大范围持续暴雪过程中多种影响系统的对比分析

持续48 h的大范围雨转暴雪天气先后影响了陕西、山西、河北、北京、天津、辽宁等地,华北地区降雪量15—30 mm。此次过程中地面影响系统复杂,有华北锢囚锋、江淮气旋、北路冷锋。利用准地转理论、凝结函数法、垂直剖面分析和常规观测资料、GFS 0.5°×0.5°再分析资料等,对比分析了华北锢囚锋和江淮气旋在降雪量和降水效率、水汽和动力条件、垂直结构等方面的特征和差异,并描述了多种地面影响系统的演变和相互作用。结果表明:（1）在降雪量和效率上,华北锢囚锋降雪量小于江淮气旋,华北锢囚锋主要影响华北西部,降雪持续24 h,江淮气旋主要影响华北中东部,降雪持续30 h;降水前半段华北锢囚锋降水效率为0.76,江淮气旋为0.58,降水后半段两者均为1.5。（2）在水汽条件上,华北锢囚锋明显弱于江淮气旋,华北锢囚锋水汽通道在700 hPa上,来自西南地区,而江淮气旋在700和850 hPa上,来自西南地区和东海;华北锢囚锋水汽含量中心和水汽辐合中心主要集中在近地面层锢囚锋附近,而江淮气旋在800—600 hPa气旋北侧偏南气流里。（3）在动力条件上,华北锢囚锋明显弱于江淮气旋,华北锢囚锋南段涡度平流垂直微差项起主要作用,北段温度平流拉普拉斯项起主要作用,江淮气旋温度平流的拉普拉斯项和涡度平流的垂直微差项均起到重要作用。（4）在垂直结构上,江淮气旋锢囚时为冷式锢囚,并有北路冷锋楔入其暖锋下面,强度明显强于华北锢囚锋。（5）在演变和相互作用上,江淮气旋的北上减弱了华北锢囚锋;北路冷锋对随江淮气旋北上的暖湿气流起到“冷垫”抬升作用。      

对1979年2月21—23日河套锢囚锋的分析——与扈忠慈同志商榷

扈忠慈同志对《气象》1979年第9期《华北春季大雪和黄渤海强东风》一文中的锢囚锋提出异议,认为河套锢囚锋最初是在河西走廊生成,并以暖性锢囚方式东移到河套地区。本文对此持不同看法,提出展开讨论,以便共同提高对复杂锋面分析的认识。 一、河套锢囚锋的形成 这次锢囚过程是积聚在蒙古地区的冷空气分东西两路南下,在河套地区汇合而形成的。 1.西路冷空气     

北京2009年“1101”暴雪的形成机制

利用多种新观测资料,对2009年11月1日北京出现的60年来降雪量最大的初雪过程的发生、发展特征进行分析,并探讨了暴雪形成机制。结果表明:此次初冬暴雪过程是在500 hPa东亚大槽斜压发展、低层锋区较强的背景下,由华北锢囚锋强迫所致。该锢囚锋是贝加尔湖南下冷空气在华北燕山和太行山地形影响下变为低层东西两股冷空气相向挤压的产物;伴随锢囚锋的形成,在北京西南37°~40°N之间形成狭窄水汽输送通道,为锢囚锋降水提供必需的水汽条件。锢囚锋区结构浅薄,主要存在于850 hPa层以下,为垂直东倾的冷式锢囚;东倾结构决定了降水落区,北京恰处于地面锢囚锋东侧的锢囚锋区中;而锢囚锋浅薄的垂直结构则决定了其强迫抬升运动并不深厚,故暴雪是降雪时间长、累积量大的结果。另外,北京雨转雪的发生是因降雪前近地面层气温下降较快接近冰点的缘故,降温主要源于雪前降雨在近地面层蒸发冷却的贡献;低层东路冷空气的平流作用则是降雪期间近地面气温维持较低的主因。     

