中北亚地区气候纬向变化特征

利用中北亚不同纬度的5个气象站（从低纬度到高纬度分别为：库什卡、阿拉木图、托木斯克、图拉、哈坦加）20世纪的气温和降水资料，采用气候倾向率法、Mann．Kendall法和移动t法对这5个站的长期气候变化特征、趋势显著性及突变点进行分析．结果表明：在研究的5个站中，20世纪气温的变化与纬度有一定的关系，纬度较低的站升温现象比纬度较高的站明显，而降水量的变化与纬度关系不大．纬度最低的库什卡站气温倾向率为0．018℃／a，其他4站均小于0．01℃／a，纬度相对较低的库什卡、阿拉木图、托木斯克3站的升温趋势显著，且在20世纪70～80年代发生突变升温；年最低气温比年最高气温的升高现象明显，且纬度最低的库什卡站的升温现象最显著．5个站的降水量倾向率约0．09％／a，但增湿的趋势不显著．

Effects of Chinese Fir，Loblolly Pine and Deciduous Oak Forests on Nutrient States of Soils in Northern Subtro－pics of China

This paper deals with a study on the effects of Chinese fir, loblolly pine and deciduous oak forests on thenutrient status of soils in northern subtropics of China, adopting the principle of forest ecology in the caseof similar climate and soil type. The experimental area was situated in the Xiashu Experimental Centre ofForest, where the soil is yellow-brown soil derived from siliceous slope wash. Sample plots of these 3 standswere established to study the nutrient status in litter, the amount of nutrient uptake by roots, the quantityof nutrient output by percolating water outside the deep layer of soil, and the seasonal dynamics of availablenutrient in surface soil. It was shown that the intensity of nutrient cycling in soil under deciduous oak wasthe highest, and the effect of oak in improving soil fertility was the best. The result of improving soil fertilityby Chinese fir was the most inferior, though the intensity of nutrient cycling under that stand was higherthan that under loblolly pine stand. The influence of loblolly pine on the improvement of soil fertility wasbetter than that of Chinese fir, in spite of its lowest intensity of nutrient cycling.

Simulation of Precipitation in Monsoon Regions of China by CMIP3 Models

The output of 25 models used in the Coupled Model Intercomparison Project phase 3 (CMIP3) were evaluated,with a focus on summer precipitation in eastern China for the last 40 years of the 20th century.Most mod-els failed to reproduce rainfall associated with the East Asian summer monsoon (EASM),and hence the seasonal cycle in eastern China,but provided reasonable results in Southwest (SW) and Northeast China (NE).The simula-tions produced reasonable results for the Yangtze-Huai (YH) Basin area,although the Meiyu phenomenon was underestimated in general.One typical regional phe-nomenon,a seasonal northward shift in the rain belt from early to late summer,was completely missed by most models.The long-term climate trends in rainfall over eastern China were largely underestimated,and the ob-served geographical pattern of rainfall changes was not reproduced by most models.Precipitation extremes were evaluated via parameters of fitted GEV (Generalized Ex-treme Values) distributions.The annual extremes were grossly underestimated in the monsoon-dominated YH and SW regions,but reasonable values were calculated for the North China (NC) and NE regions.These results suggest a general failure to capture the dynamics of the EASM in current coupled climate models.Nonetheless,models with higher resolution tend to reproduce larger decadal trends and annual extremes of precipitation in the regions studied.

Observed Diurnal Cycle of Summer Precipitation over South Asia and East Asia Based on CMORPH and TRMM Satellite Data

The characteristics of the summer precipitation diurnal cycle over South Asia and East Asia during 2001–13 are investigated based on the high spatiotemporal resolution estimates of the CPC(Climate Prediction Center) Morphing(CMORPH) technique. The results show that summer precipitation over South Asia and East Asia possesses a remarkable diurnal cycle, with obvious regional differences. Over the coastal areas, plateau, and high mountains, summer precipitation peaks in the late afternoon; while over low altitude areas, such as valleys, basins, and inshore seas, it peaks during midnight to early morning. In addition to these general features consistent with previous studies, the high resolution CMORPH technique can depict finer regional details, such as the less coherent phase pattern over a few regions. Besides, through comparative analysis of the diurnal cycle strength and precipitation fields, the authors find that for humid areas the summer precipitation diurnal cycle is especially significant over Southeast China, the Sichuan Basin, Hainan Province, Taiwan Province, the Philippines, and Indonesia. And it is relatively weak over the south of Northeast China, central East China, Yunnan Province, the central Indian Peninsula, and most oceanic areas. Comparisons between two satellite datasets—those of the CMORPH and Tropical Rainfall Measuring Mission(TRMM) 3B42 products—are also presented. For summer precipitation and the main diurnal cycle features, the results from both products agree over most regions, except a few areas, e.g., the Tibetan Plateau.

