ALLOCATION DIFFERENCE ANALYSES OF WATER SUBSTANCES DURING TYPHOON LANDING PROCESSES

Based on a successful simulation of Typhoon Haikui (2012) using WRF (Weather Research & Forecasting) model with the WSM6 microphysics scheme, a high-resolution model output is presented and analyzed in this study. To understand the cause of the average gridded rainfall stability and increases after Haikui’s landfall, this research examines the fields of the physical terms as well as the vapor and condensate distributions and budgets, including their respective changes during the landing process. The environmental vapor supply following the typhoon landfall has no significant difference from that before the landfall. Although Haikui’s secondary circulation weakens, this circulation is not conducive to typhoon rainfall stability or increases, although the amounts of the six kinds of water substances (vapor, cloud water, cloud ice, snow, rain, and graupel) increase in the outer region of the typhoon. This reallocation of water substances is essential to the maintenance of rainfall. The six kinds of water substances are classified as vapor, clouds (cloud water and ice) and precipitation (snow, rain, and graupel) to diagnose their budgets. This sorting reveals that the changes in the budgets of different kinds of water substances, caused by the reduced mixing ratios of snow and ice, the water consumption of clouds, and the transformation of graupel, induce increased concentrations of precipitation fallout, which occur closer to the ground after typhoon landfall. In addition, this pattern is an efficient way for Haikui’s rainfall to remain stable after its landfall. Thus, the allocation and budget analyses of water substances are meaningful when forecasting the typhoon rainfall stability and increases after landfall.     

A modeling analysis of rainfall and water cycle by the cloud-resolving WRF model over the western North Pacific

Simulated regional precipitation, especially extreme precipitation events, and the regional hydrologic budgets over the western North Pacific region during the period from May to June 2008 were investigated with the high-resolution （4-km grid spacing） Weather Research and Forecast （WRF v3.2.1） model with explicit cloud microphysics. The model initial and boundary conditions were derived from the National Centers for Environmental Prediction/Department of Energy （NCEP/DOE） Reanalysis 2 data. The model precipitation results were evaluated against the Tropical Rainfall Measuring Mission （TRMM） Multisatellite Precipitation Analysis 3B42 product. The results show that the WRF simulations can reason- ably reproduce the spatial distributions of daily mean precipitation and rainy days. However, the simulated frequency distributions of rainy days showed an overestimation of light precipitation, an underestimation of moderate to heavy precipitation, but a good representation of extreme precipitation. The downscaling approach was able to add value to the very heavy precipitation over the ocean since the convective processes are resolved by the high-resolution cloud-resolving model. Moreover, the water vapor budget analysis indi- cates that heavy precipitation is contributed mostly by the stronger moisture convergence; whereas, in less convective periods, the precipitation is more influenced by the surface evaporation. The simulated water vapor budgets imply the importance in the tropical monsoon region of cloud microphysics that affects the precipitation, atmospheric latent heating and, subsequently, the large-scale circulation.     

Estimates of velocity-pressure and velocity-pressure gradient interactions in the surface layer over plant canopies

The budget equations of turbulent kinetic energy and shear stress contain interaction terms of velocity-pressure and velocity-pressure gradient. These terms were estimated in the surface layer using the air pressure observed at the surface and wind velocity components over plant canopies. The magnitude of the pressure interaction terms was significantly large; it was not negligible compared with the production terms in each budget equation. The present results obtained over a rough surface also confirmed previous results that pressure terms play an important role in the turbulent kinetic energy budgets and the shear stress budget. The height dependency of nondimensional pressure terms versus (z - d)/z ₀ was not clear.     

Differences between Convective and Stratiform Precipitation Budgets in a Torrential Rainfall Event

