中国北方干旱区地表湿润状况的趋势分析

利用 1 95 1～ 1 997年中国 1 6 0站月降水和平均气温资料 ,通过计算的地表湿润指数 Hi =PPe(P为观测的月降水总量 ,Pe为月最大潜在蒸发 ) ,对比分析了中国华北、西北两个典型干旱区区域平均地表湿润指数的年代年际变化特征及季节性差异 ,并讨论了它与降水和气温的联系。最后 ,给出了地表湿润指数年及各季节变化趋势的地理分布。研究表明 :西北西部和华北地区的年际及年代际变化趋势基本相反 ,前者地表为变湿趋势 ,后者为变干趋势。华北地区的干化趋势主要发生在夏秋季节 ,而西北除东部的秋季和西部的夏季外 ,其它季节均存在变湿趋势     

宁夏地表湿润状况演变规律研究

利用1961-2004a宁夏23站月降水和平均气温资料,通过计算地表湿润指数,分析了宁夏区域平均及不同区域地表湿润指数的年代际变化特征及季节性差异.最后,给出了地表湿润指数年及各季节变化趋势的地理分布.结果表明:近40a来宁夏年地表湿润指数总趋势是下降的,即地表在变干;地表湿润指数的变化具有明显的阶段性特征,即1970s末期以前的冷湿期,1970s末至1980s中期的冷干期,1980s中期以来的暖干期;宁夏的干化趋势主要发生在秋季;宁夏年、秋季地表显著变干的中心区域主要集中在中部干旱带及南部山区的北部;冬季南部山区存在显著变湿趋势,春、夏季各地均无显著干、湿变化趋势.     

近代中国北方干湿变化趋势的多时段特征

利用CRU(Climate Research Unit)月降水和月平均气温资料, 通过构造一个既包含降水变化又考虑温度变化对潜在蒸发影响的干湿指标, 对我国北方近100年(1901～1998年)、 50年(1951～2002年)、 20年(1981～2002年)和近10年(1991～2002年)干湿变化趋势进行了系统的检测和分析, 突出了在全球增暖背景下温度变化对干湿变化的重要影响, 揭示了中国北方四个不同时段干湿变化趋势的基本特征.结果表明: 由于受温度升高的影响, 近100年我国西部地区降水尽管增加但并不存在变湿趋势, 而东部地区降水显著增加的地区明显呈现出变湿趋势, 显著变湿的范围较降水增加的范围大, 且强度明显增强, 这与这个地区温度的降低有关.在近50年, 100°E以东的北方地区是明显的干旱化趋势; 西北西部显著变湿的范围较降水显著增加的范围为小, 而东部干旱化区域的范围较降水显著减少的区域大.这充分说明了增暖能够减弱降水增加对地表水分收支的贡献, 也就是加剧降水减少的干旱化程度.在近20年, 新疆北部尽管降水量有所增加, 但并未改变该地区干旱化的时空格局, 也未发现显著的变湿趋势存在, 这个时段北方大部分地区仍然以干旱化趋势为主.特别值得注意的是, 在有些地区干湿指标的变化趋势与降水的变化趋势完全相反.在20年和近100年时段上, 我国西部大部分地区仍处在一个干旱化的进程中, 而华北地区在20年和50年时段上均表现为一个干旱化的趋势.     

中国东北地区地表干湿状况的变化及趋势分析

利用1961~2000年中国东北地区80个测站的月降水和平均气温资料，通过计算地表最大潜在蒸发、地表干燥度指数和地表水分盈亏量，分析了东北地区及其7个不同气候区域地表干湿状况的时空分布规律及其变化趋势，并探讨了它与降水和气温的关系。结果表明，东北地区及其不同区域的地表干湿状况不仅具有较大的地域差别和年际及年代际变率，而且存在着明显的阶段性和低频变化特征，特别是20世纪90年代中期以来，东北地区呈现出较强的变干倾向，并且由于气温升高所导致的潜在蒸发的加大与降水一样对这一变干倾向也有十分重要的影响。     

中国北方近百年干湿变化与太平洋年代际振荡的关系

利用CRU(Climate Research Unit)1901～2002年全球0.5°×0.5°网格点月降水和月平均气温资料,利用一个能够用于检测地表干湿变化的湿润指数,对中国北方四个典型地区干湿演变特征及与北太平洋年代际振荡的关系进行了初步的分析.结果发现:降水和湿润指数在表征干湿变化的特征时有明显的差别,特别是在干旱和半干旱地区,增暖也是影响干湿变化的一个重要因素.相关分析表明,华北和西北东部的年干湿变化与同期太平洋年代际振荡(简称PDO)指数有密切的关系,PDO指数的正位相对应两个地区的干旱时段,负位相则对应两个地区的湿润时段,而新疆南部与PDO指数同期呈显著的正相关关系,即当PDO为正位相时,该地区为湿的时段,负位相对应干的时段.以100°E为界,北方的东部干湿变化与太平洋年代际振荡指数呈反相关,而西部则相反,与PDO呈正相关关系.     

