南大洋海冰气候特征研究

应用1973～1988年海冰资料，将南大洋划分为5个海区，即:20～88°E，90～158°E，160°E～132°W，130～62°W，60°W～18°E，按这5个海区分析了南大洋海冰的空间分布特征及其时间变化特征。这些研究结果，对气候背景的研究是有益的。     

Peculiarities of the flow front structure in the Buor-Khaya Bay (the Laptev Sea) in winter

Hydrological flow front whose location and structure depend on the value of the Lena River water flow forms in winter under the ice in the Buor-Khaya Bay. The flow front is characterized by the baroclinic and thermocline components. Under the lens of desalinated waters, the layers of increased temperature and salinity alternate with the layers of decreased salinity and temperature. On the periphery of the front, the thermocline stratification results in the formation of the cold isopycnic intrusion at intermediate levels. The cross section of the cold intrusion in the bay amounted to ??50?C85 km and its thickness, from 3?C5 to 15 m. The waters of cold intrusions are rich with oxygen and favor the ventilation of the bay waters. The winter flow increase results in the significant widening of the river impact zone, warming of the coastal zone waters, and stratification intensification.     

A Case of Convection Development over the Western Mediterranean Sea: A Study through Numerical Simulations

Summary  A convective case producing heavy precipitation in the western Mediterranean region, characterized by pronounced upper level forcing and main rainfall over the sea, is studied. On the day of the event (September 28^th, 1994), more than 140 mm of precipitation were recorded in coastal lands of eastern Spain, and 180 mm were estimated over the sea with radar data. Synoptically, the case appears to combine warm and moist easterly advection at low levels, typically observed in torrential rainfall events of the region, with a less common strong upper level dynamical forcing. A set of mesoscale numerical simulations using the Hirlam model is performed to investigate the mechanisms responsible for the convection development, and to assess the influence of the orography on the rainfall field. Model output diagnosis indicates that in addition to the lower level forcing, a two-jets interaction is decisive for the triggering and driving of the convection during the event. Moreover, a non-topographic simulation reveals a relatively weak influence of the orography on this event when compared with other similar heavy precipitation cases in eastern Spain. Previous studies have shown an orographic influence of more than 90% on the rainfall whereas in this case about 50% of the precipitation over the area is attributed to the orographic forcing. The study is extended with an analysis of the individual effects of the Atlas and Iberian Peninsula, by means of a factor separation technique. It is shown that the Atlas range induces a redistribution of the precipitation over the Mediterranean, whereas local enhancements can be attributed to the Iberian topography. Received March 2, 1999     

Development of the forest fire forecast method (a Case Study for the Far East)

Presented are the first results of the development of long-range forecast of forest fire risk on the territory of the Russian Far East. Used are the main concepts presented in the papers of G.R. Bregman and B.M. Ginzburg. Forest fire risk parameters in Khabarovsk territory, Jewish autonomous region, and Amur region for the previous years are reconstructed using the heat-balance methods. Carried out is the first stage of the research based on the synoptic statistical method: the typical fields are singled out of meteorological variables in the troposphere and lower stratosphere in the midlatitudes of the Northern Hemisphere from the Azores to the Aleutian Islands. Presented is the automated system developed by the authors and separating these meteorological fields significant for the forecast of forest fire conditions on the vast territory.     

亚热带森林非甲烷碳氢化合物的研究 I.季节变化(钢瓶采样)

对中国亚热带森林地区的非甲烷碳氢化合物(NMHC)进行了一年多的钢瓶采样,并利用气相色谱仪对空气样品进行了分析,得到了大量NMHC的实测资料以及它们的季节变化规律和相互之间的关系.研究表明,NMHC的主要来源是当地植物的排放.对异戊二烯及其影响因子进行了详细研究.     

中纬度夏季一次深厚对流过程的数值模拟研究:高空热力层结和风切变影响

针对一次发生在中纬度夏季的深厚对流过程进行的数值模拟研究的结果,引入一个较详细描述深厚对流状态下云微物理过程的参数化方案,对一个有限差分三维非静力弹性大气数值模式进行了改进.数值模拟得到了与天气雷达观测一致的结果.结果还显示,对于这次穿透高度超过了对流层顶的深厚对流过程,与高空斜压扰动有关的上对流层弱稳定热力层结对系统的维持起到了重要的作用.另外,还发现强烈的对流发展到对流层顶的高度时,受上曳体的驱动,在对流层顶附近的稳定层结中产生浮力性的扰动;它们与风切变相结合,进而对系统的水平移动产生控制作用.     

