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The mid-Pliocene warm period was the most recent geological period in Earth's history that featured long-term warming. Both geological evidence and model results indicate that East Asian summer winds (EASWs) strengthened in monsoonal China, and that East Asian winter winds (EAWWs) weakened in northern monsoonal China during this period, as compared to the pre-industrial period. However, the corresponding mechanisms are still unclear. In this paper, the results of a set of numerical simulations are reported to analyze the effects of changed boundary conditions on the mid-Pliocene East Asian monsoon climate, based on PRISM3 (Pliocene Research Interpretation and Synoptic Mapping) palaeoenvironmental reconstruction. The model results showed that the combined changes of sea surface temperatures, atmospheric CO concentration, and ice sheet extent were necessary to generate an overall warm climate on a large scale, and that these factors exerted the greatest effects on the strengthening of EASWs in monsoonal China. The orographic change produced significant local warming and had the greatest effect on the weakening of EAWWs in northern monsoonal China in the mid-Pliocene. Thus, these two factors both had important but different effects on the monsoon change. In comparison, the effects of vegetational change on the strengthened EASWs and weakened EAWWs were relatively weak. The changed monsoon winds can be explained by a reorganization of the meridional temperature gradient and zonal thermal contrast. Moreover, the effect of orbital parameters cannot be ignored. Results showed that changes in orbital parameters could have markedly affected the EASWs and EAWWs, and caused significant short-term oscillations in the mid-Pliocene monsoon climate in East Asia. [ABSTRACT FROM AUTHOR]

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Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The sensitivity of the East Asian summer monsoon to soil moisture anomalies over China was investigated based on ensembles of seasonal simulations (March-September) using the NCEP GCM coupled with the Simplified Simple Biosphere Model (NCEP GCM/SSiB). After a control experiment with free-running soil moisture, two ensembles were performed in which the soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China (YRNC) was double and half that in the control, with the maximum less than the field capacity. The simulation results showed significant sensitivity of the East Asian summer monsoon to wet soil in YRNC. The wetter soil was associated with increased surface latent heat flux and reduced surface sensible heat flux. In turn, these changes resulted in a wetter and colder local land surface and reduced land-sea temperature gradients, corresponding to a weakened East Asian monsoon circulation in an anomalous anticyclone over southeastern China, and a strengthened East Asian trough southward over Northeast China. Consequently, less precipitation appeared over southeastern China and North China and more rainfall over Northeast China. The weakened monsoon circulation and strengthened East Asian trough was accompanied by the convergence of abnormal northerly and southerly flow over the Yangtze River valley, resulting in more rainfall in this region. In the drier soil experiments, less precipitation appeared over YRNC. The East Asian monsoon circulation seems to show little sensitivity to dry soil anomalies in NCEP GCM/SSiB. [ABSTRACT FROM AUTHOR]

This study identifies a decadal shift of summer surface air temperature (SAT) over Northeast Asia, including southeastern parts of Russia, Mongolia and northern China, around the mid-1990s. The results suggest that the SAT over the Northeast Asia experienced a significant warming after 1994 relative to that before 1993. This decadal shift also extends to northern China, and leads to a warmer summer over Northeast China and North China after the mid-1990s. The decadal warming over Northeast Asia is found to concur with the enhancement of South China rainfall around the mid-1990s. On the one hand, both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift only in summer, but not in other seasons. On the other hand, both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift not only in the summer seasonal mean, but also in each month of summer (June, July and August). Furthermore, the decadal warming is found to result from an anticyclonic anomaly over Northeast Asia, which can be interpreted as the response to the increased precipitation over South China, according to previous numerical results. Thus, we conclude that the warming shift of summer Northeast Asian SAT around the mid-1990s was a remote response to the increased precipitation over South China. [ABSTRACT FROM AUTHOR]