大兴安岭特大森林火灾气象成因的分析

本文分析了1987年5月大兴安岭特大森林火灾的气象成因。前期干旱、少雨及5月上旬气温的显著偏高，是发生特大火灾的气候背景。大兴安岭位于我国最北部，属于寒温带，年平均气温只有-3—-6 ℃，有机物分解缓慢，使林内可燃物越积越多，是发生火灾的物质基础。在已有大量火源存在的情况下，正逢有强干冷锋过境，平均风速达8—12 m/s，最大17.0 m/s，使火势急速蔓延，是造成特大森林火灾的最关键因素。地形与气温、积雪有密切关系，也对火场的蔓延有一定的影响。     

The turbulent characteristics in the lowest part of the sea breeze front in the atmospheric surface layer

Tower measurements for the sea breeze front in the surface layer were carried out over the Kochi plain about 2 km inland from Tosa Bay in Shikoku, Japan during the period from August 1986 to October 1987. The study shows that the penetration time of the sea breeze has an annual variation, which is around 0830 JST in summer and 12 JST in winter, and that the width of the sea breeze front depends on the ratio of the sea breeze speed and the opposing flow speed. Moreover, the frontal width also shows a seasonal variation.The characteristics of the vertical winds (w) found just before and just after the passage of the sea breeze front lead to remarkable downdrafts and updrafts, respectively, with relatively large vertical velocities. Such behaviour ofw is shown to be consistent with the flow relative to the head of the front as reviewed by Simpson (1987), influencing the magnitude of the turbulence scale and the turbulent energy dissipation near the ground surface.     

THE DIFFUSION PARAMETER AND HEAT-RELEASE RATE OF PLUMES CAUSED BY THE 1987 FOREST FIRE IN NORTHEAST CHINA

In this paper the meteorological background for the formation of plume from the forest fire in NortheastChina on 7—8 May 1987 is stated.The long-range instantaneous diffusion parameters are calculated by usingthe satellite photograph of the plumes with visible length ranging from 100 to over 500 kin.The results of cal-culation show that the relations between instantaneous diffusion parameter and travel time(up to 60000 sec.)obey the law of linear or 3/2 power.In addition,heat release from the fire on May 7—8 estimated by puffrising formula can meet,in respect to the order of magnitude,the value gained on the field survey.     

On the onset of the south china sea summer monsoon in 1998

1.IntroductionChinesescientistshavepointedoutsincethe1980sthattheAsiansummermonsooniscomposedoftheSouthAsian(Indian)monsoonsystemandtheEastAsianmonsoonsystem,whichhavetheirparticularcharacteristicsrespectivelybutalsointeractoneachother;andtheAsiansummermonsoonbreaksoutintheSouthChinaSea(SCS)regionatfirst,thenspreadsnorthwestwardandnorthwardrespectively,finallytheSouthAsiansummermonsoonandtheEastAsiansummermonsoonaresetup(TaoandChen,1987;JinandChen,1985;Zhuetal.,1986).Muchattentionhasbe…     

西藏地区强降雪过程的波包分布及传播特征

利用NCEP/NCAR高度场的再分析资料,通过波包传播诊断方法(WPD),对2005年10月19～23日西藏地区中东部及南部边缘地区一次大范围强降雪天气过程进行波包分布与波能传播特征分析。结果表明:500hPa高度场的波包分布和传播特征很好地反映此次过程;强降雪天气发生在波包大值区域内而且反映了过程的爆发和消亡;波包的分布特征与强对流天气的发生状况是一致的;波包的移动路径很好地反映了扰动能量的传播。此次过程是"积累-释放"的三次循环。     

冷锋天气大气边界层内臭氧及 氮氧化物的观测研究

利用北京325 m气象塔作为高空平台,于1997年10月观测到一次冷锋过程大气边界层内O3及NOx体积分数的变化,研究了O3及NOx体积分数与气象要素之间的关系,着重讨论了冷锋过境前后O3及NOx的体积分数变化及其与输送过程的关系。研究表明:北京大气边界层中下层存在明显的O3体积分数垂直梯度,O3的垂直输送与风速及温度梯度密切相关。冷锋过程有利于高层O3向低层输送,使O3体积分数垂直梯度明显减小,并使NOx体积分数显著降低。     

