Prediction of tropical systems over Indian region using mesoscale model

Summary The Advanced Regional Prediction System (ARPS) model developed at Center for Analysis and Prediction of Storms at Oklahoma State University, USA is used for simulation of monsoon depression and tropical cyclone over Indian region. The radiosonde data are included in the initial analyses and subsequently; the simulations are performed with 50km and 25km grid resolutions. Two sets of forecast experiments produced by two types of analyses (with radiosonde and without radiosonde data) are compared. It is found that predicted mean sea-level pressure of the depression becomes closer to mean sea level pressure reported in Indian Daily Weather Reports when initialized with analyses containing radiosonde data. The precipitation forecast also is improved when initialized with the analyses containing radiosonde data. The simulation of tropical cyclone with 25km grid resolution is able to simulate some subsynoptic scale features of the system.     

A boundary-layer model for the determination of hourly surface wind characteristics in a representative tropical African region

A quantative transposition model is introduced which determines hourly wind speeds in a representative tropical region (Central Sudan). The model consists of two parts. Firstly, a local boundary-layer model, based on the energy balance equation and the Businger-Dyer equations, is used to compute the average diurnal cycle of various characteristic boundary-layer parameters. Secondly, a horizontal transposition method is introduced to calculate wind speed behaviour at an arbitrary station from that at a reference station. This method is based on assumed spatial constancy of the turbulence parameter u _* in the period November–April in a region of about (700 × 800) km² in Central Sudan. The constancy of u _* is concluded from the very stationary character of the climate. Model-computed hourly wind speeds are consistent with the potential wind speeds (at 10 m over open country) calculated from the measured data, and provide better local wind estimates than the conventional procedure which assumes constant regional hourly wind speeds.     

黔东南森林火险气象预报方法

选取预报日连续无雨日∑d和预报日14时气温T14、风速F14和相对湿度U14作为森林火险预报因子，并根据森林火险与T14、F14和∑d成正比，与U14成反比的关系，确定森林火险预报公式。利用凯里市1997～2000年10～4月逐日T14、F14、∑d和U14值，采取对比、均衡、判断等方法确定出逐日实际森林火险等级，同时根据森林火险值计算公式计算出逐日森林火险值，最后确定出各级森林火险所对应的森林火险值范围，以点代面，这一结果适用全州甚至其它气候相似的省、地台站。     

大别山地区极端降水天气事件的天气背景分型研究

基于我国自动站与CMORPH降水产品融合的逐时降水资料和NCEP再分析资料,利用自组织特征映射方法对2008—2014年大别山地区极端降水天气事件的天气背景进行了分型研究。结果表明大别山地区极端降水背景环境的类型主要可分为三类,分别是西南强气流型(类型Ⅰ)、副高西北侧气流型(类型Ⅱ)和偏南强气流型(类型Ⅲ)。其中,类型I和类型Ⅱ的极端降水分别集中在6—8月和7—9月,代表了夏季极端降水,而类型Ⅲ的极端降水主要出现在3—6月及10—12月,属于春秋季节的极端降水。通过分析大别山地形与不同类型降水场及背景场的配置关系发现:(1)迎风坡降水是类型I极端降水的主要原因,中层的高湿度、强气流为极端降水提供水汽和抬升条件;(2)类型Ⅱ的极端降水是由气流过大别山西北侧较低山脊时在山脊前和山脊后形成,西太平洋副热带高压的北抬和西进是导致此类环流背景的重要原因;(3)偏南气流与大别山及其西南方地形的配置使得类型Ⅲ的极端降水主要分布在大别山南侧往西南方向。     

