地形性中尺度环流的数值模拟及验证

建立了一个高分辨三维边界层诊断模式以模拟下垫面热力和动力的 非均匀性对边界层结构的影响。模式模拟了广东大亚湾核电站厂址区域（12 km×12 km） 47个典型天气系统下的地形性中尺度环流,其大坑的模拟风向、风速和温度与观测值 相比,风向差小于17.5#+[o]的概率为87.5%,风速比值在0.7～1.3之间的概率为72.9%, 温度差小于0.4#+[o]C的概率为72.9%。     

2004年梅雨期武汉上空水汽的演变及其与暴雨的关系

利用2004年6—7月武汉每天两个时次探空资料计算出的可降水量以及各层的比湿和相对湿度，对比分析各种水汽量的垂直分布以及逐日演变特征，探讨了2004年梅雨期武汉上空水汽的演变及其与暴雨的关系。结果表明，武汉上空大气中水汽含量随高度递减，90％以上的水汽集中在700hPa以下；7月的水汽含量高于6月；武汉上空出现整层比湿增长或中高层比湿增长可导致整层相对湿度明显增长，而且增长的幅度随高度递增；在暴雨分析预报中，分析中高层水汽演变好于分析低层水汽演变；采用整层平均相对湿度和可降水量结合分析整层水汽演变以及将中高层平均的比湿和相对湿度结合分析中高层水汽演变时，对暴雨预报均有很好的指示意义。     

海洋对大气风应力强迫响应的数值模拟及其与El Ninño的关系

本文设计了一个一层的等效非线性浅水模式,用此模式进行了有关海洋对表面风应力强迫的试验,并用于解释El Ninño的形成过程。结果表明,当西太平洋东部的偏东风突然减弱,并转变为偏西风时,能引起太平洋东部海面高度及温度的升高。该非线性浅水模式及相应的线性浅水模式都较成功地模拟了中东太平洋大范围增暖的这类广义El Ninño事件^[1]。试验结果还表明,东部海域海面高度的升高及增暖强度与西部海域西风的强度、持续时间和扩展的范围有关,即海域西部西风愈强、持续时间愈久、扩大范围愈大,产生的El Ninño就愈强。并对用线性模式得到的结果同用非线性模式的结果进行比较,结果表明非线性平流项能影响波的传播速度,使得逆基本气流传播的波的传播速度减慢,而非线性平流项对形成El Ninño这种行星尺度的超低频事件所起的作用可能不大。     

Ningaloo Niño/Niña与华南冬季降水异常的联系

利用1979—2017年逐月平均的NOAA ERSST V3b海表温度资料、CN05.1降水资料以及NCEP/NCAR大气再分析资料,分析了Ningaloo Niño/Niña的基本特征及其与华南冬季降水异常的联系。结果表明,Ningaloo Niño/Niña是副热带东印度洋海温异常EOF第一模态,具有明显的年际变化特征和季节锁相特性。在扣除El Niño/La Niña的影响后,Ningaloo Niño/Niña与华南冬季降水异常存在着密切的联系,即Ningaloo Niño(Niña)年时,华南地区冬季降水增多(减少)。这种影响的可能机制是:Ningaloo Niño/Niña通过影响南支槽的强度变化进而影响华南冬季降水异常。Ningaloo Niño年冬季,澳大利亚西侧海表温度升高,对流增强,使南半球80°~100°E附近的Hadley环流上升支增强,造成经向环流异常,北半球低纬度地区形成一个异常的反环流圈,导致南支槽的增强。南支槽的强度与华南冬季降水呈正相关关系,南支槽强度偏强时,活跃的扰动向下游传播,槽前盛行的西南气流使得充足的水汽自孟加拉湾由西南向东北方向输入,为华南冬季降水偏多提供了条件,Ningaloo Niña年份的情形则与之相反。     

