Predictions of the Solar Cycle Past and Present. D.A. Biesecker NOAA/NWS/SWPC

Transcription

1 Predictions of the Solar Cycle Past and Present D.A. Biesecker NOAA/NWS/SWPC

2 Introduction This talk takes us through the official workshops and panels that have predicted every cycle since Cycle 21. The story begins in 1979, though of course, the real history goes back further. The story hasn t ended yet!

3 The Solar Terrestrial Prediction Workshops and the Official Prediction Panels 5 Solar Terrestrial Prediction Workshops held (+1) NASA and NOAA panels held since STP: Boulder, CO - Predictions of Cycle STP: Meudon, FRANCE - Reviewed Cycle 21 Predictions 1989 Panel: NASA/NOAA - Prediction of Cycle STP: Leura, AUSTRALIA 1990 Panel: NASA/NOAA Update of Cycle STP: Ottawa, CANADA 1995 Panel: NOAA Panel - Prediction of Cycle STP: Hitachi, JAPAN 2007 Panel: NOAA - Prediction of Cycle 24

4 Starting with the 1979 Workshop Working Group on Long-Term Predictions Predictions of cycle 21 Considered error to be ±20% The cycle begins at the time of SSN minimum Sunspots of new cycle occur at least a year before minimum Sunspots of old cycle occur for as long as a year after minimum The effects of climatic change on food production and fuel use are forcing attention to long-range prediction of climate. Evidence is accumulating that long-term solar variability is an important factor affecting climate.

5 5 Prediction Categories Influence of Planetary Tidal Action! Solar cycle period related to Planetary Alignments Statistical Treatment of Past Solar Cycles! Statistical approaches! Spectral analysis techniques! Secular Cycles Phenomena During the Previous Cycle! Precursor techniques Phenomena Around Sunspot Minimum! Another set of precursor techniques Initial Progress of the New Cycle! Given yrs of data on new cycle, we can predict coming maximum

6 Planetary Tidal Action Account for 2 predictions for Cycle 21 Jose (1965) Predicted 32 Distance of Sun from solar system COM Radius of Curvature of Sun s Path The motion of the sun about the center of mass of the solar system has a periodicity Rate of change of of Sun s yrs angular The momentum sunspot about cycle COMcontains a period of (+/- 1.05) yrs Rate of change of Sun s angular momentum about Instantaneous center of curvature Sunspot Number Wood (1979) Predicted 150 The closeness of the 11.1 yr solar cycle to the yr period of Jupiter has been noted Considered Jupiter, Venus, Earth, and Mercury (mass/(distance to Sun)^3)

7 Statistical Predictions Account for 11 of 38 predictions for Cycle 21 Pure Statistics»time series of past solar activity (SSN or F10.7) possesses an internal structure»it will continue to do so Gleissberg 1971 The Sun is an oscillator Simplest Statistical Method ~80 would yrs be the average of all observed cycles Or pick all odd cycles, or pick N most recent cycles Spectral Methods Typically Fourier Analysies applied Cole 1973 to any variable one can think of Secular Cycles Gleissberg (~88 yr), Suess (210 yr), Bond (1100 yr) Hallstatt (2300 yr) Even/Odd Cycle Effect

8 Precursor Techniques Accounted for 12 of 38 predictions for Cycle 21 Includes both Phenomena During the Previous Cycle and Phenomena Around Sunspot Minimum Examples Ohl and Ohl 1979 Brown 1979 Recurrent magnetic and auroral activity over declining phase Abnormal quiet days (when the time of the daily minimum of H deviates from typical ) Skewness of time-rate-of-change of SSN Magnitude of minimum magnetic activity (and SSN) Latitude of first new cycle sunspots Magnitude of solar polar magnetic field Occurrence of long-lived away-sectors From Dikpati of IMF Assumed to be founded in dynamo theory, whereby poloidal field of cycle N is converted into toroidal field of cycle N+1

9 Initial Progress of the New Cycle Isn t this cheating? Well, it just limits the lead time. Given yrs of data on new cycle, we can predict coming maximum For example, the Area of Spots to Faculae Brown 1979

10 How did Cycle 21 Predictions Do? Solid bars - statistical methods Shaded bars precursor methods (avg = 168) Unfilled other methods Brown 1984

11 Moving along to 1984 Solar Terrestrial Prediction Workshop - Meudon At the outset, it was agreed that there have not been any startling new developments in prediction techniques over the intervening five years. So far, for cycle predictions available Ranging from 35 to Statistical Methods (89±60) 11 Secular Methods (106±30) 6 Precursor Methods (115±20) 3 Solar System Geometry

12 The First Official Prediction April 1989 Withbroe and Chappell Report of the Working Group on Prediction of Solar Activity 1) The current solar cycle may fall outside the range of previous experience. Throughout most of its early rise phase, Cycle 22 has had sunspot numbers which were higher than those in previously observed cycles 2) At the present time a physical model for the solar cycle suitable for predictive purposes does not exist. Hence, predictions of solar activity are based on numerology, not physics.