热带气旋与西南低涡相互作用的个例研究 Ⅰ.诊断分析

通过对1989年7月8～11日西南低涡与活动于南海的强热带气旋发生远距离相互作用的诊断分析,揭示出中低纬系统相互作用在促进西南低涡发展和暴雨发生中所起的一些重要作用.     

El Ni(n)o事件大气-洋流异常与暖海温传播机理研究

利用1971～2000年逐月SODA (Simple Ocean Data Assimilation) 同化资料 (Carton等, 2004)、 1980～2000年逐月NCEP/NCAR再分析资料 (Kalnay等, 1996) 探讨中部型 (暖海水首先出现在120°W以西) 和东部型 (暖海水首先出现在120°W以东) El Ni(n)o事件赤道纬向风应力及洋流的异常变化与暖海水信号的传播特征.研究指出: (1) 中部型和东部型El Ni(n)o事件发生时, 太平洋上赤道海表最大西风应力距平在西太平洋地区都有显著的东传现象, 但中部型El Ni(n)o事件西风应力距平强度强, 造成西太平洋赤道表层的东向流可达东太平洋地区, 这类El Ni(n)o事件强度偏强.(2) 中部型El Ni(n)o事件, 赤道表层洋流辐合区及其下沉运动由西太平洋向东太平洋传播, 辐合下沉运动抑制了深层冷海水上翻, 西太平洋暖水能够传到东太平洋与西太平洋赤道表层洋流辐合区及其下沉运动的东移有关.(3) 东部型El Ni(n)o事件西太平洋赤道表层洋流辐合区及其下沉运动没能直接传到东太平洋地区, 东太平洋暖水形成与局地 (120°W以东) 辐合下沉运动抑制深层冷海水上翻有关; 东部型El Ni(n)o事件暖池次表层的暖水, 不是沿着西太平洋赤道次表层向东传播到东太平洋地区, 而是由南太平洋西边界流将暖池海水带到40°S左右的西风漂流区, 再由西风漂流平流到东太平洋.     

Controls on the Northward Movement of the ITCZ over the South China Sea in Autumn: A Heavy Rain Case Study

The autumn Intertropical Convergence Zone(ITCZ) over the South China Sea(SCS) is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds. However, the ITCZ can move north, resulting in heavy rainfall in the northern SCS(NSCS). We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010. The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE), southwesterly winds, and the easterly jet(EJ) in the NSCS. A high pressure center on the east side of Australia, strengthened by the quasibiweekly oscillation and strong Walker circulation, was responsible for the EE to intensify and reach the SCS. The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone, pushed the ITCZ north. Meanwhile, the continental high moved east, which reduced the area of the EJ in the NSCS and made room for the ITCZ. Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ. The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north. As the ITCZ approached 12°N, it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.     

中尺度非均一边界层气候的数值研究: (Ⅱ) 夏季的数值试验

用修改的Nickerson等提出的中尺度模式，对我国北方夏季非均一下垫面上的边界层气候特征进行了研究。结果表明，在晴朗、静风和无扰动系统的条件下，下垫面的非均一性对边界层气候起着决定性的影响。边界层气候特征和低空急流强度与局地环流关系密切。干燥裸地上边界层内出现的逆湿现象，是由下垫面非均一的湿度场和中尺度平流共同引起的。     

A Model Study of the Relationship between Sea-Ice Variability and Surface and Intermediate Water Mass Properties in the Labrador Sea

Sea ice plays an important role in the variability of the Labrador Sea especially in its most western part adjacent to an important region of deep convection. Winter-to-winter re-emergence and propagation of both sea-ice concentration (SIC) and sea surface temperature anomalies have been observed following years of high SIC in this region. They have potentially important links to water mass properties and freshwater and heat transports in the subpolar North Atlantic. This article builds on the results of two precursor papers and presents results from a coupled sea-ice–ocean model study of the interannual variability of sea ice in the Labrador Sea. The relationships between SIC and water column properties in the subpolar North Atlantic are assessed. Winters with high SIC and strong surface cooling are found to be conducive to intensified convection. Surface and mid-depth temperature and salinity anomalies are observed in the Labrador Sea and the northwestern North Atlantic during winters with anomalous Labrador Sea SIC. These anomalies are found to propagate along the major circulation patterns in the subpolar North Atlantic and to persist for up to three years.     

