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The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions

Climate Dynamics volume 39, pages 2917–2936 (2012)Cite this article

Abstract

In this study, the effects of volcanic forcing on North Pacific climate variability, on interannual to decadal time scales, are examined using climate model simulations covering the last 600 years. The model used is the Bergen Climate Model, a fully coupled atmosphere–ocean general circulation model. It is found that natural external forcings, such as tropical strong volcanic eruptions (SVEs) and variations in total solar irradiance, play an important role in regulating North Pacific Decadal Variability (NPDV). In response to tropical SVEs the lower stratospheric pole–to–equator temperature gradient is enhanced. The North polar vortex is strengthened, which forces a significant positive Arctic Oscillation. At the same time, dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere. Through positive feedbacks in the troposphere, the surface westerly winds across the central North Pacific are significantly weakened, and positive sea level pressure anomalies are formed in the North Pacific. This anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the North Pacific. As a result of this, warm water converges in the subtropical western North Pacific, where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean. In the eastern and high–latitude North Pacific the ocean loses more heat, and large–scale decreases in sea surface temperatures are found. The overall response of this chain of events is that the North Pacific enters a negative phase of the Pacific decadal oscillation (PDO), and this negative phase of the PDO is maintained for several years. It is thus concluded that the volcanic forcing plays a key role in the phasing of the PDO. The model results furthermore highlight the important role of troposphere–stratosphere coupling, tropical–extratropical teleconnections and extratropical ocean–atmosphere interactions for describing NPDV.

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Acknowledgments

We thank Dr. Stefan Soblowski, Dr. Jianqi Sun and Prof. Shuanglin Li for useful comments to the manuscript. Comments and helpful suggestions from the editor and two anonymous reviewers are also greatly appreciated. This work was supported by the National Basic Research Program of China (Grant No. 2010CB951901), the CAS Strategic Priority Research Program (Grant No. XDA05110203) and the Research Council of Norway through the DecCen project (Exploring Decadal to Century Scale Variability and Changes in the East Asian Climate during the last Millennium). The research leading to these results has received funding from the European Union’s Seventh Framework programme (FP7/2007-2013) under grant agreement No. 243908, “Past4Future. Climate change–Learning from the past climate”.

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Authors and Affiliations

  1. Nansen-Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China

    Tao Wang, Yongqi Gao & Huijun Wang

  2. Uni Bjerknes Centre, Uni Research, Bergen, Norway

    Odd Helge Otterå

  3. Bjerknes Center for Climate Research, Bergen, Norway

    Odd Helge Otterå & Yongqi Gao

  4. Nansen Environmental and Remote Sensing Center, Bergen, Norway

    Yongqi Gao

  5. Climate Change Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China

    Huijun Wang

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  1. Tao Wang
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Wang, T., Otterå, O.H., Gao, Y. et al. The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions. Clim Dyn 39, 2917–2936 (2012). https://doi.org/10.1007/s00382-012-1373-5

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Keywords

  • Strong tropical volcanic eruptions
  • North polar vortex
  • North Pacific Decadal Variability
  • Coupled model
  • Ocean–atmosphere interaction
  • Troposphere–stratosphere coupling