三维变分同化雷达资料暴雨个例试验

采用中国新一代数值预报模式及其同化系统开展雷达资料的三维变分同化和数值模拟研究.通过一次暴雨个例的对比试验,结果表明:不考虑垂直运动影响的情况下,仅同化多普勒雷达径向风资料可以增加初始场中的中小尺度系统信息,并在一定程度上改善预报开始阶段的降水;同化由反射率因子导出的垂直速度、雨水混合比并令上升区饱和,可以较大改善降水预报结果;联合同化径向速度和反射率因子资料将得到它们的共同影响.模拟的β中尺度对流系统6 h的演变过程与观测十分一致,基本消除了旋转加强现象.发展旺盛阶段的对流单体南北方向范围约50 km,最大上升速度位于500 hPa附近,超过3.0 m/s;雨水最大含量在400 hPa附近,超过5.0 g/kg;云水最大值位于600 hPa,约0.5 g/kg;造成的降水强度可达30 mm/h,具有明显的β中尺度系统的特征.初始场中水汽是否达到β中尺度降水维持所需条件是至关重要的,如果初始场中水汽条件较差,即使含有云水、雨水、垂直速度的信息,这些信息也会很快消亡,难以维持下去;此外,雷达资料的质量控制也是十分重要的.     

Cloud Variations under Subtropical High Conditions

The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.     

春夏季青藏高原积雪对中国夏末秋初 降水的影响及其可能机制

本文首先利用最大协方差分析方法,探讨青藏高原积雪与中国降水之间的联系,发现中国夏末秋初（8～10月,简称ASO）降水与前期及同期高原积雪有着显著联系,当春夏季青藏高原西部多雪时,其后ASO中国长江及其以南地区多雨,而东部沿海的狭长区域少雨。进一步引入最大响应估计等方法,研究中国区域降水对高原积雪异常的响应及其可能的物理机制,结果表明,冬春季高原多雪异常可持续到夏季,并通过改变地表热力状况,导致ASO南亚高压减弱,同时在高、低空激发出两支波列:高层200 hPa波列沿中高纬西风急流传播,自高原经蒙古到达日本呈现明显的“负—正—负”位势高度异常传播,日本上空为气旋性异常环流;低层850 hPa波列起于高原,经孟加拉湾至中国南海,沿着西南气流传播,导致台湾附近的反气旋性异常环流,其西侧的偏南气流,将南海丰富的水汽输送至中国南部湖南、广西;而高层中心位于日本的气旋性异常环流西侧的偏北气流利于北方天气尺度扰动向南移动,它们为长江中下游及其以南地区多雨提供了有利条件。进一步计算定常波波数也表明,高层西风急流与低层西南季风气流作为波导,有利于高原上空的扰动沿着高、低空2支通道向东传播。由于东部沿海浙江、福建为正位势高度异常区,低层反气旋性异常环流则抑制了该区域的降水。     

ANALYSIS OF STRUCTURE EVOLUTION AND ENVIRONMENTAL CONDITIONS OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC DURING EXTRATROPICAL TRANSITION

Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.     

黑龙江省闪电活动特征及其与地面相对湿度的响应关系

利用2006-2017年黑龙江省闪电定位资料和日平均地面相对湿度资料,采用数理统计、Pearson相关分析、GIS空间分析技术,研究了闪电密度和强度对地面相对湿度（R_H）的响应关系。结果表明：地面R_H过小或过大都不利于闪电活动产生;当R_H < 25%时,几乎无闪电发生,当R_H < 77%时,R_H增加有利于闪电活动发生,当R_H>79%时,随着R_H增加,闪电活动减少;当R_H < 77%时,闪电密度与之呈正相关,闪电强度与之呈负相关;当R_H>79%时,闪电密度与之呈负相关,闪电强度与之呈正相关;地面R_H的临界值域约为77%-79%;70%≤ R_H ≤ 90%区间为闪电易发湿度区间,在闪电密度与湿度相关度高的区域,闪电更趋于集中发生在闪电易发湿度区间。     

Numerical Physical Mechanism and Model of Turbulent Cascades in a Barotropic Atmosphere

In a barotropic atmosphere, new Reynolds mean momentum equauons including turbulent viscosit,dispersion, and instability are used not only to derive the KdV-Burgers-Kuramoto equation but also to analyze the physical mechanism of the cascades of energy and enstrophy. It shows that it is the effects of dispersion and instability that result in the inverse cascade. Then based on the conservation laws of the energy and enstrophy, a cascade model is put forward and the processes of the cascades are described.     

