中尺度云参数化模式的引进及初步检验

依托2009年领军人才项目,山西省人工降雨办公室引进了中国气象科学研究院人影中心已经业务运行的MM5云参数化模式.本文介绍了该模式的定制、引进、移植、优化以及业务化试运行的基本情况,并详细介绍了该模式的系统功能、模式预报产品以及模式系统特点.文章还对模式运行以来的预报产品与实际的天气过程资料作了统计对比分析,初步对模式预报的真实性作了检验.

云在气候模式中参数化的普适幂律

云滴有效半径是气候模式中辐射参数化的一个云微物理量．在讨论现有处理方法的基础上，从基本概念出发，导出联系有效半径、含水量、总云滴数及湍流强度的普适幂律．该定律：（1）表明常用参数化公式的多样性源于人们选择数学模型的主观判断；（2）启示我们应该寻找有效半径与平均单位云滴含水量（含水量与总云滴数之比）之间的关系；（3）揭示出湍流在云参数化中的重要作用．通过本文的分析，建议人们要彻底了解人类活动对成云致雨（有意识人工影响天气）和全球变化的作用需研究“大气气溶胶─云激物理─湍流（动力）─辐射”系统．

云粒子谱演化研究中的一些问题

简略介绍了描述云中水凝物粒子群尺度谱演变的方法：谱函数方法和分档方法，并给出了分档模式实例。讨论了谱参数本身以及在应用中应注意的问题。分析了两类方法的对比研究的结果指出，一些重要的云降水物理过程，如粒子类型间的转化，涉及粒子运动状态和人工播撒的效应等过程，应当用分档方法来处理。

海-陆-气全球耦合模式能量收支的误差

通过分析GOALS模式两个版本GOALS 1.1和GOALS 2的能量收支 ,并与观测对比 ,结果表明 :模式模拟的地表净短波辐射通量在高纬地区偏低 ,而净长波辐射通量又偏高 ,导致极地表面温度偏低 ,感热通量在高纬地区为很高的负值。而在陆地上感热加热作用显著偏强 ,使地表有较大的向上净能量给大气 ,引起陆地上有些暖中心也偏强 ,这也解释了模式模拟地表面空气温度场的误差原因。海洋上潜热通量偏低 ,特别是在副热带洋面上偏少更明显。陆地上的欧亚和北美大陆大部分地区潜热通量仍偏低。这也是模式降水在大部分地区偏少的重要原因。两模式大气顶OLR偏低的模拟主要是在中低纬度 ,大气顶净短波辐射通量的模拟在中低纬度虽然与NCEP结果接近 ,但与地球辐射收支试验ERBE资料比较仍偏小较多 ,说明改进中低纬度云 辐射参数化方案对改进全球能量收支的模拟有重要意义。GOALS 2模式中诊断云方案模拟的云量除赤道地区外普遍偏小 ,尤以中纬度为甚 ,造成那里能量收支出现大的误差 。

数值天气预报模式物理过程参数化方案的研究进展

数值天气预报模式对天气过程发展的物理描述主要通过物理过程参数化实现,因此,物理过程参数化方案的发展一直是国际研究热点,也是数值模式改进的难点。在阐述对流、云微物理和边界层等主要物理参数化方案的理论基础和发展历史的基础上,指出在高分辨率模式网格条件下的物理过程参数化方案改进将是未来数值模式发展的核心问题。随着高性能计算能力的迅速发展,目前业务模式网格距已逐渐精细到小于10 km,但模式所使用的物理过程参数化方案大多并未针对高分辨率网格设计,其理论假设的适用性值得商榷。根据目前国际研究趋势,探讨了今后物理过程参数化方案研究改进的重点方向。

Intercomparison of different physics schemes in the WRF model over the Asian summer monsoon region

Enhancing the ability of the WRF model in simulating a large area covering the West Pacific Ocean, China's Mainland, and the East Indian Ocean is very important to improve prediction of the East Asian monsoon climate. The objective of this study is to identify a reasonable configuration of physical parameterization schemes to simulate the precipitation and temperature in this large area. The Mellor-Yamada-Janjic （MYJ） and Yonsei University （YSU） PBL schemes, the WSM3 and WSM5 microphysics schemes, and the Betts-Miller-Janjic （BMJ） and Tiedtke cumulus schemes are compared through simulation of the regional climate of summer 2008. All cases exhibit a similar spatial distribution of temperature as observed, and the spatial correlation coefficients are all higher than 0.95. The cases combining MY J, WSM3/WSM5, and BMJ have the smallest biases of temperature. The choice of PBL scheme has a significant effect on precipitation in such a large area. The cases with MYJ reproduce a better distribution of rain belts, while YSU strongly overestimates the precipitation intensity. The precipitation simulated using WSM3 is similar to that using WSM5. The BMJ cumulus scheme combined with the MYJ PBL scheme has a smaller bias of precipitation. However, the Tiedtke scheme reproduces the precipitation pattern better, especially over the ITCZ.

Validation for a tropical belt version of WRF: sensitivity tests on radiation and cumulus convection parameterizations

Version 3.9 of WRF-ARW is run with a tropical belt configuration for a period from 2012 to 2016 in this study. The domain covers the entire tropics between 45°S and 45°N with a spatial resolution of about 45 km. In order to verify two radiation schemes and four cumulus convection schemes, eight experiments are performed with different combinations of physics parameterization schemes. The results show that eight experiments present reasonable spatial patterns of surface air temperature and precipitation in boreal summer, with the spatial correlation coefficient (COR) between simulated and observed temperature exceeding 0.95, and that between simulated and observed precipitation ranges from 0.65 to 0.82. The four experiments with the RRTMG radiation scheme show a better performance than the other four experiments with the CAM radiation scheme. In the four experiments with the RRTMG radiation scheme, the COR between simulated and observed surface air temperature is about 0.98, and that between simulated and observed precipitation ranges from 0.76 to 0.82. Comparatively, the two experiments using the new Tiedtke cumulus parameterization scheme can simulate better diurnal variation of precipitation in boreal summer than the other six experiments. In particular, for the diurnal cycle of precipitation over land and ocean, the experiment using the RRTMG radiation scheme and the new Tiedtke cumulus convection scheme shows that the peaks of precipitation rate appear at 0400 LST and 1600 LST, in agreement with observation.

