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1.
亚洲夏季风区中尺度地形降水结构及分布特征 总被引：4，自引：0，他引：4
采用高分辨率TRMM、AIRS卫星实测资料, 从气候态的降水微物理过程角度分析了亚洲夏季风期间中尺度山脉对不同性质降水垂直结构和水平分布的影响。研究表明, 中尺度山脉迎风、背风坡均以层云降水为主, 层云降水强度在迎风坡强于背风坡; 对流降水在迎风坡主要为浅对流, 背风坡主要为深对流, 对流降水强度在背风坡强于迎风坡。沿西南季风推进方向依次经过的中尺度山脉, 其两侧发生降水像素个数、 降水微物理特征等差异逐渐减小, 其中, 对流降水迎风坡向背风坡转变明显, 而层云降水背风坡向迎风坡转变明显。大气稳定度与对流降水在迎风、背风坡的分布相一致。另外, 对中尺度地形降水的研究为区域气候模式模拟高精度地形降水分布提供了实测依据。 相似文献
2.
地形对华北地区夏季降水影响的数值模拟研究 总被引：37，自引：10，他引：27
行星大气中地形效应的研究一直是人们十分重视的问题。本语文利用引进的ＮＣＡＲ－ＲｅｇＣＭ２模式就地形对华北地区夏季降水的影响进行了数值模拟研究。结果表明,华北地区西部和北部的山脉地形对华北地区夏季降水有着非常重要的影响。尤其是对一些局地地区,甚至起到了决定性的作用。当降低地形高度时,华北地区夏季降水将明显减少。其物理机制可能主要有两点,一是降低地莆高度后,使华北地区迎风坡地形抬升作用减弱,从而减少了 相似文献
3.
利用区域数值模式WRF-ARW（V3.9）开展高分辨率数值模拟试验,研究了东北地区大兴安岭和长白山地形对该地区夏季降水的单独和共同影响。结果表明,东北地区两大山脉地形可以显著影响东北及其周边区域的大气环流和降水。大兴安岭和长白山地形的阻挡作用使得夏季偏南气流在两个山脉的迎风坡一侧堆积,引起局地水汽增加并产生上升运动,因此两个山脉的迎风坡一侧降水增加;而在两个山脉的背风坡一侧,局地水汽减少并伴随下沉运动,因此两个山脉的背风坡一侧降水减少。大兴安岭地形的存在使得其东侧到松嫩平原地区夏季降水增加1.09 mm d?1（相较参照试验增幅为30%）,而使其西侧蒙古东部地区夏季降水减少0.69 mm d?1（相较参照试验减幅为24%）;长白山地形的存在使得长白山南侧到朝鲜半岛地区夏季降水增加1.76 mm d?1（相较参照试验增幅为26%）,而使其北侧三江平原地区夏季降水减少0.81 mm d?1（相较参照试验减幅为22%）。当大兴安岭与长白山同时存在时,两者的协同作用会减弱蒙古东部、松嫩平原和朝鲜半岛地区夏季降水的响应,而增强三江平原地区夏季降水的响应。该研究结果对于理解东北地区当代气候的形成具有重要的科学意义。 相似文献
4.
利用中尺度模式WRF 3.3.1模拟了2007年7月29日豫西山区强对流天气过程,并进行了地形高度敏感性试验。结果表明：模式能够很好地再现此次强对流降水过程,模拟降水范围与强降雨中心均与实况较一致。分析对比控制试验和地形敏感性试验结果可知,地形的改变能够在水平和垂直方向上影响环流形势,进而影响降水的落区和中心量级。地形升高和迎风坡梯度增大使近地面层水平风场辐合增强,中层上升运动明显增大,且低层的水汽通量增大,导致雨带横向范围和降水中心量级明显增大;而地形降低和迎风坡梯度减小使山脉对近地面层气流的阻挡作用明显减弱,低层水汽通量显著降低,中层辐合抬升运动明显减弱,迎风坡前强降水中心减弱甚至消失,而山脉下游降水则有所增强。分析地形高度与山前降水的定量关系可知,降水中心量级随着地形升高或降低相应地增大或减小,但二者并非完全的线性正相关。 相似文献
5.
