OBSERVATIONAL STUDY OF AIR-SEA FLUXES DURING THE SCS SUMMER MONSOON IN 2000——FEATURES OF THERMAL BUDGET AT THE SEA SURFACE*

This paper is devoted to the features of sea-surface heat budget during the active/break phases of the 2000 summer monsoon in the South-China Sea(SCS) by means of the observed air-sea heat fluxes and data from Xisha Weather Station and NCEP/NCAR in the same period.Results suggest that the primary factors affecting sea-surface thermal budget are solar shortwave penetrating radiation and latent heat flux.Regardless of their changes,however,the thermal gain is reduced or becomes net loss at the active stage and the thermal gain gets gradually increased in the weakening and lull periods:during the first emergence of southwest monsoon the net loss happens thanks to the dramatic diminution of penetrating radiation resulting from increased cloudiness and intense precipitation:while at the re-emergence of the wind.reduced net sea-surface thermal gain is attributed to the sharp increase in latent heat flux resulting from intense evaporation:owing to great thermal inertia of water the SST change lags behind that of heat budget over the sea surface, and the lagging is responsible for regulating the budget by affecting latent heat fluxes,which,in turn.has effect upon the change of the SST,thereby forming short-term oscillations that are in association with the active/break phases of the monsoons.Part of the conclusions have been borne out by the observational study based on 1998 and 2002 data.     

TELECONNECTION BETWEEN INDIAN MONSOON AND EAST ASIAN CIRCULATION*

Correlation analysis identified that Indian summer rainfall and East Asian 500 hPa geopotential height field are significantly correlated.A teleconnection pattern between Indian monsoon and East Asian summer circulation (IEA pattern) was proposed.We suggested that the Pacific-Japan teleconnection pattern (PJ pattern) primarily influences the meridional position of the northwestern Pacific subtropical high (NPSH) in summer,while IEA pattern partly affects its zonal stretch or the anomaly of geopotential height field over China mainland.The numerical experiments imply that the IEA pattern has important impact on East Asian circulation and it can be stimulated by the SST anomaly of the Indian Ocean.We summarized that there are two ways,a directive way and a selective way,by which ENSO exerts impacts on East Asian summer monsoon.     

2002年南海夏季风爆发期间南海北部海气通量分析与比较

利用国际北极浮冰运动观测资料 (IABP)(1979～1998)以及NCEP/NCAR月平均海平面气压再分析资料(1960～2002), 通过求解海冰运动异常的复斜方差矩阵, 研究了冬季北极海冰运动主模态构成及其与海平面气压变化的关系.冬季海冰运动主模态是由两个海冰运动优势模态的一个线性组合构成, 与这两个运动优势模态有直接关系的海平面气压变化主要发生在北极海盆及其边缘海区.尽管北极涛动(北大西洋涛动)通过影响海平面气压进而影响北极海冰运动, 但是, 北极涛动(北大西洋涛动)并不是决定海冰运动主模态的关键性因素.     

Splitting Numerical Technique with Application to the High Resolution Simulation of the Indian Ocean Circulation

The aim of this paper is twofold : To present an efficient numerical technique for the simulation of the ocean general circulation (OGC) and to apply it to the simulation of the Indian Ocean dynamics with high spatial resolution. To solve model equations we use the splitting method by physical processes and space coordinates. We select the main parts of the model operator and then perform their numerical treatment independently of one another. We describe the general methodology and some special aspects of this approach. Numerical treatment of the monsoon circulation is performed on the basis of the sigma-coordinate primitive equation model, which was developed at the Institute of Numerical Mathematics (Moscow, Russia). We present and briefly analyze the results of the numerical experiment with high spatial resolution 1/8° along latitude, 1/12° along longitude, and with 21 vertical sigma levels.The work was supported by the Russian Foundation for the Basic Research (03-05-64354, 02-05-64909) and by the Russian Academy of Sciences (10002-251/OMN-03/026-020/240603-807)     

Development and propagation of a pollution gradient in the marine boundary layer during INDOEX (1999)

The development and propagation of a pollution gradient in the marine boundary layer over the Arabian Sea during the Intensive Field Phase of the Indian Ocean Experiment (1999) is investigated. A hypothesis for the generation of the pollution gradient is presented. Infrared satellite images show the formation of the pollution gradient as the leading edge of a polluted air mass in the marine boundary layer and also its propagation over the Arabian Sea and the northern Indian Ocean. Aerosol data measured from two research vessels over the Arabian Sea show a variation in the concentrations caused by the passage of this pollution gradient. Depth of the pollution gradient was found to be about 800 m. A numerical model was used to simulate the development of this gradient and its propagation over the ocean. Results show that its formation and structure are significantly influenced by the diurnal cycle of coastal sea-land breeze circulations along India’s west coast. Transport of aerosols and gases over the Arabian Sea in the lower troposphere from land sources appears to be through this mechanism with the other being the elevated land plume.     

