The minimal solar activity in 2008–2009 and its implications for long‐term climate modeling

Variations in the total solar irradiance (TSI) associated with solar activity have been argued to influence the Earth's climate system, in particular when solar activity deviates from the average for a substantial period. One such example is the 17th Century Maunder Minimum during which sunspot numbers were extremely low, as Earth experienced the Little Ice Age. Estimation of the TSI during that period has relied on extrapolations of correlations with sunspot numbers or even more indirectly with modulations of galactic cosmic rays. We argue that there is a minimum state of solar magnetic activity associated with a population of relatively small magnetic bipoles which persists even when sunspots are absent, and that consequently estimates of TSI for the Little Ice Age that are based on scalings with sunspot numbers are generally too low. The minimal solar activity, which measurements show to be frequently observable between active-region decay products regardless of the phase of the sunspot cycle, was approached globally after an unusually long lull in sunspot activity in 2008–2009. Therefore, the best estimate of magnetic activity, and presumably TSI, for the least-active Maunder Minimum phases appears to be provided by direct measurement in 2008–2009. The implied marginally significant decrease in TSI during the least active phases of the Maunder Minimum by 140 to 360 ppm relative to 1996 suggests that drivers other than TSI dominate Earth's long-term climate change.

[1]  Eos Sorce,et al.  Laboratory for Atmospheric and Space Physics , 2000 .

[2]  C. J. Wolfson,et al.  The Solar Oscillations Investigation - Michelson Doppler Imager , 1995 .

[3]  C. Fröhlich,et al.  Evidence of a long-term trend in total solar irradiance , 2009 .

[4]  J. Lean Cycles and trends in solar irradiance and climate , 2010 .

[5]  S. Solanki,et al.  Reconstruction of solar spectral irradiance since the Maunder minimum , 2010 .

[6]  C. Schrijver,et al.  What Is Missing from Our Understanding of Long-Term Solar and Heliospheric Activity? , 2002 .

[7]  J. Lean,et al.  Modeling the Sun’s Magnetic Field and Irradiance since 1713 , 2005 .

[8]  P. Charbonneau,et al.  Intermittency and Phase Persistence in a Babcock-Leighton Model of the Solar Cycle , 2004 .

[9]  M. Schüssler,et al.  Modeling the Sun's open magnetic flux , 2006 .

[10]  C. Schrijver,et al.  The Properties of Small Magnetic Regions on the Solar Surface and the Implications for the Solar Dynamo(s) , 2002 .

[11]  S. Saar,et al.  Relations between the photospheric magnetic field and the emission from the outer atmospheres of cool stars. I - The solar CA II K line core emission , 1989 .

[12]  Crowley,et al.  Atmospheric science: Methane rises from wetlands , 2011, Nature.

[13]  S. Solanki,et al.  Reconstruction of solar total irradiance since 1700 from the surface magnetic flux , 2007 .

[14]  Mike Lockwood,et al.  SOLAR INFLUENCES ON CLIMATE , 2009 .

[15]  M. Giampapa,et al.  Sun-as-a-Star Spectrum Variations 1974-2006 , 2006, astro-ph/0612554.

[16]  Yang Liu,et al.  The Global Solar Magnetic Field Through a Full Sunspot Cycle: Observations and Model Results , 2008 .

[17]  C. Schrijver,et al.  Photospheric and heliospheric magnetic fields , 2003 .

[18]  Martin H. Israel,et al.  RECORD-SETTING COSMIC-RAY INTENSITIES IN 2009 AND 2010 , 2010 .

[19]  N. Sheeley,et al.  Magnetic Flux Transport on the Sun , 1989, Science.

[20]  S. Solanki,et al.  Evolution of the solar magnetic flux on time scales of years to millenia , 2009, 0911.4396.

[21]  C. Schrijver,et al.  The Dependence of Ephemeral Region Emergence on Local Flux Imbalance , 2008 .

[22]  J. Harvey,et al.  Seething Horizontal Magnetic Fields in the Quiet Solar Photosphere , 2007, astro-ph/0702415.

[23]  J. Lean,et al.  Meridional Flow and the Solar Cycle Variation of the Sun’s Open Magnetic Flux , 2002 .

[24]  D. Hathaway,et al.  Variations in the Sun’s Meridional Flow over a Solar Cycle , 2010, Science.

[25]  Douglas V. Hoyt,et al.  A discussion of plausible solar irradiance variations, 1700-1992 , 1993 .

[26]  Paul Charbonneau,et al.  Solar Magnetic Activity and Total Irradiance Since the Maunder Minimum , 2007 .

[27]  R. Cameron,et al.  SURFACE FLUX TRANSPORT MODELING FOR SOLAR CYCLES 15–21: EFFECTS OF CYCLE-DEPENDENT TILT ANGLES OF SUNSPOT GROUPS , 2010, 1006.3061.

[28]  C. Fröhlich,et al.  Total solar irradiance during the Holocene , 2009 .