Differences in rainfall budgets between convective and stratiform regions of a torrential rainfall event were investigated using high-resolution simulation data produced by the Weather Research and Forecasting(WRF) model. The convective and stratiform regions were reasonably separated by the radar-based convective–stratiform partitioning method, and the threedimensional WRF-based precipitation equation combining water vapor and hydrometeor budgets was further used to analyze the rainfall budgets. The results showed that the magnitude of precipitation budget processes in the convective region was one order larger than that in the stratiform region. In convective/stratiform updraft regions, precipitation was mainly from the contribution of moisture-related processes, with a small negative contribution from cloud-related processes. In convective/stratiform downdraft regions, cloud-related processes played positive roles in precipitation, while moisture-related processes made a negative contribution. Moisture flux convergence played a dominant role in the moisture-related processes in convective or stratiform updraft regions, which was closely related to large-scale dynamics. Differences in cloud-related processes between convective and stratiform regions were more complex compared with those in moisture-related processes.Both liquid-and ice-phase microphysical processes were strong in convective/stratiform updraft regions, and ice-phase processes were dominant in convective/stratiform downdraft regions. There was strong net latent heating within almost the whole troposphere in updraft regions, especially in the convective updraft region, while the net latent heating(cooling) mainly existed above(below) the zero-layer in convective/stratiform downdraft regions.     

Atmospheric and terrestrial water budgets: sensitivity and performance of configurations and global driving data for long term continental scale WRF simulations

Driving data and physical parametrizations can significantly impact the performance of regional dynamical atmospheric models in reproducing hydrometeorologically relevant variables. Our study addresses the water budget sensitivity of the Weather Research and Forecasting Model System WRF (WRF-ARW) with respect to two cumulus parametrizations (Kain–Fritsch, Betts–Miller–Janji?), two global driving reanalyses (ECMWF ERA-INTERIM and NCAR/NCEP NNRP), time variant and invariant sea surface temperature and optional gridded nudging. The skill of global and downscaled models is evaluated against different gridded observations for precipitation, 2 m-temperature, evapotranspiration, and against measured discharge time-series on a monthly basis. Multi-year spatial deviation patterns and basin aggregated time series are examined for four globally distributed regions with different climatic characteristics: Siberia, Northern and Western Africa, the Central Australian Plane, and the Amazonian tropics. The simulations cover the period from 2003 to 2006 with a horizontal mesh of 30 km. The results suggest a high sensitivity of the physical parametrizations and the driving data on the water budgets of the regional atmospheric simulations. While the global reanalyses tend to underestimate 2 m-temperature by 0.2–2 K, the regional simulations are typically 0.5–3 K warmer than observed. Many configurations show difficulties in reproducing the water budget terms, e.g. with long-term mean precipitation biases of 150 mm month^?1 and higher. Nevertheless, with the water budget analysis viable setups can be deduced for all four study regions.     

由GMS卫星资料获取我国夏季地表辐射收支

地表辐射收支是一个重要的基本辐射参数，本文导得卫星可见光和红外波段测值与地表辐射收支的基本关系，据此利用GMS静止气象卫星可见光和红外通道数值化资料和地面辐射收支观测资料，建立了几个由卫星资料估计地面辐射收支的模式，选择效果最佳的一种模式，通过内插方法求取全国辐射收支分布，回归效果与实测结果比较表明，方法有实际应用价值。     

华南春季强对流天气过程的动能收支 (一)总动能收支

本文利用常规探测资料计算和分析了1983年3月1日影响珠江三角洲的一次强对流天气过程的总动能收支。结果表明:就时间区域平均而言,动能制造项是总动能源,动能水平通量散度和次网格尺度过程则消耗区域的动能;几乎所有的主要收支项数值,都在高空急流所在的对流层上层最大;网格尺度的垂直输送使动能由对流层中、低层向高层输送,但次网格尺度过程使动能下传。在风暴影响前后,各能量的收支项都有明显的改变。      

北京一次大暴雨的水汽收支和微物理过程数值分析

利用NCEP1°×1°再分析资料和常规气象观测资料,使用WRF模式对2012年7月21日发生在北京地区的一次特大暴雨天气过程进行数值模拟。在模拟结果的基础上,分析了此次暴雨过程的形势演变和水汽条件,并分别计算了暴雨发生过程中北京全市范围内的水汽输送、水汽收支、大气可降水量和空中各相态水物质的量值大小、空间分布情况及其相互转化关系。结果发现:这次降水主要受高空槽、低涡和地面切变线的影响。有东南、西南两条水汽输送通道,计算区域上空水汽收支变化与地面雨强的演变对应很好。中低层持续而强烈的水汽净输入,为暴雨的发生发展提供了很好的水汽条件。北京各站点大气可降水量普遍超过历史极值,反映了降水的极端性。降水发展不同阶段,云内微物理过程存在差异,降水量初期以暖雨为主,降雨量不大,之后冷雨过程增强,降水量迅速增大。     