分层气流条件下地形降水的二维理想数值试验 总被引：1，自引：0，他引：1
利用WRF v3.5中尺度数值模式,在条件不稳定层结下,针对分层气流(基本气流风速和大气湿浮力频率呈二层均匀分布)过山时,地形对降水的影响进行了多组二维理想数值试验,以研究不同高度、尺度山脉和不同方向基本气流对降水形态和分布的影响。模拟结果表明,地形重力波触发对流是地形降水的主要机制之一,地形波的特征(波长、振幅)和传播均受到地形和基本气流的影响,其中,强基本气流流经高而陡峭的山脉时,更容易在其背风坡捕捉到重力波,地形降水呈现多种模态,反之亦然;当改变基本气流与山脉交角时,主要通过影响地形强迫抬升速度、基流对波动稳定性发展来进一步影响地形降水的强度和分布。 相似文献
6.
地形对超强台风罗莎降水影响的初步分析 总被引：5，自引：3，他引：2
为了进一步加深地形对台风降水影响的细节了解,用变分法合成的高分辨率降水资料和地形资料,结合日本再分析资料,对0716号台风罗莎登陆期间地形对降水的影响作了初步分析.过程降水量与地形相关分析表明,沿海地形对降水的影响较大.强降水区主要分布在沿海山体的迎风坡上.分析1小时降水量在不同强度区间的频次分布,发现在山体地形的影响下,山脉区域降水加强.浙江东南沿岸的山体引起的降水增益相对东北沿岸区域的山体偏大.利用日本再分析资料和地形资料计算了气流过沿海山体时的无量纲数Fr值.由于气流Fr较小,气流过浙江沿海地形时更容易翻越山体.抬升位置发生在迎风坡上,因而强降水区也落在迎风坡上.东南沿岸区域的地形对迎风气流的强迫垂直运动在垂直方向上的渗透比东北沿岸区域更深厚,这是导致东南沿岸区域地形对降水增益比东北沿岸区域偏大的原因. 相似文献
7.
地形对降水影响的数值试验 总被引：10，自引：8，他引：10
用MM5v3模式研究地形高度对江淮流域降水的影响,通过在模式中提高和降低大别山和黄山的地形高度来模拟降水的变化,个例是1998年6月28日和1991年6月12日的暴雨过程,进行了24 h模拟,并分析了垂直速度、涡散度、湿位涡、水汽通量等的变化,结果表明,上述各因子都在地形高度变化后有了明显变化,并因此影响了降水变化。各因子都有影响,综合各因子的影响是预测地形降水的途径之一。总的说,地形引起的降水变化主要在地形变化的附近,特别是在山的迎风面,降水有明显增加。决定降水落区和强度的主要仍是大中尺度环流,但地形起了改变落区和强度的作用。 相似文献
8.
9.
为了解决复杂地形条件下ECMWF模式预报的台风降水较实况显著小的问题,对Smith 1979年提出的地形降水方程进行改进,提出以饱和湿层高度作为方程积分上限,针对不同高度地形设定不同的降水效率;以无量纲湿弗劳德数大于1作为有、无地形降水的判据;利用ECWMF细网格预报场,通过迎风坡地形降水估算方程来订正模式预报的台风降水。用该地形降水订正方法对1617号台风“鲇鱼”的降水进行了订正预报。结果表明,虽然在一些小尺度地形区域会产生明显的空报,但是对于大尺度地形区域的强降水有显著的订正效果。对1513、1521和1614台风的订正结果进一步表明,该地形降水订正方法对改进台风极端降水预报效果显著。需要指出的是,采用的地形降水订正方法仅考虑了稳定条件下的地形降水,对于其他情形下的地形降水订正方法尚待进一步的研究。 相似文献
10.
