气流过山运动的非线性浅水理论

用一个两层密度不同的流体所组成的非线性浅水模型讨论了过山气流的变化特征。结果表明：在背风坡下游,如果弗罗德数Ｆｒ大于１,则在不同的条件下将会出现波状的、水跃的以及“破裂”的气流,如果Ｆｒ小于１,将只会出现“破裂”气流;在山地上空,地形波关于地形分布是非对称的。     

从理念到行动：温室气体与局地污染物减排的协同效益与协同控制研究综述

自20世纪90年代IPCC提出协同效益概念以来,大量研究充分证实了温室气体减排政策、措施能产生可观的局地生态环境质量和健康效益。相应地,既有研究也证实局地大气污染物减排政策、措施对温室气体减排同样具有协同效益。中国进入工业化成熟期不久,局地大气污染压力即达到峰值,又迎头遭遇国际应对气候变化浪潮,同时面临空气污染物与温室气体双重减排压力。因此,国内研究不仅关注“由碳及污”或“由污及碳”的单向协同效益评估,更加重视对综合减排措施的协同效益评价。21世纪初,美国国家环保局提出的温室气体与局地大气污染物协同控制概念在中国得到更为广泛的欢迎和接受,并由中国学者首先定义了协同控制的内涵,认为协同控制是实现最大化协同效益的手段和途径。这一进展将人们对协同效益的认识提升到“全球视野、局地行动”的新高度,推动人们从被动地接受“协同效益”,转而主动寻求“协同控制”温室气体和局地大气污染物,为统筹全球和国内（局地）两个减排战场,提供了从认识论、方法论到实践论的全方位支持。中国学者在国内外协同效益、协同控制研究基础上,构建协同控制效应评价和协同控制路径规划方法,并通过多个行业、城市、区域的案例研究证实了该方法体系的科学性和可行性。“协同控制”也已上升成为国家应对气候变化和持续改善大气环境质量的重要策略。在中国推进美丽中国建设、实现碳达峰目标和碳中和愿景的过程中,协同控制的理念、措施、政策将发挥愈加重要的作用。未来,协同控制研究需要将所关注的对象要素,从仅局限于大气扩展至整个生态环境系统;而对建立协同控制的治理体系的研究,将成为实现宏观层面气候变化与生态环境治理协同的关键。     

蒸汽射流道路除冰效率仿真研究

提出将射流冲击技术应用于路面积冰去除,将具有一定温度、压力、流量等射流参数的蒸汽流体,经过射流管上的细孔喷出,冲击冰路结合处,使该区域温度迅速升高至融化,实现积冰与路面的快速分离,结合铲斗,将冰层推走.利用Gambit和Fluent流体仿真软件建立射流除冰的数值模型,研究不同孔径大小和分布规律对除冰效率的影响规律.仿真研究结果表明:随着区域内射流孔分布密度的增加,除冰效率也相应增大,其中8孔射流嘴除冰效率达到了24 km/h,但随着孔数的增加,除冰效率并不成单调性增长,需要选择合适的最优值.     

临安区域大气本底站温室气体研究进展

为研究我国长江三角洲区域温室气体本底浓度变化的时空分布特征,自2006年以来,临安区域大气本底站开展了温室气体瓶采样的观测实验。2008年开始,陆续开展温室气体在线观测项目。观测结果将探明我国长江三角洲区域温室气体浓度时空分布、变化趋势、源汇特征。     

温室气体和硫酸盐气溶胶的辐射强迫作用

对GOALS4 .0海 陆 气耦合模式的相关部分进行了改进 ,主要改进包括温室气体的扩充和硫酸盐气溶胶“显式”方案的引入 ,并引入 2 0世纪温室气体的实际浓度变化以及硫循环模式模拟的硫酸盐气溶胶的三维全球浓度分布 ,模拟了温室气体和硫酸盐气溶胶造成的辐射强迫的空间分布和时间变化。全球平均的温室气体和硫酸盐气溶胶的辐射强迫分别为 2 .17W /m2 和 - 0 .2 9W /m2 ;温室气体造成的辐射强迫在空间上呈现明显的纬向结构 ,最大值 (大于 2 .5W/m2 )和最小值 (小于 1W /m2 )分别位于副热带和两极地区 ,在北半球主要工业区硫酸盐气溶胶的辐射强迫绝对值接近温室气体的辐射强迫值 (大于 - 2 .0W /m2 )。     

