Relationships between Springtime Sea Surface Temperatures in Different Indian Ocean Domains and Various Asian Monsoons from Late Spring to the Following Summer

We investigate the relative importance of spring sea surface temperatures(SSTs)in different Indian Ocean(IO)domains,especially the northern and southern IO,for the development and intensity of the Asian summer monsoon.By performing unsupervised neural network analysis,the self-organizing map,we extract distinct patterns of springtime IO SST.The results show that the uniform warming(cooling)of the southern IO plays a crucial role in the warming(cooling)of both the basin-wide IO and tropical IO.The southern IO thus well represents the associations of basinwide IO and tropical IO with the Asian summer monsoon,and is instrumental in the relationship between the IO and summer monsoon.A warming in the southern IO is closely related to the weakening of large-scale meridional monsoon circulation in May and summer(June–August),including suppression of the South Asian monsoon development in May and the East Asian monsoon in summer.On the other hand,a warming in the northern IO appears to be associated with an earlier South Asian monsoon onset and a stronger East Asian monsoon.In summer,the connection of the springtime IO SST with the South Asian monsoon weakens,but that with the East Asian monsoon strengthens.Finally,a robust negative correlation is found between the warming of various IO domains and the development and intensity of the Southeast Asian monsoon.

THE EFFECTS OF SEA SURFACE TEMPERATURE OVER THE EQUATORIAL WESTERN PACIFIC AND THE INDIAN OCEAN ON THE ASIAN SUMMER MONSOON

In this paper, the p-σ five layer primitive equation model segmented by mountains and physical parameterizations including short wave radiation; long wave radiation; large-scale and convective condensation; heat and moisture transport from surface to the first model level is used. The horizonial resolution is 5° lat. ×5° long. with the integration region from 25°S to 55°N and from 5°W eastward to 175°W. The model was spun up with perpetual June boundary conditions and forcing starting with June zonal mean heights and geostrophic wind field. In order to investigate the effects of SST (sea surface tempefuture) over the equatorial Western Pacific and the Indian Ocean on the Asian summer monsoon, four sets of numerical experments with positive anomalies over the equatorial Western Pacific, and positive and negative anomalies over the Western Indian Ocean, and zonal mean SST (the control case) are performed. The experimental results show that the South Asian low in the lower troposphere and the anticyclone over the South Asia in the uppet troposphere intensified when positive SST anomalies over the equatorial Western Pacific is included. A statistical test method for simulations is proposed. Finally, the influence mechanism of the SST anomalies over the equatorial oceans is discussed. It is worth stressing that the effects of the SST over the equatorial oceans on the Asian summer monsoon can arise as a result of interaction of SST anomalies, atmospheric flow field and heat sources and sinks in the atmosphere.

A novel procedure for pollen-based quantitative paleoclimate reconstructions and its application in China

Traditionally, the evaluation of pollen-based quantitative paleoclimate reconstructions focuses on the ability of calibration sets to infer present climatic conditions and/or the similarity between fossil and modem assemblages. Objective criteria for choosing the most appropriate climate parameter（s） to be reconstructed at a specific site are thus lacking. Using a novel approach for testing the statistical significance of a quantitative reconstruction using random environmental data, in combination with the advantageous large environmental gradients, abundant vegetation types and comprehensive modem pollen databases in China, we describe a new procedure for pollen-based quantitative paleoclimatic reconstructions. First, the most significant environmental variable controlling the fossil pollen assemblage changes is identified. Second, a calibration set to infer changes in this targeted variable is built up, by limiting the modem ranges of other environmental variables. Finally, the pollen-based quantitative reconstruction is obtained and its statistical significance assessed. This novel procedure was used to reconstruct the mean annual precipitation （Pann） from Gonghai Lake in the Lvliang Mountains, and Tianchi Lake in the Liupan Mountains, on the eastern and western fringe of the Chinese Loess Plateau, respectively. Both Pann. reconstructions are statistically significant （p〈0.001）, and a sound and stable correlation relationship exists in their common period, showing a rapid precipitation decrease since 3300 cal yr BP. Thus, we propose that this procedure has great potential for reducing the uncertainties associated with pollen-based quantitative paleoclimatic reconstructions in China.