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1.
A new cloud parameterization based on prognostic equations for the subgrid-scale fluctuations in temperature and total water
content is introduced for global climate models. The proposed scheme, called hybrid prognostic cloud (HPC) parameterization,
employs simple probability density functions (PDFs) to the horizontal subgrid-scale inhomogeneity, allowing them to vary in
shape in response to small-scale processes such as cumulus detrainment and turbulent mixing. Simple tests indicate that the
HPC scheme is highly favorable as compared to a diagnostic scheme in terms of the cloud fraction and cloud water content under
either uniform or non-uniform forcing. The relevance of the HPC scheme is investigated by implementing it in an atmospheric
component model of the climate model MIROC with a coarse resolution of T42. A comparison of the short-term integrations between
the T42 model and a global cloud resolving model (GCRM) reveals that the HPC scheme can reproduce, to a certain degree, the
subgrid-scale variance and skewness of temperature and total water content simulated in the GCRM. It is also found that the
HPC scheme significantly alters the climatological distributions in cloud cover, precipitation, and moisture, which are all
improved from the model using a conventional diagnostic cloud scheme. 相似文献
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《Dynamics of Atmospheres and Oceans》1997,26(2):95-130
A one-dimensional penetrative plume model has been constructed to parameterize the process of deep convection in ocean general circulation models (OGCMs). This research is motivated by the need for OGCMs to better model the production of deep and intermediate water masses. The parameterization scheme takes the temperature and salinity profiles of OGCM grid boxes and simulates the subgrid-scale effects of convection using a one-dimensional parcel model. The model moves water parcels from the surface layer down to their level of neutral buoyancy, simulating the effect of convective plumes. While in transit, the plumes exchange water with the surrounding environment; however, the bulk of the plume water mass is deposited at e level of neutral buoyancy. Weak upwelling around the plumes is included to maintain an overall mass balance. The process continues until the negative buoyant energy of the one-dimensional vertical column is minimized. The parameterized plume entrainment rate, which plays a central role in the parameterization, is calculated using modified equations based on the physics of entraining buoyant plumes. This scheme differs from the convective adjustment techniques currently used in OGCMs, because the parcels penetrate downward with the appropriate degree of mixing until they reach their level of neutral stability. 相似文献
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Implementation of a Surface Runoff Model with Horton and Dunne Mechanisms into the Regional Climate Model RegCM_NCC 总被引：1，自引：0，他引：1
A surface runoff parameterization scheme that dynamically represents both Horton and Dunne runoff generation mechanisms within a model grid cell together with a consideration of the subgrid-scaie soil heterogeneity, is implemented into the National Climate Center regional climate model （RegCM_NCC）. The effects of the modified surface runoff scheme on RegCMANCC performance are tested with an abnormal heavy rainfall process which occurred in summer 1998. Simulated results show that the model with the original surface runoff scheme （noted as CTL） basically captures the spatial pattern of precipitation, circulation and land surface variables, but generally overestimates rainfall compared to observations. The model with the new surface runoff scheme （noted as NRM） reasonably reproduces the distribution pattern of various variables and effectively diminishes the excessive precipitation in the CTL. The processes involved in the improvement of NRM-simulated rainfall may be as follows： with the new surface runoff scheme, simulated surface runoff is larger, soil moisture and evaporation （latent heat flux） are decreased, the available water into the atmosphere is decreased; correspondingly, the atmosphere is drier and rainfall is decreased through various processes. Therefore, the implementation of the new runoff scheme into the RegCMANCC has a significant effect on results at not only the land surface, but also the overlying atmosphere. 相似文献
6.
