Distinct responses of East Asian summer and winter monsoons to astronomical forcing

Z G Shi,Y B Sun,Z Liu,J Kutzbach,X D Liu,Z S An

doi:10.5194/cp-7-1363-2011

Abstract

Abstract. Influences of the Earth's astronomical forcing on the evolution of East Asian monsoon have been demonstrated with various geological records and climate models. Here, we present time series of climatic proxies from the Chinese Loess Plateau and Sanbao/Hulu caves and the winter/summer monsoon intensity index from a long-term transient climate model simulation. Both the observations and modelling results reveal consistently distinct responses of East Asian summer and winter monsoons to astronomical forcing. Different from the dominant local impact on the summer monsoon at the precession scale (~20 ka period), the East Asian winter monsoon is driven predominantly by the obliquity forcing (~40 ka period). We propose that the obliquity forcing controls the meridional insolation difference and, therefore, exerts a more significant effect on the evolution of the East Asian winter monsoon than previously expected.

Highlights

The development of East Asian monsoon (EAM) is closely linked to global climate change and exerts a profound influence on living environments in the most populous regions in the world
The seasonal reversal in the regional atmospheric circulation is traditionally considered to be driven by the ocean-land thermal contrasts, which is resulted from the seasonal variations of solar radiation
In the last 800 000 years, a strong 100-ka period consistent with global ice volume cycles is clearly found in the grain size records of Chinese loess, which indicates that the EAM system might be dominated by the changes in glacialage boundary conditions (Ding et al, 1995)

Summary

Introduction

The development of East Asian monsoon (EAM) is closely linked to global climate change and exerts a profound influence on living environments in the most populous regions in the world. Some studies argue that global climate responds linearly to astronomical-driven variation in radiation budget on these two bands (Imbrie et al, 1992) and the EAM development is associated with the local insolation in the Northern Hemisphere (NH) (Yuan et al, 2004; Wang et al, 2008). With the prescribed boundary conditions, e.g., the ice sheet and astronomical parameters, the climatic responses have been obtained after the models reach equilibrium. This restriction would lead to the absence of analyzing the long-term transient response of climate system and comparing it directly with the time series of geological climatic proxies. The distinct responses of East Asian summer and winter monsoons to astronomical forcing (precession and obliquity) and the possible driving mechanisms are

Geological records and modelling data

Time-dependent responses

Composite differences

Proposed mechanisms

Findings

Conclusions