Observing the Sun from space: Highlights from Yohkoh, SOHO, TRACE, RHESSI H.S. Hudson Space Sciences Lab University of California, Berkeley
SUMMARY OF LECTURE I. Overview of the Sun 2. Observational technique 3. The solar space observatories 4. Informal access 5. Research frontiers 6. Conclusions, solved problems, new interesting questions 2
I. Overview of the Sun QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Magnetic field Yohkoh soft X-rays 3
Yohkoh SXT: The Solar Cycle 4
Solar Atmosphere Temperature and Emission Visible/IR UV/EUV 5
How smooth is the Sun? * * Rough structure <1 mas, Oblateness ~ 10 mas (Fivian et al. 2005) 6
Physical effects in transition zone Outwards through the thin layer between τ5000 = 1 and the corona involves - a drop in opacity (thick/thin) - a loss of collisionality (Maxwellian/non) - a sudden decrease of plasma beta (high/low) This structure is thus complex, dynamic, and full of waves that become shocks - confused contribution functions; 3D structure - uncertainties in magnetic-field mapping 7
De Pontieu et al. 2003 8
Distribution of coronal plasma β = Pg/PB CH G. A. Gary, Solar Phys. 203, 71 (2001) (va ~ 200 β-1/2 km/s) 9
Photosphere High Resolution Image Sunspot umbrae Granules of rising hot plasma Image from Swedish Vacuum Solar Telescope, La Palma, 24 July 2002. here comes Solar-B! 10
2. Observational technique Imaging (movie technique) - direct YSSST - synthesis YR Spectroscopy - simple Y - dispersive (e.g., stigmatic slit) SSS - non-dispersive (pulse counting) YYR Polarimetry Solar-B Y = Yohkoh S = SOHO T = TRACE R = RHESSI 11
An example of imaging and spectroscopy (HRTS rocket) QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. 12
How to multiplex data Monochromatic imaging (x, y, λ) Stigmatic slit (x, y, λ) Non-dispersive (x, y, λ) - low resolution at longer wavelengths 13
3. The recent solar space observatories Yohkoh: HXT, SXT, BCS, WBS (1991-2001) SOHO: MDI, EIT, LASCO, MDI (>1995) TRACE: UV/EUV imager (>2000) RHESSI: Rotating modulation collimators (>2002) 14
QuickTimeª and a MPEG-4 Video decompressor are needed to see this picture. QuickTimeª and a GIF decompressor are needed to see this picture. S Y T QuickTimeª and a Photo decompressor are needed to see this picture. R QuickTimeª and a GIF decompressor are needed to see this picture. 15
Some key instruments in space SXT Yohkoh HXT Yohkoh BCS Yohkoh CDS SOHO EIT SOHO LASCO SOHO MDI SOHO SUMER SOHO UVCS SOHO Imager TRACE Spectral Imager RHESSI Soft X-ray Hard X-ray X-ray spectra EUV spectra EUV images Coronagraph Visible General Flares Flares/ARs General General CMEs UV spectra Coronal UV UV/EUV HXR/γ-ray Atmosphere Corona General Flares Helioseismology, magnetography etc 16
4. Informal access Each of the four missions sponsors some form of Web journalism Yohkoh science nuggets (http://ydac.mssl.ucl.ac.uk/nuggets/) SOHO Hot Shots (http://sohowww.nascom.nasa.gov/) TRACE picture of the day (http://trace.lmsal.com/pod/tracepod.html) RHESSI science nuggets (http://sprg.ssl.berkeley.edu/~tohban/nuggets/) 17
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5. Research frontiers A single TRACE movie illustrates several discoveries from this era: - Dimming (CME/flare relationship) - Instability (loop disruption) - Macroscopic loop oscillations - Initial field contraction 23
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Case studies Case study: Longcope et al., 2005 Case study: Sudol & Harvey, 2005 Case study: Kopp et al., 2004 25
GONG SOHO/MDI db B Flare of 2003 Oct. 29 26
Flare of 2001 Aug. 25 GONG + TRACE 1600A Other examples with GOES times 27
Interpretation of field changes The line-of-sight photospheric B field changes impulsively and irreversibly during every flare The patterns of change can guide us to a more complete understanding of the coronal restructuring: Will we at last have the means to observe flux transfer in flares directly? This can done much better with vector magnetograms at rapid temporal cadence (<< 1 min) - Solar-B? SDO? ATST? FASR? 28
Example of magnetic domain structure based on photospheric fields Longcope et al. 2005 29
Flare luminosity The major solar space observatories are not the whole story Kopp et al. (2004) => Lflare ~ 102 Lx Flare luminosity has a major contribution from the impulsive phase at UV/EUV wavelengths 30
Kopp et al., 2004 31
Conclusions The four CCD-era solar space observatories have revolutionized solar physics The data are informally accessible, but are also generally in the public domain with their software New missions will follow soon: Solar-B, STEREO, SDO 32
New exciting questions Can before/after magnetograms identify magnetic reconnection in flares/cmes? Does the pre-flare corona initiate the nonthermal process? Can we obtain closure on CME mass, energy, and helicity? How do we relate the solar cycle to stellar X-ray luminosities? How do we explain HXR/γ-ray footpoint disagreements? And many more 33