一次海风锋天气过程分析与数值模拟

利用NCEP再分析资料、自动气象站观测数据、多普勒天气雷达反射率因子和WRF模式,对2015年5月24日午后,海南岛东北部出现的一次较强的海风锋降水天气进行过程分析和数值模拟。结果表明:强降水发生期间,海南岛处于副热带高压边缘,中低层水汽来源充沛,降水前后K指数变化明显;两支分别来自海口海岸线向东南移动与来自文昌海岸线向西北移动的海风锋的发展、增强与移动,是导致本次降水的主要原因。另外,中部山区小尺度的地形辐合有利于过程期间海风锋的加强与发展;WRF模式的模拟结果说明,海风锋发展最旺盛的时候,锋面高度达约1000 m,宽度约0.15个经度;海风锋垂直环流圈的建立伴随着地面降水的加强;地面降水减弱时,海风锋环流圈逐渐消失。     

在一种寒潮情况下的水平温度场及冷锋构造

本文选择了一次大气物理过程比较简单的寒潮作为例子,讨论其温度场及冷锋的构造。事实看出,寒潮前沿的冷锋,在黄河流域时与在华南时,构造是不同的。本文对于锋的构造的改变进行了初步的讨论。再者,寒潮末期的高空温度场改变很大,作者试用锋生公式计算,结果指出,温度平流值的变化起着主导作用。     

西南季风潮与2004年5月我国南方暴雨

以2004年5月初及5月中旬我国华南等地两次较大暴雨过程为例, 分析了西南季风潮与我国前汛期降水的关系。初步结论指出:西南季风潮的爆发与我国华南降水, 特别是大暴雨的形成关系极为密切, 而这次西南季风潮的爆发又与来自南半球的越赤道气流直接有关。同时指出, 这次西南季风潮的爆发主要与来自85°~95°E孟加拉湾地区所在经度的越赤道气流有关, 它们是印度洋“半球间宏观系统”的一个部分。而南海季风潮仅仅是西南季风潮的一种特例, 在这两次重大降水过程中没有南海季风潮的爆发和影响。     

东亚—西北太平洋地区夏季季节内振荡的年代际变化

本文重点分析对比热带夏季季节内振荡(Boreal Summer Intraseasonal Oscillation,BSISO)1987—1995年(P1),1996—2007年(P2)和2008—2017年(P3)三阶段东亚—西北太平洋地区(East Asian-Western North Pacific,EAWNP)5—9月BSISO年代际变化的季节内差异特征。结果表明,在P1和P3两阶段,5—7月EAWNP BSISO强度几乎相同,但P2中每个月均显著增强,表明5—7月EAWNP BSISO经历了P1—P2增强和P2—P3减弱的年代际变化。8月,EAWNP BSISO强度从P1到P3逐渐增强,P3阶段比P1有显著增强,孟加拉湾和东亚副热带区域的BSISO活动增强。和P1相比,南海地区BSISO活动在P2阶段异常活跃,在5—7月强度增强,并且北传显著。在P2阶段,负位相的太平洋年代际(Interdecadal Pacific Oscillation,IPO)对应的赤道西太平洋和印度洋海温增暖,及Walker环流的增强为5—7月BSISO活动提供了水汽和对流发展的有利条件,而南海地区北传对流的叠加作用以及南海海温增暖进一步加强了BSISO的强度和北传。在P3阶段,8月孟加拉湾BSISO活动增强,除了热带印度洋一致增暖和太平洋ENSO型海温为BSISO活动提供水汽和对流发展的条件外,70°~90°E区域局地Hadley环流引起的上升运动也对BSISO的强度增强和北传有贡献。     