大小兴安岭林区风场动力降尺度对比研究

对2017年春季黑龙江省大、小兴安岭林区的6个代表站点10 m风场进行降尺度分析,并结合观测数据对比分析了WRF模式和CALMET降尺度模式的10 m风速、风向预报结果。结果表明：两模式逐小时风速预报与观测的相关系数为0.5-0.7,且随着风速的增加,模式的预报准确率逐渐提高,夜间的风速预报偏差较大,进入白天后,偏差明显减小。WRF模式对风速变化趋势的预报效果优于CALMET模式,与观测的风速相关性更高,而CALMET模式对较大风速的预报效果优于WRF模式。在风向预报方面,WRF和CALMET的风向模拟与观测风向均有较好的一致性,模式预报准确率较高的两个风向也刚好对应各站的盛行风向。同时,本文用回归方法对日平均风速进行订正发现,订正后各站的日平均风速预报准确率平均提高了50%,具有较好的业务应用价值。     

Heat,momentum and moisture budgets of the katabatic layer over the melting zone of the west Greenland ice sheet in summer

The budgets of momentum, heat and moisture of the atmospheric boundary layer overlying the melting zone of the west Greenland ice sheet during an 8-day period in summer are calculated. To do so, the governing budget equations are derived and presented in terms of vertically averaged quantities. Moreover, stationarity is assumed in the present study. Measurements collected during the GIMEX-91 experiment are used to calculate the contribution of the different terms in the equations to the budget.During summer, a well developed katabatic wind system is present over the melting zone of the Greenland ice sheet. The budgets show that advection in the katabatic layer is small for momentum, heat and humidity, when the horizontal length scale of the integration area is sufficiently large (>50 km). This indicates that in principle one-dimensional atmospheric models can be used to study the boundary layer over the melting zone of the Greenland ice sheet. The background stratification plays a crucial role in the heat and moisture budget. Vertical divergence of longwave radiation provides one-third and the turbulent flux of sensible heat the rest of the cooling of the boundary layer. Moisture is added to the boundary layer by evaporation which is a significant term in the moisture budget. Negative buoyancy (katabatic forcing) dominates the momentum budget in the downslope direction. Coriolis forcing is important, stressing the large spatial scale of the katabatic winds on the Greenland ice sheet.     

一次梅雨暴雨的动能谱特征分析及收支诊断

利用WRF模式和NCEP再分析资料,对一次梅雨暴雨个例进行了数值模拟,基于高分辨率的模拟结果计算了水平动能谱、涡旋动能谱及辐散动能谱,诊断了动能收支谱方程。结果表明:在暴雨发展阶段,各个高度上都有中尺度动能增长,其显著增加始于中尺度低端,这导致了在中尺度波段出现谱转折特征,但在不同高度转折尺度不同;对流层高层涡旋动能大于辐散动能,平流层低层反之;不同降水阶段、不同高度和不同尺度上动能的来源不同,对流层高层,中尺度动能倾向由非线性项和气压项贡献;平流层低层,气压项的作用更为明显。     

The heat and water budgets of a beaver pond

Small water bodies create their own characteristic local meteorological environments. The heat and water budgets will generally vary with surface area and water depth. If a small pond gradually becomes covered by vegetation, its meteorological conditions will change. On occasion, a vegetated area may change into a pond, complete with vegetation established in the water and extending above the surface. Such are beaver ponds and other flooded areas.

The paper discusses the main features of the development of beaver ponds and their heat and water budgets at different stages. The energy budget programme used was previously developed by the authors, but it has been modified to account for the different phases of the pond development. The effects of the various physical changes are evaluated by comparing the individual heat and water budget terms for different stages between an open lake surface and a forest cover.

The local heat budget will only be affected on a small scale by the establishment of a beaver pond, but the influence on the water budget has far‐reaching consequences.     