Simulation of tropical cyclone Vamei (2001) using the PSU/NCAR MM5 model

Summary In this study, a rare tropical cyclone Vamei was simulated using the non-hydrostatic version 3.6 of the Penn State University (PSU) – National Center for Atmospheric Research (NCAR) mesoscale model MM5. This unusual cyclone was generated on 26 December 2001 in an area close to the equator in the southern part of the South China Sea. The model was integrated for 80 h from 0000 UTC 26 December 2001 to 1800 UTC 29 December 2001. To examine the model performance, several important simulated fields including sea-level pressure, surface wind speed and precipitation were compared to observations. The model simulated track of the cyclone was also compared to the best track provided by the Joint Typhoon Warning Center (JWTC). Overall, the model performed reasonably well, particularly in simulating the cyclone track and precipitation amount and spatial distribution. The analysis of the model output indicated the important role of the latent heat flux in the genesis and intensification of tropical cyclone Vamei.     

Crop yield model validation for Cameroon

A crop simulation model must first be capable of representing the actual performance of crops grown in any region before it can be applied to the prediction of climate variability and change impacts. A cropping systems model (CropSyst) simulations of crop productivity in the sub-Saharan Central African (using Cameroon as the case study) region, under the current climate were compared with observed yields of maize, sorghum, groundnut, bambara groundnut and soybean from eight sites. The model produced both over-and-under estimates, but with a mean percentage difference of only –2.8%, ranging from –0.6% to –4.5%. Based on these results, we judged the CropSyst simulations sufficiently reliable to justify use of the model in assessing crop growth vulnerability to climatic changes in Cameroon and else where.     

Customization of regional climate model (RegCM4) over Indian region

The regional climate model (RegCM4) is customized for 10-year climate simulation over Indian region through sensitivity studies on cumulus convection and land surface parameterization schemes. The model is configured over 30° E–120° E and 15° S–45° N at 30-km horizontal resolution with 23 vertical levels. Six 10-year (1991–2000) simulations are conducted with the combinations of two land surface schemes (BATS, CLM3.5) and three cumulus convection schemes (Kuo, Grell, MIT). The simulated annual and seasonal climatology of surface temperature and precipitation are compared with CRU observations. The interannual variability of these two parameters is also analyzed. The results indicate that the model simulated climatology is sensitive to the convection as well as land surface parameterization. The analysis of surface temperature (precipitation) climatology indicates that the model with CLM produces warmer (dryer) climatology, particularly over India. The warmer (dryer) climatology is due to the higher sensible heat flux (lower evapotranspiration) in CLM. The model with MIT convection scheme simulated wetter and warmer climatology (higher precipitation and temperature) with smaller Bowen ratio over southern India compared to that with the Grell and Kuo schemes. This indicates that a land surface scheme produces warmer but drier climatology with sensible heating contributing to warming where as a convection scheme warmer but wetter climatology with latent heat contributing to warming. The climatology of surface temperature over India is better simulated by the model with BATS land surface model in combination with MIT convection scheme while the precipitation climatology is better simulated with BATS land surface model in combination with Grell convection scheme. Overall, the modeling system with the combination of Grell convection and BATS land surface scheme provides better climate simulation over the Indian region.     

Generation of a stochastic precipitation model for the tropical climate

Theoretical and Applied Climatology - A tropical country like Malaysia is characterized by intense localized precipitation with temperatures remaining relatively constant throughout the year. A...     

热带气旋海棠(2005)强度数值模拟试验

通过设计台风追随自移动嵌套网格、考虑海洋飞沫作用改进MRF边界层参数化方案、设计垂直-倾斜对流参数化方案等对MM5 V3.7中尺度模式进行改进,以NCEP逐日再分析资料为初始场,对2005年第5号热带气旋"海棠"进行了数值模拟试验。结果表明:通过设计自移动嵌套网格解决了热带气旋业务数值预报模式中细网格区域大小和位置难于确定问题,通过提高模式分辨率能大幅增强数值模式对热带气旋强度的预报能力;考虑海洋飞沫作用后,热带气旋范围内低层热通量明显增强,从而使模式大气低层增温和增湿明显,有利热带气旋内对流发生发展;考虑倾斜对流不稳定作用后,使倾斜对流有效位能得到释放,进一步提高了模式对热带气旋内部物理过程的描述能力。通过改进MM5模式,有效提高了热带气旋强度的数值模拟能力。     

