2016—2017年冬季华北地区一次重污染过程的气象条件分析

以华北地区为研究区域,利用地面监测数据、高空观测资料、NCEP FNL资料及HYSPLIT后向轨迹模式,对2016年12月26日至2017年1月9日该地区的雾霾天气过程进行综合分析。结果表明,雾霾期间高空以纬向环流为主,冷空气势力偏弱,主要受高压、弱高压或均压场控制,有利于华北地区静稳天气形成。同时,雾霾期间边界层平均高度约600~900 m,污染物浓度与边界层高度呈负相关,且污染物浓度变化较边界层高度变化存在滞后现象。逆温层的长期存在,不利于污染物垂直扩散,能见度一直维持在5 km以下。后向轨迹集合模拟与聚类分析表明,以北京地区为核心的华北地区雾霾天气期间,外来污染物中,80%来自西北方气团,20%来自河北西南地区气团。     

The Observed and Simulated Major Summer Climate Features in Northwest China and Their Sensitivity to Land Surface Processes

Northwest China （NWC） is a typical arid and semi-arid region. In this study, the main summer climate features over NWC are presented and the performance of an atmospheric general circulation model （NCEP GCM/SSiB） over this region is evaluated. Satellite-derived vegetation products are applied in the model. Based on comparison with observational data and Reanalysis II data, the model generally captures major features of the NWC summer energy balance and circulation. These features include： a high surface tem- perature center dominating the planetary boundary layer; widespread descending motion; an anticyclone （cyclone） located in the lower and middle （upper） troposphere, covering most parts of central NWC; and the precipitation located mainly in the high elevation areas surrounding NWC.
The sensitivity of the summer energy balance and circulation over NWC and surrounding regions to land surface processes is assessed with specified land cover change. In the sensitivity experiment, the degradation over most parts of NWC, except the Taklimakan desert, decreases the surface-absorbed radiation and leads to weaker surface thermal effects. In northern Xinjiang and surrounding regions, less latent heating causes stronger anomalous lower-level anticyclonic circulation and upper-level cyclonic circulation, leading to less summer precipitation and higher surface temperature. Meanwhile, the dry conditions in the Hexi Corridor produce less change in the latent heat flux. The circulation change to the north of this area plays a domi- nant role in indirectly changing lower-level cyclonic conditions, producing more convergence, weaker vertical descending motion, and thus an increase in the precipitation over this region.     

基于BJ-RUCv2.0预报系统对大雾形成和发展关键条件的数值分析

为了弄清北京地区持续性雾-霾天气过程的演变规律、揭示大雾形成和发展的关键条件,利用常规气象观测资料、高速路自动气象站观测资料和大气成分观测资料分析了2013年1月26~31日雾-霾天气过程的演变特征和有利于大雾形成和发展的天气形势。在此基础上,采用先进的北京快速循环同化中尺度数值预报系统（BJ-RUC v2.0）开展数值模拟,分析大雾形成的水汽、动力和热力条件,得出:模式对1月30日夜间至31日前半夜的雾区模拟较好,但对28日夜间至29日白天（大雾天气伴严重大气污染）雾区的模拟偏差较大。发现近地层的持续性东南风使950 hPa以下湿度增大是大雾形成的关键条件。上层（975~800 hPa）的明显暖平流导致逆温层的加强和维持,使大气层结稳定度增强,是大雾天气发展和维持的重要条件。另外,近地层950 hPa以下为风场辐合、其上层为风场辐散的结构有利于雾的进一步发展。     

CHARACTERISTICS OF EVAPOTRANSPIRATION IN THE YANGTZE DELTA REGION FOR PAST 40 YEARS AND MAIN INFLUENCE FACTORS*

The Kotoda-Bortan (KB) model (Liu and Kotoda 1998) used for estimating evapotranspiration was modified.The monthly evapotranspiration for various surfaces in the Yangtze Delta (118-123°E,28-33°N) was calculated using the modified model,and the annual regional average of evapotranspiration from 1961 to 1998 was obtained using a weighting method.The spatial and temporal distribution characteristics of evapotranspiration were analyzed.It is found that the regional averaged annual evapotranspiration has a decreasing trend over the past 40 years;the value dropped by about 24mm from 1961 to 1998.The main reason for this tendency is due to the change of land surface condition.Compared with the case of 1980,the current proportions of paddy field,farmland and water surface have decreased by 1.353%,4.42% and 2.597% respectively,while the proportions of urban area and non-agriculture land have increased by 3.345%.These changes clearly result in a decrease of the regional averaged evapotranspiration.     

