一次强对流降水及雨水蒸发对其影响的数值研究

基于中尺度数值模式(WRF v3.4),对发生在湖北省红安地区的一次强对流降水天气过程进行了数值模拟。结果表明,此次强对流天气是在水汽充足,高层辐散、低层辐合以及不稳定能量较大的条件下发生发展的。模式模拟得到的地面累积降水和雷达反射率因子与实况相符,云下雨水蒸发过程显著。进行敏感性试验,将雨水蒸发率分别降至1/2、1/4以及完全关闭后,雷达回波强度减弱,对流演变特征发生变化。蒸发过程的减弱使得降水始发阶段以及后期消散阶段的降水强度增强,在对流旺盛阶段降水强度减弱。同时雨水蒸发过程减弱导致云中上升气流减弱,冰雪晶及霰粒子含水量极大值减小、极大值所在高度降低。可见,雨水蒸发对对流云团动力、热力结构及云微物理结构以及云物理过程均有一定程度的影响。     

The effect of temperature-dependent exchange coeeficients on poleward heat flux by oceanic gyres

The gravitational stability of the air overlying the sea surface is determined by the air-sea temperature difference. Air-sea exchange coeeficients have been shown to increase when the air is unstable and decrease when the air is stable. This stability dependence of the wind stress has been approximated by a linear law relating wind stress to air-sea temperature difference and it has been shown that this thermal feedback generates a warm, Gulf-Stream-like jet emerging from the western boundary current eastward into the interior. Here, the thermal correction is applied tot he wind stress and to the air-sea heat exchange coefficient to study the effects on the circulation and on the poleward heat flux. The basic dynamical model is linear, wind-driven and has an anticyclonic gyre in the southern half and an equally intense cyclonic half in the northern half basin. The thermodynamic model uses the vertically averaged, convective-diffusive heat equation. Thermal feedback leads to a compression of the anticyclonic gyre to a narrower lattitude band near the western boundary and to a warm Gulf Stream extending eastward into the interior. The redistribution of the dynamical properties in the anticyclonic gyre resembles that due to inertial processes. In the cyclonic gyre the changes are quite unlike those due to inertial effects. The main quantitative change is the poleward heat flux across the gyre boundary, which can be several times the value obtained without feedback and should be important for climate studies.     

Penumbral and foliage distribution effects on Pinus sylvestris canopy gas exchange

Summary  Tree canopy water use and foliage net CO₂ uptake (NPP) were simulated for a 31-year-old Pinus sylvestris (Scots pine) plantation near Hartheim, in the Upper Rhine Valley, Germany with a mechanistically-based, three-dimensional stand gas-exchange model (STANDFLUX) for a ten-day period during spring 1992. STANDFLUX was formulated to include the effects of penumbra caused by the fine structure of the needles on light distribution within crowns. Good correspondence was found between simulated rates of tree canopy water use when including penumbral effects and eddy-covariance ET and sap flow transpiration measurements. Water use was 8–13% lower and NPP was 10–17% lower in simulations for the ten-day period when penumbral effects were not included. Simulated water use and CO₂ uptake were compared with similar outputs from a simplified layer canopy model (including or not including penumbra) which assumed horizontal homogeneity in canopy structure (GAS FLUX). Our results for the Pinus sylvestris stand indicate that penumbral effects were more important than the degree of model simplification with respect to foliage distribution (three-dimensional vs. layered structure) for estimating stand-level fluxes for these pines. Simulated maximum hourly NPP was similar to rates measured for other Pinus sylvestris stands using other methods. Predicted decreases in tree transpiration due to the modelled response of needle gas exchange to increasing vapour-pressure deficit agreed with measured changes in transpiration, and suggested that stomatal response may have been more important than decreasing soil water availability in controlling water flux to the atmosphere during this period. The overall results of the study demonstrate that current approaches in canopy modelling that separate light into sun versus shade intensities can be effective, but must be applied with caution when attempting to predict long-term water and carbon balances of forests. Received May 1, 1999 Revised November 9, 2000     

The effect of agricultural trade liberalisation on land-use related greenhouse gas emissions