The earth’s surface is characterized by small-scale heterogeneity attributable to variability in land cover, soil characteristics and orography. In atmospheric models, this small-scale variability can be partially accounted for by the so-called mosaic approach, i.e., by computing the land-surface processes on a grid with an explicit higher horizontal resolution than the atmosphere. The mosaic approach does, however, not account for the subgrid-scale variability in the screen-level atmospheric parameters, part of which might be related to land-surface heterogeneity itself. In this study, simulations with the numerical weather prediction model COSMO are shown, employing the mosaic approach together with a spatial disaggregation of the atmospheric forcing by the screen-level variables to the subgrid-scale. The atmospheric model is run with a 2.8?km horizontal grid resolution while the land surface processes are computed on a 400-m horizontal grid. The disaggregation of the driving atmospheric variables at screen-level is achieved by a three-step statistical downscaling with rules learnt from high-resolution fully coupled COSMO simulations, where both, atmosphere and surface, were simulated on a 400-m grid. The steps encompass spline interpolation of the grid scale variables, conditional regression based on the high-resolution runs, and an optional stochastic noise generator which restores the variability of the downscaled variables. Simulations for a number of case studies have been carried out, with or without mosaic surface representation and with or without atmospheric disaggregation, and evaluated with respect to the surface state variables and the turbulent surface exchange fluxes of sensible and latent heat. The results are compared with the high-resolution fully coupled COSMO simulations. The results clearly demonstrate the high importance of accounting for subgrid-scale surface heterogeneity. It is shown that the atmospheric disaggregation leads to clear additional improvements in the structures of the two-dimensional surface state variable fields, but to only marginally impacts on the simulation of the turbulent surface exchange fluxes. A detailed analysis of these results identifies strongly correlated errors in atmospheric and surface variables in the mosaic approach as the main reason for the latter. The effects of these errors largely cancel out in the flux parameterization, and thus explain the comparably good results for the fluxes in the mosaic approach without atmospheric disaggregation despite inferior performance for the surface state variables themselves. Inserting noise in the disaggregation scheme leads to a deterioration of the results. 相似文献
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Significant improvements are occurring in the representation of physical processes in atmospheric convection models. They should go along with parallel improvements in the parameterization of subgrid scale turbulent processes. This problem appears to be particularly delicate in the presence of clouds, due to the local release of latent heat.Two important points are the choice of adequate turbulent thermodynamic variables and of the method for truncating the statistical moment equations. These topics are discussed here within the framework of the three-dimensional convection model under development at the Laboratoire de Météorologie Dynamique. Assuming the need for at least a simplified second-order closure, two improvements are tested on a numerical simulation of the Porto Rico experiment conducted by the National Center for Atmospheric Research (U.S.A.) in 1972. They concern the use of a rate equation for sub-grid scale turbulent kinetic energy and of specific variables which are approximately conserved in the condensation process. 相似文献
8.
A simple parameterization is proposed to obtain longwave radiative cooling rates, which can be used for atmospheric boundary-layer simulations on clear days in mid-latitudes. The net flux difference which is set to zero at the surface, can be parameterized with the use of three variables: the surface temperature, the lowest level (1.5 m) air temperature, and the total amount of water vapor. If these three elements, along with the water vapor profile are known, it is possible to estimate the cooling rate due to longwave radiation. The results of this parameterization are in good agreement with those of a precise scheme (Roach and Slingo, 1979), within a range of ± 1°C/day of diurnal change for boundary-layer simulations. 相似文献
9.