IMPACTS OF CUMULUS PARAMETERIZATION AND RESOLUTION ON THE MJO SIMULATION

Madden-Julian Oscillations (MJO) in six integrations using an AGCM with different cumulus parameterization schemes and resolutions are examined to investigate their impacts on the MJO simulation. Results suggest that the MJO simulation can be affected by both resolution and cumulus parameterization, though the latter, which determines the fundamental ability of the AGCM in simulating the MJO and the characteristics of the simulated MJO, is more crucial than the former. Model resolution can substantially affect the simulated MJO in certain aspects. Increasing resolution cannot improve the simulated MJO substantially, but can significantly modulate the detailed character of the simulated MJO; meanwhile, the impacts of resolution are dependent on the cumulus parameterization, determining the basic features of the MJO. Changes in the resolution do not alter the nature of the simulated MJO but rather regulate the simulation itself, which is constrained by cumulus parameterization schemes. Therefore, the vertical resolution needs to be increased simultaneously. The vertical profile of diabatic heating may be a crucial factor that is responsible for these different modeling results. To a large extent, it is determined by the cumulus parameterization scheme used.

Development of a toy column model and its application in testing cumulus convection parameterizations

A single-column model is constructed based on parameterizations inherited from the Finite-volume/Spectral Atmospheric Model F/SAMIL and tested in simulations of tropical convective systems. Two representative convection schemes are compared in terms of their performances on precipitation types, individual physical tendencies, and temperature and moisture fields. The main difference between the two selected schemes is in their representation of entraining/detraining process. The Tiedtke scheme assumes bulk entrainment, while the Zhang–Mc Farlane scheme parameterizes entrainment/detrainment rates under the spectrum concept. Large-scale forcing and verification data are taken from the GATE phase III field campaign, during which abundant convective events were observed. Given the same triggering function and closure assumption, results show that entrainment/detrainment representation remains the dominant factor on the simulation of cumulus mass flux and of temperature and moisture fields. By analyzing sources and sinks of heat and moisture, this study reveals how parameterization components compensate for each other and make model results insensitive to parameterization changes in certain fields, thus suggesting the need to treat parameterizations as systems rather than individual components.

Sensitivity of simulated tropical intraseasonal oscillations to cumulus schemes

The sensitivity of simulated tropical intraseasonal oscillations (ISO) to different cumulus parameterization schemes was analyzed using an atmospheric general circulation model (latest version-SAMIL2.2.3) developed at the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences.Results show that the basic features of tropical climatological intraseasonal oscillations (CISO) can be captured using all three cumulus schemes.The CISO simulated by the Tiedtke scheme was found to be more realistic than that of the Manabe and Zhang-McFarlane schemes.The results of simulated transient intraseasonal oscillations (TISO) indicate that although the Tiedtke and the Zhang-McFarlane schemes in the new version SAMIL2.2.3 have been adjusted according to different problems,only the latter can simulate the eastward propagation of the 27-50-day TISO mode.It may be associated with the more realistic diabatic heating profile simulated by the Zhang-McFarlane scheme.In addition,the Manabe scheme in SAMIL2.2.3 is the same as that in the prior version SAMIL2.08.However,some aspects of the physical process,such as the radiation scheme and aerosol condition,have been changed.Conversely the eastward propagation from 100°E to the west of the tropical 27-50-day TISO mode only can be simulated using the Manabe scheme of SAMIL 2.08.Consequently,not all the improvements of physical parameterization schemes work well in every respect.The coordinated developments between dynamic frame and physical processes,and among different physical processes,are important methods that may be used to improve the model.

Features of rainfall and latent heating structure simulated by two convective parameterization schemes

Using the latest version of SAMIL (Spectral Atmosphere Model of IAP LASG) developed by LASG/IAP,we evaluate the model performance by analyzing rainfall,latent heating structure and other basic fields with two different convective parameterization schemes:Manabe Scheme and Tiedtke Scheme.Results show that convective precipitation is excessively overestimated while stratiform precipitation is underestimated by Tiedtke scheme,thus causing less stratiform rainfall proportion compared with TRMM observation.In contrast,for Manabe scheme stratiform rainfall belt is well simulated,although precipitation center near Bay of Bengal (BOB) spreads eastward and northward associated with unrealistic strong rainfall downstream of the Tibet Plateau.The simulated latent heating structure indicates that Tiedtke scheme has an advantage over Manabe scheme,as the maximum convective latent heating near middle of troposphere is well reproduced.Moreover,the stratiform latent heating structure is also well simulated by Tiedtke scheme with warming above freezing level and cooling beneath freezing level.As for Manabe scheme,the simulated maximum convective latent heating lies near 700 hPa,lower than the observation.Additionally,the warming due to stratiform latent heating extends to the whole vertical levels,which is unreasonable compared with observation.Taylor diagram further indicates that Tiedtke scheme is superior to Manabe scheme as higher correlation between model output and observation data is achieved when Tiedtke scheme is employed,especially for the temperature near 200 hPa.Finally,a possible explanation is addressed for the unrealistic stratiform rainfall by Tiedtke scheme,which is due to the neglect of detrained cloud water and cloud ice during convective process.The speculation is verified through an established sensitivity experiment.