对华北锢囚锋个例的数值模拟分析

运用非静力中尺度模式（ＭＭ５）对１９９８年１１月２０～２０日的华北锢囚锋形成过程进行数值模拟,结果表明：本次锢囚锋结构在空间尺度上小于典型温带气旋锢囚锋,降水落区与锢囚锋性质（暖性）有关,因此,潜热释放对锢囚锋的维持起一定的作用,去掉太行山后,锢囚锋形成的时间会偏早,地点偏西,强度偏弱,因此,太行山的存在对本次锢囚锋生成发展起至关重要的作用。     

用10层准拉格朗日有限区域模式对高原东侧锋生过程的数值模拟

本文对一次引起夏季华北暴雨的锋生过程进行了研究。在诊断分析的基础上,我们采用十层准拉格朗日有限区域模式对此个例进行了48小时的模拟,并对模拟输出结果进行解释与再次诊断。表明:(1)夏季高原东侧有时两支气流交绥很清楚,温度对比明显,与梅雨锋的情况很不相同,这在夏末尤其如此。这种温度对比区虽比冬季弱,但是,与夏季天气系统的发展及降水是有关系的。(2)模拟结果与实际观测资料是很相似的,再现了两支气流形成切变线的三维结构、移动与演变,并模拟出了在对流层中存在着深厚的24小时变温区;模拟发现,一条东北-西南向的锋生     

冷空气对台风“海葵”(1211)倒槽特大暴雨作用分析

针对2012年8月10日发生在台风"海葵"(1211)减弱低压倒槽顶部的特大暴雨过程,利用加密自动气象站、卫星云图、NCEP再分析资料,结合中尺度数值模式的模拟结果,分析了这次特大暴雨期间的中尺度对流系统演变特征及形成机理。研究表明,东北冷涡后部南下的冷空气为特大暴雨的发生提供了有利的热动力条件,促进了降水的发展。冷空气主体偏北,仅从对流层中层侵入低压倒槽北部,而对流层低层并无明显冷空气影响,使暴雨区上空形成冷平流叠置于暖平流之上的温度平流垂直分布结构,促进这一地区对流不稳定层结的建立和发展。冷空气与低压倒槽内辐合上升的暖湿空气对峙于对流层中层,引起中层锋生,锋生效应使风场辐合加强,进一步促进锋生。两者相互作用促进暴雨区及附近的中小尺度对流系统发展,在暴雨区上空强迫出一支对流尺度的强上升气流,加强低层水汽向上输送,使暴雨区上空水汽辐合层迅速增厚,从而引发局地特大暴雨天气发生。     

青奥开幕式期间南京地区浅层对流成因及逆向移动特征分析

利用常规观测资料、加密自动站资料、多普勒雷达资料及NCEP 1°×1°再分析资料,针对第二届青年奥运会开幕式期间形成发展于对流层低层偏东气流中的对流引发南京局地短时强降水天气进行了分析,探讨了低层偏东气流中浅层弱对流的形成机制、降水期间伴随在降水云系中逆向移动的两类对流单体的雷达特征和移动原因。结果表明,降水期间,南京上空对流层低层维持偏东风,中层以上则为西南风,两者之间的过渡区对应一干层,该干层由对流层中层的一支偏北气流携至的干空气形成,叠置于对流层低层较浅薄偏东暖湿气流之上,促进了对流层中低层对流不稳定层结的发展。地面风场扰动形成的局地辐合及地面非锋性斜压带激发了对流层低层偏东气流中对流的形成。镶嵌于降水回波中逆向移动的两类对流单体结构差异明显,两类对流单体质心高度、垂直伸展厚度与所在高度层中所盛行的背景风场决定了对流单体的传播与移动。     

一次比较典型的暖性锢囚锋

1979年2月21—23日,华北北部出现了一次特大降雪天气过程,北京南苑降水量达31.4毫米,除1959年2月下旬那场大雪外,从1847年到现在一百三十多年还没有出现过这样大的降雪。有人指出,这是一次有高空低涡配合的地面锢囚降雪天气过程(范永祥等,1979年《气象》第9期,9—10页)。对于这次天气过程中锢囚锋的分析,本人有以下几点不同看法。     

