GRAPES-MESO模式浅对流参数化的改进与试验

参考Berg 等2005、2013年提出的扰动对流触发函数方法,对GRAPES-Meso模式积云对流参数化方案(KF eta)中的浅对流激发进行改进设计和试验,将单一的温、湿度触发改为对近地层进行一组温度、湿度扰动后的触发,并且用与该组扰动相关的边界层温、湿度分布确定的联合概率密度函数(JPDF)来表征浅对流云的特征参量及计算浅对流的强度。 着重分析了改进方案的浅对流激发、浅对流对环境场的反馈、模式地面降水和2 m气温的相关响应等,并与原方案和相关观测比较,验证了改进方案的合理性。 结果显示,改进方案比原方案能较早地激发出浅对流,且浅对流的激发频次高,浅对流激发的增加致使在模式低层距地数百米至2—3 km的垂直层内对环境温、湿度场和云雨水反馈增大,对GRAPES-Meso浅对流激发偏弱有改进作用,并对格点尺度与次网格尺度降水分配比不协调有改进。 对连续两个月批量试验的检验表明,浅对流激发的改进,可对GRAPES-Meso的24 h降水预报技巧的提高和2 m气温偏差的减小等产生不同程度的正影响。     

The role of shallow convection in the water and energy cycles of the atmosphere

The Canadian Centre for Climate Modelling and Analysis atmospheric general circulation model (AGCM4) is used to study the role of shallow convection in the hydrologic and energy cycles of the atmosphere. Sensitivity tests with AGCM4 show a marked effect of the parameterization of shallow convection in the model. In particular, including the parameterization of shallow convection produces considerably enhanced vertical mixing and decreased stratiform cloud amounts in the lower subtropical atmosphere over the oceans. The differences in simulated stratiform cloud amounts are associated with a change in the globally averaged outgoing shortwave radiative flux at the top of the atmosphere of about 11 W m⁻². Additionally, precipitation rates are considerably reduced for stratiform clouds and enhanced for convective clouds in the subtropics, if the parameterization of shallow convection is included in the model. Additional tests show that the simulated responses in cloud amounts and precipitation to the treatment of shallow convection are robust. Additional simulations with modified closures for deep convection and other changes to the treatment of convection in the model still lead to similar responses of the model results.     

The role of shallow convection in promoting the northward propagation of boreal summer intraseasonal oscillation

Theoretical and Applied Climatology - By conducting idealized experiments in a general circulation model (GCM) and in a toy theoretical model, we test the hypothesis that shallow convection (SC) is...     

中国冷季高架对流个例初步分析

通过对3个中国冷季高架对流个例进行详细分析,试图揭示中国冷季不同类型高架对流在环境背景、雷达回波结构、产生的天气类型和主要形成机理方面的主要特征,包括共同点和差异。利用常规高空和地面观测、NCEP分析和雷达回波资料,采用对不同类型多个典型个例分析的方法进行研究。首先给出了中国冷季高架对流的定义,然后分别仔细分析了3个不同类型冷季高架对流个例,探讨他们各自的环境背景特征,生成与发展机理,对他们的相同点和差异进行了对比。3个个例的共同特点是斜压性和深层风垂直切变都很强,对流发生区在地面锋面冷区一侧数百千米。不同点是前2个个例为条件不稳定结合水汽和抬升触发等条件导致的垂直对流,低层暖平流都很强,但对流有效位能差异很大,对流强度和导致的天气差异很大。第3个个例为条件对称不稳定结合水汽等条件形成的倾斜对流个例,倾斜对流区在地面锋面以北500-600 km处,冷垫非常深厚。第1个例子于2012年2月27日发生在华南,最不稳定气块对流有效位能只有100 J/kg左右,深层风垂直切变很强,850-700 hPa的辐合切变线触发了该高架对流,对流较弱,最强反射率因子在40-45 dBz,只产生了雷电、霰和小冰雹。第2个例子于2007年3月30日晚上出现在山东半岛,最不稳定气块对流有效位能达1400 J/kg,0-6 km风垂直切变（风矢量差）达32 m/s,形成数个结构类似超级单体的对流风暴,多个多单体强风暴,和大量多单体风暴,最强反射率因子将近70 dBz,导致6个站出现冰雹,其中1个站观测到直径23 mm的大冰雹,另1个站点出现21 m/s对流大风。其最有可能的触发机制是以泰山为中心的山地激发出来,在低层为稳定层,以上为深层条件不稳定层和强风垂直切变环境下形成的较大振幅俘获中尺度重力波。该俘获重力波可能还对对流生成后对流的组织形态和对流群的整体结构具有显著调制作用。最后1个例子是发生在2008年1月中国南方大范围冰冻雨雪期间1月27日安徽、江苏和浙江的区域性大暴雪,分析表明,条件对称不稳定导致的倾斜对流是产生此次大暴雪的主要原因之一。      