日将发射温室气体观测卫星 观测范围几乎覆盖全球

据日本共同网消息,用于温室气体浓度观测的“呼吸”号卫星于1月23日在日本鹿儿岛县种子岛宇宙中心发射升空。“呼吸”是日本宇航研究开发机构与日本环境省、国立环境研究所的共同研究项目。该卫星装备了高精度的观测设备,将利用二氧化碳和沼气等温室气体吸收特定波长红外线的特点,     

北京地区大气污染分布的“南北两重天”现象

利用2006年北京地区空气质量监测站和自动气象站网资料,以及华北地区中尺度气象观测资料,分析了北京地区大气污染分布的“南北两重天”现象.通过对此类现象发生过程中天气形势和北京地区气象要素的分析,指出了造成该现象的天气学成因和气象要素特征.研究结果表明,2006年北京共发生47次“南北两重天”现象,其中大部分发生在秋、冬季的午夜至次日上午,且多为南差北好的污染物分布情景.该现象的发生与北京地区中-α尺度天气系统活动的一些特征有关,特别是与干冷空气进入北京地区的路径以及移动速度的区域差异有关.另外,在弱天气系统控制下,北京西南部地区经常出现的小尺度辐合型流场,也是形成北京地区“南北两重天”现象的重要原因.     

局地废气排放污染影响的实验模拟

本文给出了一项在南京大学NJU环境风洞中实施的实验模拟研究。试验模拟一座位于城市街区的排放塔的废气排放，通过流场测量，放烟显示和示踪气体扩散试验，分析气流分布与污染物浓度分布，得出对局地环境影响的一些结论。文中还以模拟扩散试验资料为实验基础，建立修正的扩散模式，探讨污染物浓度预测的可靠途径。研究结果表明，风洞流体模拟手段是有成效且实用的。     

ＧｈｏｓｔＦｌｕｉｄ方法在运动边界射流问题数值模拟中的应用

把解决多物质流问题的ＧｈｏｓｔＦｌｕｉｄ方法应用到具有运动边界的单物质流的数值模拟中去,结合求解界面追踪问题的Ｌｅｖｅｌ Ｓｅｔ方法,提出了有效求解运动边界问题的虚拟流体算法,用数值模拟重现了“声学整流”效应现象,并用等压装配法解决了发生在流体和活塞界面上的“Ｏｖｅｒｈｅａｔｉｎｇ”效应．数值实验表明：水平管道的长度和活塞振动频率是射流形成的关键因素,数值实验中如果频率和长度设置合理,则理想气体在做简谐振 动的活塞驱动下,可以产生稳定的射流．     

我国实际大气与国际标准大气

在进行压力高度计校准、飞机和火箭设计、飞机性能计算及弹道制表等工作时,需要了解大气温度、压力、密度等参数随高度的分布情况。为此,国际上曾有过多种能用简单方式近似地表示大气参数垂直分布的大气模式(称为标准大气或参考大气),对于“低空”(对流层、平流层),国际标准化组织所采用的标准     

粤西沿海海雾天气气候特征及微物理结构研究

利用粤西12个测站2000-2010年常规气象资料及2010年3月湛江东海岛一次海雾过程观测数据,分析了粤西沿海海雾发生的天气气候特征以及湛江东海岛海雾的微物理特征。结果表明：粤西沿海年均雾日数呈西部（17．8d·a^-1）〉东部（7．7d·a^-2）〉中部（3．5d·a^-1）的特点;年际变化差异明显,除2008年外呈逐步升高趋势;年雾日数冬、春季多,夏、秋季少;一天中海雾大部分出现在02：00—08：00,这一时段雾生成的平均概率为50．8％;最多持续时间在1-3d内。海雾生成的综合气象条件主要为：气温15．025．0℃、3小时变压-3．5-2．5hPa、温度露点差0．0-2．0℃、多发风向为NNE-ESE或静风,风速≤7m·s^-1。成雾的天气形势可以分为高压型、低槽型、冷锋型、静止锋型和鞍型或均压场型5类。雾过程中各阶段能见度变化及雾滴谱分布差异较大,平均雾滴谱分布符合指数递减规律,谱型大体上呈“单峰”结构,整个滴谱明显偏向小滴一端,雾滴谱径主要出现在2～10μm。     

