西安市大气能见度变化规律及与空气污染关系

利用1980—2005年西安市大气能见度资料对大气能见度变化规律统计分析,并利用2005年西安市逐日污染物质量浓度资料,分析与能见度的相关性,结果表明:大气能见度有较明显的年际变化、月季变化和日变化特征。年际变化总体呈增大趋势,20世纪90年代中期以来明显好于80年代到90年代前期;能见度与空气污染物质量浓度呈负相关,污染物质量浓度对能见度的影响冬季最明显,秋季次之,夏季最差。     

厦门城市能见度和雾的特征与城市环境演变

利用厦门城市1980～2000年21年地面资料和探空资料，对能见度和雾演变特征及其物理成因进行分析，结果表明：厦门城市夏季能见度明显好于冬季，这可能与冬夏盛行风向不同，输送排放污染源地不同以及不同季节天气气候条件相关。厦门城市冬季和夏季能见度呈下降趋势，尤以夏季为突出，轻雾以上的频数也日益增加，其重要因素是城市的热岛效应。厦门城市能见度虽然明显好于污染较为严重的北京，但冬季厦门城市能见度与北京呈反位相演变趋势。夏季厦门城市能见度有着明显的日间变化，这与夏季海陆风日变化的垂直环流圈有密切关系。     

近37年佛山市大气能见度的变化特征

利用佛山市南海区、顺德区、三水区3个代表站1980—2016年的能见度观测资料,使用累积百分率、Ridit能见度出现频率等方法,分析了佛山市近37年来大气能见度的特征和变化趋势,探讨了东亚季风指数和污染物对能见度的影响。结果表明:(1)无论是能见度中值、低值还是Ridit值,在改革开放初期能见度变化曲线呈现下降趋势;经济持续发展时期的20世纪90年代初至2000年前后,佛山市能见度变化趋势处于相对平稳波动期; 2000年前后至2012年佛山市能见度变化处于波动式上升; 2012年至2016年即环保效益期佛山市能见度呈现急剧上升趋势。(2)东亚季风的强弱对于南海区和顺德区能见度有较明显的影响,即能影响顺德整体的能见度,但只影响南海低值的状况,中值的状况仍然受到整体城镇化效应的影响。(3)空气污染物年均值变化趋势与能见度年变化趋势大体表现为反相位。     

临沂市气温变化规律及其与大气环流的关系

利用临沂市53年气温资料和北半球大气环流资料，采用相关分析、小波分析方法，对临沂市气温变化特征及其与北半球大气环流特征的关系进行分析，发现临沂市年平均气温变化具有明显的阶段特征，季节变化不同步。近年来气候变暖的主要因素是冬季平均气温及平均最低气温升高。气温变化与副高面积指数、强度指数，极涡面积指数，经、纬向环流指数等的变化密切相关，与南方涛动指数、太阳黑子相对数、东亚大槽位置等关系不显著。     

基于序列重建的湖北省大范围持续性霾过程特征分析

利用1961—2013年湖北省76个气象站逐日天气现象、相对湿度和能见度等观测资料,重建了湖北省霾日序列,建立大范围持续性霾过程的强度等级评价模型及指数,并分析了湖北省霾日和大范围持续性霾过程的时空变化特征。结果表明:1961—2013年湖北省霾日序列重建前和重建后时空分布的年代际变化差异较小,但变化趋势相反。基于霾日的重建序列,近50 a湖北省霾日具有明显的年代际变化特征,2000年后霾日增加趋势尤其明显,冬季为霾易发季节。湖北省大范围持续性霾过程主要出现在20世纪70年代及21世纪初,2013年尤为突出;三峡河谷至鄂西北东部和鄂东中北部地区为持续性霾过程高发地区。经验证,大范围持续性霾过程指数(LSCHI)的评估效果较好。     

长江中下游降水以及东亚夏季风环流的年代际变化

采用NCEP再分析资料及有关长江中下游的梅雨期降水量进行合成或诊断分析,目的是研究长江梅雨以及相应的大气环流的年代际变化,得出梅雨量的年代际变化和东亚大气环流以及厄尔尼诺现象的年代际变化密切相关的初步结果,具体结论如下：（1）与东亚季风指数相联系的长江中下游地区6-7月降水量及梅雨量在最近15年有持续增长的趋势。与此同时鄂霍茨克海地区的500hPa高度也有持续增长的趋势,并配合有厄尔尼诺频繁出现的趋势。（2）东亚夏季风指数与前年秋季NINO-3区域海温在最近20年有很好的相关,但是20年以前相关不好。意味着厄尔尼诺对东亚夏季环流的影响在加深。（3）近20年的PDO暖位相与东亚大气环流的年代际变化基本同步。     

1996年我国南方洪涝的海气环境场分析

选用 1 95 1～ 1 996年中国 1 6 0站逐月降水资料 ,太平洋逐月平均网格点海温资料( 1 0°S～ 5 0°N,1 2 0～ 80°E) ,逐月大尺度环流指数资料 ,分析并探讨造成 1 996年南方洪涝的环流特征、气候背景及海温影响机制。结果表明 :大气环流指数与前期太平洋海温场有明显的遥相关关系。冬、春季海温的冷暖变化程度 ,可预示后期 7月各环流系统的趋势变化 ,环流系统指数自身演变存在较明显的年代际变化规律 ,1 996年南方洪涝就是在这种气候背景下形成的。海温冷暖变化影响大气环流系统的这种演变关系 ,对南方洪涝的短期气候预测具有一定的指示意义。     

