Decadal-centennial-scale change in Asian-Pacific summer thermal contrast and solar activity

Abstract

To study the temporally varying features of summer thermal contrast between the Asian continent and the adjacent ocean on decadal-centennial time scales and the links between thermal contrast and solar irradiance, we used a time series of the reconstructed Asian-Pacific oscillation index and solar irradiance over the past millennium. The results showed that thermal contrast in the Asian monsoon region has quasi-90-year, 10–13-year, and 3–7-year periods. On the centennial time scale, thermal contrast showed three abrupt changes, occurring in 1305–1315, 1420–1430, and 1625–1635. There is a significant positive correlation between thermal contrast and solar irradiance, which is particularly strong at 250-year, 120–160-year, 60–70-year, and quasi-15-year periods. The three abrupt changes in thermal contrast corresponded to a significantly weakening or strengthening of solar irradiance, lagging 12–22 years behind the solar irradiance, which possibly reflects an effect of solar irradiance on the abrupt change in Asian monsoon climate on the centennial time scale. On the decadal time scale, the abrupt change in the thermal contrast was not closely associated with solar irradiance, which implies that solar activity may not be a major factor affecting the decadal abrupt change in Asian-Pacific thermal contrast. Relative to thermal contrast, the decadal abrupt change in Northern Hemispheric annual mean surface temperature is more closely associated with solar activity, while its centennial abrupt change has a weaker relationship with solar activity.