Accurate pressure gradient calculations in hydrostatic atmospheric models

Most models of atmospheric flow which use the primitive equations require a diagnostic equation to determine local total pressure. In hydrostatic models, this equation is the vertically integrated hydrostatic equation. A frequently used approximation to this integration is to hold the temperature constant within model layers yielding a linear proportionality between p or (Exner's function) and z. This procedure yields static pressures with errors on the order of 10^–3mb.If terrain following coordinates are used, terms arise in the horizontal momentum equations involving the gradient of total pressure along the coordinate surface, less a correction for the variation of the hydrostatic pressure along a sloped surface. Erroneous horizontal accelerations are common in these models which result from spurious pressure gradients that are due to inaccurate computation of the static pressure. This error may be amplified if the computation of the slope correction term of the horizontal pressure gradient is not consistent with the method of calculating the total pressure.We derive a methodology to be used in the vertical pressure integrations that is exact if the potential temperature lapse rate is constant between integration limits. The method is applied to both the integration of the hydrostatic equation and the computation of the slope correction term in the horizontal pressure gradient. The method employs a fixed vertical grid and a dynamic one defined by the significant levels in the vertical temperature distribution. With this methodology, the error in calculation of the horizontal pressure gradient acceleration is greatly reduced, especially in situations where the isothermal surfaces are not parallel to the vertical coordinate surfaces. The problem of aliasing and the treatment of significant temperature levels is described.     

1713号台风“天鸽”与1822号台风“山竹” 大风过程对比及成因分析

利用常规观测、地面自动气象站、FY-2E 卫星红外云图以及多普勒天气雷达资料等,对登陆珠江三角洲沿海的1713号台风“天鸽”和1822号台风“山竹”的大风过程进行对比及成因分析。结果表明：台风本身的强度、结构及其变化对台风的影响范围、出现时间和持续时间有密切关系;地面气压场的分布对台风大风的出现时间起到了重要作用,且气压梯度加大有助于增加大风影响范围和影响时间;“喇叭口”地形的狭管效应对风速有加强作用。卫星云图对预测台风大风的影响时间和影响范围有一定参考作用;当台风中心进入雷达的监测范围时,雷达产品可以有效估测风速大小、影响时间和影响范围。     

Improving Multi-Model Ensemble Forecasts of Tropical Cyclone Intensity Using Bayesian Model Averaging

This paper proposes a method for multi-model ensemble forecasting based on Bayesian model averaging (BMA), aiming to improve the accuracy of tropical cyclone (TC) intensity forecasts, especially forecasts of minimum surface pressure at the cyclone center (P_min). The multi-model ensemble comprises three operational forecast models: the Global Forecast System (GFS) of NCEP, the Hurricane Weather Research and Forecasting (HWRF) models of NCEP, and the Integrated Forecasting System (IFS) of ECMWF. The mean of a predictive distribution is taken as the BMA forecast. In this investigation, bias correction of the minimum surface pressure was applied at each forecast lead time, and the distribution (or probability density function, PDF) of P_min was used and transformed. Based on summer season forecasts for three years, we found that the intensity errors in TC forecast from the three models varied significantly. The HWRF had a much smaller intensity error for short lead-time forecasts. To demonstrate the proposed methodology, cross validation was implemented to ensure more efficient use of the sample data and more reliable testing. Comparative analysis shows that BMA for this three-model ensemble, after bias correction and distribution transformation, provided more accurate forecasts than did the best of the ensemble members (HWRF), with a 5%–7% decrease in root-mean-square error on average. BMA also outperformed the multi-model ensemble, and it produced “predictive variance” that represented the forecast uncertainty of the member models. In a word, the BMA method used in the multi-model ensemble forecasting was successful in TC intensity forecasts, and it has the potential to be applied to routine operational forecasting.     

Relationship between persistent heavy rain events in the Huaihe River valley and the distribution pattern of convective activities in the tropical western Pacific warm pool