1987年5月大兴安岭森林大火的烟团扩散参数及热释放率的估计

本文叙述了1987年5月8日大兴安岭森林火灾烟羽形成的气象背景,由卫星烟羽照片计算了行走时间在6×10~4s以内的瞬时烟羽扩散参数。计算结果表明长度为100km的烟流瞬时扩散较接近线性律,更长的烟流则对3/2律符合得更好些,此外还用烟团抬升公式估计了5月7至8日大火的热释放量,计算值能与现场调查值在量级上相一致。     

冬半年副热带西风南支槽结构和演变特征研究

南支槽是冬半年副热带南支西风气流在高原南侧孟加拉湾地区产生的半永久性低压槽, 本文从气候学角度探讨其结构和演变特征。结果表明: (1) 南支槽10月在孟加拉湾北部建立, 冬季 (11～2月) 加强, 春季 (3～5月) 活跃, 6月消失并转换为孟加拉湾槽; 10月南支槽建立表明北半球大气环流由夏季型转变成冬季型, 6月南支槽消失同时孟加拉湾槽建立是南亚夏季风爆发的重要标志之一。 (2) 南支槽在700 hPa表现明显, 其槽前干暖平流的输送有利于昆明准静止锋形成和维持, 槽后冷湿平流也与孟加拉湾冷涌关系密切。 (3) 冬季辐散环流下沉支抑制了南支槽前上升运动的发展, 这时低层辐合, 中层辐散, 南支槽前上升运动一般只伸展到对流层中层600 hPa左右。春季随着辐散环流减弱, 东亚急流入口区南侧辐散中心的出现使得垂直运动向上迅速伸展。 (4) 从气候平均看冬季水汽输送较弱, 上升运动浅薄, 无强对流活动, 南支槽前降水不明显, 雨区主要位于高原东南侧昆明准静止锋至华南一带。春季南支槽水汽输送增大, 同时副高外围暖湿水汽输送加强, 上升运动发展和对流增强, 南支槽造成的降水显著增加, 因此春季是南支槽最活跃的时期。     

南海夏季风建立的模式诊断研究

应用全球谱模式 (T42L9)对 1 986年和 1 987年个例进行了一系列有、无凝结潜热加热和地表感热以及地形作用的单因子敏感性数值预报试验 ,对预报模式输出的大气凝结潜热量和地面感热通量的时空变化特征进行了诊断分析。个例敏感性试验结果表明 ,大气凝结潜热对南海地区西南风的建立极为重要。诊断分析结果指出 ,在南海夏季风建立前 ,中南半岛地区是强大的凝结潜热加热区 ,远比印度半岛地区强。地形和中南半岛凝结潜热的共同作用可能是导致南海夏季风早于印度夏季风建立的重要原因。 1 987年 5月份在中南半岛地区的凝结潜热量比 1 986年明显偏低 ,直到 5月底 6月初才明显上升 ,这可能是该年南海夏季风建立晚的一个原因 ,中南半岛地区凝结潜热的变化可能是影响季风建立早晚的重要因子之一。     

高原边坡复杂地形下短时强降水的云型特征分类

利用逐时雨量资料、常规高低空观测资料及FY-2卫星云图,对2010—2015年5—9月甘肃省高原边坡复杂地形下76次短时强降水过程个例的天气形势配置及卫星云图演变特征进行统计分析。结果表明,与甘肃省短时强降水过程相关的特征云型共有6类:副热带高压边沿型、逗点云型、冷锋前部型、冷锋尾部与南亚高压东侧叠置型、冷涡后部型、弱冷锋前部椭圆形MαCS型。其中,副热带高压边沿型、冷锋前部型、弱冷锋前部椭圆形MαCS型与低层暖平流强迫有关。逗点云型、冷锋尾部与南亚高压东侧叠置型主要受高低空冷暖平流强烈交汇影响。冷涡后部型是高空冷平流强迫下形成。冷锋尾部与南亚高压东侧叠置型具有较好的预报指示意义。     

