ: • - element composition and ion state • - plasma velocity • - particle energies • - magnetic field • Launched in August, 1997, • the spacecraft is still operating • and has fuel to continue at L1 • until ~ 2024

23. SOHO – cooperative project between ESA and NASA • Spacecraft is also located at the Lagrange L1 point between Earth and Sun • - 1.5 x 106 km from Earth • Includes set of 12 instruments • to study: • - Solar Interior • - Solar Atmosphere • - Extended Corona and particles • ( in-situ) • Launched in December, 1995, • the spacecraft is still • operating

24. SOHO EUV Imaging Telescope – Use of Multilayer Passbands • EIT has 4 different Mo/Si coatings with layer thicknesses tuned for 175 Å, 195 Å, 284 Å, 304 Å • to observe lines of Fe IX/X, Fe XII, Fe XV and He II • Rotatable quadrant shutter can select each of the four mirror sectors in turn • CHIANTI theoretical spectrum shown with a) 175 Å passband and b) resulting line intensities a) b) 24

25. TRACE Solar Telescope – Example of Multilayer Application • Schematic of the TRACE EUV telescope is shown below – a 0.3 m Cassegrain system • Primary and secondary mirrors are sectored in four quadrants, three with Mo2C/Si layers • Quadrant shutter allows one sector at a time to view the Corona and register images on the • CCD in the appropriate passband • Reflectivity curves are shown for two of the three quadrants – peaks at 173 Å and 195 Å • Mo2C/Si layers have enhanced performance • compared to Mo/Si

26. EUV Corona - TRACE Images • The four TRACE passbands obtain images of the • photosphere, chromosphere and corona for • 5000 K ≤ Te ≤ 4 MK • - image cadence:30s • - pixel size: 0.5 arcsec • - FoV: 8.5 arcmin x 8.5arcmin Fe IX 171 1 MK TRACE: AR Loops on 06 NOV 1999 H I Ly-a 10,000 K TRACE: AR Loops on 19 APR 2001 TRACE Cooling Loops Fe IX 171 1 MK Fe IX 171 1 MK 25

27. SOT EIS FPP XRT Japanese Hinode Spacecraft in Cooperation with US and UK • Spacecraft is in 800 km Sun-synchronous orbit • Includes set of three instruments: • - 0.5m Solar Optical Telescope (SOT) for • 150 km images and vector magnetograms • - EUV Imaging Spectrometer (EIS) for • plasma velocity, temperature and density • - X-ray Telescope (XRT) to image X-ray • emitting coronal structures • Hinode was launched in September, • 2006 • - making major advances in high resolution • structure and magnetic field studies • Instrument responsibilities: • - SOT/FPP: NAOJ, ISAS/Lockheed, HAO • - EIS: MSSL, Birmingham, RAL with US NRL • - XRT: Harvard CfA, NAOJ, ISAS 26

28. 50000km (size of Earth) Solar Optical Telescope (SOT) on Hinode Emerging Magnetic Flux Convection 27

29. Hinode SOT Observation of Prominence Dynamics • Ca II H-line observations of a hedgerow prominence on the W-limb, 30-NOV-06 (Berger, 2007) • Dark channels rise vertically at ~ 10km/s • to ~ 15 Mm above the limb • Associated bright channels show related • downflows • Suggests hot rising thermal plumes and • density enhanced turbulent downflows • Current models have low-b prominence • plasma constrained to follow B field • Observation suggests turbulent B field • motion or the presence of convection in • high-b plasma

30. Polar Coronal Activity – XRT and EIS Jet Observations + • Hinode XRT sees • constant activity in • polar Coronal Holes • - coronal jets • First observed with • Yohkoh SXT by • Shibata et al. (1995) • Flux emerging in open magnetic field structure can produce jets • Blueshift of 30 km/s above the bright point in the polar coronal hole is interpreted as a jet caused by • reconnection (Kamio et al. 2007) 29