光学测风经纬仪的使用技巧

通过对GYR1型电子式光学测风经纬仪使用方法的阐述、分析,得出经纬仪在架设、标定、快速定向、抓球、数据传输、日常维护等方面的使用技巧,为新设备的正常使用提供参考,以实现所有台站对电子经纬仪的熟练使用,充分发挥其在高空气象业务中的重要作用。     

系留气艇探测风速的误差订正及其应用评估

使用系留气艇探空系统在常州、苏州、南京市区对边界层风速、温度、湿度廓线进行了观测,原始数据表明探测结果存在明显的系统误差。本文主要讨论风速订正问题,分析发现风速误差与高度和风速有关,据此提出了依据高度和依据风速的两种订正方案。对比结果表明:两种方案都能有效修正系留气艇测量风速的系统误差,高度订正方案表现更好。本文还用订正后的系留气艇探测结果与苏州市气象局的风廓线雷达资料进行对比,结果显示风廓线雷达探测结果在500 m以下系统偏小。     

Statistics of shallow convection on Mars based on large-eddy simulations. Part 1: shearless conditions

Results of large-eddy simulations of shallow, quasi-steady, shear-less convection in the Martian boundary layer are presented and discussed. In the considered three cases, turbulence is forced by the radiative flux divergence, prescribed as given functions of height, and the strength of the surface heat flux. It is constrained by the temperature inversion at the boundary-layer top. The resulting convective boundary layer exhibits horizontal cellular structures. The presence of radiative heating causes dimensionless statistics of turbulence to depend on the parameter F, defined in terms of the integrated radiative and turbulent heating rates in the boundary layer.     

Statistics of shallow convection on Mars based on large-eddy simulations. Part 2: effects of wind shear

Effects of wind on quasi-steady, shallow convection in the Martian boundary layer are studied using a large-eddy simulation model. Convection in the model is generated by the radiative flux divergence and the strength of the surface heat flux, which do not vary in time. The resulting convective boundary layer exhibits transient, irregular, horizontal cellular structures, transported by wind, and a lack of well-pronounced regular horizontal rolls, observed for analogous conditions on Earth. The dimensionless statistics of turbulence are generally similar to those generated in the windless conditions, and depend on the ratio F, defined in terms of the integrated radiative and turbulent heating rates in the boundary layer. The simulations show that variations of the radiative heating influence the temperature statistics, while their effects on the wind velocity are relatively small. The horizontal velocity variances do not show a strong dependence on parameter F, in contrast with the vertical velocity variances, which are strongly dependent on F.     

Initiation of deep convection caused by land-surface inhomogeneities in West Africa: a modelled case study

Simulations with the Consortium for Small Scale Modelling model were performed to investigate the impact of land surface inhomogeneities on the initiation of convection. A case from the African Monsoon Multidisciplinary Analysis campaign, 11 June 2006, was selected. On this day, a mesoscale convective system was observed and simulated. The simulation scenarios included a realistic and an increased initial soil moisture distribution as well as a homogeneous soil moisture and texture field. Land use and orography were the same in all runs. Heat and moisture budget calculations were applied to analyse the processes responsible for the evolution of pre-convective atmospheric conditions and convection-triggering thermally induced circulation systems. Convective cells were initiated in all experiments. However, the amount of cells, their origin, evolution, and precipitation amount differed. First shallow clouds were initiated over areas with higher sensible heat fluxes. The evolution of subsequent deep convection was triggered by secondary circulation systems caused by baroclinic conditions generated by clouded and unclouded regions. The further evolution of the precipitation cells strongly depended on convective inhibition in the areas the cells moved into.     

