Simulations of the impact of orbital forcing and ocean on the Asian summer monsoon during the Holocene

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Abstract

The importance of orbital forcing and ocean impact on the Asian summer monsoon in the Holocene is investigated by comparing simulations with a fully coupled ocean–atmosphere general circulation model (FOAM) and with the atmospheric component of this model (FSSTAM) forced with prescribed modern sea-surface temperatures (SSTs). The results show: (1) the ocean amplifies the orbitally-induced increase in African monsoon precipitation, makes somewhat increase in southern India and damps the increase over the southeastern China. (2) The ocean could change the spatial distribution and local intensity of the orbitally-induced latitudinal atmospheric oscillation over the southeastern China and the subtropical western Pacific Ocean. (3) The orbital forcing mostly enhances the Asian summer precipitation in the FOAM and FSSTAM simulations. However, the ocean reduces the orbitally-induced summer precipitation and postpones the time of summer monsoon onset over the Asian monsoon region. (4) The orbital forcing considerably enhances the intensity of upper divergence, which is amplified by ocean further, over the eastern hemisphere. But the divergence is weaker in the FOAM simulations than in the FSSTAM simulations when the orbital forcing is fixed. (5) The orbital forcing can enhance the amplitude of precipitation variability over the subtropical Africa, the southeastern China and northwestern China, inversely, reduce it over central India and North China in the FOAM and FSSTAM simulations. The ocean obviously reduces the amplitude of precipitation variability over most of the Asian monsoon regions in the fixed orbital forcing simulations. (6) The areas characterized by increased summer precipitation in the long-term mean are mostly characterized by increased amplitude of short-term variability, whereas regions characterized by decreased precipitation are primarily characterized by decreased amplitude of short-term variability. However, the influences of orbital forcing or dynamical ocean on regional climate depend on the model.

Introduction

Changes of the Earth's orbital parameters produce more summer solar radiation (compared to present) and cause an enhancement of summer monsoon activity in the Holocene (Kutzbach and Otto-Bliesner, 1982, Hall and Valdes, 1997, Masson and Joussaume, 1997, Joussaume, 1999, Braconnot et al., 1999, Braconnot et al., 2000, Bush, 2001, Diffenbaugh and Sloan, 2004, Wei and Wang, 2004). However, the major contribution of ocean is to enhance the inland moisture advection (Braconnot et al., 1999) and then to induce the summer monsoon flow penetrates farther north into the Sahara (e.g. Braconnot et al., 2000). The simulated increase in SSTs and associated changes in atmospheric circulation (Braconnot et al., 1997, Bush and Philander, 1999, Toracinta et al., 2004) enhanced the summer monsoon precipitation of northern Africa (Kutzbach and Liu, 1997, Braconnot et al., 1999). Liu et al. (2003a, 2004) studied the global monsoons and pointed out ocean produce a further enhancement of the northern African monsoon and the North American monsoon, namely, ocean produce amplification of orbitally-forced signal. However, Liu et al. (2004) also indicated that ocean damp the response to orbital forcing over Asia — the monsoon is still substantially enhanced compared to the present but less than would be produced by the atmospheric response to orbital forcing alone.

The factors that drive intensities of the monsoonal annual cycle share common features with the external (geographic and orbital) forcing, while the differences in interannual variability between the Indian monsoon and East Asian monsoon are primarily due to internal factors of the coupled atmosphere–ocean–land system (Wang et al., 2003). However, the impact of ocean–atmosphere interaction on precipitation is not yet within reach and requires further research (Enfield and Mestas-Nuñez, 1999). No matter orbital forcing or ocean impact (including the dynamic, thermodynamic and coupled effects) can change the atmospheric temperature gradients. Moreover, the changes in atmospheric temperature gradients impact on the monsoon circulation, which is due to the sea-land thermal contrast, and then lead to variation of monsoon precipitation. But, the atmospheric circulation response to changes in the temperature gradients is governed by large-scale dynamical mechanisms, with rising motion and precipitation in one region often linked directly to sinking motion and dry conditions in another region (Clement et al., 2004).

Previous studies on orbital forcing (the external forcing) and ocean impact (the internal forcing) have involved the monsoons (Kutzbach and Liu, 1997, Braconnot et al., 1999, Braconnot et al., 2000, Liu et al., 2003a, Tuenter et al., 2003, Liu et al., 2004). However, most of them investigate orbital forcing or ocean impact on the African monsoon or summarily on global monsoons. Although some studies have investigated the Asian monsoon (e.g. Wei and Wang, 2004), many open science questions cannot be solved right away and still need to be analyzed in detail, such as the response of the Asian monsoon to orbital forcing, ocean and their synergistic impact.