不同年代际背景下AO与冬季中国东北气温的关系

采用1951—2006年北极涛动指数序列、NCEP/NCAR再分析资料和我国160站气温资料,利用滑动相关分析研究了不同年代际背景下北极涛动与冬季中国东北气温年际异常关系的变化情况。结果表明,两者的关系在20世纪60年代中后期显著增强,在80年代中后期减弱。不同年代际背景下,与AO相关联的中高纬度大气环流异常发生的明显改变是AO与东北冬季气温关系发生年代际变化的原因。强相关年代,西伯利亚高压与阿留申低压均明显减弱,东亚冬季风偏弱,对流层中下层异常东南风控制东北地区,对流层中层东亚大槽明显减弱,环流的经向性减弱,使该地区冬季气温偏高;相关较弱的年代则以上表现不明显。     

北极区近30年环流的变化及对中国强冷事件的影响

利用1971—2000年NCEP再分析资料和中央气象台提供的我国强冷空气过程统计资料,分析了近30年冬半年北极区及中高纬度地区大气环流形势的气候变化以及对中国强冷事件的影响。结果表明,20世纪70~90年代北极区大气温度发生了明显变化,极涡系统也随之改变。80年代中期前,极涡范围偏大;之后面积减小。从长期趋势来看,70年代中期至90年代中期,极涡强度与面积呈反位相变化;同期,亚洲中高纬地区大气环流也相应调整,总体趋势由低指数向高指数模态转变,环流经向度减小;东亚大槽东迁,槽线90年代比70年代东移了近1个经距,冬季则更为突出,平均东移2.2个经距;西伯利亚冷高压也发生了年代变迁,70年代高压强度弱、控制范围偏小,80年代增强,范围明显扩大,90年代高压中心强度变化不大,但高压主体向南扩展的纬度较80年代偏北1~2个纬距,主体面积减小了5%。研究表明,正是由于极区、近极区环流系统的改变,造成近30年我国强冷空气爆发的事件特性发生了年代际变化。70年代强冷事件最为频繁,以西路冷空气为主,80年代频次明显减少,以偏西北路冷空气为主,但多源自新地岛东部,极端强冷事件降温距平达到最大,单次冷空气势力最强;90年代强冷事件频次又有所增加,但冷空气强度明显减弱。究其原因,主要与气候增暖、积温偏高,易产生降温有关。而上述近30年冷事件频次和强度的变化特征符合极端天气事件与气候变化的关系,因此我国强冷空气爆发事件特性的改变可能也是气候增暖的结果和反映。     

东亚低纬地区局地Hadley环流特征及其与大气臭氧的关系

利用1975—2008年NCEP/NCAR的逐月平均风场资料及1975—2001年ECMWF的逐月多层臭氧质量混合比资料,用大气环流三维分解方法研究了东亚低纬度地区之局地Hadley环流的结构及年代际演变特征,分析了该区域局地Hadley环流异常时对应大气臭氧的空间距平分布。研究结果表明:(1)东亚低纬度地区局地Hadley环流既与纬圈平均Hadley环流具有明显的季节变化,但又具有明显区别于纬圈平均Hadley环流的自身结构特征:除冬季存在明显向南、向北输送的两闭合环流圈外,局地Hadley环流在其余季节均以向南输送为主;(2)该局地Hadley环流具有不同于纬圈平均Hadley环流的年代际演变特征,在整个研究时段上以振荡变化为主,并没有表现出象纬圈平均值那样明显的增强趋势;(3)区域赤道上空平流层20～50 hPa大气臭氧的正负距平异常中包含有局地Hadley环流的异常信息:当局地Hadley环流异常强时,区域赤道上空20～50 hPa大气臭氧有一显著负距平异常中心,反之亦然。     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

VARIABILITY OF INTER-ANNUAL RELATIONSHIP BETWEEN INDIAN OCEAN DIPOLE AND HUAXI REGION’S AUTUMN PRECIPITATION

The moving-window correlation analysis was applied to investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the synchronous autumn precipitation in Huaxi region, based on the daily precipitation, sea surface temperature (SST) and atmospheric circulation data from 1960 to 2012. The correlation curves of IOD and the early modulation of Huaxi region’s autumn precipitation indicated a mutational site appeared in the 1970s. During 1960 to 1979, when the IOD was in positive phase in autumn, the circulations changed from a “W” shape to an ”M” shape at 500 hPa in Asia middle-high latitude region. Cold flux got into the Sichuan province with Northwest flow, the positive anomaly of the water vapor flux transported from Western Pacific to Huaxi region strengthened, caused precipitation increase in east Huaxi region. During 1980 to 1999, when the IOD in autumn was positive phase, the atmospheric circulation presented a “W” shape at 500 hPa, the positive anomaly of the water vapor flux transported from Bay of Bengal to Huaxi region strengthened, caused precipitation ascend in west Huaxi region. In summary, the Indian Ocean changed from cold phase to warm phase since the 1970s, caused the instability of the inter-annual relationship between the IOD and the autumn rainfall in Huaxi region.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on