Association of Indian Ocean ITCZ Variations with the Arctic Oscillation during Boreal Winter

In this study,the authors analyzed the associations between the Arctic Oscillation(AO)and the tropical Indian Ocean(TIO)intertropical convergence zone(ITCZ)in boreal winter for the period 1979–2009.A statistically significant AO-TIO ITCZ linkage was found.The ITCZ vertical air motion is significantly associated with the AO,with upward(downward)air motion corresponding to the positive(negative)AO phase.The Arabian Sea anticyclone plays a crucial role in linking the AO and the TIO ITCZ.The Arabian Sea vorticity is strongly linked to high-latitude disturbances in conjunction with jet stream waveguide effects of disturbance trapping and energy dispersion.During positive(negative)AO years,the Arabian Sea anticyclone tends to be stronger(weaker).The mean vorticity over the Arabian Sea,averaged from 850hPa to 200 hPa,has a significant negative correlation with AO(r=0.63).The anomalous anticyclone over the Arabian Sea brings stronger northeastern winds,which enhance the ITCZ after crossing the equator and result in greater-than-normal precipitation and minimum outgoing long-wave radiation.     

Observations and Modeling of Ice Water Content in a Mixed-Phase Cloud System

The ice water content(IWC) distribution in a mixed-phase cloud system was investigated using Cloud-Sat data,aircraft measurements,and the Weather Research and Forecasting(WRF) model.Simulated precipitation and IWC were in general agreement with rain gauge,sat-ellite,and aircraft observations.The cloud case was char-acterized by a predominant cold layer and high IWC throughout the cloud-development and precipitation stages.The CloudSat-retrieved products suggested that the IWC was distributed from 4.0 to 8.0 km,with the maximum values(up to 0.5 g m-3) at 5.0-6.0 km at the earlymature stage of cloud development.High IWC(up to 0.8 g m-3) was also detected by airborne probes at 4.2 and 3.6 km at the late-mature stage.The WRF model simulation re-vealed that the predominant riming facilitated rapid ac-cumulation of high IWC at 3.0-6.0 km.     

Influence of Vertical Shear of Basic Tangential Wind on the Development and Maintenance of Typhoon

By using a linear symmetric Conditional Instability of Second Kind (CISK) model containing basic flow, we study the interactions between basic flow and mesoscale disturbances in typhoon. The result shows that in the early stage of typhoon formation, the combined action of vertical shear of basic flow at low level and CISK impels the disturbances to grow rapidly and to move toward the center of typhoon. The development of disturbances, likewise, influences on typhoon’s development and structure. Analysis of the mesoscale disturbances’ development and propagation indicates that the maximum wind region moves toward the center, wind velocity increases, and circulation features of an eye appear. Similarly, when a typhoon decays, the increase of low-level vertical wind shear facilitates the development of mesoscale disturbances. In turn, these mesoscale disturbances will provide typhoon with energy and make the typhoon intensify again. Therefore, it can be said that typhoon has the renewable or self-repair function.     

Modeling Study of the Effect of Anthropogenic Aerosols on Late Spring Drought in South China

In this study,the mechanisms underlying the decadal variability of late spring precipitation in South China are investigated by using the latest Community Earth System Model version 1 （CESM1）.We aim to unravel the effects of different climate forcing agents such as aerosols and greenhouse gases （GHGs） on the decadal variation of precipitation,based on transient experiments from pre-industry （for year 1850） to present-day （for year 2000）.Our results reveal that：（1） CESM1 can reproduce the climatological features of atmospheric circulation and precipitation for the late spring in South China; （2） only simulations including the forcing of anthropogenic aerosols can reproduce the observed decreasing trend of late spring precipitation from 1950-2000 in South China; （3） aerosols affect the decadal change of precipitation mainly by altering the large-scale atmospheric circulation,and to a less extent by increasing the lower-tropospheric stability to inhibit the convective precipitation; and （4） in comparison,other climate forcing agents such as GHGs have much smaller effects on the decadal change of spring precipitation in South China.     

对流云盐粉催化的数值模拟研究

利用三维对流云盐粉催化模式对一次对流云降水进行了盐粉催化模拟试验。模式中考虑了盐粉与云雨滴和冰相粒子间的相互作用。模拟结果显示,当采用20μm粒径的盐粉进行单次催化时,催化效果较好,地面总雨量可增加20%,催化次数的增多会导致降水的减少。霰融化成雨是雨滴增长的主要机制,霰碰并过冷云水是霰增长的主要机制,催化后霰融化成雨和霰碰并过冷云水的速率均有提高。催化会引起水成物云滴、冰晶、霰和雨滴的比质量变化。霰和云滴的粒径也在催化后出现了明显的增大。催化后短时间内动力过程出现了变化。     