边界层参数化方案对南海秋季台风“莎莉嘉”(2016)模拟的影响 总被引：2，自引：2，他引：2
利用美国中尺度数值模式WRF,选取两个局地(QNSE、MYJ)闭合和两个非局地(YSU、ACM2)闭合的边界层参数化方案对台风“莎莉嘉”(2016)进行了4组模拟试验,结果表明,不同边界层方案对台风路径影响较小,但对台风强度和结构有明显的影响,就本个例研究而言,非局地闭合边界层方案明显优于局地闭合边界层方案。台风强度的差异是热力和动力共同作用的影响。局地闭合方案模拟的地表焓通量、水汽通量和动量通量更大,台风偏强;局地闭合方案模拟的边界层高度更高、边界层顶的夹卷过程更强、垂直混合更强、台风暖心结构更强,从而台风也更强。台风强度的差异和台风结构的变化密切相关。 相似文献
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A subgrid parameterization of orographic precipitation 总被引：6，自引：0，他引：6
Summary Estimates of the impact of global climate change on land surface hydrology require climate information on spatial scales far smaller than those explicitly resolved by global climate models of today and the foreseeable future. To bridge the gap between what is required and what is resolved, we propose a subgrid-scale parameterization of the influence of topography on clouds, precipitation, and land surface hydrology. The parameterization represents subgrid variations in surface elevation in terms of probability distributions of discrete elevation classes. Separate cloud, radiative, and surface processes are calculated for each elevation class. Rainshadow effects are not treated by the parameterization; they have to be explicitly resolved by the host model. The simulated surface temperature, precipitation, and snow cover for each elevation class are distributed to different geographical locations according to the spatial distribution of surface elevation within each grid cell.The subgrid parameterization has been implemented in the Pacific Northwest Laboratory's climate version of the Penn State/NCAR Mesoscale Model. The scheme is evaluated by driving the regional climate model with observed lateral boundary conditions for the Pacific Northwest and comparing simulated fields with surface observations. The method yields more realistic spatial distributions of precipitation and snow cover in mountainous areas and is considerably more computationally efficient than achieving high resolution by the use of nesting in the regional climate model.With 17 Figures 相似文献
11.
The understanding of the cloud processes of snowfall is essential to the artificial enhancement of snow and the numerical simulation of snowfall. The mesoscale model MM5 is used to simulate a moderate snowfall event in North China that occurred during 20–21 December 2002. Thirteen experiments are performed to test the sensitivity of the simulation to the cloud physics with different cumulus parameterization schemes and different options for the Goddard cloud microphysics parameterization schemes. It is shown that the cumulus parameterization scheme has little to do with the simulation result. The results also show that there are only four classes of water substances, namely the cloud water, cloud ice, snow, and vapor, in the simulation of the moderate snowfall event. The analysis of the cloud microphysics budgets in the explicit experiment shows that the condensation of supersaturated vapor, the depositional growth of cloud ice, the initiation of cloud ice, the accretion of cloud ice by snow, the accretion of cloud water by snow, the deposition growth of snow, and the Bergeron process of cloud ice are the dominant cloud microphysical processes in the simulation. The accretion of cloud water by snow and the deposition growth of the snow are equally important in the development of the snow. 相似文献
12.
利用中尺度数值模式WRF选取3种边界层参数化方案（YSU、MYJ和ACM2）对2018年8月20日和2019年8月2日宁夏两次低涡暴雨过程进行敏感性试验,对比分析不同边界层参数化方案对暴雨过程模拟的影响。结果表明：YSU和MYJ方案对暴雨的预报性能均较优,ACM2方案对强降水的空报率较大;YSU方案对逐时中等强度降水的模拟效果更优。YSU方案对低涡系统的移动路径和中心强度模拟效果最好。相比ACM2方案,YSU和MYJ方案对环境场物理量和边界层内水汽混合比的模拟更接近实况,并且YSU方案能准确地反映边界层内位温分布特征。YSU与ACM2方案的湍流混合强度更强,后者维持较强湍流的时间更长。总体上,YSU方案对宁夏低涡暴雨过程的模拟效果最优。 相似文献
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利用高分辨率WRF单气柱模式,选取了两种边界层参数化方案(YSU,MYJ),对TWP-ICE(Tropical Warm Pool International Cloud Experiment)试验期间的个例进行数值模拟,比较了两种方案对边界层结构、云和降水模拟的影响。结果表明:季风活跃期,YSU方案模拟的湍流交换系数较小,湍流混合偏弱,边界层内热通量偏小,使地表热量和水汽不易向上输送,水汽含量在近地表明显偏多,而在边界层及其以上大气层具有显著的干偏差,因此该方案模拟的云中液态水和固态水含量偏低,云量偏少,降水率偏小;MYJ方案对于季风活跃期的边界层结构具有较好的模拟能力,其模拟的云和降水更为准确。季风抑制期,MYJ方案模拟的夜间边界层结构存在较大误差,这是因为该方案模拟的夜间湍流交换系数较大,湍流混合偏强,边界层内热通量偏大,模拟的位温和水汽混合比在边界层内随高度变化较小,而观测廓线在边界层内存在较大梯度。季风抑制期两种方案模拟的云和降水均比观测值偏多,方案之间的差异较小。 相似文献
14.