Using daily outgoing long-wave radiation （OLR） data from the National Oceanic and Atmospheric Administration （NOAA） and the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data of geopotential height fields for 1979-2006, the relationship between persistent heavy rain events （PHREs） in the Huaihe River valley （HRV） and the distribution pattern of convective activity in the tropical western Pacific warm pool （WPWP） is investigated. Based on nine cases of PHREs in the HRV, common characteristics of the West Pacific subtropical high （WPSH） show that the northern edge of the WPSH continues to lie in the HRV and is associated with the persistent ＂north weak south strong＂ distribution pattern of convective activities in the WPWP. Composite analysis of OLR leading the circulation indicates that the response of the WPSH to OLR anomaly patterns lags by about 1-2 days. In order to explain the reason for the effects of the distribution pattern of convective activities in the WPWP on the persistent northern edge of the WPSH in the HRV, four typical persistent heavy and light rain events in the Yangtze River valley （YRV） are contrasted with the PHREs in the HRV. The comparison indicates that when the distribution pattern of the convective activities anomaly behaves in a weak （strong） manner across the whole WPWP, persistent heavy （light） rain tends to occur in the YRV. When the distribution pattern of the convective activities anomaly behaves according to the ＂north weak south strong＂ pattern in the WPWP, persistent heavy rain tends to occur in the HRV. The effects of the ＂north weak south strong＂ distribution pattern of convective activities on PHREs in the HRV are not obvious over the seasonal mean timescale, perhaps due to the non-extreme status of convective activities in the WPWP.     

Precision of evaporation measurements using the Bowen ratio

Energy balance/Bowen ratio estimation of evapotranspiration is examined to determine the effects of different sources of error. General usage of the approximate psychrometric equation which neglects terms of order 1/p (p atmospheric pressure) can lead to large bias errors if the wet-bulb temperature depression is large. Temperature and pressure corrections on the psychrometric constant cannot be neglected without the risk of a bias error in excess of precision limits placed on a result. Aspiration to an isothermal block for wet-bulb temperature measurement compared with measurement at the air stream source does not necessarily lead to a more precise estimate of the Bowen ratio.     

Methane emission measurements in urban areas in Eastern Germany

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m²/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States.     

松花江流域初夏降水分布型的环流特征及差异

利用1961-2017年松花江流域31个气象站初夏降水资料、NCEP/NCAR再分析资料,采用多种统计方法,讨论了松花江流域初夏降水时空分布及影响环流特征。结果表明：松花江流域初夏降水具有全流域一致型、西北-东南反位相型和东北-西南反位相型3个主要分布模态。影响3个分布型的主要环流特征分别为贝加尔湖以东低值系统-鄂霍茨克海阻塞高压（西南低-东北高）、乌拉尔山脊-西西伯利亚槽-外兴安岭脊（两脊一槽型）、渤海/华北低值系统及其东北部高压,东部局地高压或阻塞形势对松花江流域初夏降水的3个模态起到非常重要的作用。东亚-太平洋型和极地-欧亚型是对第一模态降水分布起重要作用的遥相关型。     

梅雨锋暴雨过程潜热及反馈机理个例分析

在对2003年6月24~25日的一次江南北部梅雨锋暴雨过程进行合理模拟的基础上,应用模式输出资料,系统分析了暴雨过程中大尺度稳定凝结加热(Hs)及对流凝结加热(Hc)的时空分布特点以及其潜热在暴雨过程中的反馈作用。研究表明在这次暴雨过程中,主要以Hc为主,平均的Hs、Hc均主要分布在900~250 hPa,最大值位于400 hPa附近;在暴雨发展过程中,Hs、Hc随暴雨的增大而增大,且加热层次不断加深;去除潜热的“干”敏感性试验表明,潜热释放加热了深厚的大气层,使得高层加压辐散,暴雨北侧高空西北急流加强,低层减压辐合,暴雨南侧的低空西南急流加强,同时使得低层的切变线得以维持加强。     

A sensitivity experiment for the removal of Arctic sea ice with the French spectral general circulation model

Sea ice has a major influence on climate in high latitudes. In this paper we analyzed the impact of removal of Arctic sea-ice cover on the climate simulated by a T42 20-level version of the French spectral model Emeraude. The control experiment was the second winter of an annual cycle simulation of the present climate. In the perturbed simulation the Arctic sea-ice cover was replaced by open ocean maintained at the freezing temperature of sea water. The zonal mean patterns of the model response were found to be in good agreement with earlier simulations of Fletcher et al. and Warshaw and Rapp. The atmospheric warming, caused by the increase of upward fluxes of sensible and latent heat and of longwave radiation from the ice-free ocean surface, is largely limited to the high latitudes poleward of 70° N and the lower half of the troposphere and leads to a surface pressure decrease and a precipitation increase over this area. We also analyze the geographical distribution of the response and the mechanisms that can explain the simulated cooling over Eurasia in relation to the energy budget at the surface. Finally, we discuss the reduction of cloud cover over the ice-free Arctic, which was an unexpected result of our simulation, and conclude that further studies are necessary to resolve the question of cumulus convection and cloud process parameterization in high latitudes.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil