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1.
高层东风波引起的一次超级单体雹暴天气数值研究 总被引：1，自引：0，他引：1
利用WRF中尺度模式对2018年7月26日发生在浙中北的一次超级单体雹暴过程进行数值研究,结合自动站资料,天气雷达资料、NCEP再分析资料等分析冰雹天气发生的环流背景,冰雹云的雷达回波和流场结构特征,并探究冰雹形成的物理机制。结果表明:此次强对流天气是在高层东风波环流背景下,由地面辐合线触发的超级单体雹暴过程。雹暴发生在强的对流有效位能、上干下湿的层结和弱垂直风切变的环境场中。模拟试验成功地模拟出了雹暴云团的发展演变过程。0℃层位于5 km的高度,-20℃层位于8. 5 km的高度,且超过40 dBZ的强回波向上扩展至-20℃层以上,有利于冰雹的生长。雹云发展旺盛时呈现典型的低层辐合、高层辐散特征。雹云右侧出现悬垂回波和有界弱回波区。雹云中存在大量的过冷云水,冰雹粒子的核心生长区位于0℃层和-20℃层之间,主要由霰粒子转化而成,并通过不断碰并过冷云水和过冷雨水增长。 相似文献
2.
利用常规高空、地面观测资料和多普勒雷达资料,采用中尺度数值模式(WRF),对发生在浙江省的一次冰雹天气过程进行了综合分析和数值模拟,从气流、温度结构以及雹云中的各类微观物理量的时空变化分析了此次冰雹过程的宏微观演变特征及形成机制。结果表明,该次强对流天气是在大尺度动力不稳定、热力不稳定的环境场和上干下湿的不稳定层结下发生发展的,边界层中尺度辐合线作为抬升触发机制释放不稳定能量。模式模拟得到的地面累积降水和雷达反射率因子与实况基本符合;模拟的水汽辐合区、能量锋区以及雷达反射率因子高值区接近辐合线。模拟的雹云属多单体风暴,具有明显的合并发展特征;霰(雹胚)通过雪晶的碰冻过程及过冷雨滴冻结产生,后碰并增长转化形成冰雹,冰雹通过碰冻过冷水滴和碰撞收集冰雪晶快速增长,最终降落至地面。其中,雹云内的过冷雨水累积带对霰及雹的产生及增长至关重要。 相似文献
3.
利用WRF中尺度数值模式,模拟了2005年5月31日发生在北京的冰雹强对流过程,成功地再现了冰雹天气发展过程中起重要作用的冷涡底部的小槽、低层暖湿舌、地形辐合线等中尺度系统;模拟的地面降水、强对流(雹)云移动路径与实况基本符合;模拟的一个长生命史强对流(雹)云的演变及单体结构与北京多普勒雷达观测的沿城市中轴线的雹云相似,具有超级单体概念模型给出回波墙-有界弱同波区(穹窿)-悬挂回波结构、对峙的倾斜上升下沉气流、分裂右移发展等特征.基于数值模拟结果,结合雷达观测,重点分析了这块雹云的演变过程,解剖了超级单体三维动力、热力及回波结构. 相似文献
4.
《气象与环境学报》2017,(4)
利用多普勒雷达和4DVAR反演的0.5—5.0 km中低层风场资料及地面、高空、区域自动气象站等观测资料,对2016年6月8日秦皇岛地区一次致灾性强对流天气过程中风暴的生成和发展进行了综合分析,并探讨了多单体风暴的短临预警。结果表明:上干冷、下暖湿的层结条件有利于强对流天气的发生,地面辐合线和露点锋是秦皇岛地区此次强对流天气的触发机制,区域自动气象站风场和温度的突变对风暴单体的出流阵风锋具有指示作用。当风暴加强为超级单体并与阵风锋接近时,在超级单体的中低层(0.5—5.0 km),出流与入流形成的辐合上升运动位于回波强度为15—30 d Bz的边缘区域,而低层较强回波区域多为下沉气流,上升和下沉运动的分离确保了超级单体可以维持长时间的发展,出现传播运动;出流阵风锋远离成熟风暴单体后侧,在其后侧约15.0—20.0 km处触发生成新的对流单体,导致对流系统的后向传播运动。通过传播运动矢量方向的估算可以提前预判风暴单体的发展区域,预警时效可以提前30 min,垂直累积液态水含量密度持续大于4 g·m-3对2—5 cm大冰雹的预报具有重要指示作用。 相似文献
5.