WRF模式中的微物理过程及其预报对比试验

WRF(Weather Research Forecast)模式系统是由许多美国研究部门及大学的科学家共同参与进行开发研究的新一代中尺度同化预报系统。本文主要对公开发布的WRF模式V2.0版本中使用的微物理过程方案进行简单介绍,并在国家气象中心建立的与T213中期预报模式相嵌套的预报系统的基础上,对不同微物理过程方案进行了降水预报对比试验和检验,对各方案的降水预报性能进行初步评估。试验结果表明,总体预报效果LIN方案较好,而对流参数化方案从降水落区预报和对流降水对总降水的贡献两方面看则是KF和NKF方案的预报效果较好。     

应用WRF模式对江西一次暴雨过程的模拟分析

利用新一代数值预报模式WRF耦合RUC、NOAH两个陆面过程,对2006年4月11-12日发生在江西境内的一次暴雨过程进行模拟,并对模式输出的水文平衡和能量,尤其是土壤湿度、地表径流、土壤温度等的变化进行了分析.结果显示,WRF模式耦合两个陆面过程均能模拟出此次暴雨过程的降水空间、时间分布和强度,而WRF-RUC提供了...     

The radiation budget in a regional climate model

The long- and short-wave components of the radiation budget are among the most important quantities in climate modelling. In this study, we evaluated the radiation budget at the earth??s surface and at the top of atmosphere over Europe as simulated by the regional climate model CLM. This was done by comparisons with radiation budgets as computed by the GEWEX/SRB satellite-based product and as realised in the ECMWF re-analysis ERA40. Our comparisons show that CLM has a tendency to underestimate solar radiation at the surface and the energy loss by thermal emission. We found a clear statistical dependence of radiation budget imprecision on cloud cover and surface albedo uncertainties in the solar spectrum. In contrast to cloud fraction errors, surface temperature errors have a minor impact on radiation budget uncertainties in the long-wave spectrum. We also evaluated the impact of the number of atmospheric layers used in CLM simulations. CLM simulations with 32 layers perform better than do those with 20 layers in terms of the surface radiation budget components but not in terms of the outgoing long-wave radiation and of radiation divergence. Application of the evaluation approach to similar simulations with two additional regional climate models confirmed the results and showed the usefulness of the approach.     

Impact of time sampling on atmospheric energy budget residuals

Summary Diagnostic time-mean budgets of energy and water are evaluated in many atmospheric process studies. The errors of budget-derived quantities like sub-gridscale fluxes or diabatic heating are governed by the errors of the budgets. Here we consider 3D-budgets on the meso-β scale over Europe. They are compiled from analyses of state quantities available from forecast centres. In the present study we found that the mandatory 6 hours sampling interval between synoptic observations is the main error source for routine time-mean budgets. The errors have been quantified (i) by first sampling forecast data of the German Europamodell every 5 minutes and averaging them over 12 hours (reference budget), and (ii) by sampling the same data only every 6 hours and averaging these also over 12 hours (routine budget). With this method we find that routine budgets in single atmospheric meso-β scale columns show relative random errors of typically 200% and systematic errors of up to 20%, exclusively due to undersampling. Thus routine budgets, if applied to specific days at individual locations, cannot be expected to yield useful results, except perhaps for cases with extremely strong signal. Compositing over several hundreds of columns with similar weather reduces the random budget error down to about 50%; this seems to be the best one can achieve for routine budgets. The systematic error of some budget quantities is caused by a correlation between the time of occurence of certain processes (mainly convection) and the sampling times. While this error cannot be reduced through compositing, we find that it can be crudely estimated by using different time averaging methods. As application for this method we determine sub-gridscale budget quantities over the BALTEX catchment (August-September 1995) for an ensemble of convectively active and an ensemble of rain-active columns. For the ensemble mean profiles we find, in terms of the diagnosed sub-gridscale test quantities diabatic heating and vertical moist enthalpy flux divergence, that their accuracy is sufficient to detect statistically significant differences between both ensembles. The diabatic heating is about the same for both ensembles, while the flux divergence in the convective ensemble is about three times as large as in the rain ensemble. Received November 7, 2001 Revised April 4, 2001     

A Heavy Rainfall Event in Autumn over Beijing-Atmospheric Circulation Background and Hindcast Simulation Using WRF