Synoptic climatology of transient tropical intraseasonal convection anomalies: 1975–1985

Summary Pentad mean anomaly maps were used to study the climatology of tropical intraseasonal convection anomaly (TICA) as a dynamic system. One hundred and twenty-two events were identified and classified into three categories: eastward (77), independent northward (27), and westward (18) propagation. The eastward propagation is more active in boreal winter than in summer, while the independent northward propagation, which is not associated with equatorial eastward propagation, occurs in boreal summer from May to October.The eastward moving TICA exhibits three major paths: 1) eastward along the equator from Africa to the mid-Pacific, 2) first eastward along the equator, then either turning north-east to the northwest Pacific or turning southeast to the southwest Pacific at the maritime continent, and 3) the main anomaly moves eastward along the equator with split center(s) moving northward over the Indian and/or western Pacific Oceans. The equatorial Indian Ocean and the western Pacific intertropical convergence zone are preferred geographic locations for their development, while the maritime continent and central Pacific are regions of dissipation.Independent northward propagation is confined to the Indian and western Pacific monsoon regions. Its existence suggests that the mechanism responsible for meridional propagation may differ from that for eastward propagation.The dynamic effect of the equator and the thermodynamic effect of the underlying warm ocean water are basic factors in trapping TICA in the deep tropics, while the annual march of maximum SST (thermal equator) and the monsoon circulation have profound influences on the annual variation and meridional movement of TICA.With 12 FiguresContribution No. 89-11, Department of Meteorology, University of Hawaii.     

2010年5月6日重庆强对流过程的天气学分析

利用常规观测、NCEP/NCAR再分析、FY-2E卫星、多普勒雷达以及自动站观测资料,对2010年5月6日重庆强风雹、暴雨天气过程进行了天气学分析。详细讨论了各尺度天气系统的发展演变及相互作用关系,并在此基础上提出了此次强对流发生的天气背景概念模型。研究结果表明:这次强对流过程发生在中纬度气旋、反气旋和高空槽增强发展的背景下,地面气旋与反气旋之间的冷锋也在南移中逐渐增强,而中纬度系统与西南地区低压和副热带高压间构成的鞍形场在重庆北侧造成锋生,一方面使得冷锋西段增强,另一方面通过次级环流与中层急流正反馈相互作用,加剧重庆中低层辐合抬升运动,既降低了大气稳定度,又为对流的触发形成提供了有利条件。与此同时,重庆低层始终位于西南地区低压东北部,偏南气流不仅输送了充足的水汽,其伴随的暖平流还与太阳辐射共同造成了重庆低层的显著升温,形成了条件不稳定层结。5月5日夜间冷锋移至重庆地区,锋面附近的强辐合造成了对流的初始发展,这一过程很可能与冷锋进入四川盆地后的下坡地形有关。另外,此次天气过程中副热带高空急流造成的强垂直风切变和高空辐散也为对流的强烈发展提供了有利条件。     

青藏高原东部牧区雪灾的气候特征分析

通过对 196 7— 1996年 2 5个测站的雪灾资料分析 ,揭示了青藏高原东部牧区有雪灾期从上年10月到当年 5月长达 8个月 ,雪灾在一年之中有 3个高发月 :11月、3月和 2月 ;雪灾主要发生在巴颜喀拉山南缘和东麓地区 ,近 30a来呈上升趋势。 196 8— 1976年冬春为一较长时段的雪灾发生的低值期 ,从 1977— 1992年有 3个高峰期和 2个低谷期 ,从 1993年开始又进入高发期 ;高原东部牧区冬春雪灾存在着明显的 5 6a的和较弱的 2 3a周期变化。本文中定义发生在 15月的雪灾为后冬雪灾 ,发生在10 12月的雪灾为前冬雪灾。研究表明 ,70年代是前冬雪灾的高发期 ,80年代末到 90年代是后冬雪灾的高发期。雪灾期西太副高的年际差异是雪灾发生年际振荡的一个可能原因     