13 The First Official Prediction April 1989 Withbroe and Chappell Report of the Working Group on Prediction of Solar Activity 1) The current solar cycle may fall outside the range of previous experience. Throughout most of its early rise phase, Cycle 22 has had sunspot numbers which were higher than those in previously observed cycles 2) At the present time a physical model for the solar cycle suitable for predictive purposes does not exist. Hence, predictions of solar activity are based on numerology, not physics. The main concern at this time is drag estimates " primarily for the Hubble Space Telescope

14 The First Official Prediction Consensus Estimate! 200 Clearly based on precursor methods and on the observed rise behavior of Cycle 22

15 Later in 1989 Solar Terrestrial Prediction Workshop Leura, Australia The working group report tells us: 1) The central point of discussion was the comparison of the different prediction methods 2) The relevance of the present solar activity indices was also the subject of lively discussion I think this report serves as an example of what not to write.

16 Highlights of 1989 Reviewing the proceedings: ~10 papers on solar cycle prediction Precursors becoming more favored: R. Thompson The most highly regarded, and successful, technique for predicting the amplitude of a solar cycle before solar minimum is known as the precursor technique Thompson 1989 G. Brown We re up to 36 predictions Note, the range of predictions now extends up to 190 These higher predictions are all precursor methods

17 Oops, we better reconsider Withbroe and Chappell - redux Concern for HST re-entry prompted an April 1990 update to the 1989 official prediction Minority opinion: we are past maximum Consensus opinion: SSN! 170

18 Moving on to 1992 Solar Terrestrial Predictions Workshop Ottawa Major finding: Predictions based on geomagnetic indices or solar magnetic fields at the poles were better than those which used the statistics of sunspot numbers. Kunches 1992

19 Moving on to 1996 Solar Terrestrial Prediction Workshop Hitachi, Japan The working group report tells us: 1) Is cycle amplitude prediction a solved problem with the precursor technique? 2) Can we refine the precursor techniques for predicting the solar cycle directly from solar parameters (e.g. solar polar field) rather than using proxy indicators (e.g. geomagnetic disturbances) There are also indications that solar cycle forecasting has improved to the point of providing reasonably accurate forecasts of cycle amplitude. Gee, I guess it s all been solved!

20 The Second Official Prediction Predicting Cycle 23 NOAA panel, led by J.A. Joselyn report issued in 1997 Used 6 categories, including 2 new ones Technique Prediction Even/Odd Behavior 200 ± 35 Precursor 160 ± 20 Spectral 155 ± 25 Recent Climatology 155 ± 30 Neural Networks 140 ± 30 Climatology 115 ± 40 Consensus 160 ± 30 Cycle The scientific community should be encouraged to develop a Fundamental understanding of the solar cycle that would provide The physical rather than empirical basis for prediction methods.

21 Something new in 2004 M. Dikpati et al published a prediction for cycle 24 based on a fluxtransport model of the solar dynamo Predicted cycle 24 would be 30%-50% larger than cycle 23. Main reason being that polar fields get advected down to the shear layer at sunspot latitudes after years Flux transport by meridional flow (Dikpati, de Toma & Gilman, GRL 2006 )

22 The Third Official Prediction NOAA Panel chaired by Biesecker: report released 2007 Predictions ranged from 40 to 185 Panel No consensus yet!

23 The Cycle 24 Consensus Consensus on Solar Minimum: March, 2008 ± 6 months Solar maximum is a bit of a problem: Either 140±20 in Oct, 2011 or 90±10 in Aug, 2012 Error! 15% What s the main difference between the predictions? Big solar memory lasts yrs Heavy influence from Dikpati Small solar memory lasts 11 years Heavy influence from precursors

24 What did the panel agree on? Solar minimum will be in March, 2008 (±6 months) The SOLIS VSM has detected several new cycle bipolar magnetic regions starting in June Old cycle New cycle 3 Jan June July July 2006

25 Summary We thought we were done 10 years ago with precursors the clear winner We ve finally introduced a more physical model and it promises to throw the game wide open How long does it take the Sun to recycle the polar fields? Are we at solar minimum? Will Cycle 24 be above average or below average? I guess we have to wait and see!