The Korean Integrated Model (KIM) System for Global Weather Forecasting

The Korea Institute of Atmospheric Prediction Systems (KIAPS) began a national project to develop a new global atmospheric model system in 2011. The ultimate goal of this 9-year project is to replace the current operational model at the Korea Meteorological Administration (KMA), which was adopted from the United Kingdom’s Meteorological Office’s unified model (UM) in 2010. The 12-km Korean Integrated Model (KIM) system, consisting of a spectral-element non-hydrostatic dynamical core on a cubed sphere grid and a state-of-the-art physics parameterization package, has been launched in a real-time forecast framework, with initial conditions obtained via the advanced hybrid four-dimensional ensemble variational data assimilation (4DEnVar) over its native grid. A development strategy for KIM and the evolution of its performance in medium-range forecasts toward a world-class global forecast system are described. Outstanding issues in KIM 3.1 as of February 2018 are discussed, along with a future plan for operational deployment in 2020.     

利用海-气-浪耦合模式(COAWST)对北印度洋一次强热带风暴\

相对中国其他海域,三面环陆的黄渤海区域海洋与中纬度大气间的相互作用有其独特性,在该区域开展海气耦合模式对气象要素的影响研究十分必要。本文基于大气和海洋的全球预报和再分析资料,利用高分辨率区域海气耦合模式（简称耦合模式）和非耦合模式,开展数值模拟试验。并根据国家地面常规气象观测站和埕北石油A平台实况观测资料,对比分析了2020年6月两种模式对近地层大气温湿要素预报结果,并结合海温、海气热通量变化和风场调整情况,分析了海气双向耦合过程对近地层温湿要素预报影响的原因。结果表明：耦合模式对近地层的湿度要素预报改进较大,以增湿效应为主;海气双向耦合对温湿要素的影响范围可扩展至黄渤海周边省市全域,可提升耦合模式对黄渤海周边区域近地层湿度和白天温度的预报效果;湿度对海气双向耦合的响应速度明显快于温度,说明耦合模式先改进了近地层湿度预报效果;耦合模式海表向上的潜热通量增加是近地层温湿要素预报改进的主要原因。

     

Wave dynamics of super cloud clusters over the tropical region

A wave dynamics for the super cloud clusters associated with the tropical intraseasonal oscillation is constructed. Under the present framework, the basic state of super cloud clusters is considered to be a large-scale convergence of the zonal wind. This convergence is created by a nonlinear diabatic Kelvin wave front, which moves eastward slowly without change of shape. When interacting with free equatorial waves with n=−1, 0, 1 and 2, this basic flow will suppress those waves which move eastward except for free Kelvin waves, and permit westward propagating modes such as the mixed Rossby-gravity wave, the inertio-gravity waves with n=1 and 2 to appear in the large-scale convergent region. Among these waves, only fast modes, that is, inertio-gravity waves with n=1 and 2 are regarded to be responsible for the presence of cloud clusters which move westward within a super cloud cluster, while the multiplicity of the occurrences of super cloud clusters, which move eastward within the large-scale convergent region, is due to the superposition of free Kelvin wave upon these inertio-gravity waves.     