Evaluation of a Lagrangian advection scheme for cloud droplet diffusion growth with a maritime shallow cumulus cloud case

A Lagrangian advection scheme (LAS) for solving cloud drop diffusion growth was previously proposed (in 2020) and validated with simulations of cloud droplet spectra with a one-and-a-half dimensional (1.5D) cloud bin model for a deep convection case. The simulation results were improved with the new scheme over the original Eulerian scheme. In the present study, the authors simulated rain embryo formation with the LAS for a maritime shallow cumulus cloud case from the RICO (Rain in Cumulus over the Ocean) campaign. The model used to simulate the case was the same 1.5D cloud bin model coupled with the LAS. Comparing the model simulation results with aircraft observation data, the authors conclude that both the general microphysical properties and the detailed cloud droplet spectra are well captured. The LAS is robust and reliable for the simulation of rain embryo formation.摘要云滴凝结增长的拉格朗日平流方案(LAS)于2020年提出, 并通过一维半(1.5D)分档云模式模拟深对流个例得到验证. 相比原先的欧拉平流方案, 新方案的使用改进了模拟结果. 本研究中, 我们进行了海洋性浅积云雨胚形成的个例模拟研究, 个例取自RICO (Rain in Cumulus over the Ocean) 外场试验. 浅积云个例的模拟同样使用耦合了LAS的1.5D分档云模式. 对比飞机观测数据, 我们认为模拟结果较好的刻画了积云的总体微物理特征和精细的云滴谱分布, 利用LAS模拟雨胚形成是合理可信的.     

Integration of the shallow water equations in a plane geometry using semi-Lagrangian and Eulerian schemes

Summary Extended integrations of semi-Lagrangian and Eulerian shallow water primitive equation models are performed. The semi-Lagrangian model used the semi-implicit two-time-level scheme. The Eulerian model used a conserving nonlinear advection scheme.For low resolution and longer integrations, difficulties were encountered with the semi-Lagrangian model which were absent in the Eulerian model. These difficulties are discussed.With 14 Figures     

Adjoint of a parameterized moisture convection model

Summary Adjoint models have found use as dynamical tracers, helping to track a feature or phenomenon back to its origin. Their application to the study of atmospheric convection, however, is challenged by the complexity and nonlinearity of diabatic processes. Herein, the adjoint of a significantly simpler parameterized moisture (PM) model is described and tested. The PM model eliminates explicit moisture by making latent heating conditionally proportional to updraft velocity and providing a lower tropospheric heat sink mimicking rainwater evaporation.The PM adjoint, of course, is useful only if the parameterization can produce realistic results. Earlier work suggested that the PM framework possessed a fundamental flaw that made its storms have an excessive impact on their upstream environments. In fact, the adjoint was used to identify the origin of the discrepancies between PM and traditional cloud model storms, thereby leading to the parameterization improvements and dynamical insights recently discussed in Fovell (2002). The present paper is a companion to that study, describing how the adjoint model was constructed, tested and utilized. In addition, an even more realistic adjoint framework is described.     

浅水波方程在全球上的变时间步长积分

本文讨论了浅水波方程在全球上的变时间步长(以下简称变步长)积分。并讨论了两步Lax-Wendroff的变时间步长(以下简称TLW变步长)积分,发现积分结果对平滑系数κ很敏感,必须选择合适。井将常数时间步长(以下简称定步长)的积分结果和两种变步长的积分结果进行比较。发现用实际资料作预报,变步长法的预报均方根误差比定步长法的小。还发现变步长的24小时预报对近极地系统移动偏慢的问题比定步长的有较大的改善。变步长积分的计算稳定性也优于定步长。     

Water resources for agriculture in a changing climate: international case studies

This integrated study examines the implications of changes in crop water demand and water availability for the reliability of irrigation, taking into account changes in competing municipal and industrial demands, and explores the effectiveness of adaptation options in maintaining reliability. It reports on methods of linking climate change scenarios with hydrologic, agricultural, and planning models to study water availability for agriculture under changing climate conditions, to estimate changes in ecosystem services, and to evaluate adaptation strategies for the water resources and agriculture sectors. The models are applied to major agricultural regions in Argentina, Brazil, China, Hungary, Romania, and the US, using projections of climate change, agricultural production, population, technology, and GDP growth.For most of the relatively water-rich areas studied, there appears to be sufficient water for agriculture given the climate change scenarios tested. Northeastern China suffers from the greatest lack of water availability for agriculture and ecosystem services both in the present and in the climate change projections. Projected runoff in the Danube Basin does not change substantially, although climate change causes shifts in environmental stresses within the region. Northern Argentina's occasional problems in water supply for agriculture under the current climate may be exacerbated and may require investments to relieve future tributary stress. In Southeastern Brazil, future water supply for agriculture appears to be plentiful. Water supply in most of the US Cornbelt is projected to increase in most climate change scenarios, but there is concern for tractability in the spring and water-logging in the summer.Adaptation tests imply that only the Brazil case study area can readily accommodate an expansion of irrigated land under climate change, while the other three areas would suffer decreases in system reliability if irrigation areas were to be expanded. Cultivars are available for agricultural adaptation to the projected changes, but their demand for water may be higher than currently adapted varieties. Thus, even in these relatively water-rich areas, changes in water demand due to climate change effects on agriculture and increased demand from urban growth will require timely improvements in crop cultivars, irrigation and drainage technology, and water management.     