This study explores the effects of agricultural trade liberalisation and concomitant changes in agricultural areas and livestock production on greenhouse gas emissions using the coupled LEITAP–IMAGE modelling system. The results indicate that liberalisation leads to an increase in total greenhouse gas emissions by about 6% compared to the reference scenario value in 2015. The increase in CO₂ emissions are caused by vegetation clearance due to a rapid expansion of agricultural area; mainly in South America and Southeast Asia. Increased methane emissions in the case of full liberalisation are caused by less intensive cattle farming in regions such as South America and Southeast Asia. This pattern is observed up to 2050. Total global production of milk, dairy and beef do not change with full liberalisation, but production shifts were observed from North America and Europe to South America and Southeast Asia. Results are less pronounced in variants where trade liberalisation is only implemented partially. Remarkably, our study shows in the trade barrier removal scenario larger numbers of dairy cows in Australia and New Zealand (ANZ) then with full liberalisation scenario or a variant in which only milk quota are abolished. This illustrates that different types of liberalisation need to be analysed regionally and per commodity before general conclusions on the impact of trade liberalisation can be drawn. Our study contributes new information on greenhouse gas emissions to a vast number of trade liberalisation studies that focus on economic impacts. The combined economic-environmental impacts need to be assessed in detail before general conclusions on trade liberalisation can be given.     

强降水预报思路引导系统

数值预报是提高日常天气预报准确率的最有效手段和技术,本系统能帮助预报员在较短的时间内对所关心的天气系统确立正确的预报思路.     

贵阳地区酸雨情况浅析

根据酸雨观测资料,对贵阳地区的酸雨情况进行分析,得出贵阳地区1年中酸雨的轻重情况,并提出防治措施。     

强降水预报思路引导系统

数值预报是提高日常天气预报准确率的最有效手段和技术,本系统能帮助预报员在较短的时间内对所关心的天气系统确立正确的预报思路。     

江西中西部地区一次暴雨过程的地形敏感性试验

利用常规观测、加密自动站资料和NCEP再分析资料,分析2005年5月江西萍乡地区春季一次暴雨过程发现,该过程仅萍乡南部地区出现暴雨,而中北部地区为小到中雨。考虑到萍乡中南部特殊地形,通过WRF中尺度模式模拟再现这次暴雨过程,并设计降低、增高和移除地形三组敏感性试验探究地形对降水的影响。结果表明：（1）萍乡地形的屏障作用在南部地区造成的风场辐合是南部产生暴雨的重要原因;（2）地形通过影响切变线附近风场辐合以及水汽汇集的位置和强度来改变暴雨的落区与强度;（3）较高的地形造成气流在山前堆积,造成明显的水平气压梯度,使局地气流与背景气流在山前辐合,有利于山前降水增强。     

The effects of below-cloud aerosol on the acidification process of rain

Using a model of the acidification process of rain, we calculate and analyze the effects and contributions of a below-cloud aerosol in its different concentrations and acidities on the pH and ion components of rain (SO ₄ ^2– , H⁺, NO ₃ ^– , NH ₄ ⁺ , etc.) under the conditions of different concentrations of pollution gases. The results show that the aerosol has an acidification or alkalization effect on the rain which changes the pHs of rain and aerosol. As acidifying pollution gas concentrations (SO₂, HNO₃) are low, the acid aerosol has important effects on the pH and H⁺ of rain, but as the gas concentrations are high, the acid aerosol has very little effect. The alkalizing aerosol makes the pH of rain increase by between 0.3 and 0.5 and neutralizes about 60% of H⁺ in the rain. As alkalizing pollution gas NH₃ exists, the acid aerosol has important effects on the pH and H⁺ of rain. But the alkalizing aerosol has very little effect, especially as the NH₃ concentration is high. The percentage contribution of the aerosol to SO ₄ ^2– in rain is generally 7–15%, the contribution of the aerosol to NO ₃ ^– is nearly the same as that of HNO₃=1 ppb, and the contribution of the aerosol to NH ₄ ⁺ is nearly the same as that of NH₃, from 5 to 7 ppb, and is an important source of NH ₄ ⁺ in rain. Finally, according to the actual conditions of typical regions in the south and north of China (Chongqing and Beijing), we analyze the effects of aerosol and pollution gases on the ion components of rain.     

