Understanding Sun-Climate Connection by Analysis of Historical Sunspot, Auroral and Weather Records

Fifty years of galactic cosmic ray data show changes with the solar cycle. Deflection of the highly energetic particles from exploding supernovae by the solar wind and associated magnetic field also modulates cosmogenic radioisotope production high in the atmosphere. The same trends are seen in carbon-14 and beryllium-10 abundances from long-lived trees and polar ice cores, respectively. Total solar irradiances measured by satellite radiometers show a 0.1% variance over the last two solar cycles, with only a small effect on global temperatures. A longer view is obviously needed. During the Maunder Minimum (1645-1715) sunspots were rarely seen. Total solar irradiances, reconstructed from historical sunspot data, were 0.24% lower, correlating nicely with an estimated 0.5-degree drop in Northern Hemisphere surface temperatures during the Little Ice Age [Lean and Rind, J. Clim. 11, 3069, 1998]. A longer time series has been reconstructed from even earlier records. From the frequencies of sunspot and auroral sightings in East Asian and European chronicles, C-14 and Be-10 abundances we have reconstructed the recent history of a variable Sun. In the past 1800 years the Sun has gone through nine cycles of brightness change. Although these long-term changes were <1% they have clearly affected the climate [Pang and Yau, Eos 83, No. 43, 481, 2002]. We have also analyzed Chinese historical weather records for comparison. Reports of unseasonable cold are classified by their degree of severity: (1) Late (April-June) or early (July-Sept.) killing frosts; (2) Bitter cold/heavy snowfall; and (3) Heavy sustained snowfall, bitter cold with frozen wells, lakes, rivers and icebound seas. The latter cases were often widespread and multi-year. All categories occurred most often during Maunder Minimum. The Category 3 episodes were in 1652-54, 1656, 1664, 1670-72, 1676-77, 1683, 1688-91, 1716 and 1718-19. The coldest time 1670-1697 coincides with lows in aurora sightings and numerical model simulated temperatures, and highs in radioisotope production. There was only one Category 3 episode between the Maunder and Dalton Minima-in 1761 (due to a big eruption); and two in the Dalton Minimum (1795-1825)-in 1796 and 1814-17. The 1815 Tambora eruption, with the reduced solar luminosity, seem to have been responsible for the "year without summer" and long-cold spell. The Sun has brightened since the Dalton Minimum, but the climate of China stayed cold through the 19th century. However there were only two Category 3 episodes: in 1841 and 1877. The onset of global warming reduced that to just once in the 20th century: 1955. The climate of China seems to have been warm during the Late 14th-Century Maximum (1350-1410). We have found only one Category 1 episode: in 1393. It then turned cold during the Sporer Minimum (1410-1590). Category 3 episodes occurred in 1453-54, 1493, 1513, 1569, and 1577-78. The early 1453 great Kuwae eruption apparently deepened and prolonged the first [Pang, Eos 74, No. 43, 106, 1993; Simarski, Aramco World 47, No.6, 8, 1996]. We conclude that the climate of China in the past 650 years generally follows world trend. The major forcing seems to have been changing solar luminosity, as all but four severe weather episodes coincide with solar minimum. The exact mechanism remains unknown, but could have been increased cloudiness.