一次华北大雪的卫星云图分析

1979年2月下旬,华北出现大范围大雪,积雪达一尺多深,降水量一般在10—20毫米,华北东部和南部均超过20毫米。这场雪对减轻春旱有利,但对交通却造成了一定影响。 造成这场大雪的系统共有5个,其中西北涡、锢囚锋、南支槽是属于天气尺度系统,西南涡和暖切变属于中间尺度系统。从卫星云图上能较早地分析出这些系统的独特云型及其移动发展,这对做好降雪预报有较大帮助的。     

一次β-中尺度暴风雪的成因及动力热力结构

利用多普勒雷达、地面加密自动站监测资料、常规观测资料、4DVAR雷达风场反演和中尺度数值模式WRF模拟结果,对华北东部一次β-中尺度暴风雪的成因和影响天气系统的热力、动力结构及演变进行了分析。结果表明,(1)造成暴风雪的天气系统是回流形势下的冷锋锢囚锋,其在形成过程、生命史、尺度范围等方面均与温带气旋锢囚锋不同。(2)暴风雪过程分为东路弱冷锋降雪、锢囚降雪、西路强冷锋降雪3个阶段。降雪回波顶高在3～4km,回波强度均在35dBz以下。降雪量集中在锢囚降雪阶段。(3)风廓线(VWP)下层东风层和上层西南风的厚度在降雪各阶段不同,东风急流和西南风急流的变化和配置与降雪量关系密切。锢囚降雪阶段,地面和低层水平风场具有β-中尺度气旋性环流,是造成降雪回波旋转且长时间维持的动力。"人"字状回波的形成是因为风向或风速辐合线的作用。(4)锢囚锋的垂直结构和锢囚过程表明,西路冷锋比东路冷锋陡峭且势力强大,暖湿气团被东西两侧冷锋夹挤、抬升;锢囚时,两侧锋面形成冷式锢囚;锢囚消失时,大风首先在900hPa高度附近出现,进而下传到地面。     

Climate policy strength compared: China,the US,the EU,India, Russia,and Japan

The few systematic international comparisons of climate policy strength made so far have serious weaknesses, particularly those that assign arbitrary weightings to different policy instrument types in order to calculate an aggregate score for policy strength. This article avoids these problems by ranking the six biggest emitters by far – China, the US, the EU, India, Russia, and Japan – on a set of six key policy instruments that are individually potent and together representative of climate policy as a whole: carbon taxes, emissions trading, feed-in tariffs, renewable energy quotas, fossil fuel power plant bans, and vehicle emissions standards. The results cast strong doubt on any idea that there is a clear hierarchy on climate policy with Europe at the top: the EU does lead on a number of policies but so does Japan. China, the US, and India each lead on one area. Russia is inactive on all fronts. At the same time climate policy everywhere remains weak compared to what it could be.

Policy relevance

This study enables climate policy strength, defined as the extent to which the statutory provisions of climate policies are likely to restrict GHG emissions if implemented as intended, to be assessed and compared more realistically across space and time. As such its availability for the six biggest emitters, which together account for over 70% of global CO₂ emissions, should facilitate international negotiations (1) by giving participants a better idea of where major emitters stand relative to each other as far as climate policy stringency is concerned, and (2) by identifying areas of weakness that need action.     

1,800 Years of abrupt climate change, severe fire, and accelerated erosion, Sierra Nevada, California, USA

This paper provides both a detailed history of environmental change in the Sierra Nevada over the past 1,800 years and evidence for climate teleconnections between the Sierra Nevada and Greenland during the late Holocene. A review of Greenland ice core data suggests that the magnitudes of abrupt changes in temperature and precipitation increased beginning c. 3,700 and 3,000 years ago, respectively. Precipitation increased abruptly 1,300 years ago. Comparing paleotemperature data from Cirque Peak, CA with paleoprecipitation data from Pyramid Lake, NV suggests that hot temperatures occurred at the beginnings of most severe droughts in the Sierra Nevada over the past 1,800 years. Severe fires and erosion also occurred at Coburn Lake, CA at the beginning of all severe droughts in the Sierra Nevada over the past 1,800 years. This suggests that abrupt climate change during the late Holocene caused vegetation and mountain slopes in some areas to be out of equilibrium with abruptly changed climates. Finally, the ending of drought conditions in Greenland coincided with the beginning of drought conditions in the Sierra Nevada over the past 1,800 years, perhaps as a result of the rapidly changed locations of the Earth??s major precipitation belts during abrupt climate change events.     