Summary Subgrid-scale parameterization related to moist process are discussed. In the first half of the paper, a turbulence closure scheme, including the effect of condensation, is proposed. In this parameterization, the subgrid-scale transfer is limited within a single vertical layer of a model per each time step, and the specification of condensation is of yes-or-no type. Therefore, the scheme is suited for a mesoscale circulation model.In the second half of this paper, the bounded derivative method of Kreiss (1980) is applied to the formulation of parameterizations. One example is the derivation of various hierarchial versions in turbulence closure schemes, such as Mellor and Yamada (1974). Another example is an interpretation of the key assumption in Arakawa-Schubert (1974) theory of cumulus convection, i.e., the equilibrium of cloud-work function.With 2 Figures 相似文献
15.
We present a statistical cloud scheme based on the subgrid-scale distribution of the saturation deficit. When analyzed in large-eddy simulations (LES) of a typical cloudy convective boundary layer, this distribution is shown to be bimodal and reasonably well-fitted by a bi-Gaussian distribution. Thanks to a tracer-based conditional sampling of coherent structures of the convective boundary layer in LES, we demonstrate that one mode corresponds to plumes of buoyant air arising from the surface, and the second to their environment, both within the cloud and sub-cloud layers. According to this analysis, we propose a cloud scheme based on a bi-Gaussian distribution of the saturation deficit, which can be easily coupled with any mass-flux scheme that discriminates buoyant plumes from their environment. For that, the standard deviations of the two Gaussian modes are parametrized starting from the top-hat distribution of the subgrid-scale thermodynamic variables given by the mass-flux scheme. Single-column model simulations of continental and maritime case studies show that this approach allows us to capture the vertical and temporal variations of the cloud cover and liquid water. 相似文献
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Summary A completely new nonhydrostatic model system known as the Advanced Regional Prediction System (ARPS) has been developed in
recent years at the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma. The ARPS is designed
from the beginning to serve as an effective tool for basic and applied research and as a system suitable for explicit prediction
of convective storms as well as weather systems at other scales. The ARPS includes its own data ingest, quality control and
objective analysis packages, a data assimilation system which includes single-Doppler velocity and thermodynamic retrieval
algorithms, the forward prediction component, and a self-contained post-processing, diagnostic and verification package.
The forward prediction component of the ARPS is a three-dimensional, nonhydrostatic compressible model formulated in generalized
terrain-following coordinates. Minimum approximations are made to the original governing equations. The split-explicit scheme
is used to integrate the sound-wave containing equations, which allows the horizontal domain-decomposition strategy to be
efficiently implemented for distributed-memory massively parallel computers. The model performs equally well on conventional
shared-memory scalar and vector processors. The model employs advanced numerical techniques, including monotonic advection
schemes for scalar transport and variance-conserving fourth-order advection for other variables. The model also includes state-of-the-art
physics parameterization schemes that are important for explicit prediction of convective storms as well as the prediction
of flows at larger scales.
Unique to this system are the consistent code styling maintained for the entire model system and thorough internal documentation.
Modern software engineering practices are employed to ensure that the system is modular, extensible and easy to use.
The system has been undergoing real-time prediction tests at the synoptic through storm scales in the past several years over
the continental United States as well as in part of Asia, some of which included retrieved Doppler radar data and hydrometeor
types in the initial condition.
