Thierry Dudok de Wit University of Orléans, France Radio Monitoring of the Sun and Space Weather 1 1. Communications Satellites Natural and Physical Damage 1, 2, Man-Made 3, 4, to Spacecraft 5, 13 Anik Intelsat Debris DSCS Leasat Heat and Expand FLTSATCOM Milstar the Upper X-Ray Event AFSATCOM UFO Sudden Atmosphere Ionospheric Increased Neutral 4, 6, 2. Navstar Global Positioning System (GPS) Density and Drag 7, 8, Disturbance 9, 18 Range Errors on (LEO) Satellites 3. Defense Support Program (DSP) LF and VLF 11 Energetic Solar Optical Flare Navigation 4. Defense Meteorological Satellite Program (DMSP) and Other Low Flare Event High Energy Systems Earth Orbit (LEO) Satellites Solar Particles Polar Cap Spacecraft (CME) Absorption Event Commanding 2 5. Geostationary Operational Environmental Satellite (GOES) and Problems Other Geostationary Meteorological Satellites Spacecraft Surface 1, 2, Charging and 3, 4, 6. Tactical Warning and Attack Assessment (TW/AA) and Space Radio Burst 5, 13 Discharge Surveillance Network (SSN) Mechanical Tracking Radars Short Wave 10 Fadeout ALCOR (Kwajalein) Kaena Point Auroral Zone ALTAIR (Kwajalein) Millstone Hill Severely Degraded Antigua MMW (Kwajalein) HF Propagation at 10 Ascension NAVSPASUR High Latitudes 1, 2, Clear Pirinclik Radio Frequency 3, 4, 5, 6, Haystack TRADEX (Kwajalein) Coronal Mass Interference (Solar 7, 8, Haystack Auxiliary (HAX) Radio Noise) 10, Ejection (CME) Radar Auroral 17, 18 (Erupting Promi- 6, 7, 7. TW/AA and SSN Phased Array Radars Medium Energy Clutter, Noise, and 8, 10, nence or Disap- Particles Interference 17 pearing Filament) (Auroral Paths) Cobra Dane PARCS Eglin Pave Paws Location Errors on 2 Navstar GPS Fylingdales Thule Geomagnetic Fluctuating Total Scintillation on 8. Passive Radio Frequency (RF) Tracking Receivers Coronal Hole Electron Content Transionospheric Disturbance (TEC) Paths Signal Fade, 1, 2, 9. Ground-Based Electro-Optical Deep Space Surveillance 3, 4, (GEODSS) System and Other Optical Tracking Systems Change in Phase, 5, 6, Polarization, and 7, 8, Change in Solar Angle of Arrival 18 GEODSS - Socorro, Maui, and Diego Garcia Air Force Maui Optical Station (AMOS) Wind Velocity, Geomagnetically 14, 15 Density, and/or Induced Currents Maui Optical Tracking and Identification Facility (MOTIF) Direction 10. High Frequency (HF) Communications Systems Hazard to Exposed 12 Humans in Space HF Direction Finding 1, 2, Fixed and Relocatable OTH-B Radar Systems High Energy Single Event Upset 3, 4, (SEU), Satellite 5, 12, Galactic Particles 13, 11. Low Frequency (LF) Long Range Navigation (Loran) and Disorientation 21 Depressed Very Low Frequency (VLF) Omega Navigation Systems Maximum Usable 10 Frequencies 12. Astronauts On Board the Space Shuttle and Passengers On Internal Satellite (MUFs) Board High Altitude Aircraft (SST, U-2) 1, 2, Equatorial Charging/Damage 3, 4, Anomaly to Internal Elec- 5, 13 13. Launch Vehicles tronic Components 14. Electric Power Transmission Lines, Petroleum Pipelines, and Difficulty Unloading 4 “Dumping” Torque Telecommunications Cables Repeated Deterioration of Passage through 1, 2, 15. Precision Instruments, Manufacturing Equipment, and Computers Spacecraft Surface 3, 4, Trapped Particle Materials, Sensors 5, 13 Radiation Belts and Solar Panels 16. Magnetic Compasses, Navigation, and Survey Instruments Radar Range, (Homing Pigeons) Range Rate, and 6, 7 Direction Errors 17. Very High Frequency (VHF) Communications Systems Exposure to Geostationary Atoms (O) in the Magnetopause 19 18. Air Force Satellite Control Network (AFSCN) and Other Thermosphere Crossing (GMC) Direct Thermal Spacecraft Ground Tracking Stations Input to Low 20 Temperature (IR) 19. Satellites that Depend Upon the Earth’s Magnetic Field for Systems Reference in Spin Axis Alignment False Star Sensor Readings, Attitude 13, 21 20. Spacecraft with Passive Radiators Designed to Operate at Control Problems Temperatures Below 100 K Fluctuating 15, 16, Geomagnetic 19 21. Spacecraft that Depend Upon Star Patterns for Attitude Control Field Non-Great Circle 10 HF Propagation Severely Degraded Dashed line indicates theoretically possible, but unlikely, impact. HF Propagation on 10 Transequatorial Paths 2 Radio waves : the other side of the solar spectrum Radio waves 3 Why are radio measurements of interest for space weather ? • Radio measurements presently provide the best remote access to fast earthbound CMEs • Coronal magnetograms can be made with radio measurements in the GHz range (no other instrument can) • Radio imaging, coordinated with other observations, should allow the complete evolution of flare-CME events to be tracked But the radio observation of CMEs is still a largely unexplored territory 4 Outline • The physics behind solar radio emissions • What are the different radio signatures of the Sun ? • What aspects of radio emission are relevant for space weather ? ➜ radio imaging ➜ radio bursts ➜ triangulation ➜ interplanetary scintillation • Existing and future facilities 5 TheThe physicsphysics ofof solarsolar radioradio emissionsemissions just a brief introduction... 