To what extent does solar variability contribute to climate change?. Dr. David H. Hathaway NASA/Marshall Space Flight Center National Space Science and Technology Center. Outline. Solar Variability The Solar Sunspot Cycle Solar Variability and NH Temperature
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Dr. David H. Hathaway
NASA/Marshall Space Flight Center
National Space Science and Technology Center
Solar activity includes flares, prominence eruptions, and coronal mass ejections (CMEs) along with associated electromagnetic emission at wavelengths from gamma-rays to radio-waves and energetic particles from electrons and protons to heavy nuclei.
Over its 4.5 billion year history the Sun has slowly increased in brightness (Luminosity) as it has burned hydrogen to form helium in its core. It is now some 30% brighter than is was 4 billion years ago.
The sunspot cycle was discovered in 1844 by a Swiss Apothecary – Heinrich Schwabe. The number of sunspots rises and falls with a period of about 11-years. Individual cycles vary in amplitude, cycle length, and cycle shape. In 1854 Rudolf Wolf proposed the “Relative Sunspot Number” index and used historical records to extend the record back to 1749.
Sunspots are regions where intense magnetic fields loop up out of the Sun and back into its interior. These fields are shuffled around by flows at, and below, the surface. This leads to the generation of waves and magnetic reconnection above the surface – heating the corona and driving flares, prominence eruptions, and CMEs.
Active regions erupt in two bands on either side of the Sun’s equator that start at about 30° north and south and slowly drift toward the equator over each sunspot cycle. A broad equatorial jet and a poleward meridional flow advect magnetic elements across the surface while cellular convective flows shred the field and scatter the elements in random directions.
30-years of magnetic measurements reveal the characteristics of the Sun’s magnetic cycle: different polarities at low- and high-latitudes that reverse from hemisphere-to-hemisphere and cycle-to-cycle; poleward drift of high-latitude polarity that reverses the polar fields at about the time of cycle maximum.
Sunspot Area change?
10.7cm Radio Flux
GOES X-Ray Flares
Climax Cosmic-Ray Flux
Geomagnetic aa indexSolar Activity and Sunspots
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 (14C) and ice cores (10Be).
Yearly sunspot numbers back to 1610 (the invention of the telescope) show significant variations in the amplitudes of the sunspot cycles. This includes periods of inactivity like the Maunder Minimum (1645-1715) and the Dalton Minimum (1800-1825). Similar variations are seen in estimates of the Northern Hemisphere temperatures as given by Mann et al. (1998), Moberg et al. (2005), and others (variations of a few tenths of a degree Celsius).
Formerly known as the “Solar Constant,” the Total Solar Irradiance (TSI) varies by about 0.1% over the last three solar cycles. (Larger dips in TSI are due to the passage of large sunspots across the visible disk of the Sun.) This 0.1% variation only produces a 0.1 °C change in Northern Hemisphere Temperature when introduced in most climate models.
Efforts to model the TSI appear to be quite successful. Models include dark sunspot umbrae and lighter (but still dark) sunspot penumbrae from “white light” images of the Sun. And bright faculae as determined by locations of small-scale, weaker, magnetic features.
Magnetic features explain more than 90% of the variability. Both the day-to-day variations and the overall rise from minimum to maximum are modeled very well with just one parameter – a filling factor for faculae.
Krivova et al. 2003 A&A Lett
TSI measurements have been taken by satellite-based instruments for 30 years. The measurements are very precise (able to distinguish small variations) but the accuracy (actual value) varies from one instrument to another.
The ACRIM reconstruction showed a significant difference in TSI for the 1986 and 1996 minima. The PMOD reconstruction showed no such variation but now shows a significant variation between the 1996 and 2007 minimum.
This variation cannot be explained by magnetic features and raises the question: Could TSI have varied by more than 0.1% during the Maunder and Dalton Minima?
Although TSI only varies by about 0.1% over the last three cycles, the Sun’s UV irradiance (at wavelengths that influence ozone production in the stratosphere) varies by several percent. These variations may produce more significant tropospheric variations than TSI.
The flux of cosmic rays has been measured at mountain-top observatories for several decades. These measurements show significant (~20%) decreases at mid-latitudes that are associated with solar activity.
The solar cycle modulation of cosmic rays leaves a record of solar activity in 14C in tree rings and 10Be in ice cores.
Carslaw et al. (2002) as lifted from Lockwood (2002)
There are indications that the modulation of cosmic rays may modulate cloud cover.
Carslaw et al. (2002) as lifted from Marsh & Svensmark (2000)
Carslaw et al. (2002)