The temperature dependent,infrared absorption cross-sections for the chlorofluorocarbons: CFC-11, CFC-12, CFC-13, CFC-14, CFC-22, CFC-113, CFC-114, and CFC-115

The infrared absorption cross-sections for eight commonly used halogenated methanes and ethanes have been measured as a function of temperature from 203 to 293 K. High resolution spectra (0.03 cm^-1) have been used to derive integrated band strengths and peak cross-sections associated with the spectral features in the infrared region from 600 to 1500 cm^-2. The values obtained in this study are compared to those from previous reports, and recommendations are made for uses in atmospheric sensing and radiative energy transfer models. The observed temperature dependence in the spectral features is also discussed.     

Wind-driven, double-gyre, ocean circulation in a reduced-gravity, 2.5-layer, lattice boltzmann model

A coupled lattice Boltzmann （LB） model with second-order accuracy is applied to the reduced-gravity, shallow water, 2.5-layer model for wind-driven double-gyre ocean circulation. By introducing the secondorder integral approximation for the collision operator, the model becomes fully explicit. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretization accuracy of the LB equation. The feature of the multiple equilibria solutions is found in the numerical experiments under different Reynolds numbers based on this LB scheme. With the Reynolds number increasing from 3000 to 4000, the solution of this model is destabilized from the anti-symmetric double-gyre solution to the subtropic gyre solution and then to the subpolar gyre solution. The transitions between these equilibria states are also found in some parameter ranges. The time-dependent variability of the circulation based on this LB simulation is also discussed for varying viscosity regimes. The flow of this model exhibits oscillations with different timescales varying from subannual to interannual. The corresponding statistical oscillation modes are obtained by spectral analysis. By analyzing the spatiotemporal structures of these modes, it is found that the subannual oscillation with a 9-month period originates from the barotropic Rossby basin mode, and the interarmual oscillations with periods ranging from 1.5 years to 4.6 years originate from the recirculation gyre modes, which include the barotropic and the baroclinic recirculation gyre modes.     

基于L波段探空的云区边界识别改进算法

利用气象业务中使用的L波段探空数据和毫米波云雷达观测资料,分析探空相对湿度在入云和出云时的变化规律,提出一种基于探空相对湿度阈值与梯度相结合的云区边界识别改进算法,并利用云雷达观测数据对算法识别结果进行验证.利用北京市南郊观象台2019年1—6月层状云样本验证分析,结果表明:改进算法相比相对湿度阈值法,对云区边界识别更...     

The microstructure of selected, small, isolated, cumulus clouds near Red Deer, Alberta

Physical experiments designed to explore the potential of rain augmentation through airborne glaciogenic seeding on small, isolated non-precipitating cumuliform clouds near Red Deer, Alberta were carried out during the period 1982–1985. The microstructure of 90 cumulus congestus clouds have been documented through repeated in-situ sampling using a cloud physics instrumented aircraft platform. Observations from the inspection passes of 57 clouds seeded with either dry ice pellets or silver iodide pyrotechnics, and all the passes of 33 natural clouds are presented.Measurements of the cloud droplet concentration indicate that Alberta cumulus clouds are typically continental in nature, with an average droplet concentration of 535 cm⁻³ and an average droplet diameter of 10.6 μm. Alberta clouds have average liquid water contents of 0.57 g m⁻³, with a peak 1-sec value of 3.17 g m⁻³. The 1-km average liquid water contents are 0.83 g m⁻³, with a peak value of 2.81 g m⁻³. Cloud lifetimes vary between 11 and 20 minutes. Concentrations of naturally occurring ice crystals are found to be low. The average maximum 1-km ice concentration was 31⁻¹, and the peak 1-km concentration was 73.11⁻¹ in the natural cloud dataset. Evidence of precipitation-sized particles was detected in 21% (7 of 33) of the clouds, and precipitation below cloud base was detected in 6% (2 of 33) of the clouds.A comparison of the Alberta cloud characteristics to the cumulus clouds from different locations showed that there are some distinct differences between Alberta clouds and the clouds from the other regions.     

