Monday, October 28, 2013

New paper finds the Sun controlled precipitation in Tibet over past millennium

A new paper published in Quaternary Research reconstructs precipitation over the past 1,000 years on the Northeastern Tibetan Plateau and finds precipitation may have been controlled by solar activity and the natural Pacific Decadal Oscillation [PDO]. According to the authors, the precipitation data "suggests possible linkage with solar variation and the Pacific Decadal Oscillation (PDO). [The precipitation proxy] also shows coherent patterns with solar irradiance variation: the precipitation tends to reach low values during the well-known solar minimum." The paper adds to many others finding solar activity correlated to precipitation, droughts, and floods over the past several millenia. 

The authors find "Dry spells, even more severe than the 1920s drought, occurred during AD 1139–1152, 1294–1309, 1446–1503 and 1708–1726," but that there is nothing unusual or unprecedented about current levels of precipitation.

Figure 4. Comparison among the total solar irradiance (TSI), the Pacific Decadal Oscillation (PDO), PC1 and the correlation coefficient between the filtered PDO and PC1. (a) TSI (Bard, 2000); (b) [Precipitation proxy] PC1 filtered by 31-yr running average; (c) PDO (MacDonald and Case, 2005) filtered by 31-yr running average; (d) The running correlations between the filtered PDO and PC1, with a window of 101 yr and a step of 5 yr (values for the correlation are at the middle of the 101-yr period). Two black lines show the 95% confidence level. Significance tests were carried out using the random phase method (Ebisuzaki, 1997). The hatched bars show the solar minimums. Vertical light gray bars indicate the PC1 in phase with the PDO, whereas the vertical dark gray bar indicates the PC1 in anti-phase with the PDO.

Precipitation variations and possible forcing factors on the Northeastern Tibetan Plateau during the last millennium
  • a MOE Key Laboratory of Western China's Environmental Systems, Collaborative Innovation Centre for Arid Environments and Climate Change, Lanzhou University, Lanzhou 73000, China
  • b State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
  • c Department of Earth Science, University of Bergen, N-5007 Bergen, Norway
  • d Bjerknes Centre for Climate Research, N-5007 Bergen, Norway

Abstract

Understanding precipitation variation, drought and flood history, and their associated forcing mechanisms are important to human society. In this study, five moisture-sensitive tree-ring width chronologies are used to represent variations in precipitation over the past millennium on the Northeastern Tibetan Plateau (NETP). We find a strong coherency between chronologies in the NETP, indicating a common response to regional climate during the last millennium. The first principal component of the five chronologies (PC1) correlates significantly with regional precipitation and can thus be used as an indicator of regional precipitation variations. Dry spells, even more severe than the 1920s drought, occurred during AD 1139–1152, 1294–1309, 1446–1503 and 1708–1726. Previous studies in this area using other proxies also identified these droughts. Multi-Taper spectral analysis demonstrates significant periodicities at 205 yr and 73 yr, plus a range of ~ 2 yr cycles, suggesting possible linkage with solar variation and the Pacific Decadal Oscillation (PDO). PC1 also shows coherent patterns with solar irradiance variation: the precipitation tends to reach low values during the well-known solar minimum.

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