钟形地形动力抬升和重力波传播与地形云和降水形成关系研究 总被引：4，自引：0，他引：4
地形云和降水过程在区域水循环、水资源、生态环境及气候变化中具有十分重要的作用。本文利用中尺度数值模式WRF 数值模拟试验,以及通过引入表示大气层流速度、层结稳定度和地形特征的关系参数——湿Froude 数(Fw),研究了北京2009 年5 月1 日湿条件不稳定大气层结下,地形云和降水形成过程与地形动力抬升和地形重力波传播之间的关系及形成机理。研究表明,在地形最大高度2 km、半宽10 km 的条件下,层流速度从2.5 m/s 逐步增加到25 m/s 时,对应的湿Fw 数从0.19 增加到1.81。当Fw≤1 时,地形的阻挡起主要作用,由地形抬升形成的地形云主要产生在迎风坡一侧。地形重力波主要产生在迎风坡,并向上游传播,先形成层状云,最后演变为准稳定浅对流波状云。最大降水主要发生在紧靠山顶的迎风坡一侧,但当Fw 很小时,地形云不产生降水。当Fw>1 时,地形抬升形成的云主要发生在山顶附近,而地形重力波主要形成在背风坡,并向下游方向传播,形成准稳定波状云。最大降水主要产生在紧靠山顶的背风坡一侧。另外,在弱湿条件不稳定大气层流下,地形降水主要由地形动力抬升造成的暖云微物理过程产生,地形重力波形成的波状云几乎不产生降水。 相似文献
11.
Summary Idealized numerical simulations using the Weather and Research Forecast (WRF) model indicate that three flow regimes, based on the moist Froude number, can be identified for a conditionally unstable, rotational, horizontally homogeneous, uniformly stratified flow over an idealized, three-dimensional, mesoscale mountain stretched spanwise to the impinging flow: (I) a quasi-stationary upslope convective system and an upstream-propagating convective system, (II) a quasi-stationary upslope convective system, and (III) a stationary upslope convective system and a quasi-stationary downstream convective system. Several major differences from a similar type of flow with no rotation over a two-dimensional mountain range are found. One important finding is that relatively strong mean flow produces a quasi-stationary mesoscale convective system (MCS) and maximum rainfall on the windward slope (upslope rain), instead of on the mountain peak or over the lee side.We found that the Coriolis force helps produce heavy upslope rainfall by making transition from flow-around the eastern part of the upslope to flow-over the western part of the upslope (transits to a higher flow regime) by deflecting the incident southerly flow to become east–southeasterly barrier winds. We found that the addition of the western flank of the arc-shaped mountain helps slow down the barrier wind from east and causes the maximum rainfall to move east of the windward slope. A lower-Froude number flow tends to produce a rainfall maximum near the concave region.Several other important facts can also be found in this study. The ratio of the maximum grid scale rainfall to the sub-grid scale rainfall increases when the moist Froude number increases. When the CAPE decreases, it is found that the upstream moist flow tends to shift to a higher Froude-number regime. Therefore, the Froude number cannot solely be used to define a moist flow regime when different CAPEs are considered. In another word, other parameters, such as CAPE, might play an important role in determining moist flow regimes. 相似文献
12.
地形影响的飞机颠簸及其数值仿真实验 总被引：1，自引：1，他引：1
首先利用中尺度数值模式ARPS模拟气流过山生成飞行数值仿真所需要的风场，然后利用飞机载荷因数变量方程进行飞机飞行的数值仿真试验。研究结果表明，气流过山产生的山脉重力波由于风切变临界层破碎，一方面能在对流层产生较强的湍流引起晴空飞机颠簸，另一方面也能在山脉背风面产生强烈下坡风，背风转子环流及低空湍流，影响飞机的起飞和着陆。揭示了飞机在过山脉地形背风面所产生的大气湍流中飞行时引起飞机颠簸的物理机制，有助于增强飞机颠簸的预测能力和飞行气象保障能力。 相似文献
13.
