A data-model comparison pinpoints Holocene spatiotemporal pattern of East Asian summer monsoon

The authors argue that a reduction to the stochastic forcing of the El Nino–Southern Oscillation (ENSO) wrought by Pacific-wide climate changes in response to mid-Holocene (6000 BP) orbital forcing is a viable hypothesis for the observed reduction of ENSO activity during that time. This conclusion is based on comprehensive analysis of an intermediate coupled model that achieves significant reduction to ENSO variance in response to mid-Holocene orbital forcing. The model’s excellent simulation of the tropical Pacific interannual variability lends credibility to the results. Idealized simulations demonstrate that the mid-Holocene influence is communicated to the tropical Pacific largely via climate changes outside of the tropical Pacific, rather than from insolation changes directly on the tropical Pacific. This is particularly true for changes to the ENSO, but also with changes to the cold tongue annual cycle. Previously proposed mechanisms for teleconnected mid-Holocene ENSO changes, including fo...

Pacific Climate Change and ENSO activity in the mid-Holocene

Summary Taiwan is an island located in the western Pacific, and falls under the influence of tropical to sub-tropical climate with two monsoons during summer and winter. This makes it an ideal location to study water vapor dynamics and its influence on the rainfall. The tropical convection/cyclones and south-west monsoon dominate the rainfall in summer while in winter, north-east monsoon overwhelms. To investigate the influence of moisture source variation, recycling and rain–vapor interaction, continuous measurements of the concentration and oxygen and hydrogen isotopic compositions (δ 18 O and δD) of the near surface atmospheric water vapor have been carried out in Taipei, Taiwan, using a commercial cavity ring down spectrometer. The water vapor mixing ratio varies between 15,000 and 38,000 ppmv, with maximum in the summer months and minimum in the winter. The isotopic composition of water vapor varies between −11‰ to −21‰ for δ 18 O and −75‰ to −150‰ for δD, but no clear seasonal variation is observed unlike that in the monthly rainwater. Therefore, the usual assumption that the monthly composite samples of rainfall reflect the isotopic variability of near surface water vapor is not valid here. Variation in δ 18 O, δD and deuterium excess (d-excess) in vapor reflects its interaction with rainwater superimposed by temperature variation and moisture recycling. To study how rainwater interacts with water vapor, two events are selected: a mei-yu event and typhoon Saola, the later affected Taiwan in 2012. Annual rainfall is dominantly contributed by these two types of meteorological phenomena in Taiwan. We find that the vapor and the rainwater are nearly in isotopic equilibrium during typhoon while they are deviated significantly during the mei-yu. A significant contribution of the vapor from recycling of surface water is observed in winter assessed using d-excess in the vapor isotopes.

Stable isotopic composition of near surface atmospheric water vapor and rain–vapor interaction in Taipei, Taiwan

Three-phase structure of the East Asia summer monsoon during Heinrich Stadial 4 recorded in Xianyun Cave, southeastern China

Abstract The relationship between the hydrological cycle and the temperature is rather complex and of great importance to human socioeconomic activities. The prevailing theory suggests that as temperature increases the hydrological cycle is intensified. Practically, this means more and heavier precipitation. However, the exact magnitude of hydrological cycle response and its spatio-temporal characteristics is still under investigation. Looking back in Earth’s hydroclimatic history, it is easy to find some periods where global temperature was substantially different than present. Here, we examine some of these periods to present the current knowledge about past hydrological cycle variability (specifically precipitation), and its relationship to temperature. The periods under investigation are the Mid-Miocene Climate Optimum, the Eemian Interglacial Stage, the Last Glacial Maximum, the Heinrich and Dansgaard–Oeschger Events, the Bølling–Allerød, the Younger Dryas, the 8.2 ka event, the Medieval Climate Anomaly, and the Little Ice Age. We report that the hypothesis that a warmer climate is a wetter climate could be an oversimplification, because the response of water cycle appears to be spatio-temporally heterogeneous. 

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Yun Chuan Chung

Papers

Hydroclimate variability of central Indo-Pacific region during the Holocene