强沙尘暴发展与干飑线—黑风暴形成的一个机理分析

该文分析了１９９３年５月５日黑风暴的发展过程和景观以及天气形势，研究了干飑线和强冷锋前干飑线发展同黑风暴爆发的关系。分析结果指出：由于强冷锋过境时冷锋前干飑线移至被强烈太阳辐射加热的地表以及条件不稳定大气层结结构，干飑线进一步发展至使黑风暴爆。黑风暴的沙墙是类似于飑线阵风锋面的干飑线阵风锋面的干飑线沙暴锋面。它是阵风锋面前沿反向上升气流卷起干燥地表尘沙面形成的。     

An observational study of instability and turbulence in nighttime drainage winds

A detailed analysis of two nighttime drainage wind events that commenced on the evenings of 7 and 8 October, 1980 is presented. Data on wind velocity and temperature (10-s values), obtained from each of the eight instrumented levels of the Boulder Atmospheric Observatory, are used to construct 10-min means and root-mean-square values of all the variables. Additional information is provided by acoustic sounder data for 8 October.The analyses reveal that the passage of the drainage front occurs abruptly, between two 10-s observations, on both days. Relatively intense root-mean-square variability in the velocity and temperature fields accompanies the passage of the drainage front. In addition, the undercutting cold drainage air initiates significant variability in the vertical velocity field that extends above the 300 m level of the tower. The most significant variability in the other meteorological fields is primarily restricted to the lowest 150 m with the passage of the drainage front.A principal feature of the analysis is the delineation of Kelvin-Helmholtz instability and billow development, breakdown into turbulence and ultimate decay to a less turbulent state that occurs intermittently behind the drainage front. These features are interpreted in light of Thorpe's (1973a, b) experimental work on stability and turbulence in stratified shear flow and the predictions of linear instability theory. The interpretations are carried out by considering the distributions of the Richardson number, the peak shears of the mean flow and the vertical fluxes of horizontal momentum associated with the unstable growth of the disturbances. Additional comparisons are made between the turbulent structures in Thorpe's laboratory experiments and the turbulence exhibited in traces of the 10-s vertical velocity data measured at various levels both above and below the interface.The relevance of the present results to the design of future field programs, and to the observational data requirements that should be met to incorporate turbulent entrainment processes in models of pollutant dispersal is discussed.     

Case studies of frontal passages in a mountain valley with direct access to the bavarian pre-Alpine region results from the German Front Experiment 1987

Summary The orographic impact on cold fronts is investigated in the Loisach River Valley area by means of two events obtained during the German Front Experiment 1987. The discussion is focussed on the frontal passages in the Garmisch area traced from continuous recordings of three meteorological/ air-chemical stations at different heights, viz: valley floor (735m), wank peak station (1780m) and Zugspitze station (2964m); the analysis also includes some aerological data (pibal ascents at Farchant near Garmisch) and sensitive pressure data from temporary stations in the Bavarian foreland, respectively.In the case of the west-east (or parallel to the mountains) moving front A (October 8, 1987), with prefrontal foehn, the following features were observed: i) formation of large (up to 7hPa/100 km up-valley directed pressure gradients after the frontal passage in the foreland, ii) intrusion of cold air from the foreland into the valley (lasting for several hours, filling the whole valley and even traceable at crest height), iii) destruction of upper level foehn current during the intrusion-phase, iv) retardation of the front (progressing rapidly in the foreland but being retarded by the mountains located to the west). In the case of the high-reaching, southward (or perpendicular to the mountains) moving D-front (December 18/19, 1987), such striking orographic modifications were not observed. In that case the mountains located to the west obviously did not act as noticeable barrier and, therefore, the flow around and over the mountains prevented the for ation of large pressure gradients between the foreland and the valley (and an intrusion into the valley).In both events it was confirmed that trace gas measurements provide a very promising tool to localize atmospheric flows indirectly.With 14 Figures