为研究降雹超级单体风暴的三维结构特征,利用厦门、龙岩、梅州3部新一代天气雷达（CINRAD/SA）基数据,采用基于动态地球坐标系的双雷达和三雷达三维风场反演技术,分析了2016年4月8日傍晚福建省南部漳州地区出现的一次冰雹过程的回波强度、三维风场及相关物理量分布变化。主要结果为：（1）冰雹云初生、发展阶段,低层水平流场出现气旋性辐合,云体内部形成较强的上升运动。（2）冰雹云强盛阶段,回波顶高度达16 km,其中大于60 dBz的回波高度由5.3 km发展至9 km,最强回波达74.5 dBz,伴随出现最长达25 km的三体散射长钉回波和32.7 km的旁瓣回波。低层水平维持气旋性流场的同时,高层出现反气旋性流场。4-8 km高度内,大于20 m/s的强上升气流持续近37 min。最大垂直速度达51.06 m/s,出现在超级单体悬垂部（约7.5 km高度处）。（3）降雹时段,出现明显的下沉气流。降雹超级单体的三维流场结构表现为：风暴移向前沿低层气旋性气流进入风暴后逐渐倾斜上升,到达风暴顶形成反气旋性气流,并逐渐向下形成下沉气流。（4）系统减弱阶段,出现系统性下沉气流,强回波底及地。双雷达和三雷达能较好地反演降雹超级单体的三维风场精细结构,有助于加深对冰雹云结构的认识进而提高冰雹预报能力。 相似文献
6.
贵州地区冰雹云微物理过程及发展机制数值模拟研究 总被引：2，自引：1，他引：1
为了进一步探究贵州地区冰雹云的形成、发展机制和冰雹增长的微物理转化条件,运用三维冰雹云模式对该地区2012—2015年12个冰雹个例进行数值模拟研究,结果发现:各种水成物有利的空间分布是雹粒增长的物质基础,且上升气流与水汽相变之间存在一个正反馈效应,冰雹粒子主要以霰粒子为胚胎进行增长,增长方式以霰自动转化成雹为主。在再生冰雹云发展过程中,雹云首次发展过程结束时,高空仍维持4 km及以下很低的0℃层高度,是再生冰雹云发展的热力环境条件。降雹区地面气流辐散,导致两侧区域形成较强的气流辐合上升,是再生冰雹云发展的动力条件。气流在辐合的同时,又使原降雹区的水汽源源不断地向两侧气流辐合区汇合,是再生冰雹云发展的水汽来源。冰雹云中冰晶和霰粒子含量的迅速增加,为冰雹的再次增长提供了有利的微物理物质转化条件。 相似文献
7.
一次冰雹云过程及其冰雹形成机制的模拟研究 总被引：7，自引：0，他引：7
利用常规气象资料和多普勒天气雷达资料,从天气形势和雷达回波演变特征等方面对2011年6月24日发生在洛阳嵩县的一次冰雹过程进行了分析,并利用三维弹性冰雹云催化模式对该冰雹云进行了模拟研究,分析其冰雹形成的物理机制。结果表明:本次过程在天气形势上属于下滑冷槽型。多普勒天气雷达资料上表现为单个单体的强对流风暴,最大反射率≥65 dBz,回波顶高达到14 km,降雹前垂直积分液态含水量具有明显的跃增;径向速度场上出现了大范围明显的逆风区。三维冰雹云模式对该冰雹云具有较好的模拟能力,模式模拟的最强回波与实况一致,雹云中含水量中心与强上升气流有很好的配置,在云的发展阶段,主含水量中心是强上升气流的指示。冰雹的雹胚主要来自冻滴和霰,在冰雹形成期间,冻结形成的冻滴和转化产生的霰数量上相差不大,但是冻滴向雹的转化比例却是霰的6倍,即在地面强降雹之前,雹云中的雹胚主要来源于冻滴;而冰雹的增长在前期主要靠收集过冷雨水,后期主要靠收集过冷云水;适量的冰晶、雪和丰富的过冷水的存在对雹的形成和增长极为有利。 相似文献
8.
一次冰雹天气过程的多源资料观测分析 总被引：2，自引：1，他引：1
利用地基微波辐射计、风廓线雷达和雨滴谱仪等观测资料,对2015年4月28日发生在南京的一次冰雹天气进行了分析,探讨新型探测资料在冰雹监测预警中的应用。结果表明:(1)华北冷涡后部冷空气南下,与低层暖湿气流交汇,是产生这次冰雹的天气背景;高空冷平流叠加在低层暖湿气流之上,使得对流层中低层形成不稳定层结;地面辐合中心及辐合线是降雹的触发机制。(2)微波辐射计监测显示,降雹期间冰雹云中上升气流将底层空气的感热和潜热向上输送,导致2 km以上大气有明显升温,由于低层水汽聚集及冰雹在近地层融化造成降雹时近地层相对湿度、水汽密度增大。冰雹发生在云液态水含量快速增长的波峰上,对冰雹的发生具有较好指示意义。(3)对比南京3站风廓线雷达资料表明各站上空环境风场存在一定差异,六合地区降雹前6 km高度高空急流有利于六合上空形成有利的辐散形势,降雹时0~6 km存在较深厚的垂直风切变,配合地面中尺度低压,降雹最为强烈;南京站降雹时,对流层中下层有一槽过境,而高淳地区冰雹由近地面垂直风切变激发。(4)六合站、高淳站雨滴谱仪分析表明不同降水相态对应的滴谱特征有差异,两站雨滴谱型分别呈指数型、多峰型分布。高淳站雨滴谱仪监测到直径达到15 mm的冰雹粒子,六合站冰雹直径最大为5 mm。两站速度谱大致为单峰型,在较强降水时刻,粒子下落峰值速度在3~4 m·~(-1)。(5)影响六合的超级单体存在钩状回波、回波悬垂、三体散射等雷达回波中尺度特征,地面中尺度低压系统、中低层的中气旋及高层的辐散环流配置造成了雹云中维持较强的旋转上升气流,有利于出现大冰雹。 相似文献
9.
《湖北气象》2021,40(4)
利用地面观测资料、探空资料以及石家庄多普勒天气雷达和饶阳双偏振雷达资料等,对2018年6月13日影响河北中南地区的一个长生命史超级单体风暴的环流背景、雷达观测特征等进行了分析。结果表明:(1)此超级单体发生在涡后横槽转竖的环流背景下。(2)风暴生命史长204 min,其中超级单体维持时间长达138 min,其间雷达最大反射率因子基本上维持在65 dBz以上。(3)中气旋深厚并强烈发展是超级单体发展和维持的重要动力机制。中气旋底高最低可达风暴底部,顶高变化幅度较小,低质心中气旋和高质心中气旋的形成和发展都可能引起地面降雹,降雹期间对应超级单体短暂减弱。(4)超级单体维持期间一直伴有气旋、反气旋涡旋对特征。超级单体的钩状回波特征明显,表现为典型的回波墙-弱回波区-悬挂回波的垂直结构;低层辐合、高层辐散,高空辐散大于低层辐合,有利于超级单体内部强烈的旋转上升运动;有明显的三体散射和旁瓣回波,三体散射最长超过60 km,持续时间长达150 min。(5)双偏振雷达探测的超级单体反射率因子≥55 dBz,对应位置差分反射率-0.5~0.5 dB,差分传播相移率仅1.5~2.0°/km,相关系数在0.75~0.92之间,表明超级单体内同时存在液滴和较大冰雹。 相似文献
10.
利用常规观测资料、多普勒天气雷达和风廓线雷达资料,对一次罕见的鄂西南冬季强冰雹（直径1～3 cm）天气过程进行了分析,结果表明:强冰雹产生在上干冷、下暖湿,低空辐合、高空辐散的环流背景下,地面中尺度辐合和“喇叭口”的有利地形,给冷锋前暖区对流性天气提供了触发机制;地面冷锋南下伴随的垂直风切变增强有利于已经生成的对流风暴的维持和加强。强冰雹分别由孤立的超级单体和超级单体复合体（多单体结构中含有占支配地位的超级单体）产生。比较而言,孤立的超级单体发展更为高大,持续时间更长。风暴具有中气旋、高悬的强回波、低层入流、弱回波区与回波悬垂、中层径向辐合、风暴顶强辐散等超级单体风暴的典型特征;垂直累积液态含水量及其密度分别较长时间维持在35 kg·m-2和4 g·m-3以上的冬季高值;新一代天气雷达冰雹探测算法输出的冰雹指数产品预测到高概率的强冰雹。此次过程出现在冬末,虽然对流出现之后呈现出典型的风暴结构,可以提前10～30 min做出强冰雹的临近预警,但对于对流出现之前的提前数小时的强冰雹短时潜势预报而言,常用做判断强降雹潜势的探空特征（包括对流有效位能... 相似文献
11.
12.
Summary The boundary-layer wind field during weak synoptic conditions is largely controlled by the nature of the landscape. Mesoscale
(sub-synoptic) circulations result from horizontal gradients of sensible heat flux due to variation in local topography, variation
in surface-cover, and discontinuities such as land-sea contrasts. Such flows are usually referred to as thermally-driven circulations,
and are diurnal in nature and often predictable. In this paper we use a state-of-the-art non-hydrostatic computer model to
shed light on the physical mechanisms that drive a persistent easterly wind that develops in the afternoon in the Mackenzie
Basin, New Zealand. The easterly – Canterbury Plains Breeze (CPB) – is observed early in the afternoon and is often intense,
with mean wind speeds reaching up to 12 m s−1. Although computer modelling in mountainous terrain is extremely challenging, the model is able to simulate this circulation
satisfactorily. To further investigate the mechanisms that generate the Canterbury Plains Breeze, two additional idealized
model experiments are performed. With each experiment, the effects of the synoptic scale wind and the ocean around the South
Island, New Zealand were successively removed. The results show that contrary to previous suggestions, the Canterbury Plains
Breeze is not an intrusion of the coastal sea breeze or the Canterbury north-easterly, but can be generated by heating of
the basin alone. This conclusion highlights the importance of mountain basins and saddles in controlling near-surface wind
regimes in complex terrain. 相似文献
13.
A. Henderson-Sellers 《Climatic change》1993,23(4):337-377
A simplified vegetation distribution prediction scheme is used in combination with the Biosphere-Atmosphere Transfer Scheme (BATS) and coupled to a version of the NCAR Community Climate Model (CCM1) which includes a mixed-layer ocean. Employed in an off-line mode as a diagnostic tool, the scheme predicts a slightly darker and slightly rougher continental surface than when BATS' prescribed vegetation classes are used. The impact of tropical deforestation on regional climates, and hence on diagnosed vegetation, differs between South America and S.E. Asia. In the Amazon, the climatic effects of removing all the tropical forest are so marked that in only one of the 18 deforested grid elements could the new climate sustain tropical forest vegetation whereas in S.E. Asia in seven of the 9 deforested elements the climate could continue to support tropical forest. Following these off-line tests, the simple vegetation scheme has been coupled to the GCM as an interactive (or two-way) submodel for a test integration lasting 5.6 yr. It is found to be a stable component of the global climate system, producing only ~ 3% (absolute) interannual changes in the predicted percentages of continental vegetation, together with globally-averaged continental temperature increases of up to + 1.5 °C and evaporation increases of 0 to 5 W m–2 and no discernible trends over the 67 months of integration. On the other hand, this interactive land biosphere causes regional-scale temperature differences of ± 10 °C and commensurate disturbances in other climatic parameters. Tuning, similar to the q-flux schemes used for ocean models, could improve the simulation of the present-day surface climate but, in the longer term, it will be important to focus on predicting the characteristics of the continental surface rather than simple vegetation classes. The coupling scheme will also have to allow for vegetation responses occurring over longer timescales so that the coupled system is buffered from sudden shocks. 相似文献
14.
Earlier GCM studies have expressed the concern that an enhancement of greenhouse warming might increase the occurrence of summer droughts in mid-latitudes, especially in southern Europe and central North America. This could represent a severe threat for agriculture in the regions concerned, where summer is the main growing season. These predictions must however be considered as uncertain, since most studies featuring enhanced summer dryness in mid-latitudes use very simple representations of the land-surface processes ("bucket" models), despite their key importance for the issue considered. The current study uses a regional climate model including a land-surface scheme of intermediate complexity to investigate the sensitivity of the summer climate to enhanced greenhouse warming over the American Midwest. A surrogate climate change scenario is used for the simulation of a warmer climate. The control runs are driven at the lateral boundaries and the sea surface by reanalysis data and observations, respectively. The warmer climate experiments are forced by a modified set of initial and lateral boundary conditions. The modifications consist of a uniform 3 K temperature increase and an attendant increase of specific humidity (unchanged relative humidity). This strategy maintains a similar dynamical forcing in the warmer climate experiments, thus allowing to investigate thermodynamical impacts of climate change in comparative isolation. The atmospheric CO 2 concentration of the sensitivity experiments is set to four times its pre-industrial value. The simulations are conducted from March 15 to October 1st, for 4 years corresponding to drought (1988), normal (1986, 1990) and flood (1993) conditions. The numerical experiments do not present any great enhancement of summer drying under warmer climatic conditions. First, the overall changes in the hydrological cycle (especially evapotranspiration) are of small magnitude despite the strong forcing applied. Second, precipitation increases in spring lead to higher soil water recharge during this season, compensating for the enhanced soil moisture depletion occurring later in the year. Additional simulations replacing the plant control on transpiration with a bucket-type formulation presented increased soil drying in 1988, the drought year. This suggests that vegetation control on transpiration might play an important part in counteracting an enhancement of summer drying when soil water gets limited. Though further aspects of this issue would need investigating, our results underline the importance of land-surface processes in climate integrations and suggest that the risk of enhanced summer dryness in the region studied might be less acute than previously assumed, provided the North American general circulation does not change markedly with global warming. 相似文献
15.
