Long-Term Space Weather and Terrestrial Climate. David H. Hathaway NASA/MSFC National Space Science and Technology Center Huntsville, AL 2004 December 17. Outline. Space Weather – What is it? Sunspots and the Sunspot Cycle Long Term Changes in Space Weather
David H. Hathaway
National Space Science and Technology Center
2004 December 17
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.
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 13th 1989 fried a $10M transformer in NJ. The same storm interrupted power to the province of Quebec for 6 days.
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.
International Sunspot Number – devised by Rudolf Wolf in the 1850s
(1749-Present but incomplete before 1850)
SSN = 10 G + N
(G = # of Groups, N = # of spots)
Group Sunspot Number – devised by Hoyt and Schatten in the 1990s
(1610-Present more complete than Wolf’s sunspot number)
GSSN = 12.08 G
Sunspot numbers are also generated by NOAA in Boulder, CO and by
the American Association of Variable Star Observers
Cycle periods are normally distributed with a mean period of 131 months and a standard deviation of 14 months.
Sunspot number is well correlated with other measures of solar activity. The long record of sunspot numbers helps to characterize the solar cycle.
10.7cm Radio Flux
GOES X-Ray Flares
Geomagnetic aa index
Climax Cosmic-Ray Flux
The sunspot cycles are asymmetric – the time to rise to maximum is less than the time to fall to minimum. Furthermore, large cycles take less time to reach maximum than do small cycles.
The amplitude of a cycle is anti-correlated to the period of the previous cycle. Large cycles follow short cycles.
The amplitude of a cycle is correlated with the size of the minimum that precedes the cycle.
Big cycles start early and grow fast. This directly produces the Waldmeier Effect. By doing so they cut short the previous cycle (Amplitude-Period Effect) and produce a higher minimum due to the overlap (Amplitude-Minimum Effect).
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.
Sunspots appear in two bands on either side of the equator. These bands spread in latitude and then migrate toward the equator as the cycle progresses. Cycles often overlap around the time of minimum.
This movie shows the equatorward drift of the active regions and Hale’s polarity law. It also reveals the differential rotation (faster at the equator, slower at high latitudes) and poleward meridional flow.
The polarity of the polar magnetic fields reverses at about the time of the solar activity maximum.
Active regions are tilted so that the following polarity spots are slightly poleward of the preceding polarity spots. This tilt increases with latitude.
Howard, R.F., Solar Phys. 136, 251-262 (1991)
Helioseismology finds a rapidly rotating equator with radial shear in layers at the top and bottom of the convection zone along with a poleward meridional flow in the outer convection zone.
Dynamo models that incorporate a deep meridional flow to transport magnetic flux toward the equator at the base of the convection zone appear promising. The current cycle period and the strength of the N+2 cycle are inversely proportional to the meridional flow speed.
Dikpati and Charbonneau, ApJ 518, 508-520, 1999
Per ~ V-1α-1/7η1/4
We examined the latitude drift of the sunspot zones by first separating the cycles where they overlap at minimum.
We then calculated the centroid position of the daily sunspot area averaged over solar rotations for each hemisphere.
[Hathaway, Nandy, Wilson, & Reichmann, ApJ 589. 665-670 2003 & ApJ 602, 543-543 2004]
The drift rate in each hemisphere and for each cycle (with one exception) slows as the activity approaches the equator. This behavior is expected from dynamo models with deep meridional flow.
The sunspot cycle period is anti-correlated with the drift velocity at cycle maximum. The faster the drift rate the shorter the period. This is also expected from dynamo models with deep meridional flow.
The drift velocity at cycle maximum is positively correlated with the amplitude of the second following (N+2) cycle. This is contrary to the prediction by dynamo models with deep meridional flow but it does provide a prediction for the amplitudes of future cycles.
The Group Sunspot Number of Hoyt and Schatten closely follows the International Sunspot number as well as other indicators of solar activity. It has the advantage of extending back in time through the Maunder Minimum to 1610.
The Group Sunspot Number shows a significant secular increase in cycle amplitude since the Maunder Minimum.