天气雷达回波衰减订正算法的研究(Ⅱ):数值模拟与个例实验

通过数值模拟研究雷达反射率因子呈均匀分布情况下的“可订正厚度”，计算了“无误差”情况下的订正效果以及“观测误差”、“k的误差”、库分辨等因素对订正效果的影响，还用实际观测个例进行衰减订正实验，并与解析算法和迭代算法的订正结果进行比较。结果表明，逐库算法，尤其是逐库近似算法，比迭代法计算效率高，比解析法有更大的稳定范围。     

Impact of Climate Change on Agricultural Production in the Sahel – Part 2. Case Study for Groundnut and Cowpea in Niger

During the last 30 years, the climate of the West African Sahel has undergone various changes, especially in terms of rainfall. This has large consequences for the poor-resource farmers depending mainly on rainfed agriculture. This paper investigates the impacts of current climate variability and future climate change on groundnut and cowpea production in Niger for three major agricultural regions, including the groundnut basin.Niger was one of the largest West African groundnut producing and exporting countries. Groundnut production – as a cash crop – dropped fromabout 312,000 tons in the mid 1960s (about 68% exported) to as low as 13,000tons in 1988 and increased again to 110,000 tons in 2000. Cowpea, a food crop, showsa different tendency, going from 4,000 tons in the mid fifties to a maximum of 775,000 tons in 1997, and its cultivated area is still increasing. It is also a cash crop in local economies (especially for women).To highlight the impact of climate change on groundnut and cowpea production (significantly determined by rainfall in July, August and September), the following components of the rainfall regime were calculated for the period 1951–1998: mean annual and monthly rainfall, beginning, end and lengthof the rainy season, number of rainy days per month, amount of rainfall per rainy day and the maximum length of dry spell per month. Three sub-periods whose duration varied per region were defined: for Dosso 1951–1968,1969–1984 and 1985–1998; for Maradi 1951–1970, 1971–1987 and1988–1998; and for Zinder 1951–1966, 1967–1984 and 1985–1998. A change in rainfallregime components was observed between the three sub-periods, which were characterized in chronological order by wet, dry and intermediate conditions. To assess the impact of climate variability and change on groundnut and cowpea production, a statistical modeling approach has been followed, based on thirteen predictors as described and discussed in the preceding paper. Climate change is mimicked in terms of reduced total amount of rainfall for the three main rainfall months and an increased temperature, while maintaining other significant predictors at a constant level. In 2025,production of groundnut is estimated to be between 11 and 25% lower, while cowpeayield will fall maximally 30%. Various strategies to compensate thispotential loss are presented for the two crops.     

北京一次对流云人工催化作业效果检验

利用北京SA波段天气雷达每6 min一次的体扫数据和FY-2气象卫星云图,以2015年8月22日北京平谷地区一次人工影响天气作业为例,分析作业单元和与之条件相似的对比单元两者雷达回波参数的变化,并运用非参数检验方法进行显著性检验,对冷涡后局地新生的强对流风暴群的人工催化效果进行检验。结果表明,第一次地面作业后,在作业点位置的回波明显减弱,第二次地面作业后,作业点位置的回波持续减弱,组合反射率大于30 dBz的回波逐渐减弱消失,同时作业点东北方的回波不断增强合并,并向东边移动。此次作业所在区域的对流发展强烈,组合反射率大于45 dBz的回波直径为5—20km,组合反射率大于50 dBz的持续时间较长。显著性检验表明,作业回波与对比回波的最大组合反射率和平均组合反射率的衰减率通过了信度为0.15的显著性检验,存在显著差异;回波面积衰减速率通过了信度为0.3的显著性检验;且作业回波的各物理量的衰减率均小于中值和平均值,表明催化作业对维持云系发展起到积极作用。     