Effects of tropical instability wave (TIW)-induced surface wind feedback in the tropical Pacific Ocean

Tropical instability waves (TIWs) arise from oceanic instability in the eastern tropical Pacific and Atlantic Oceans, having a clear atmospheric signature that results in coupled atmosphere–ocean interactions at TIW scales. In this study, the extent to which TIW-induced surface wind feedback influences the ocean is examined using an ocean general circulation model (OGCM). The TIW-induced wind stress (τ_TIW) part is diagnostically determined using an empirical τ_TIW model from sea surface temperature (SST) fields simulated in the OGCM. The interactively represented TIW wind tends to reduce TIW activity in the ocean and influence the mean state, with largest impacts during TIW active periods in fall and winter. In December, the interactive τ_TIW forcing induces a surface cooling (an order of ?0.1 to ?0.3 °C), an increased heat flux into the ocean, a shallower mixed layer and a weakening of the South Equatorial Current in the eastern equatorial Pacific. Additionally, the TIW wind effect yields a pronounced latitudinal asymmetry of sea level field across the equator, and a change to upper thermal structure, characterized by a surface cooling and a warming below in the thermocline, leading to a decreased temperature gradient between the mixed layer and the thermocline. Processes responsible for the τ_TIW–induced cooling effects are analyzed. Vertical mixing and meridional advection are the two terms in the SST budget that are dominantly affected by the TIW wind feedback: the cooling effect from the vertical mixing on SST is enhanced, with the maximum induced cooling in winter; the warming effect from the meridional advection is reduced in July–October, but enhanced in November–December. Additional experiments are performed to separate the relative roles the affected surface momentum and heat fluxes play in the cooling effect on SST. This ocean-only modeling work indicates that the effect of TIW-induced wind feedback is small but not negligible, and may need to be adequately taken into account in large-scale climate modeling.     

2001年春季（3—5月）山东天气评述

利用500hPa月平均高度场及距平场等相关气象资料，分析山东今春风多雨少、气温偏高、干旱持续的天气特点及环流形势背景，介绍了春季影响山东的主要天气过程，并进行了天气影响评价。     

A study of suspended particulate matter in Lahore (Pakistan)

The results obtained from an investigation of suspended particulate matter in the metropolitan city of Lahore (Pakistan) are reported and analysed in this paper. X-ray diffraction studies of the airborne matter collected from va-rious urban and suburban sites show that non-clay minerals such as quartz, calcite and albite are contained in most of the samples in almost comparable amounts. Chemical analysis of some samples was carried out for complementing the x-ray diffraction data. The amount of quartz in the samples of dusty areas was found to be an order of magnitude more than in the samples of relatively cleaner areas. As the dust particles of these compounds are poor substrate for promoting nucleation of ice in the atmospheric clouds, they are liable to stay steadily in the atmosphere as pollutants.A comparison of the results of the airborne particulates and the soil samples collected from various sites show that the sources of quartz, calcite and albite in the airborne matter are both local and remote.     

不同类型大尺度环流背景下首都国际机场的雷暴特征分析

二进制粒子群-贝叶斯判别准则（Binary Particle Swarm Optimization-Bayes Discriminatory Criterion,BPSO-BDC）方法,能够使用二进制粒子群（Binary Particle Swarm Optimization,BPSO）算法智能地选取出贝叶斯判别准则（Bayes Discriminatory Criterion,BDC）雷暴预报模型的最优子集,克服了BDC在因子选择时的缺点。为了建立BDC雷暴最优模型,利用2010—2014年T511数值预报产品和单站观测资料,对漳州、义乌、乐东三站BDC雷暴预报模型进行研究。通过选取适应度函数,提出了BPSO搜索BDC模型最优子集的计算方法,得到了三站的最优子集模型,并与BDC和逐步判别模型进行对比。结果表明：在24 h的雷暴预报结果中,BPSO-BDC模型的平均TS评分达到了0.697,空报率为0.256,漏报率为0.048,在48 h的雷暴预报结果中,BPSO-BDC模型的平均TS评分达到了0.418,空报率为0.222。BPSO-BDC模型的预报结果明显优于BDC和逐步判别模型。对BPSO-BDC模型进行稳定性检验,TS评分都在0.21~0.35之间,变化幅度较小且处于较高水平。说明BPSO-BDC方法预报效果明显优于BDC和逐步判别方法,且具有良好的稳定性。