6 How it started • In 1942, J.S. Hey (GB), who was working on radars, noticed that inference occurred during solar flares • In 1943, J.C. Southworth (USA) started studying the Sun in the cm frequency range • After the war, a lot of veterans of the radar effort turned to radio astronomy 7 Solar radio emission : some facts • There are 3 distinct radio emission mechanisms in the solar atmosphere ➜ Thermal free-free bremsstrahlung ➜ Gyromagnetic emission ➜ Plasma emission • The spectrum in the (10 MHz - 10 GHz) range is dominated by the former two • Spectral lines play no role and most of the polarisation is affected by Faraday rotation • The emission exhibits a rich dynamics near active regions and shocks 8 Radio waves : the characteristic figures Plasma Micro waves waves 1 km 100 m 10 m 1 m 10 cm 1 cm 1 mm 100 kHz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz Not accessible from ground ThermalGyroresonancePlasma waves free-free emission bremsstrahlung (synchrotron : emission) • causedemittedcoherent by by plasma ion-electron energetic waves electrons collisionsare excited in strong by energetic magnetic fields • stronglymildlyelectron polarised polarisedbeams through nonlinear mechanisms 2 • electromagneticincreasesintensity dependswith ne ,waves ondecreases which are emittedharmonics with f at arethe absorbedlocal plasma frequency, or harmonics thereof they’re the ones that are of interest for space weather 9 A solar flare as seen at various wavelengths Microwave emission (GHz) is strongly correlated with hard X- ray emission, and to a lesser extent with EUV emission they all describe the same population of energetic electrons 10 RadioRadio imagingimaging atat highhigh frequenciesfrequencies 11 The Sun in cm wavelengths (17 GHz) Total intensity Circular polarisation only Nobeyama radioheliograph, T. Bastian activeactive regionsregions withwith strongstrong magneticmagneticpost-flarepost-flareprominencesprominences loopsloops : :(associated(associated bremmsstrahlungbremmsstrahlung withwith fieldsfields (>1500(>1500 GG inin thethe corona),corona), emittingemittingandandCMEs)CMEs) gyrosynchrotrongyrosynchrotron emittingemitting bremsstrahlungbremsstrahlung emissionemission fromfrom circularlycircularly polarisedpolarised gyrosynchrotrongyrosynchrotron emissionemission100100 keVkeV electronselectrons 12 The Sun in m wavelengths (150-300 MHz) f=164 MHz f=327 MHz EUV (EIT Fe195) 13 The Bastille-day event in m wavelengths f=164 MHz f=236 MHz f=327 MHz (Nançay radioheliograph, K.-L. Klein, 2001) 14 A CME in m wavelengths Two successive images from the LASCO coronagraph Movie from the Nançay radioheliograph @ f=164 MHz : synchrotron emission from relativistic electrons accelerated at the shock 15 Gyromagnetic emission Comparison between radio emission (from the VLA) and optical measurements (T. Bastian) In regions where the magnetic field is strong, synchrotron emission (1-30 GHz range) can be used to determine iso-B surfaces J. Lee 16 The various uses of radio emission in solar physics • The emission at higher frequencies (visible, EUV, ...) is optically thin in the corona, whereas radio emission is mostly optically thick multifrequency radio emission can be used to ‘peel away’ layers of the solar atmosphere • radio data provide an almost direct access to the temperature and/or the magnetic field. They are the key the understanding of particle acceleration. • radio emission presently provides the best technique for determining magnetic fields in the corona 17 A proxy for sunspots : the f10.7 index • For historical and practical reasons, the radio emission at 10.7 cm (3 GHz), integrated over the whole solar surface, is widely used today as an proxy for the sunspot number. sunspots f10.7 index 18 A proxy for sunspots : the f10.7 index • Almost all thermospheric and ionospheric models still use the f10.7 index as a proxy for the electromagnetic energy input from the Sun. • There have been suggestions to replace it with spectral lines from the EUV range ConclusionConclusion :: inin spacespace weather,weather, anan easilyeasily accessibleaccessible butbut empiricalempirical quantityquantity isis oftenoften preferablepreferable toto aa physicallyphysically moremore meaningfulmeaningful quantityquantity thatthat isnisn’’tt readilyreadily availableavailable 19 RadioRadio burstsbursts 20 A taxonomy of solar radio bursts TypeType IVIV :: broadbandbroadband gyro-gyro- synchrotronsynchrotron emissionemission associatedassociated