Evaluation of the Community Microwave Emission Model Coupled with the Community Land Model over East Asia

The Community Microwave Emission Model (CMEM) developed by the European Centre for Me-dium-Range Weather Forecasts (ECMWF) can provide a link between surface states and satellite observations and simulate the passive microwave brightness temperature of the surface at low frequencies (from 1 GHz to 20 GHz).This study evaluated the performance of the CMEM cou-pled with the Community Land Model (CLM) (CMEM-CLM) using C-band (6.9 GHz) microwave brightness temperatures from the Advanced Microwave Scanning Radiometer on Earth Observing System (AMSR-E) over East Asia.Preliminary results support the argument that the simulated brightness temperatures of CMEM-CLM from July 2005 to June 2010 are comparable to AMSR-E observational data.CMEM-CLM performed better for vertical polarization,for which the root mean square error was approximately 15 K,compared to over 30 K for horizontal polarization.An evaluation performed over seven sub-regions in China indicated that CMEM-CLM was able to capture the temporal evolution of C-band brightness temperatures well,and the best correlation with AMSR-E appeared over western Northwest China (over 0.9 for vertical polarization).However,larger biases were found over southern North China and the middle and lower reaches of the Yangtze River.

Holocene vegetational and climatic variation in westerly-dominated areas of Central Asia inferred from the Sayram Lake in northern Xinjiang,China

Changes in the vegetation and climate of the westerly-dominated areas in Central Asia during the Holocene were interpreted using pollen-assemblages and charcoal data from a 300-cm-long sediment core of the Sayram Lake,northern Xinjiang.Accele-rator Mass Spectrometry(AMS) radiocarbon dating methods were applied to bulk organic matter of the samples.Artemisia spp./Chenopodiaceae ratios and results from principal component analysis were used to infer that the lake basin was dominated by desert vegetation before ca.9.6 cal.ka BP,which suggests a warm and dry climate in the early Holocene.Desert steppe/steppe expanded during 9.6-5.5 cal.ka BP,indicating a remarkable increase both in the precipitation and temperature during the mid-Holocene.Desert vegetation dominated between 6.5 and 5.5 cal.ka BP,marking an extreme warmer and drier interval.The steppe/meadow steppe recovered,and temperatures decreased from 5.5 cal.ka BP in the late Holocene,as indicated by the increased abundance of Artemisia and the development of meadows.Holocene temperatures and moisture variations in the Sayram Lake areas were similar to those of adjacent areas.This consistency implies that solar radiation was the main driving factor for regional temperature changes,and that the effect of temperature variations was significant on regional changes in humidity.The evolution of climate and environment in the Sayram Lake areas,which were characterized as dry in the early Holocene and relatively humid in the middle-late Holocene,are clearly different from those in monsoonal areas.Dry conditions in the early Holocene in the Sayram Lake areas were closely related to decreased water vapor advection.These conditions were a result of reduced westerly wind speeds and less evaporation upstream,which in turn were caused by seasonal changes in solar radiation superimposed by strong evaporation following warming and drying local climate.

Impact of El Nio on atmospheric circulations over East Asia and rainfall in China： Role of the anomalous western North Pacific anticyclone

This paper presents a review on the impact of El Nio on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific(WNPAC). It explains the formation mechanisms of the WNPAC and physical processes by which the WNPAC affects the rainfall in China. During the mature phase of El Nio, the convective cooling anomalies over western tropical Pacific caused by the weakened convections trigger up an atmospheric Rossby wave response, resulting in the generation of the WNPAC. The WNPAC can persist from the winter when the El Nio is in its peak to subsequent summer, which is maintained by multiple factors including the sustained presence of convective cooling anomalies and the local air-sea interaction over western tropical Pacific, and the persistence of sea surface temperature anomalies(SSTA) in tropical Indian and tropical North Atlantic. The WNPAC can influence the atmospheric circulations over East Asia and rainfall in China not only simultaneously, but also in the subsequent summer after an El Nio year, leading to more rainfall over southern China. The current paper also points out that significant anomalies of atmospheric circulations over East Asia and rainfall over southern China occur in El Nio winter but not in La Nio winter, suggesting that El Nio and La Nio have an asymmetric effect. Other issues, including the impact of El Nio diversity and its impact as well as the relations of the factors affecting the persistence of the WNPAC with summer rainfall anomalies in China, are also discussed. At the end of this paper some issues calling for further investigation are discussed.