条件不稳定大气中二维小尺度双脊地形上空对流及降水特征 总被引：3，自引：1，他引：2
在条件不稳定大气条件下,二维小尺度双脊钟形地形上空对流触发、传播和降水分布特征主要决定于地形上游基流强度、双脊地形配置形式、地形高度及其山谷宽度。双脊地形在沿基流方向上有两种配置:高脊地形位于上游和低脊地形位于上游。对于高脊地形位于上游的双脊地形,上游高地形将起主导作用,山地上空对流及降水特征与单脊地形类似。对于低脊地形位于上游的双脊地形,上游低地形可明显地改变下游高地形的前方来流,同时,下游高地形也能够对上游低地形背风侧流动产生影响,从而导致出现地形上空复杂的对流传播、降水分布特征。对于低脊地形位于上游的双脊地形,其山谷宽度主要决定了双脊地形与单脊地形之间在对流、降水分布等的差异;当山谷宽度较小时,双脊地形可以近似为一个包络地形,此时地形上空的对流、降水特征与单脊地形类似;当山谷宽度较大时,双脊上空流动相互影响较小,此时双脊地形可以分成两个单脊地形;当山谷宽度在一定范围内,其上空的对流及其降水分布与单脊地形有明显差异。对于低脊地形位于上游、中等山谷宽度的双脊地形上空降水主要呈现4种类型:(1)山谷与低脊迎风坡降水;(2)高脊迎风坡降水;(3)低脊山峰与高脊迎风坡降水;(4)低脊背风侧、双脊山峰准静止降水。 相似文献
14.
Summary Two-thirds of the land mass of Taiwan island is covered by mountains that affect precipitation systems over the island. To understand the influence of such terrain on a precipitation system was one of the objectives of TAMEX (Taiwan Area Mesoscale Experiment, Kuo and Chen, 1990). During the passage of these precipitation systems, Doppler radar readings as well as conventional data were collected. On 17 June, 1987 a precipitation system moving toward northeastern Taiwan dumped over 100 mm of rainfall per day near the mountain foothills, not far from the ocean. Over the lee side, the precipitation amount was less. The radar data results indicate that a series of cells formed about 10 km upstream of the coastal area and moved toward the mountains under the influence of an easterly wind. The zonal speed was about 4 to 8 ms–1. The time interval for the formation of these convective cells was about 40 minutes. They intensified near the coastal area, the foot hills and the mountain slope, but their intensity decreased on the lee-side. A two-dimensional, nonhydrostatic model with a terrain-following coordinate system was employed to study the influence of environmental wind patterns and terrain on the characteristics of a precipitation system. Simulation results indicate that a series of clouds associated with an updraft formed at the middle level, about 10 to 20 km east of the mountain foothills (near the coast line), under the influence of easterly winds in a very moist environment. Then, updrafts associated with cloud water travelled westward from the cloudy region, intensifying near the bottom of the mountains and in the coastal areas due to orographic lifting. Then, convective cells formed. As these cells continued moving westward and upward near the foothills as well as the upslope area near the mountain top, their intensity increased. But once they passed over the mountain top to the lee side, their intensity decreased. The time interval for the formation of cells was about 35 minutes and the size of the cells was about 5 to 8 km horizontally. The numerical results are qualitatively consistent with the observations. Sensitivity studies indicate that the magnitude of the wind speed influenced the formation of the cells. The low level wind profiles affected the movement of cells on the lee-side of the mountain, and the height of mountain also had an impact on the characteristics of the precipitation cells.With 18 Figures 相似文献
15.
条件不稳定湿大气中三维理想地形上空对流的动力学特征 总被引：5，自引：1，他引：4
条件不稳定湿大气情况下,气流经过三维地形可以形成不同性质的对流系统以及不同特征的地形流结构,其对流系统、地形流的性质主要取决于地形上空的对流触发、对流-地形流-重力波三者之间的相互作用,同样这些过程对于地形降水的性质、分布起重要的作用.根据不同湿Fr数(Froude number),湿条件不稳定大气经过三维小尺度山地上空时其对流和地形流动存在4种不同的流域(flow regirnes):(1)下游传播对流模态;(2)上游传播和下游传播共存对流模态;(3)山峰附近准静止和下游传播共存对流模态;(4)下坡稳定和下游传播对流共存模态.地形上空对流系统主要可以通过两种不同机制形成:(1)地形直接的抬升或减速作用;(2)在地形流形成后,由于地形流本身特性(如上游分离、背风涡旋和下坡重力波破碎)触发.在较大的Fr数情况下,地形上空对流生成后反过来可以破坏上、下游的地形流结构,但对背风坡的重力波破碎影响较小.不同初始对流有效位能(CAPE)不仅可以影响对流系统的传播、发展,而且可以影响整体地形流性质.较低的初始CAPE有利于地形流的形成,此时对流对地形流结构特征的影响相对较小,其流场性质与低Fr数流域性质相似. 相似文献
16.