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) There is some evidence for periodic behavior with a period of about 9-cycles (Gleissberg).
The Radio Isotope Story
The complex magnetic structures in the solar wind at the time of solar activity maximum scatter galactic cosmic rays out of the solar system. This decreases the production of radio isotopes such as 14C and 10Be. (The strongest anti-correlation is obtained with an 8-month time lag – the time it takes for the solar wind to travel ~ 60 AU.)
14C activity in reservoir
Carbon fraction in reservoir
Earth magnetic field
Solar wind magnetic field
Atmosphere & Biosphere
Geo/heliomagnetic modulation of 14C production rate
14N 14C, 14CO2 (T½ : 5730 yr)
t 7 yrs
Ocean mixed layer
Diffusive deep ocean
95%14C pre-industrial distribution
Slide Source: Bernd Kromer
Stuiver et al, The Holocene, 1993
Through the Maunder Minimum
The solar cycle continued (without spots) through the Maunder Minimum but with a longer period (Δ14C results).
Solanki et al., Nature 431 1084-1087 (2004) have reconstructed the sunspot number over the last 11,400 years using 14C data. Comparisons with the observed Group Sunspot Numbers (GSN) and sunspot numbers reconstructed from 10Be ice core data show good agreement. They conclude that the high levels of solar activity seen in the last 60 years have not been seen for 8000 years. (Note, however, that this high level of activity is seen only in actual sunspot number.)
Independent reconstructions of Sunspot Number (Solanki et al. 2004) and Interplanetary Magnetic Field (Caballero-Lopez, Moraal, McCracken, and McDonald in press) show nearly identical behavior – giving further confidence to the results.
Further characterizations of the solar activity cycle from these data are underway.
Solanki et al. 2004
Caballero-Lopez et al. in press.
Changes in the Earth’s climate (long-term temperature) appear to be connected to solar activity, both show similar variations.
The Friis-Christensen and Larsen (1991) study has been questioned on two points – 1) cycle length is poorly correlated with activity and 2) the method of smoothing and then using end points improperly smoothed compromises the recent data points.
Yearly Sunspot Numbers and Reconstructed Northern Hemis-phere Temperature (Mann, Bradley & Hughes Nature 392, 779-787, 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.
Grand Maxima and Minima
Measurements of the variations in 14C in tree rings from what would be expected from constant production/decay rates shows deep minima and high maxima in solar activity over century and millennia time scales.
Ice rafted debris found in North Atlantic sediment is used as an indicator of temperature (more debris – cooler temperatures). Bond et al. 2001 Science 294, 2130 find good correlation with 14C production.
Solar Irradiance Variations
Cosmic Ray “Cloud Seeding”
A brighter Sun at solar activity maxima could make the climate warmer.
Fewer clouds at solar activity maxima could make the climate warmer.
Seven different TSI radio-meters have been used, with offsets.
The trend in the composite depends on the introduced corrections.
(modified P-model; 0 FP;
Fontenla et al. 1993;
Unruh et al. 2000)
f (t)filling factor of faculae
(MDI magnetograms; 1 FP)A 4-component Irradiance Modelwith 1 Free Parameter
Iq(μ,)quiet Sun intensity
(Fontenla et al. 1993; 0 FP)
Iu(μ,)spot umbral intensity
Ip(μ,)spot penumbral intensity (cool Kurucz models; 0 FP)
u(t)filling factor of umbra
p(t)filling factor of penumbra
(MDI continuum; 0 FP)
Krivova et al. 2003 A&A Lett
The 0.1% variations in the visible and IR are probably too small to produce the observed variations. While the solar irradiance at wavelengths shorter than 300 nm is weak, it is highly variable over the solar cycle (3% @ 300 nm to 100% @ 100 nm). This should produce changes in stratospheric chemistry.
Correlations have been found between cloud cover and cosmic rays (Svensmark and Friis-Christensen, 1997) and between stratospheric aerosols and cosmic rays (Vanhellemont, Fussen, and Bingen, 2002).