一次南支槽背景下地形对贵州水城南部特大暴雨的作用

利用欧洲中期天气预报中心逐日客观分析资料、常规观测资料、FY2C卫星、雷达和区域加密自动站资料,对2009年6月28日夜间发生在贵州省水城县发耳乡特大暴雨天气进行分析。结果表明,2009年6月28日贵州省水城县发耳乡特大暴雨的发生,有南支槽、中低层切变和强盛的西南暖湿气流等天气条件的有效合理配置;强降水的落区与中-γ尺度云团有很好的对应关系,云团的移动、合并、发展、停滞以及减弱能很好地指示降水的落区及强度;产生于低层辐合区的强对流回波单体在位于水城县西北部的乌蒙山脉（主峰2901m）的阻挡下在发耳乡附近停滞不前,使水城县中部以南地区降水雨团合并加强,这是发耳特大暴雨形成的重要原因;发耳特殊的地形,使得其附近流场发生变化,不仅使地形性垂直上升运动加强、维持,而且也使得水汽不断向云内卷入,延长了暴雨云团在其上空的停留时间;喇叭口地形的收缩作用也加强了迎风坡的辐合上升运动;区域自动站的资料显示,中小尺度天气系统对水城县发耳乡及附近降水雨团的形成和加强起到了重要作用,并对此次特大暴雨的短时临近预报具有指示意义。     

地形对门头沟一次大暴雨动力作用的数值研究

2002年6月24—25日,北京门头沟附近发生了一次大暴雨过程。为探讨地形在本次过程中的动力作用,采用美国俄克拉荷马大学风暴分析预测中心开发的ARPS模式,对大暴雨过程进行了数值试验。控制试验采用27、9 km双重单向嵌套网格,网格覆盖范围约为3000 km×3000 km、900 km×900 km。两层网格均采用全物理过程,使用的都是全球30″的地形资料。在控制试验的基础上,进行了3组敏感性试验:第1组试验采用干过程模拟,即不考虑凝结潜热的作用;第2组试验将地形整体向东/西平移1°;第3组试验是将门头沟西部的局地地形抠除一部分。试验结果表明,在不考虑凝结潜热作用时,东南风气流仍然可以爬升到2 km以上,超过了大气的抬升凝结高度,证实了地形的动力作用是本次大暴雨的触发机制;将地形向东/西平移1°后,由于大气的对流稳定度发生了改变,模拟的降水强度和落区也发生了变化,表明山坡和山顶的对流不稳定大气是导致本次大暴雨的必要条件;抠除局地地形后,模拟的降水量也发生了不同程度的改变,再次证明大暴雨是在多尺度地形以及一定的天气系统配置下产生的。     

The effect of mountainous topography on moisture exchange between the “surface” and the free atmosphere

Typical numerical weather and climate prediction models apply parameterizations to describe the subgrid-scale exchange of moisture, heat and momentum between the surface and the free atmosphere. To a large degree, the underlying assumptions are based on empirical knowledge obtained from measurements in the atmospheric boundary layer over flat and homogeneous topography. It is, however, still unclear what happens if the topography is complex and steep. Not only is the applicability of classical turbulence schemes questionable in principle over such terrain, but mountains additionally induce vertical fluxes on the meso-γ scale. Examples are thermally or mechanically driven valley winds, which are neither resolved nor parameterized by climate models but nevertheless contribute to vertical exchange. Attempts to quantify these processes and to evaluate their impact on climate simulations have so far been scarce. Here, results from a case study in the Riviera Valley in southern Switzerland are presented. In previous work, measurements from the MAP-Riviera field campaign have been used to evaluate and configure a high-resolution large-eddy simulation code (ARPS). This model is here applied with a horizontal grid spacing of 350 m to detect and quantify the relevant exchange processes between the valley atmosphere (i.e. the ground “surface” in a coarse model) and the free atmosphere aloft. As an example, vertical export of moisture is evaluated for three fair-weather summer days. The simulations show that moisture exchange with the free atmosphere is indeed no longer governed by turbulent motions alone. Other mechanisms become important, such as mass export due to topographic narrowing or the interaction of thermally driven cross-valley circulations. Under certain atmospheric conditions, these topographical-related mechanisms exceed the “classical” turbulent contributions a coarse model would see by several times. The study shows that conventional subgrid-scale parameterizations can indeed be far off from reality if applied over complex topography, and that large-eddy simulations could provide a helpful tool for their improvement.     