承德市一次由快速发展气旋诱发的大风天气分析

利用常规观测资料和NCEP/NCAR(1°×1°)逐6 h再分析资料,对承德市2017年5月5—6日大风天气的环流形势和物理量进行分析,结果表明气旋的快速发展(气旋加深率0.84 B)导致锋生加强,引发气压和变压梯度加大是导致大风的直接原因。500 hPa高压脊东移迫使冷空气向南堆积,高空槽不断发展成为冷涡,温度平流为地面气旋的发展提供热力条件,高低层涡度平流的差异,也是地面气旋快速发展的重要原因;当1.5 PVU位涡面伸展至对流层低层时,局地位涡异常在气旋的发展过程中不可忽视;高空急流出口区发生质量调整,出口区左侧的辐散强度达10×10~(-5) s~(-1),使低层大气减压,有利于气旋发展。     

Governance,complexity, and resilience

This special issue brings together prominent scholars to explore novel multilevel governance challenges posed by the behavior of dynamic and complex social-ecological systems. Here we expand and investigate the emerging notion of “resilience” as a perspective for understanding how societies can cope with, and develop from, disturbances and change. As the contributions to the special issue illustrate, resilience thinking in its current form contains substantial normative and conceptual difficulties for the analysis of social systems. However, a resilience approach to governance issues also shows a great deal of promise as it enables a more refined understanding of the dynamics of rapid, interlinked and multiscale change. This potential should not be underestimated as institutions and decision-makers try to deal with converging trends of global interconnectedness and increasing pressure on social-ecological systems.     

Linking vulnerability, adaptation, and resilience science to practice: Pathways, players, and partnerships

Vulnerability, adaptation and resilience are concepts that are finding increasing currency in several fields of research as well as in various policy and practitioner communities engaged in global environmental change science, climate change, sustainability science, disaster risk-reduction and famine interventions. As scientists and practitioners increasingly work together in this arena a number of questions are emerging: What is credible, salient and legitimate knowledge, how is this knowledge generated and how is it used in decision making? Drawing on important science in this field, and including a case study from southern Africa, we suggest an alternative mode of interaction to the usual one-way interaction between science and practice often used. In this alternative approach, different experts, risk-bearers, and local communities are involved and knowledge and practice is contested, co-produced and reflected upon. Despite some successes in the use and negotiation of such knowledge for ‘real’ world issues, a number of problems persist that require further investigation including the difficulties of developing consensus on the methodologies used by a range of stakeholders usually across a wide region (as the case study of southern Africa shows, particularly in determining and identifying vulnerable groups, sectors, and systems); slow delivery of products that could enhance resilience to change that reflects not only a lack of data, and need for scientific credibility, but also the time-consuming process of coming to a negotiated understanding in science–practice interactions and, finally, the need to clarify the role of ‘external’ agencies, stakeholders, and scientists at the outset of the dialogue process and subsequent interactions. Such factors, we argue, all hinder the use of vulnerability and resilience ‘knowledge’ that is being generated and will require much more detailed investigation by both producers and users of such knowledge.     

江苏三次不同量级降雪过程的对比分析

利用常规观测资料和NCEP 1°×1°再分析资料,通过对发生在江苏的三次不同量级的区域性暴雪、大雪和中雪过程典型个例进行对比分析,发现降雪时,700hPa低空急流的位置和强度是影响降雪量级的主要因素之一;降雪区上空涡度的垂直分布遵循低层负涡度、中层正涡度和高层负涡度的配置,暴雪时正涡度强且正涡度区最为深厚,动力抬升作用强,中雪发生时正涡度区相对最为浅薄,不利于形成强辐合抬升,动力抬升作用弱。且暴雪和大雪发生时基本上整层都为垂直螺旋度正值区,中雪时没有出现明显的正值区;暴雪和大雪过程时中低层都具有明显的逆温层,中高层西南急流造成的对流层中层的爆发性增温是逆温层形成的关键,中雪发生时不一定有逆温层结;降雪强度与湿位涡分量绝对值存在一定的正相关关系。