A 24-h simulation with the Advanced Regional Prediction System (ARPS) nonhydrostatic model is performed for the heavy snowfall event of 3–4 February 1998 along the eastern coast of Korean Peninsula; the results are used to understand the snowfall process, including why the precipitation maxima formed along the Yeongdong coastal region rather than over the mountain slope and ridge top during. The numerical simulation with a 4-km horizontal grid spacing and 43 levels reproduces very well the narrow snowband located off the eastern Korean coast, away from, instead of over, the Yeongdong coastal mountain range. The general evolution of the snowband agrees quite well with radar observations, while the water-equivalent precipitation amount agrees reasonably well with radar precipitation estimate. The simulation results clearly show that the snow band developed due to the lifting by a coastal front that developed because of the damming of cold air against the eastern slope of the coastal mountain range. The damming was enhanced by the advection of cold air by a low-level mountain-parallel jet from the north, formed due to geostrophic adjustment as the on-shore upslope air was decelerated by the mountain blocking. As the onshore flow weakened later due to synoptic-scale flow pattern change, the cold front propagated off shore and the precipitation dissipated. 相似文献
17.
The synoptic‐ and planetary‐scale signatures of precipitating systems over the Mackenzie River Basin
Abstract The synoptic‐ and planetary‐scale signatures of precipitating systems over the Mackenzie River Basin (MRB) are elucidated using composites based on a 28‐year sample of widespread precipitation events. These wet events are defined as days on which 5 or more of 12 surface stations in the MRB receive at least 2.5 mm of precipitation. Seasonal composites based on a total of 600 wet events reveal a sequence of statistically significant flow anomalies. Examination of individual wet events motivates stratification of the seasonal samples according to sea‐level pressure distribution. One evolution that is particularly common during fall, winter and spring involves lee cyclogenesis over the southern MRB in association with a strong cyclone over the Gulf of Alaska; such events are dubbed Gulf Redevelopment (GR) cases. A composite based on 59 wintertime GR events indicates upslope flow north of the lee cyclone and warm advection along an east‐west oriented warm front during the precipitation event. Composites of the Q‐vector and the divergence of this field confirm the presence of quasigeostrophic (QG) forcing for ascent over the MRB during this period. A thermally indirect “topographic tilting” mechanism, involving downs‐lope warming over the southern MRB and upslope cooling to the north, is hypothesized to increase warm‐frontal baroclinicity over the MRB. The GR composite 500 hPa geopotential height anomaly pattern is characterized by a series of anomalies extending from the Bering Sea to the Gulf of Mexico. The western (eastern) anomalies tend to decay (amplify) with time. The composite exhibits a positive anomaly over the Bering Sea, a negative anomaly over the Gulf of Alaska that moves eastward into the MRB during the precipitation event, and a positive anomaly that moves eastward over western and central North America. The presence of large, slow‐moving flow anomalies and an extended period of enhanced southwesterly geostrophic flow over the MRB in the composite suggests that a persistent influx of Pacific moisture is required to moisten the atmosphere over the MRB sufficiently for widespread precipitation. An independent composite of dry MRB cyclone events exhibits substantially weaker southwesterly geostrophic flow into the MRB relative to the wet GR composite. 相似文献
18.