H. E. Eisma J. M. Tomas M. J. B. M. Pourquie G. E. Elsinga H. J. J. Jonker J. Westerweel 《Boundary-Layer Meteorology》2018,169(2):185-208
Simultaneous particle-image velocimetry and laser-induced fluorescence combined with large-eddy simulations are used to investigate the flow and pollutant dispersion behaviour in a rural-to-urban roughness transition. The urban roughness is characterized by an array of cubical obstacles in an aligned arrangement. A plane fence is added one obstacle height h upstream of the urban roughness elements, with three different fence heights considered. A smooth-wall turbulent boundary layer with a depth of 10h is used as the approaching flow, and a passive tracer is released from a uniform line source 1h upstream of the fence. A shear layer is formed at the top of the fence, which increases in strength for the higher fence cases, resulting in a deeper internal boundary layer (IBL). It is found that the mean flow for the rural-to-urban transition can be described by means of a mixing-length model provided that the transitional effects are accounted for. The mixing-length formulation for sparse urban canopies, as found in the literature, is extended to take into account the blockage effect in dense canopies. Additionally, the average mean concentration field is found to scale with the IBL depth and the bulk velocity in the IBL. 相似文献
16.
T. Vrhovec 《Meteorology and Atmospheric Physics》1991,46(1-2):91-99
Summary A formation of a cold air lake in a basin is studied with a mesometeorological model.A dynamic Boussinesq hydrostatic mesoscale numerical model is developed in a staggered orthogonal grid with a horizontal resolution of 1 km and with a varying vertical grid. The topography is presented in a block shape so that computation levels are horizontal.The mesometeorological model is tested in three idealized topography cases (a valley, a single mountain, a basin) and test results are discussed.In an alpine basin surrounded by mountains and plateaus the air is supposed to be stagnant at the beginning of the night. Due to differences in radiation cooling an inversion layer is formed in the basin and local wind circulation is studied by model simulations.With 14 Figures 相似文献
17.
通过分析2004年8月25日发生在浙江省宁波市的一次台风前部龙卷发生发展的环境特征, 发现该龙卷发生在台风前部风切变区里, 尽管当时涡度、散度等物理量对于深对流发展不是非常有利, 但下湿中干、强的垂直风切变及地形条件等还是有利于局地弱龙卷的产生; 在宁波新一代天气雷达产品上表现为强的钩状回波, 速度场上有相邻的正负速度中心及强的组合切变值等。通过多个反射率产品、剖面产品等综合分析了该风暴的三维结构, 初步了解此类弱龙卷的发生机理, 为以后的预报提供一些经验。 相似文献
18.
Measurements made with instruments aboard a remotely-piloted multicopter flying across the Weser river in Germany provide information on the thermal structure of the boundary layer over the river and adjacent land, in this case in summer for late afternoon, the evening transition and early night on a clear calm day. The river has a characteristic width of 100 m. The stratification over the land and river are of opposite signs at the lower levels, except during part of the evening transition. The multicopter allows to qualitatively estimate the evolution of the thermal contrast between both surfaces, showing that the river banks experience very significant daytime cooling and nocturnal warming due to river-bank circulations, with the change of sign taking place well before sunset. 相似文献
19.
该文以连续10 a审核无错情经验为基础,从原始记录的审查、自记记录的检查、备注栏和记录要检的填写、微机审核报表等几方面,分析了基层台站如何做好气象报表的预审工作。 相似文献