Heavy rainfall events often occur in Beijing during summer but rarely in autumn. However,during 3-5 September2015, an exceptionally heavy rainfall event occurred in Beijing. Based on the reanalysis data and the Weather Research and Forecasting(WRF) model simulations, the main contributing factors and the predictability of this heavy rainfall event were examined through comprehensive analyses of vorticity advection and water vapor transport/budget. The results indicate that a "high-in-the-east-low-in-the-west" pattern of 500-hPa geopotential height over the Beijing area played an important role. The 850-hPa low-level jet(LLJ) provided a mechanism for rising motion and transported abundant water vapor into the Beijing area. Two-way nested hindcast experiments using WRF well reproduced the atmospheric circulation and LLJ. Quantitative analysis indicates that the WRF model with the rapid update cycle(RUC) land surface scheme and the single-moment 6-class(WSM6) microphysics scheme exhibited the best skill, and the model performance improved with a higher resolution. Further analysis indicates that the bias in the precipitation forecast was caused by the bias in water vapor transport.     

A Heavy Rainfall Event in Autumn over Beijing—Atmospheric Circulation Background and Hindcast Simulation Using WRF

Heavy rainfall events often occur in Beijing during summer but rarely in autumn. However, during 3–5 September 2015, an exceptionally heavy rainfall event occurred in Beijing. Based on the reanalysis data and the Weather Research and Forecasting (WRF) model simulations, the main contributing factors and the predictability of this heavy rainfall event were examined through comprehensive analyses of vorticity advection and water vapor transport/ budget. The results indicate that a “high-in-the-east–low-in-the-west” pattern of 500-hPa geopotential height over the Beijing area played an important role. The 850-hPa low-level jet (LLJ) provided a mechanism for rising motion and transported abundant water vapor into the Beijing area. Two-way nested hindcast experiments using WRF well reproduced the atmospheric circulation and LLJ. Quantitative analysis indicates that the WRF model with the rapid update cycle (RUC) land surface scheme and the single-moment 6-class (WSM6) microphysics scheme exhibited the best skill, and the model performance improved with a higher resolution. Further analysis indicates that the bias in the precipitation forecast was caused by the bias in water vapor transport.     

Increases in Anthropogenic Heat Release from Energy Consumption Lead to More Frequent Extreme Heat Events in Urban Cities

With economic development and rapid urbanization,increases in Gross Domestic Product and population in fastgrowing cities since the turn of the 21st Century have led to increases in energy consumption.Anthropogenic heat flux released to the near-surface atmosphere has led to changes in urban thermal environments and severe extreme temperature events.To investigate the effects of energy consumption on urban extreme temperature events,including extreme heat and cold events,a dynamic representation scheme of anthropogenic heat release(AHR)was implemented in the Advanced Research version of the Weather Research and Forecasting(WRF)model,and AHR data were developed based on energy consumption and population density in a case study of Beijing,China.Two simulations during 1999?2017 were then conducted using the developed WRF model with 3-km resolution with and without the AHR scheme.It was shown that the mean temperature increased with the increase in AHR,and more frequent extreme heat events were produced,with an annual increase of 0.02?0.19 days,as well as less frequent extreme cold events,with an annual decrease of 0.26?0.56 days,based on seven extreme temperature indices in the city center.AHR increased the sensible heat flux and led to surface energy budget changes,strengthening the dynamic processes in the atmospheric boundary layer that reduce AHR heating efficiency more in summer than in winter.In addition,it was concluded that suitable energy management might help to mitigate the impact of extreme temperature events in different seasons.     

季风湿润区夏季水汽收支的年代际变化特征

采用1983—2002年NCEP/NCAR再分析资料和我国660站降水资料,对我国东部季风湿润区夏季水汽收支变化与大气环流和我国降水异常特征的关系进行研究。结果表明:20世纪80—90年代夏季水汽收支时间序列表现出明显的年代际变化增加趋势,与降水时间序列的相关系数为0.71;水汽收支高值、低值年代不仅能够指示季风湿润区经向风的异常变化,还能够指示东亚夏季风的强弱和降水异常变化。合成的水汽输送年代际异常在东亚—西太平洋区表现为4个异常环流,异常水汽通量辐合区位于长江流域及以南地区。水汽收支高值年代,亚洲大陆高纬度地区低压偏弱,大陆表面温度及西太平洋海温偏高,我国东部沿海盛行异常偏南风,低层气流辐合、高层气流辐散强,垂直上升运动强烈;低值年代则相反。合成的经向水汽收支占总收支的71.3%,合成的异常降水量最大达100 mm以上。