基于信息扩散理论的甘肃省农业旱灾风险分析

干旱灾害是甘肃省最严重的自然灾害。以甘肃省1990～2010年的干旱受灾面积和播种面积的统计数据为基础,采用基于信息扩散理论的模糊数学方法,建立甘肃省农业旱灾风险分析模型,对甘肃省农业旱灾进行分析。结果表明,甘肃省旱灾受灾指数在22%时的旱灾受灾概率最大,超过80%的旱灾受灾可能性就很小;旱灾风险值显示,农业旱灾受灾指数>10%～20%时的风险概率为1～1.6 a一遇,农业旱灾受灾指数>50%时的风险概率为12.2 a一遇,呈现出干旱发生周期短、发生频率高的特点,这说明甘肃省的农业旱灾出现频率高,发生周期短,灾情不容忽视。研究结果增加了对甘肃省农业旱灾的认识,对地区防灾减灾工作具有指导意义。     

“9.16”广东旱区罗定特大暴雨灾害天气成因分析

用常规天气观测资料、ncep再分析资料、卫星云图、天气雷达等资料对2009年9月16日出现在广东最少雨区之一的罗定市的强降水特大暴雨过程进行分析,结果表明:"巨爵"减弱后的低压系统移动缓慢,其与西伸的"方头"副高之间气压梯度增大,偏南急流在粤西加强和维持是形成"9.16"暴雨的最主要天气系统;边界层内持续的水汽输送和强辐合上升运动是特大暴雨产生的最主要原因;地面弱冷空气的渗透也为暴雨的产生提供了有利的条件;罗定特殊的地形对此次暴雨的形成也十分有利。卫星云图上罗定上空云系稳定少动和雷达回波上南北向的对流云带中的列车效应是这次强降水过程的显著特点。     

夏季湖北电网气象敏感负荷预测模型研究

利用2009-2010年湖北电网日用电负荷资料和气象资料,提出了基于电网负荷的分解算法,将电网日最大负荷分解为基础负荷与气象敏感负荷2个主要分量.其中,气象敏感负荷与气温、相对湿度及风速的综合气象敏感负荷条件指数相关.提出了基于权重指数的湖北省面平均气象敏感负荷条件指数的算法.利用相关比法,分析了湖北省气象敏感负荷与面均气象敏感负荷条件指数的非线性关系.基于均方偏差最小原理和非线性最小二乘法,建立了夏季湖北电网气象敏感负荷与面均气象敏感负荷条件指数的多项式预测关系模型.经2010年9月模型应用检验表明,预测平均误差低于6％.该模型可用于夏季湖北省电力专业气象服务工作.     

Poleward expansion of the hadley circulation in CMIP5 simulations

Observational analyses have demonstrated that the Hadley circulation has expanded poleward in recent decades. Important issues are what caused the widening of the Hadley circulation and whether the observed widening is related to anthropogenic forcing. In the present study, we use currently available simulations of the Coupled Model Intercomparison Project Phase-5 (CMIP5) to analyze changes in the width of the Hadley circulation. It is found that CMIP5 historical simulations with greenhouse gas (GHG) forcing generate a total widening of ～0.15o0.06o in latitude (10 yr)-1 for the period 1979--2005, and the widening in CMIP5 historical simulations with all forcings is ～0.17o0.06o per decade. Similar to that in CMIP3, the simulated poleward expansion in CMIP5 is much weaker than the observational reanalyses. In CMIP5 projection simulations for the 21st century, magnitudes of widening of the Hadley circulation increase with radiative forcing. For the extreme projected radiative forcing of RCP8.5, the total annual-mean widening of the Hadley circulation is ～0.27o0.04o(10 yr)-1 in the 21st century. Although CMIP5 underestimates observed poleward expansion of the Hadley circulation, the results of this study suggest that the observed trends in the width of the Hadley circulation are caused by anthropogenic forcing and that increasing GHGs play an important role in the observed poleward expansion of the Hadley circulation, in addition to other forcings emphasized in previous studies.     

Intraseasonal Oscillation in Global Ocean Temperature Inferred from Argo

The intraseasonal oscillation(ISO;14-97-day periods) of temperature in the upper 2000 m of the global ocean was studied based on Argo observations from 2003-2008.It is shown that near the surface the ISO existed mainly in a band east of 60 E,between 10 S and 10 N,and the region around the Antarctic Circumpolar Current(ACC).At other levels analyzed,the ISOs also existed in the regions of the Kuroshio,the Gulf Stream,the Indonesian throughflow,the Somalia current,and the subtropical countercurrent(STCC) of the North Pacific.The intraseasonal signals can be seen even at depths of about 2000 m in some regions of the global ocean.The largest amplitude of ISO appeared at the thermocline of the equatorial Pacific,Atlantic and Indian Ocean,with maximum standard deviation(STD) exceeding 1.2 C.The ACC,the Kuroshio,and the Gulf Stream regions all exhibited large STD for all levels analyzed.Especially at 1000 m,the largest STD appeared in the south and southeast of South Africa-a part of the ACC,with a maximum value that reached 0.5 C.The ratios of the intraseasonal temperature variance to the total variance at 1000 m and at the equator indicated that,in a considerable part of the global deep ocean,the ISO was dominant in the variations of temperature,since such a ratio exceeded even 50% there.A case study also confirmed the existence of the ISO in the deep ocean.These results provide useful information for the design of field observations in the global ocean.Analysis and discussion are also given for the mechanism of the ISO.