How Solar Flares Work H. S. Hudson SSL, UC Berkeley

SPD May 27, 2008 Academic Background Rice (1961), UC Berkeley (1966) Kinsey Anderson (PhD Minnesota 1955) John Winckler (PhD Princeton 1946) Rudolph Ladenburg (PhD Munich 1906) Wilhelm Conrad Röntgen (PhD Zurich 1869) August A.E.E. Kundt (PhD Berlin 1864) Heinrich Gustav Magnus (PhD Berlin 1827) Miscellaneous German chemists…

SPD May 27, 2008 Personal Research History I The Planned Parts PhD: X-rays, the magnetosphere (1966) UCSD postdoc: X-rays, astronomy (1968) UCSD: X-rays, the Sun, flares (1970) Infrared, the Sun, flares (1975) Infrared, the stars (1973) Optical, the stars (1975) Optical, cosmology (1976) Infrared, the Sun, not flares (1975)

SPD May 27, 2008 Personal Research History I The Planned Parts PhD: X-rays, the magnetosphere (1966) UCSD postdoc: X-rays, astronomy (1968) UCSD: X-rays, the Sun, flares (1970) Infrared, the Sun, flares (1975) Infrared, the stars (1973) Optical, the stars (1975) Optical, cosmology (1976) Infrared, the Sun, not flares (1975)

SPD May 27, 2008 Personal Research History I The Planned Parts PhD: X-rays, the magnetosphere (1966) UCSD postdoc: X-rays, astronomy (1968) UCSD: X-rays, the Sun, flares (1970) Infrared, the Sun, flares (1975) Infrared, the stars (1973) Optical, the stars (1975) Optical, cosmology (1976) Infrared, the Sun, not flares (1975)

SPD May 27, 2008 Research History II The Unplanned Parts Infrared: the solar constant ACRIM: the solar constant Yohkoh: flares and soft X-rays RHESSI: flares and hard X-rays RHESSI et al: searches for axions RHESSI: the solar radius Asteroseismology via photometry

SPD May 27, 2008 Research History II The Unplanned Parts Infrared: the solar constant ACRIM: the solar constant Yohkoh: flares and soft X-rays RHESSI: flares and hard X-rays RHESSI et al: searches for axions RHESSI: the solar radius Asteroseismology via photometry How bright is the Sun?

SPD May 27, 2008 Research History II The Unplanned Parts Infrared: the solar constant ACRIM: the solar constant Yohkoh: flares and soft X-rays RHESSI: flares and hard X-rays RHESSI et al: searches for axions RHESSI: the solar radius Asteroseismology via photometry How bright is the Sun? How round is the Sun?

SPD May 27, 2008 Research History II The Unplanned Parts Infrared: the solar constant ACRIM: the solar constant Yohkoh: flares and soft X-rays RHESSI: flares and hard X-rays RHESSI et al: searches for axions RHESSI: the solar radius Asteroseismology via photometry How bright is the Sun? How round is the Sun? Flares!

SPD May 27, 2008 More faces - kind, helpful, wise friends

SPD May 27, 2008 One last memory of Berkeley …thanks to J. Henry Primbsch and Kinsey Anderson

SPD May 27, 2008 How do solar flares work? The “stick and slip” behavior of the flare process dominates coronal variability Flares and CMEs remain theoretically ill-understood - “magnetic reconnection,” perhaps, but there are many unknowns in the physics The machinery required to explain solar flares probably has broad applications

SPD May 27, 2008 What to explain about solar flares? The “stick and slip” behavior of the flare process dominates coronal variability Flares and CMEs remain theoretically ill-understood - “magnetic reconnection,” perhaps, but there are many unknowns (note Mark Linton’s Harvey prize) The machinery required to explain solar flares probably has broad applications

SPD May 27, 2008 Three epochs of flare observation I. The 19th century, the photosphere II. Early 20th century, the chromosphere III. Late 20th century, the corona

SPD May 27, 2008 The beginning of “space weather” Flare (the A,B,C,D) Ionosphere (X-rays) Magnetosphere Carrington, 1859

SPD May 27, 2008 The Carrington flare in Greenland ice McCracken et al This single event dominates the nitrates record for a decade: SEPs are an even more extreme example of the stick-and-slip, very flat power-law flare distribution in event energy

SPD May 27, 2008 Flare movie from TRACE (171Å)

SPD May 27, 2008 Christe et al., 2008 Frequent microflares

SPD May 27, 2008 A Hinode microflare movie

SPD May 27, 2008 GONG SOHO/MDI B LOS maps  B LOS maps Sudol & Harvey (2005), X10 flare of 2003 Oct. 29 Stepwise changes in the photospheric field

SPD May 27, 2008 How do we put all these things together? Magnetic signatures Yohkoh mystery RHESSI  -rays RHESSI coronal hard X-rays RHESSI Microflares Coronal mass ejections Integral  -rays Solar energetic particles Magnetic “implosion”? X-ray jets Heliopause ENAs Magnetars!

SPD May 27, 2008 A Cartoon, of course! (

SPD May 27, 2008 The standard MHD cartoon model Schmieder, Forbes et al. 1987

SPD May 27, 2008 The standard thick-target model (e.g. Kane & Anderson ‘69, Brown ’71, Hudson’72) Coronal accelerator Coronal electron transport (generally, 1D and no treatment of plasma collective effects). Much unfinished work, yet… Bremsstrahlung HXRs and heating/excitation in a “thick target” (ie, stopping) in the chromosphere HXRs, UV, WL chromosphere electron beam

SPD May 27, 2008 Waving goodbye * to the “thick-target model” Large-scale restructuring => flare energy Large Alfvén speed in the low corona Energy transport by Alfvén-mode wave pulses, not electron beams Fletcher & Hudson 2007 * cf. RHESSI Science Nugget

SPD May 27, 2008 What have we learned about flares? The hard X-rays,  -rays, and radio waves tell us that particle acceleration is dominant The “stick and slip” flare mechanism has different physics from that of ordinary coronal heating We have found a close relationship with “coronal mass ejections” We can track the magnetic field changes as flares happen

SPD May 27, 2008 Different kinds of astrophysics “Solar cosmic rays” Neutrons In-situ measurement Energetic neutral atoms Stereoscopy Simulation

SPD May 27, 2008 Flare movie from STEREO Courtesy Sam Freeland

SPD May 27, 2008 Is the solar corona some sort of “Rosetta Stone” for plasma astrophysics? Yes, we have novel astrophysical tools Yes, the Sun is close by and bright Yes, in principle then we can apply more complete levels of plasma physics But… solar flare theory is still mostly mired in MHD and does not take proper advantage of magnetospheric concepts

SPD May 27, 2008 Alternative solar paradigms Work with G. Micela presented at Cool Stars 14 on stellar-flare analogs The solar “reconnection flare” concept is deceptive There are several other applicable forms of solar activity that should be considered

SPD May 27, 2008 Thank you!

SPD May 27, 2008