A Study of the Extratropical Transformation of Typhoon Winnie （1997）

The complicated evolutive process of how a tropical cyclone transforms into an extratropical cyclone is still an unresolved issue to date, especially one which arises in a weakly baroclinic environment. Typhoon Winnie （1997） is studied during its extratropical transformation stage of extratropical transition （ET） with observational data and numerical simulations. Results show that Winnie experienced its extratropical transformation to the south of the subtropical high without intrusion of the mid-latitude baroclinic zone. This is significantly different from previous studies. Analyses reveal that the cold air, which appeared in the north edge of Winnie circulation, resulted from the precipitation drag and cooling effect of latent heat absorption associated with the intense precipitation there. The cooling only happened below 3 km and the greatest cooling was below 1 km. With the cold air and its advection by the circulation of Winnie, a front was formed in the lower troposphere. The front above is related not only to the cooling in the lower level but also to the warming effect of latent heat release in the middle-upper levels. The different temperature variation in the vertical caused the temperature gradient over Winnie and resulted in the baroclinicity.     

A Study on the Mesoscale Convective Systems during the Summer Monsoon Onset over the South China Sea in 1998Part I: Analysis of Large-Scale Fields for Occurrence and Development of the Mesoscale Convective Systems

1. Introduction China is located in the East Asian monsoon re- gion. Every year's weather and climate in this region is deeply affected by the monsoon activities. Es- pecially, during flooding season (May to September), the summer monsoon controls large-scale precipitation patterns, the movement of seasonal rain belt and oc- currence of drought/flood disasters. The Asian mon- soon can be divided into two systems (Tao and Chen, 1987). As a major component and its unique location, the South …     

A Study on the Mesoscale Convective Systems during the Summer Monsoon Onset over the South China Sea in 1998 Part Ⅰ: Analysis of Large-Scale Fields for Occurrence and Development of the Mesoscale Convective Systems

The summer monsoon onset over the northern South China Sea (SCS) in May 16-20, 1998 was characterized by the abrupt onset of mesoscale convective activities and rapid increase of precipitation. The possible mechanism for formation of the mesoscale convective systems (MCSs) and related rain belts were revealed through discussing their forming physical conditions under the large-scale background: (1) The high pseudo-equivalent potential temperature and the convective instability in the lower troposphere, the low-level southwesterly confluence and the high-level divergence over South China and the northern SCS provided the favorable large-scale thermodynamic and dynamic conditions for development of MCSs. The southwesterly flow from the Bay of Bengal (BOB) interacted with that to the western flank of the subtropical high, which constituted the major moisture channels, thus bringing about deep wet layers and strong moisture convergence;(2) triggered by several cold troughs from high and mid latitudes, the convectively unstable energy was released and the convective activities over the northern SCS broke out abruptly;(3)analysis of retrieved precipitation based on the dual-Doppler radar during South China Sea Monsoon Experiment (SCSMEX) indicated that active convection influenced by the monsoon trough and corresponding wind shear line organized and formed continually some mesoscale convective rainbelts. During May 15-19,about 12 precipitation processes with 6-12-hour life span or more were observed;and (4) under the favorable synoptic conditions, establishment of the monsoon trough and shear line in the low levels, as well as production and development of mesoscale low vortex were all necessary conditions for the formation and maintenance of MCSs.     

华北强天气的水汽图象特征研究

利用1991～1993年共37个时次的NOAA TOVS反演的红外水汽亮度温度图、卫星云图及常规气象资料，分析华北地区夏季强天气过程，归纳出降水和强对流天气的水汽图象4种基本类型，为分析和预报此类天气提供了新的依据。     

Testing and Improving the Performance of the Common Land Model:A Case Study for the Gobi Landscape

Land surface processes take place on the interface between the earth and atmosphere, exerting significant influences on the weather and climate. Correct modeling of these processes is important to numerical weather forecast and climate prediction. In order to obtain a more thorough understanding of the land surface processes over the Gobi landscape, we evaluated the performance of the Common Land Model(Co LM) at Dunhuang station in Gansu Province of China to determine whether the model formulation, driven by observational data, is capable of simulating surface fluxes over the underlying desert surface. In comparison with the enhanced observation data collected at Dunhuang station over the period 22–28 August 2008, the results showed that the surface albedo simulated by Co LM was larger than that in the observation, and the simulated surface temperature was lower than the observed. After the measured values were used to correct the surface albedo, the solar radiation absorbed by the ground surface was more consistent with the measurements. A new empirical relationship of the surface thermal exchange coefficient rah was used to modify the thermal aerodynamic impedance. The simulated soil surface temperature became significantly closer to the observed value, and the simulated surface sensible heat as well as net radiative fluxes were also improved.