土地利用变化对我国区域气候影响的数值试验

使用RegCM2区域气候模式单向嵌套澳大利亚CSIRO R21L9全球海-气耦合模式,通过将中国区域植被覆盖由理想状况改变为实际状况的数值试验对比分析,探讨了当代中国土地利用变化对中国区域气候的影响,并对结果进行了统计显著性检验。研究表明,土地利用的变化,会导致我国西北等地区年平均降水减少,导致年平均气温在内陆部分地区升高和在沿海个别地区降低,引起许多地方夏季日平均最高气温升高,而冬季日平均最低气温则在我国东部部分地区降低的同时在西北地区升高,土壤湿度的变化表现为大范围的降低。研究同时表明,相同的土地变化在不同的地理环境下引起的气候要素变化有一定的不一致性。     

复杂条件陆-气相互作用研究领域有关科学问题探讨

实际大气都是在复杂条件之下,所以复杂条件带来的问题已成为陆-气相互作用研究领域面临的最大科学挑战,严重制约了该领域研究成果在解决实际天气气候问题中的应用。在概要总结近年来中国复杂条件陆-气作用研究领域进展的基础上,对复杂条件下陆-气相互作用有关的科学问题进行了探讨。从陆面过程和大气边界层这两个陆-气相互作用的关键环节分析了影响陆-气相互作用复杂条件的机制,归纳了复杂条件下陆-气相互作用研究领域面临的关键科学问题。同时,以复杂下垫面陆面过程和非均匀大气边界层问题为重点讨论了突破复杂条件陆-气相互作用关键科学问题的基本思路,并对进一步开展复杂条件陆-气相互作用研究提出了初步的科学建议。      

阜康葡萄双层覆膜防寒越冬实验效果分析

阜康葡萄双层覆膜防寒越冬实验结果表明：丰雪年雪被保温效果明显,双膜内平均气温增加11.3℃,双膜内最低温度在1.7～-4.5℃间;枯雪年双膜内平均气温增加8.3℃,双膜内最低温度在0.3～-9.2℃之间,葡萄可安全越冬。双膜内20cm处最低温度在丰雪年增温15.0℃,在枯雪年增温14.2℃。影响双膜内温度的主要因子为外界的平均气温、最高气温、最低气温及日照时数等。经分析,选用透光性好的覆盖物促使膜内地温快速回升,揭膜日期提前可避免春季的高温热害。根据天气变化灵活掌握揭膜和覆膜时间可有效避免葡萄遭受倒春寒危害。     

安徽省雾、霾、晴空天气的气象条件对比分析

使用2008~2012年逐日地面观测资料,揭示了安徽不同地区雾、霾、晴空天气气象条件的差异,指出不同地区要根据本地特点建立雾、霾预报指标和预报方法。3类天气差异最大的地面气象要素是能见度和相对湿度。根据3种天气前一日和当日能见度和相对湿度分布特征,全省站点可以分为3类:1)从雾、霾到晴空,能见度递增、相对湿度递减,且差异显著,如合肥站;2)雾、霾天的能见度和相对湿度均很接近,但与晴空天差别较大,如阜阳站;3)能见度在雾、霾天无明显差别,但相对湿度在雾、霾天差异显著,如安庆站。地级市测站雾后即霾的可能性较大(大于50%),县城测站雾后即霾的可能性较低(低于25%)。垂直方向,雾时相对湿度随高度下降很快,850 h Pa中位值已降到20%(安庆)和45%(阜阳)以下,霾时相对湿度随高度下降缓慢,850 h Pa中位值仍在60%左右;另外,霾天边界层中上部风切变较小,雾天和晴空天边界层中上部都存在较大的风切变。     

Evaluation of Agricultural Climatic Resource Utilization During Spring Maize Cultivation in Northeast China Under Climate Change

Agricultural climatic resources （such as light,temperature,and water） are environmental factors that affect crop productivity.Predicting the effects of climate change on agricultural climatic resource utilization can provide a theoretical basis for adapting agricultural practices and distributions of agricultural production.This study investigates these effects under the IPCC （Intergovernmental Panel on Climate Change） scenario A1B using daily data from the high-resolution RegCM3 （0.25° ×0.25°） during 1951-2100.Model outputs are adjusted using corrections derived from daily observational data taken at 101 meteorological stations in Northeast China between 1971 and 2000.Agricultural climatic suitability theory is used to assess demand for agricultural climatic resources in Northeast China during the cultivation of spring maize.Three indices,i.e.,an average resource suitability index （Isr）,an average efficacy suitability index （Ise）,and an average resource utilization index （K）,are defined to quantitatively evaluate the effects of climate change on climatic resource utilization between 1951 and 2100.These indices change significantly in both temporal and spatial dimensions in Northeast China under global warming.All three indices are projected to decrease in Liaoning Province from 1951 to 2100,with particularly sharp declines in Isr,Ise,and K after 2030,2021,and 2011,respectively.In Jilin and Heilongjiang provinces,Isr is projected to increase slightly after 2011,while Ise increases slightly and K decreases slightly after 2030.The spatial maxima of all three indices are projected to shift northeastward.Overall,warming of the climate in Northeast China is expected to negatively impact spring maize production,especially in Liaoning Province.Spring maize cultivation will likely need to shift northward and expand eastward to make efficient use of future agricultural climatic resources.     

华家岭2008年电线积冰的变化特征与气象条件分析

利用华家岭气象站不同高度、不同方向、不同导线直径的电线积冰观测资料,分析了电线积冰在不同高度、不同方向、不同导线的变化特征,以及与气温、水汽压、风速等气象要素的关系。分析表明,电线积冰量随高度增加而增加,随电线直径增大而增大;在相同高度、相同导线上,不同方向的积冰量与风向有关。电线积冰量与水汽压、风速分别呈正相关和反相关。在一定阈值内,电线积冰量和气温存在较好的相关性。