ABSTRACTA detailed analysis is performed on an inland-penetrating atmospheric river (AR) driven by and coupled to a Colorado cyclone in the first week of February 2016. This winter weather system was initiated by a trough of low pressure moving across the Rocky Mountains from the California coast. The low-level jet ahead of the trough was capable of extracting water vapour from the Gulf of Mexico to feed a cyclone on the lee side of the Rocky Mountaains, and the jet stream eventually transformed into a powerful AR. The warm, moist flow from the south produced a narrow band of heavy precipitation along the major axis of the AR across the central and eastern United States and generated significant freezing rain in parts of the northeastern United States and eastern Canada as the AR flowed over the warm front. It is suggested that, in an operational weather forecasting and warning environment, ARs can be easily identified by using the vertically integrated horizontal water vapour transport, and the major AR contribution to heavy precipitation can be estimated from the horizontal moisture convergence. It is demonstrated that the AR analysis in this case can assist operational meteorologists in understanding and conceptualizing winter storm development and the associated high-impact weather pattern. The operational predictability of this winter storm and its possible teleconnection with the Madden–Julian Oscillation (MJO) are also investigated. Our lagged composite analysis reveals that a statistically significant increase in water vapour transport from the Gulf of Mexico over the North American continent could occur about 10–20 days after the MJO-related convection anomaly reaches the tropical Indian Ocean. 相似文献
19.
In Part I the dry version of a new large-eddy simulation (LES) model was presented that is specifically designed to simulate air flow and clouds above highly complex terrain. Here the implemented moisture physics are described and a new method for the generation of turbulent inflow conditions for meteorological LES is proposed. As a typical area of application the new model is applied to simulate banner clouds developing downwind of pyramidal mountain peaks. Banner clouds are shown to be primarily a dynamical phenomenon, and form in the lee of steep mountain peaks as a result of dynamically forced lee upslope flow. Due to the highly asymmetric flow field induced by the extreme orography, banner clouds can form even under horizontally homogeneous initial conditions regarding both moisture and temperature. Thus, additional leeward moisture sources, distinct air masses on both windward and leeward sides, or radiation effects are no prerequisite for banner-cloud formation. The probability of banner-cloud formation increases with increasing obstacle height and steepness and is, to a first approximation, independent of the pyramid’s orientation. Simulations with and without moisture physics reveal that, for the set-up chosen, moisture is of only secondary importance for banner-cloud dynamics. The reinforcement of lee upslope flow and corresponding cloud formation due to latent heat release turns out to be almost negligible. Nevertheless moisture physics are shown to induce a dipole-like structure in the vertical profile of the Brunt-Väisälä frequency, which in turn leads to a moderate increase in leeward turbulence. 相似文献
20.
基于2019—2021年1月1日至3月15日北京冬奥会延庆赛区（以下简称海陀山）降水观测资料和ERA5再分析资料,对期间34次降水过程进行天气分型,并对各天气型下不同海拔的降水实况特征开展统计分析。研究结果表明：冬季海陀山降水根据天气系统及地形影响可分为偏北气流型、偏东气流型、低涡低槽型、回流低涡低槽型四种天气型。不同天气型下海陀山地形高度以下主要气流方向和强度、水汽垂直分布等条件,以及与地形相互作用使得不同海拔之间降水量、持续时间等呈现显著差异。偏北气流型受500 hPa槽后整层强偏北气流控制,形成越山气流,降水集中在高海拔地区;偏东气流型受低层偏东气流影响,降水集中在低海拔地区,以上两种天气型无天气尺度系统配合,由地形强迫作用主导,降水量不大、持续时间相对较短。低涡低槽型受高空东移低涡低槽作用,配合低层西南气流,高海拔降水量更多,同时该型也是海陀山冬季最主要的降水天气型;回流低涡低槽型受高空东移低涡低槽影响,配合降水前东风回流对低层增湿并起到冷垫作用,低海拔降水量更多,以上两种天气型均存在天气尺度系统,并叠加海陀山地形作用,降水量显著且持续时间长,会对赛事运行造成较大影响。上述特征统计结果在2022年北京冬奥会期间一次强降雪预报服务中得到验证和应用,证明上述结果可以在冬季海陀山复杂地形降水预报中发挥作用。 相似文献