空调系统对城市大气温度影响的模拟研究

人为热排放对城市边界层气候效应的影响起着举足轻重的作用。在人为热源的组成中,建筑物内部的能源消耗、热量产生以及室内外热量传输与交换,对于城市热环境的改变有着非常重要的作用。因此,为研究室内空调系统的产热和通过屋顶、墙面、地面进行室内外热量传输扩散,并对室外热环境产生的影响,运用WRF（Weather Research and Forecasting Model）模式,选取BEP+BEM城市冠层参数化方案,即基于多层城市冠层方案BEP（Building Effect Parameterization）增加室内空调系统影响的建筑物能量模式BEM（Building Energy Model）的方案,以南京2010年8月2—3日,夏季三伏天晴天小风天气作为背景天气进行模拟研究。结果表明,采用WRF模式考虑空调系统室内、外能量交换的BEP+BEM参数化方案,能够更好地模拟出夏季晴天城市近地层气温。当假设空调全天开启时,白天模拟值与观测值吻合较好。夜间温度模拟值高于观测值,在22时—次日00时（北京时）,存在1℃左右的偏差。白天空调系统开启对于城市近地层气温的影响不明显,而夜间使得城市气温普遍升高0.6℃,尤其是在居民区密集的地方,22—23时最大有2℃左右的升温。当调整室内空调目标温度从25℃调至27℃时,空调系统能量总释放量减少12.66%,13—16时温度下降最大,平均约为1℃,建筑物越是密集,温度下降幅度越大。      

宁夏南部山区雨雪天气分类模型的构建

为深入了解宁夏南部山区雨雪天气形成原因,用天气学、统计学和逻辑学方法,分析大量雨雪天气个例中的天气系统配置、物理量数据等.研究结果表明:雨雪天气发生时,参与系统至少有500 hPa冷气压槽(或温度槽)、700 hPa低涡切变和地面冷锋等;冷干空气和暖湿气流路径配置约有7种,地面锋面和700 hPa零度等温线配置情形约有5种,700 hPa温度在零度附近及以下.强雨雪天气发生时,水汽输送好、辐合上升层厚、冷暖对比明显、参与系统多、移动较慢.最后给出3个漏报原因.     

边界层和陆面过程对中国暴雨影响研究的进展

以华中区域中尺度业务模式WRF3D为平台,使用MYJ、ACM2边界层方案完成2012年7月的批量敏感试验,重点研究不同边界层方案对中国中东部地区夏季降水预报的影响。与高分辨率降水实况相比,白天（夜晚）的降水预报差异主要由降水面积（降水强度）决定,以MYJ方案在白天预报过大降水面积和ACM2方案在夜晚预报过强降水最为突出。对模式结果的进一步诊断表明,MYJ方案下的大面积降水由白天大范围启动积云对流方案形成隐式降水造成,而ACM2方案下的强降水与夜间更易激发云微物理方案形成过强显式降水有关。在此基础上,从边界层方案设计原理出发,指出不同方案下的垂直混合强度是导致降水预报差异的根本原因。

     

The influences of boundary layer parameterization schemes on mesoscale heavy rain system

1.Introducti0nThemesoscaleoperationalmodel-whichisoftenused,isMM4orMM5'butMM4isusedfrequentlyonlO3kmscale.Thephysicalprocessesinthismodeldevelopconstantly.FororiginalMM4,thecomputationofsurfacefluxesisnotaccurate,andKmodelfortheturbu-lencefluxesbetweenany2levelsneedstobeimprovedbynewtreatment.Inordertostudytheinfluencesofboundarylayerparameterizationschemesonmesoscaleheavyrainsystem,sur-facefluxesandKmodelinoriginalMM4areimprovedbytherecentresearchinthispaPer.Theflux-profilerelationsforv…     

Measurements of spray at an air-water interface

The spray content in the surface boundary layer above an air—water interface was determined by a series of measurements at various feteches and wind speeds in a laboratory facility. The droplet flux density N(z) can be described in terms of the scaling flux density N_* and von Karman constant K throguh the equation, N(z)/N_* = −(1/K) ln(z/z_0d) where z is height above the mean water level and z_0d is the droplet boundary layer thickness. N_* is given by a unique relationship in terms of the roughness Reynolds number u_*σ/ν where σ is the root-mean-square surface displacement. Spray inception occurred for u_* 0.3. The dominant mode of spray generation in the present and most other laboratory tests, as well as in available field data, appears to be bubble bursting.