As the first of a two-part paper series, we describe herein the dynamic and numerical framework of the model, together with
the subgrid-scale turbulence and the PBL parameterization. The model dynamic and numerical framework is then verified using
idealized and realistic mountain flow cases and an idealized density current. Other physics parameterization schemes will
be described in Part II, which is followed by verification against observational data of the coupled soil-vegetation model,
surface layer fluxes and the PBL parameterization. Applications of the model to the simulation of an observed supercell storm
and to the prediction of a real case are also found in Part II. In the latter case, a long-lasting squall line developed and
propagated across the eastern part of the United States following a historical number of tornado outbreak in the state of
Arkansas.
Received April 14, 2000 Revised July 17, 2000 相似文献
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利用WRF模式中三种云微物理参数化方案(Lin、Eta和WSM6)对青藏高原一次强降水过程进行模拟试验,将模拟降水结果与实测资料进行对比,以评估不同云微物理参数化方案对该区域降水过程的模拟性能。结果表明:三种方案均能够模拟出此次降水天气过程的发生,但在主要降水区域和降水强度两方面仍与实测资料存在偏差;在水凝物方面,三种方案对冰粒子的模拟较接近,Lin和WSM6方案模拟的雪粒子差异较大,但霰粒子无明显差异。进一步对比分析了Lin和WSM6方案模拟的云微物理转化过程,结果表明:这两种方案都表现出了霰向雨水转化的特点。在Lin方案中,通过水汽向霰粒子凝华、霰碰并水汽凝华生成的雪粒子以及霰碰并云水这三种过程生成的霰粒子最终融化为雨水。而在WSM6方案中,一方面水汽凝结成云水,云水被雪和霰粒子碰并收集转化为霰,之后霰融化为雨水;另一方面水汽凝华为冰粒子,一部分冰转化为雪,雪直接融化为雨水或转化为霰融化为雨水,另一部分冰转化为霰,霰融化为雨水。 相似文献
19.
Based on different parameterization schemes of planetary boundary layer (PBL), the uncertainty of intensity and structure of the Super-strong Typhoon Rammasun (1409) is investigated using the WRF model (v3.4) with six PBL parameterization schemes. Results indicate that PBL uncertainty leads to the uncertainty in tropical cyclone (TC) prediction, which increases with forecast time. The uncertainty in TC prediction is mainly reflected in the uncertainty in TC intensity, with significant differences in the TC intensity forecasts using various PBL schemes. The uncertainty in TC prediction is also reflected in the uncertainty in TC structures. Greater intensity is accompanied by smaller vortex width, tighter vortex structure, stronger wind in the near-surface layer and middle and lower troposphere, stronger inflow (outflow) wind at the lower (upper) levels, stronger vertical upward wind, smaller thickness of the eye wall, smaller outward extension of the eye wall, and warmer warm core at the upper levels of eye. PBL height, surface upward heat flux and water vapor flux are important factors that cause the uncertainty in TC intensity and structure. The more surface upward heat flux and water vapor flux and the lower PBL height, the faster TC development and the stronger TC intensity. 相似文献
20.
显式云物理方案的研究进展 总被引：4，自引：1，他引：4
回顾了近年来显式云物理方案的研究进展。显式云方案主要有体积水方法和详细微物理方法(分档法)。体积水方法有单参数和双参数两种谱描述方法,根据模式预报变量和物理过程的不同,可以分为暖云方案、简单冰相方案和复杂冰相方案。详细的微物理方法由于预报变量繁多、计算量巨大而一般多应用于研究工作。不同的模式,有不同的显式云方案,并不是粒子分类越复杂模拟效果就越好,需要根据研究的重点、计算资源的许可选择使用不同的物理方案。物理过程参数化需要建立在理论和实验研究的基础上,因此应加强这方面的理论和实验研究,使物理参数化具有更坚实的物理基础。 相似文献