Thus, in this paper, we will primarily focus on the impacts of orbital forcing and ocean on the Asian summer monsoon (June, July and August) using a longer simulation with the fast ocean–atmosphere model (FOAM) and its atmosphere equivalent (FSSTAM). We investigate some possible relationships between the long-term climate change (contrast the multi-year summer mean between the present and the Holocene conditions) and the short-term variability in the monsoon (including interannual and interdecadal variability for the present and the Holocene, respectively) as well. The present study will confirm some previous conclusions, show some different viewpoints, and share some new aspects. In Section 2, the major features of the FOAM and simulation experiments will be described. In the present study, there are two control experiments, one coupling the fixed SSTs (atmosphere-only simulation, FSSTAM) and the other coupling the dynamical ocean (coupled simulation, FOAM) with the present conditions. Then, the impacts of orbital forcing and ocean are analyzed and contrasted in the results (Section 3). Finally, a summary description and discussion about the entire study will be presented in Section 4.

Section snippets

Model description

The FOAM (Jacob, 1997, Jacob et al., 2001) is a fully coupled ocean–atmosphere general circulation model. In the FOAM, the atmospheric physics is equivalent to CCM3.6 (Kiehl et al., 1996). The version used in this study has a horizontal resolution of R15 (4.5° latitude × 7.5° longitude) and 18 sigma levels in the vertical. The land-surface scheme follows that in CCM2 (Hack et al., 1993) and includes prescribed vegetation characteristics and a simple soil bucket model. The ocean model (OM3) is a

Simulated response to 11 kyr and 6 kyr orbital forcing in FOAM

The monsoon response in FOAM is forced by the direct orbital forcing and feedback from orbitally-induced changes in the ocean. The change in orbital forcing during the early and mid-Holocene leads to higher-than-present surface temperatures in summer over much of northern Africa and Eurasia (Fig. 1a, b), which confirm the associations of orbital forcing and continental temperatures (Hall and Valdes, 1997, Liu et al., 2003b, Liu et al., 2004). Mean summer temperature in central Eurasia is

Summary and discussion

With the orbital forcing of early and middle Holocene in the FOAM and FSSTAM simulations, the present study confirmed the higher-than-present surface temperatures are induced over much of northern Africa and Eurasia in the boreal summer. The sea-level pressure is decreased over the Afro-Asian land mass and there is the increased cyclonic inflow at the surface. The enhanced monsoons bring increased precipitation to the Sahelian and southern Saharan, northern India, central and southeastern China

Acknowledgments

The author would like to thank Dr. Robert Jacob for his valuable help on the modeling with FOAM. I also thank Dr. Oswald Haan and Manfred Kastowsky for their support in using GWDG supercomputer and two anonymous reviewers. This research is funded by the German Climate Research Program (DEKLIM) and the EU-funded MOTIF project. At the final stage, this work was supported by the Chinese Ministry of Science and Technology under Contract 2001BA611B-01.

References (44)

  • F.H. Chen et al.

    Abrupt Holocene changes of the Asian monsoon at millennial- and centennial-scales: evidence from lake sediment document in Minqin Basin, NW China

    Chin. Sci. Bull.

    (2001)
  • A.C. Clement et al.

    The importance of precessional signals in the tropical climate

    Clim. Dyn.

    (2004)
  • M. Crucifix et al.

    ‘Climate evolution during the Holocene: a study with an Earth system model of intermediate complexity’

    Clim. Dyn.

    (2002)
  • N.S. Diffenbaugh et al.

    Mid-Holocene orbital forcing of regional-scale climate: a case study of western North America using a high-resolution RCM

    J. Climate

    (2004)
  • D.B. Enfield et al.

    Multiscale variabilities in global sea surface temperatures and their relationships with tropospheric climate patterns

    J. Climate

    (1999)
  • A.K. Gupta et al.

    Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean

    Nature

    (2003)
  • J.J. Hack et al.

    Describtion of the NCAR Community Climate Model (CCM2)

  • N.M.J. Hall et al.

    A GCM simulation of the climate 6000 years ago

    J. Climate

    (1997)
  • S.P. Harrison et al.

    Mid-Holocene climates of the Americas: a dynamical response to changed seasonality

    Clim. Dyn.

    (2003)
  • Jacob, R. 1997. Low frequency variability in a simulated atmosphere ocean system. PhD Thesis, University of...
  • R. Jacob et al.

    Computational design and performance of the Fast Ocean Atmosphere Model, Version One, Proc

  • S. Joussaume et al.

    Monsoon changes for 6000 years ago: results of 18 simulations from the Paleoclimate Modeling Intercomparison Project (PMIP)

    Geophys. Res. Lett.

    (1999)
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