如何提高探空气球的施放高度

该文总结了施放探空气球过程中对气球施放高度造成影响的多个主要因素,并采取相应的措施,提高气球施放高度,以便获取更多更全的高空大气探测资料。     

An observational study of entraining convection using balloon-borne turbulence probes and high-power Doppler radar

Features associated with the upper limit of convection, observed by turbulence probes supported by a tethered kite balloon and by high-power Doppler radar, are described. The observations illustrate the interaction of thermal plumes with the capping inversion (and stable air aloft) and confirm the existence of non-turbulent, intermittently turbulent and fully turbulent layers. Evidence is presented for entrainment processes occurring on scales ranging from a few metres to several hundred metres. Individual distortions of the inversion interface, tracked by the radar, have a lifetime of about 5 minutes. Other, larger scale (i.e., > 1 km) perturbations of the top of the boundary layer were observed over longer periods, and are thought to be due to topographical effects.Now at the Meteorological Office, Bracknell, U.K.     

Occurrence of roll circulations in a shallow boundary layer

Meteorological measurements taken at the Näsudden wind turbine site during slightly unstable conditions have been analyzed. The height of the convective boundary layer (CBL) was rather low, varying between 60 and 300 m. Turbulence statistics near the ground followed Monin-Obukhov similarity, whereas the remaining part of the boundary layer can be regarded as a near neutral upper layer. In 55% of the runs, horizontal roll vortices were found. Those were the most unstable runs, with -z _i/L > 5. Spectra and co-spectra are used to identify the structures. Three roll indicators were identified: (i) a low frequency peak in the spectrum of the lateral component at low level; (ii) a corresponding increase in the vertical component at mid-CBL; (iii) a positive covariance {ovvw} together with positive wind shear in the lateral direction (V/z) in the CBL. By applying these indicators, it is possible to show that horizontal roll circulations are likely to be a common phenomenon over the Baltic during late summer and early winter.     

Turbulent characteristics of a shallow convective internal boundary layer

Turbulent characteristics of a 50 to 100 m deep convective internal boundary layer (I.B.L.) have been studied. The data were gathered at a flat coastal site (Näsudden on the island of Gotland, Sweden) during three consecutive days in May 1980 which were characterized by a steady, very stable stratified marine approach flow. The site is situated on a flat area ca. 1500 m from the shoreline. Only daytime runs have been analysed in the present paper. The sensible heat flux at the ground was typically 200 W m^-2 and was found to decrease more or less linearly with height throughout the I.B.L., being slightly negative at greater heights. The momentum flux was also found to decrease with height, but nevertheless shear production of turbulent kinetic energy was found to be large throughout the entire I.B.L. The analysis shows that the turbulent regime has a mixed character. Certain characteristics, such as the rate of growth of the I.B.L., appear to be almost entirely controlled by mechanical turbulence, while others, notably temperature variance and the spectrum of vertical velocity, scale remarkably well with w _* and z _i, in accordance with the results found in fully convective conditions during the experiments at Minnesota and Aschurch. Other turbulent characteristics, such as spectra of the horizontal wind components measured near the top of the I.B.L. tend to adhere to mixed-layer scaling in the high frequency range, exhibiting much increased energy in the lower (reduced) frequency range. Spectra of the velocity components from 10 m are shown to be in general agreement with findings from ‘ideal’, homogeneous sites (Kansas) when properly normalized, although the low frequency part of u- and v-spectra are slightly reduced compared to the case with deep convection.     

河套地区一次雷暴的特征分析

应用内蒙古高空、地面观测资料及卫星云图、新一代天气雷达资料,分析了2015年7月29日河套地区一次雷暴天气,同时对比分析2004年6月7日、7月23日呼和浩特市及2015年8月7日20时山东半岛发生的3次强对流天气,结果表明:高空前倾槽结构为此次强对流天气提供了有利的环流条件;700、850h Pa切变线的交汇及高空急流出口辐散抽吸有利于上升运动的形成和维持;此类风暴云团均呈三角形,尖角指向中高层入流方向一侧,云团边界清晰,对流中心均位于尖角附近;新一代天气雷达回波较强且呈三角形分布,顶角≤50o,入流一侧边界清晰,回波中心接近迎风顶角,回波强度≥55d Bz,具有涡管特征。