1951—2009年中国地表湿润状况变化趋势研究

利用1951—2009年中国160站的月降水和月平均温度资料,通过计算地表湿润指数,在分析其与降水及气温联系的基础上,探讨了中国区域平均地表湿润指数的年代际变化特征差异,给出了地表湿润指数年趋势的地理分布。结果表明：1951—2009年,中国北方的西北地区东部、华北和东北地区长江中下游地区及东南部分地区以干旱化趋势为主...     

1951—2009年中国地表湿润状况变化趋势研究

利用1951—2009年中国160站的月降水和月平均温度资料,通过计算地表湿润指数,在分析其与降水及气温联系的基础上,探讨了中国区域平均地表湿润指数的年代际变化特征差异,给出了地表湿润指数年趋势的地理分布。结果表明：1951—2009年,中国北方的西北地区东部、华北和东北地区长江中下游地区及东南部分地区以干旱化趋势为主,这些地区干旱化趋势的产生与降水年际变差大、年内分配不均,降水持续减少和气温升高密切相关。东南、西南地区及西藏地区于20世纪90年代初期有湿向干的趋势转换,虽然长江中下游地区在70年代初期有明显的干向湿的趋势变换,但于90年代同样出现湿向干的趋势转换,并一直持续显著的干旱化。     

西藏近35年地表湿润指数变化特征及其影响因素

利用1971-2005年西藏25个气象站月平均最高气温、最低气温、风速、相对湿度、日照时数、降水量等资料,应用Penman-Monteith模犁计算了最大潜在蒸散、地表湿润指数,分析了其空间分布、年际变化特征及季节差异,并讨论了影响地表湿润指数变化的气象因子.研究表明:近35年,西藏年降水量表现为显著的增加趋势,增幅为15.0 mm/(10 a);年最大潜在蒸散呈不同程度的减小趋势,为-4.6--71.6 mm/(10 a).阿里地区西南部、聂拉木年地表湿润指数为不显著的减小趋势,其他各地均呈增大趋势,增幅为0.02-0.09.就西藏平均而言,年地表湿润指数以0.04/10 a的速率显著增大,尤其足近25年增幅更为明显.各季节地表湿润指数也表现为增大趋势,以夏季增幅最明显.20世纪70年代剑80年代主要表现为以低温低湿为主的年际变化特征,进入90年代后,气温持续升高,地表湿润指数明显增加,呈现山暖湿型的气候特征.降水量和相对湿度的明显增加,以及平均气温日较差的显著减小是地表湿润指数显著增加的主要原因,平均风速和日照时数的明显减少,在湿润指数增加趋势中也起着重要作用.     

北美和欧亚大陆冬季快速增温与地表干湿变化

采用东英吉利大学气候研究中心（CRU）提供的月地表温度和降水资料,分析了全球年平均及冬季地表温度变化趋势,发现在北半球中高纬地区半干旱区冬季快速增温。在此基础上通过分析帕默尔干旱指数（PDSI）研究了北美和欧亚大陆冬季地表干湿变化的时空特征和差异,并讨论北美和欧亚大陆冬季快速增温对地表干湿变化的影响。结果表明,北美大陆南部微弱变湿,加拿大北极群岛变湿明显,而在北美大陆的中西部有明显的变干趋势;欧亚大陆大部分地区在冬季有一定的变干趋势,其中尤以西欧南部,中国华北、东北,蒙古中北、东北部及俄罗斯远东地区变干最为显著。但北美和欧亚大陆1950-2008年冬季降水并无显著变化趋势,地表干湿变化主要受气温的影响,尤其是在冬季增温最为快速的地区。     

黑龙江省地表湿润状况及趋势分析

利用1958～2003年黑龙江省均匀分布的16站月降水和平均气温资料,通过计算地表最大潜在蒸发、地表干燥度指数、地表水分盈亏量,对比分析了黑龙江省各不同干湿气候区域地表干湿状况的分布规律及其变化趋势,并讨论了它与降水和气温的关系。给出了地表干燥度指数的地理分布和变化趋势。研究表明:全省及各区地表干燥度均存在变干的趋势,特别在进入21世纪以后,变干的趋势更加明显。但各地变干的特征差别较大,其中西部地区地表变干的程度最为严重,北部地区最轻,甚至个别地区还有变湿的倾向。     

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.     

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.     

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.     

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