Solar Cycle Update Dr David H Hathaway NASANSSTC

Solar Cycle Update Dr. David H. Hathaway NASA/NSSTC Huntsville Hamfest 2007 August 18

Outline • • • Significance of the Solar Cycle Characteristics of the Sunspot Cycle Characteristics of the Magnetic Cycle Predictions for Solar Cycle 24 Conclusions

Significance of the Solar Cycle

Solar Activity: The Bastille Day Event Solar activity (including: flares, prominence eruptions, coronal mass ejections, solar energetic particle events, and high-speed solar wind streams from coronal holes) varies in frequency with the solar cycle.

A Prominence Eruption

Coronal Mass Ejections

From the Sun to the Earth

Solar Activity Affects…

Effects of Solar Activity: On Satellites Radiation (protons, electrons, alpha particles) from solar flares and coronal mass ejections can damage electronics on satellites. Heating of the Earth’s upper atmosphere increases satellite drag. • 1991 GOES • 1995 Deutsche Telekom • 1996 Telesat Canada • 1997 Telstar 401 • 2000/07/14 ASCA • 2003 Mars Odyssey • 4500 spacecraft anomalies over last 25 years

Effects of Solar Activity: On Power Grids Solar disturbances shake the Earth’s magnetic field. This sets up huge electrical currents in power lines and pipe lines. The solar storm of March 13 th 1989 fried a $10 M transformer in NJ. The same storm interrupted power to the province of Quebec for 6 days.

Effects of Solar Activity: On Radio Wave Propagation Variations in ionizing radiation (UV, EUV, X-rays) from the Sun alter the ionosphere – changing the Maximum Usable Frequency for high frequency radio communications and altering position information for GPS systems.

Effects of Solar Activity: On Airline Operations HF Communication only • Polar flights departing from North America use VHF (30 -300 MHz) comm or Satcom with Canadian ATCs and Arctic Radio. • Flights rely on HF (3 – 30 MHz) communication inside the 82 degree circle. • Growth: Airlines operating China-US routes goes from 4 to 6 and then number of weekly flights goes from 54 to 249 over the next 6 -years.

Effects of Solar Activity: On Climate? Yearly Sunspot Numbers and Reconstructed Northern Hemisphere Temperature (Mann, Bradley & Hughes Nature 392, 779787, 1998) smoothed with an 11 -year FWHM tapered Gaussian and trimmed to valid smoothed data. The correlation coefficient from the overlapping period is 0. 78.

Characteristics of the Sunspot Cycle

Sunspot Number and Solar Activity Sunspot number is well correlated with solar activity. The 400 year length of the sunspot number record helps to characterize the solar cycle. The connection with cosmic rays leaves even longer records of solar activity in tree rings (14 C) and ice cores (10 Be). Sunspot Area Total Irradiance 10. 7 cm Radio Flux GOES X-Ray Flares Geomagnetic aa index Climax Cosmic-Ray Flux

The 11 -year Sunspot or Wolf Cycle [Schwabe, 1844] Heinrich Schwabe, a Swiss apothecary, reported a cycle of about 10 years length in the number of sunspot groups and spotless days from 18 years of his own observations. Rudolf Wolf then initiated daily counts of sunspots and attempted to extend the count back to 1749.

The Shape of the Solar Cycle The sunspot cycles are asymmetric in shape with rapid rises to maximum and slower declines to minimum. Bigger cycles take less time to reach maximum than do smaller cycles (The Waldmeier Effect). Cycle periods have been normally distributed about a mean of about 131 months.

Sunspot Latitude Drift – Spoerer’s Law [Carrington, 1858] Sunspots appear in two bands on either side of the equator. These bands spread in latitude and migrate toward the equator as the cycle progresses. Cycles often overlap at minimum.

The Maunder Minimum [Maunder, 1894] Sunspot cycles vary widely in amplitude with occasional periods of inactivity like the Maunder Minimum (1645 -1715). Dalton Minimum

Multi-Cycle Variability After removing the secular trend, there is little evidence for any significant periodic behavior with periods of 2 -cycles (Gnevyshev. Ohl) or 3 -cycles (Ahluwalia), and only weak evidence for variability over 7 - to 10 -cycles (Gleissberg).