Review of the Study of Nonlinear Atmospheric Dynamics in China （1999-2002）

Researches on nonlinear atmospheric dynamics in China (1999-2002) are briefly surveyed. This review includes the major achievements in the following branches of nonlinear dynamics: nonlinear stability theory,nonlinear blocking dynamics, 3D spiral structure in the atmosphere, traveling wave solution of the nonlinear evolution equation, numerical predictability in a chaotic system, and global analysis of climate dynamics.Some applications of nonlinear methods such as hierarchy structure of climate and scaling invariance, the spatial-temporal series predictive method, the nonlinear inverse problem, and a new difference scheme with multi-time levels are also introduced.     

全球数值模式中的台风初始化Ⅱ: 业务应用

由于缺少大量有效的观测资料,台风初始化对数值天气预报业务模式而言,仍然是一个悬而末决的难题.中国国家气象中心自从1996年将台风数值预报系统投入业务运行以来,一直使用经验的人造bogus涡旋台风初始化技术.实际上,不同时期的台风有着不同的环流结构,即使同一个台风在不同的生命期也具有不同的结构特征,而这些结构特征的差异并不能依靠现有的bogus涡旋技术体现出来,这种主观方法的统一性与台风在时空上的差异性形成了强烈的反差.最近,基于国家气象中心全球资料分析同化-预报循环系统,设计和发展了一套新的台风初始化业务方案,它主要由初始涡旋形成、涡旋重定位和涡旋调整3部分过程组成.相比于业务中使用的人造bogus涡旋台风初始化方案,新方案在很大程度上减少了人为因素对台风涡旋结构的影响,而更多地是依靠数值模式自身的动力和物理过程来协调约束产生三维空间的涡旋结构.应用新方案,文中对生成于西北太平洋的2006年0605号台风格美(Kaemi)进行了数值试验,初步分析表明,新方案在实现台风涡旋环流结构的初始化方面效果较好,同时,对台风格美多个时次的预报结果也显示,相比于业务使用的bogus方案而言,新方案对台风路径平均预报误差有了大幅度的降低.     

超低仰角扫描改进高山雷达降水估测

利用2004年5月云南大暴雨过程的26次昆明雷达超低仰角对比观测体扫资料,分析了昆明雷达0°和0.5°仰角数据以及对比了定量估测降水的情况。结果表明：0°仰角探测到的降水分布范围更大;与0.5°仰角相比,通过定量计算,探测降水范围能提高约9.96%,估测的降水总量约为11.6%。从探测到的降水量和范围来看,0°仰角较0...     

SENSITIVITY TESTS OF INTERACTION BETWEEN LAND SURFACE PHYSICAL PROCESS AND ATMOSPHERIC BOUNDARY LAYER*

In this paper,an interactive model between land surface physical process and atmosphere boundary layer is established,and is used to simulate the features of soil environmental physics,surface heat fluxes,evaporation from soil and evapotranspiration from vegetation and structures of atmosphere boundary layer over grassland underlying.The sensitivity experiments are engaged in primary physics parameters.The results show that this model can obtain reasonable simulation for diurnal variations of heat balance,soil volumetric water content,resistance of vegetation evaporation,flux of surface moisture,and profiles of turbulent exchange coefficient,turbulent momentum,potential temperature,and specific humidity.The model developed can be used to study the interaction between land surface processes and atmospheric boundary layer in city regions,and can also be used in the simulation of regional climate incorporating a mesoscale model.