31. XRT HeII 256 FeXV 284 Hinode XRT Image EIS spectrum (1arcsec slit width) CoronalDynamics Hinode/EIS Spectral Imaging Observations • EIS scanned a 40 arcsec • wide strip with a height of • 7 arcmin • Slot images, 40 arc sec • wide, are displayed for • lines of He II and Fe XV • Resolved spectrum taken • with a 1 arcsec slit from • a pixel near the bottom of • the slit is shown • “First Light” spectrum in • early November, 2006 Wavelength (nm) 30

32. 5 – 10 Minute Break 31

33. STEREO Mission • Solar-Terrestrial Relations Observatory • Two identical spacecraft leading and following the Earth • Launch - October, 2006 • Four instrument packages • SECCHI • PLASTIC • SWAVES • IMPACT • Goal: • Understand the origin and consequences of CMEs 32

34. SECCHI - US NRL Sun-Centered Imaging Package (COR-1, COR-2, EUVI) EUV Corona and 1.4 – 15 R White Light PLASTIC Instrument U. New Hampshire High Charge Ions IMPACT Solar Energetic Particles (SEP) U. Cal Berkeley Deployed SWAVES Radio Burst Antennae U. Paris Meudon SECCHI - UK RAL Heliospheric Imager (HI: 12 – 300 R) Deployed IMPACT Boom IMPACT Magnetometer (MAG) IMPACT Suprathermal Electron Detector (STE) IMPACT Solar Wind Electron Analyzer (SWEA) STEREO-B (Behind) Spacecraft and Instruments • Stereo-A (Ahead) has identical instrument suite • A and B spacecraft are now 150 deg apart

35. SECCHI – EUVI • EUV multilayer solar telescope - Images at Fe IX 171Å, Fe XII 195Å, Fe XIV 211Å, He II 304Å • Larger detector than EIT (2048x2048 pixels) leads to - Higher spatial resolution (1.6 arcsec vs. 2.5 arcsec) - Larger field-of-view (1.7 Rʘ vs. 1.4 Rʘ) • Higher data rate ensures higher image cadence (2.5 min vs 30 min) SECCHI – COR1 & COR2 • Two coronagraphs do a similar job to the three coronagraphs on LASCO • COR1 • - 1.1 - 3.0 Rʘ and 7.5 arcsec pixels • - Measures polarization • COR2 • - 2 - 15 Rʘ and 14 arcsec pixels • - Higher spatial resolution and time cadence than LASCO C3 34

36. STEREO Mission OrbitsTwo identical spacecraft “lead” and “lag” Earth 4 yr. 3 yr. Ahead @ +22/year 2 yr. 1 yr. Sun Sun Earth 1yr. Ahead Behind @ -22/year Earth 2yr. Behind 3 yr. 4 yr. Heliocentric Inertial Coordinates (Ecliptic Plane Projection) Geocentric Solar Ecliptic Coordinates Fixed Earth-Sun Line (Ecliptic Plane Projection)

37. STEREO Post-launch Positioning– Day 1 to Day110

38. STEREO Orbit Evolution: Day 60 to Day 790

39. STEREO Spacecraft Positions • On 5th August 2010, positions were with 150 degree separation - to see the positions at any time go to: http://stereo-ssc.nascom.nasa.gov/where/ 710 790 38

40. NASA Solar Dynamics Observatory (SDO) • SDO is the first mission to provide full-sun imaging both above and below the Sun’s surface • Includes set of three instruments: - High Resolution Imager (HRI) for precision velocity measurements and vector magnetograms - Atmospheric Imaging Array (AIA) uses 4 telescopes for high-speed EUV images of the Corona - Extreme Ultraviolet Variablity Experiment (EVE) gives well calibrated EUV irradiance measurements • SDO, launched in February, 2010, is designed to operate for 10 years - All instruments are fully operational - Generates ~ 2 Tbyte/day of data from its main instruments!