亚洲季风区感热凝结潜热对副高带季节演变的影响

利用1958-1998年NCEP／NCAR的逐日再分析资料，探讨了亚洲夏季风建立期间感热、凝结潜热和副高带季节演变的气候特征，并重点分析它们相互耦合的特征。结果表明：亚洲季风区的地表感热、凝结潜热影响印缅槽生成和阿拉伯副高西移的机制是相似的，5月初，印度半岛较强的感热通量和中南半岛较强的凝结潜热共同影响副高带的断裂及印缅槽的生成，5月底-6月上旬阿拉伯半岛较大的感热通量和印度半岛西侧较强的凝结潜热有利于阿拉伯副高的西移。     

2004年5月西南季风潮及天气影响

2004年5月13—22日广东省的连阴雨天气过程是典型的华南前汛期天气过程。它是与孟加拉湾西南季风潮发生发展相联系的。分析发现，这次孟加拉湾西南季风潮发生发展过程大致上可分为“起潮”过程、“浪花”过程和“落潮”过程三个阶段。在这次过程中，印度洋南半球越赤道气流起了激发的作用。     

副热带高压强度变化的模糊聚类诊断预测

采用模糊C均值聚类 (FCM)、遗传算法 (GA) 和模糊减法聚类 (FSC) 交叉融合、优势互补思想进行副热带高压影响因子的综合聚类分析和副热带高压指数的诊断预测。在统计分析的基础上, 通过选择若干与副热带高压指数关系密切的影响因子构成了高维特征空间, 进行了综合聚类分析, 实现了副热带高压指数的聚类判别和诊断预测。该文提出的综合聚类方法既可克服FCM/GA算法全局/局部寻优的不足, 又可客观确定聚类数目。试验结果表明, 该方法具有良好的分类效果, 判别结果与实况基本相符。     

Carbon dioxide exchange and the mechanism of environmental control in a farmland ecosystem in North China Plain

CO2 flux was measured continuously in a wheat and maize rotation system of North China Plain using the eddy covariance technique to study the characteristic of CO2 exchange and its response to key environmental factors. The results show that nighttime net ecosystem exchange (NEE) varied exponentially with soil temperature. The temperature sensitivities of the ecosystem (Q10) were 2.94 and 2.49 in years 2002-2003 and 2003-2004, respectively. The response of gross primary productivity (GPP) to photosynthetically active radiation (PAR) in the crop field can be expressed by a rectangular hyperbolic function. Average Amax andαfor maize were more than those for wheat. The values ofαincreased positively with leaf area index (LAI) of wheat. Diurnal variations of NEE were significant from March to May and from July to September, but not remarkable in other months. NEE, GPP and ecosystem respiration (Rec) showed significantly seasonal variations in the crop field. The highest mean daily CO2 uptake rate was -10.20 and -12.50 gC·m-2·d-1 in 2003 and 2004, for the maize field, respectively, and -8.19 and -9.50 gC·m-2·d-1 in 2003 and 2004 for the wheat field, respectively. The maximal CO2 uptake appeared in April or May for wheat and mid-August for maize. During the main growing seasons of winter wheat and summer maize, NEE was controlled by GPP which was chiefly influenced by PAR and LAI. Rec reached its annual maximum in July when Rec and GPP contributed to NEE equally. NEE was dominated by Rec in other months and temperature became a key factor controlling NEE. Total NEE for the wheat field was -77.6 and -152.2 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively, and -120.1 and -165.6 gC·m-2·a-1 in 2003 and 2004 for the maize field, respectively. The cropland of North China Plain was a carbon sink, with annual -197.6 and -317.9 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively. After considering the carbon in grains, the cropland became a carbon source, which was 340.5 and 107.5 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively. Affected by climate and filed managements, inter-annual carbon exchange varied largely in the wheat and maize rotation system of North China Plain.     

亚洲夏季风爆发与热源强迫下的热带大气Rossby波

对南海夏季风爆发前的风场和局地对流凝结加热强迫作用进行了合成分析, 表明南海夏季风爆发前局地对流凝结加热作用对与南海夏季风爆发密切相关的低频涡对的产生起着重要作用.然后, 从动力学的角度研究了带有外部热源强迫的赤道β平面上的Rossby波, 利用Gardner-Morikawa变换和摄动展开方法, 得到了热源强迫下描写赤道Rossby的mKdV方程, 进而得到了不同热源形式下切变气流中赤道非线性Rossby波的解析解.结果表明, 不同类型的热源对赤道Rossby波的结构起着非常重要的作用, 同时也为南海夏季风爆发前低频涡对的形成给出了一种动力学解释.