Short-Term Variability A number of short-term periodicities have been reported for solar activity. In most, if not all cases, the period and the phase of the oscillations vary with time. Empirical Mode Decomposition Monthly sunspot numbers 20 21 22 Decadal time scale variations (The solar cycle) Bi-annual/Annual time scale variations (Double peaks for some cycles depending on phase) Annual/Semi-annual time scale variations (152 d periodicity from 1980 to mid-1983) Monthly time scale variations (Largely noise)

Hemispheric Differences The hemispheres display distinct asymmetries (North - South) that are evident in a variety of indicators. Yet, both hemispheres are more-or-less locked in phase.

Magnetic Cycle Characteristics

Solar Magnetism

Active Region Tilt: Joy’s Law [Hale et al. , 1919] Active regions (sunspot groups) are tilted so that the following polarity spots are slightly poleward of the preceding polarity spots. This tilt increases with latitude. Howard (1991)

Hale’s Polarity Law [Hale et al. , 1919] The polarity of the preceding spots in the northern hemisphere is opposite to the polarity of the preceding spots in the southern hemisphere. The polarities reverse from one cycle to the next. Cycle 23 Cycle 22 2000/06/26 1989/08/02

The Sun’s Magnetic Cycle Magnetic field erupts through the surface as tilted bipoles in two bands on either side of the equator. Individual regions decay by spreading out over the surface. Remnant magnetic elements are sheared apart by differential rotation and carried poleward by a meridional flow.

Polar Field Reversals [Babcock, 1959] The polarity of the polar magnetic fields reverses at about the time of the solar activity maximum.

Dikpati & Charbonneau Dynamo This is a 2 D kinematic dynamo which uses the observed internal differential rotation, a realistic meridional circulation, a reasonable diffusivity, and a parameterized α-effect. It produces a reversing magnetic field configuration with a 22 -year period an equatorward propagation of active zones. In/CCW Out/CW

Solar Cycle Predictions

A Dynamo Prediction Dikpati, de Toma & Gilman (2006) have fed sunspot areas and positions into their numerical model for the Sun’s dynamo and reproduced the amplitudes of the last eight cycles with unprecedented accuracy (RMS error < 10). Recent results for each hemisphere shows similar accuracy. Cycle 24 Prediction ~ 160 ± 15

Precursor Predictions Precursor techniques use aspects of the Sun and solar activity prior to the start of a cycle to predict the size of the next cycle. The two leading contenders are: 1) geomagnetic activity from high-speed solar wind streams prior to cycle minimum and 2) polar field strength near cycle minimum. Geomagnetic Prediction ~ 160 ± 25 (Hathaway & Wilson 2006) Polar Field Prediction ~ 75 ± 8 (Svalgaard, Cliver, Kamide 2005)

Other Amplitude Indicators Hathaway’s Law: Big cycles start early and leave behind a short period cycle with a high minimum. Amplitude-Period Effect: Large amplitude cycles are preceded by short period cycles (currently at 130 months → average amplitude) Amplitude-Minimum Effect: Large amplitude cycles are preceded by high minimum values (currently at 12. 6 → average amplitude)

Minimum Timing – Spotless Days without sunspots are an indicator of approaching sunspot cycle minimum. The first day without spots typically occurs about 40 months before minimum (currently 43 months ago). The first month with 10 or more spotless days typically occurs about 18 months before minimum (currently 18 months ago). The first month with 20 or more spotless days typically occurs about 6 months before minimum (currently 4 months ago).

Minimum Timing – New Cycle Spots Minimum occurs when the number (increasing) of new cycle spots become greater than the number (decreasing) of old cycle spots. We can differentiate between new and old cycle spots by their latitude positions (old at low latitudes, new at high latitudes) and magnetic polarities (opposite). The first new cycle spot typically appears about 20 months before minimum (current candidate was 9 months ago). The second new cycle spot typically appears 10 months before.

Cycle 24 Predictions Based on the appearance of the remains of a new cycle spot at 33°N in late November 2006 and the number of spotless days, we expect to go through minimum in the spring of 2008. A large cycle (sunspot number ~ 160) would then peak in late 2011 while a small cycle (sunspot number ~ 75) would peak in late 2012.

Conclusions • The solar cycle displays numerous significant characteristics which should be reproduced by dynamo models. • Explicit Dynamo modeling predicts a larger than average and late starting cycle 24 (sunspot number ~ 160). • Geomagnetic precursor activity also indicates a much larger than average cycle 24 (sunspot number ~ 160). • Polar field strength indicates a smaller than average cycle 24 (sunspot number ~ 75). • The late start for cycle 24 is typical of smaller cycles. See: http: //solarscience. msfc. nasa. gov/