41. Recent Images from the SDO AIA Instrument • Four dual-channel telescopes of similar design • to TRACE obtain images of photosphere, • chromosphere and corona for • 5000 K ≤ Te ≤ 20 MK • - 8 images/10s; pixel size: 0.6 arcsec; • FoV: 41arcmin x 41arcmin (full Sun) • Fe XX, Fe XXIII and Fe XXIV bands • available for the high Te flare plasma SDO: AR and Filament SDO: Pre-flare AR Structures SDO: AR Loops (AIA) B-field (HMI) Blue: -ve Orange: +ve Fe IX 171 1 MK Fe IX 171 1 MK

42. Solar Orbiter – Mission to the Inner Heliosphere • ESA/NASA mission - launch ~2017 • Approach to 0.29 AU of the Sun - up to 35o above ecliptic plane • Carries remote sensing and in-situ instruments • In-situ: • - Energetic Particle Detector • - Magnetometer • - Radio and Plasma Wave detector • - Solar Wind Analyser • Remote sensing: • - Visible Imager and Magnetograph • - EUV Imager • - EUV Spectrometer • - Coronagraph • - Heliospheric Imager • - X-ray Imager 41

43. Solar Probe Plus – NASA Solar Encounter Mission • Launch 2015 or 2017 • - remains in ecliptic plane • - approach to within 0.05 AU of Sun • No forward viewing solar instruments • - emphasizes in-situ observations • - sample plasmas and dust in outer corona • In-situ instruments include • - Fast Ion and electron analyzers • - Ion Composition Analyzer • - Energetic Particle Instrument • - Magnetometer • - Plasma Wave Instrument • - Neutron/Gamma-ray Spectrometer • - Coronal Dust Detector • Also carries side-viewing Heliospheric • Imager • Observations complimentary to those • of Solar Orbiter

44. Japan’s SOLAR-C - two mission concepts under study Plan A - out-of-ecliptic magnetic field, X-ray, optical andhelioseismic observations - emphasise studies at high solar latitude - investigate meridional flow and magnetic structure inside Sun to convection zone base Plan B - high spatial resolution, throughput and cadence spectroscopic/polarimetric observations at optical, EUV and X-ray wavelengths - emphasise photosphere to corona connection - investigate solar magnetism and its role in the heating and dynamics of solar atmosphere Launch Date: Japanese fiscal year 2016(provisional) - anticipate productive joint observations with complimentary solar missions - NASA SDO (whole sun field of view) - ESA/NASA Solar Orbiter - NASA Solar Probe Plus 44

45. Sun-Earth Connection

46. Sun – Earth Connection Sun Interplanetary Medium Near-Earth Environment Flares, Coronal Mass Ejections, Energetic Particles Coronal Mass Ejection, Solar Wind Shock Ionosphere Atmosphere Radiationbelt

47. Filament Eruption and Flare – 19-May-2007 Ha movie from Kanzelhöhe Observatory STEREO – A and – B reconstruction of erupting material in He II 304 Å and Fe VIII 171 Å emission TRACE 171 Å movie – flare ribbons and eruption

48. Halo CME on 28-OCT-2003 • Halo CMEs are likely to be Earth-directed • - disturbances near Earth when ejected magnetic field is opposite to Earth’s field

49. CME-related Magnetic Clouds Near-Earth • At the Sun CMEs always involve twisted magnetic field structures or “fluxropes” • CMEs are observed in situ as transients in IP space with changes to physical parameters • stronger magnetic field (low b value) with smooth rotation indicating a twisted flux rope structure • higher density and lower temperature than the surrounding solar wind with boundary discontinuities • Spacecraft intercepting a cloud near Earth can measure its magnetic and plasma properties • - components of B give cloud magnetic Flux • - cloud model and B values yield magnetic Helicity B - Axial • Magnetic Flux is associated with a solar region • or area e.g. Active Region, Filament channel • -Φ = ∫ ∫ B. dS weber(maxwells) • MagneticHelicity H = ∫V A.B dV where A is the • vector potential with B = xA B - Azimuthal • Magnetic Helicity a globally conserved quantity • - Convection zone → Corona → IPM • In-situ measurements with magnetometers and ion analysers

50. ACE In-situ Observation of a Magnetic Cloud – 15th May, 1997 Solar Wind proton velocity step shows shock arrival Shock  Density decreases through sheath to low value in cloud Magnetic Cloud  Sheath Magnetic field shows strength increase after shock  Magnetic field direction angle shows uniform rotation inside cloud  Electron pitch angle distribution suggests bi-directional flow 