利用热带测雨卫星的测雨雷达资料对1997/1998年ElNio后期热带太平洋降水结构的研究

利用热带测雨卫星的测雨雷达 (TRMMPR)的探测结果 ,对 1 997 1 998年ElNin～o后期热带太平洋的降水结构进行了研究 ,并对比了非ElNin～o的 1 999年和 2 0 0 0年的同期降水情况 ,取得如下结果 :( 1 ) 1 997 1 998ElNin～o后期与非ElNin～o期间相比 ,1 997 1 998ElNin～o后期 ,热带东、中太平洋层云降水和对流云降水的比例明显增大、平均降水率也增大 ,并且层云强降水的比例增多 ,而层云弱降水比例减少。 ( 2 )在非ElNin～o期间 ,热带东、中太平洋对流云降水系统较为浅薄 ,冻结层高度比西太平洋低约 0 5km ;而在 1 997 1 998ElNin～o后期 ,这种差异明显减小 ,热带东、中太平洋对流云降水和层云降水都变得深厚 ;对流云降水和层云降水的降水率随高度的变化也发生了变化。 ( 3)对大气环流的分析表明 ,对应于降水结构的变化 ,热带太平洋地区的高空辐合辐散分布也发生了改变 ,导致Walker环流在 1 997 1 998ElNin～o后期减弱。     

1998年7月21日武汉特大暴雨的数值模拟

利用16层中尺度η坐标模式对1998年7月21日武汉特大暴雨进行了数值模拟，结果表明：本次暴雨过程具有较强的中尺度特征，暴雨区上空中、低层近东西向的切变线及其强烈的辐合是暴雨产生的触发机制，西南水汽的输送以及层结不稳定也对暴雨的产生有重要作用。     

"01.19"区域暴雪天气过程的数值诊断分析

对2006年1月18日-19日山西中南部区域暴雪天气过程从垂直环流结构、形成机制、螺旋度数值诊断等方面进行了分析,得出：暴雪发生在高空极涡加强南压期间,北路强冷空气直灌山西,受700hPa西北涡东移影响所致。暴雪区上空,垂直螺旋度柱为上正下负,正螺旋度柱的两个中心分别位于300hPa和500hPa,在500hPa出现了强度高达14×10^-6m·s^-2的强中心,负螺旋度柱中心相对较弱。垂直螺旋度强度的变化对暴雪的出现有明显指示意义。涡散场的分布存在“高空辐散、低层辐合”的垂直配置,暴雪出现在500hPa涡度梯度最大的地方,暴雪出现12h后,正涡度中心强度迅速增强,对应暴雪出现一个增幅期。暴雪区上空,锋面坡度较大,湿层厚度达到600hPa左右,整个系统深厚稳定。低空、超低空急流的存在,不仅为暴雪提供了水汽来源和热量输送,而且使得重力惯性波不稳定发展,是强降雪的重要触发机制。     

中国东部夏季分区降水对海温异常响应特征的研究

用刘征宇最新发展的广义平衡反馈方法结合经验正交分析和旋转经验正交分析法,研究中国东部6个分区夏季降水异常对各海盆海温异常(SSTA)模态的响应特征,探讨了东北区降水异常对SSTA的响应机制。结果表明:各分区降水异常对SSTA的响应特征有明显差异。东北区降水异常对热带太平洋SSTA的回应显著,当SSTA表现为类似El Niño模时,该区夏季降水增加;江淮区降水异常同时受到中纬度以及热带SSTA的强迫,对热带太平洋SSTA的类似La Niña Modoki模、北大西洋SSTA三极型模等回应显著;西南地区的降水异常主要与中纬度SSTA有密切关联。对流层高度场对热带太平洋SSTA类似El Niño模的直接回应在热带太平洋上空为显著正异常。通过东亚—太平洋型遥相关波列使东北地区上空高度场出现负异常,并在其西侧形成负异常中心,对流层低层为气旋性环流异常。这一环流回应与东北地区夏季降水偏多时的环流特征相近。     

春季厄尔尼诺快速衰减对华北夏季降水的影响

利用再分析的陆地降水、环流和辐射数据,以及表征大气波动的指数,对比了1951—2020年期间El Niño春季快速衰减年和缓慢衰减年的东亚环流和华北夏季降水异常情况,并从大气波动强度的角度探讨了为何El Niño在一些年份的春季会发生快速衰减。结果表明,相较于其他不发生El Niño衰减的年份,El Niño春季快速衰减年华北7、8月的降水量显著偏多,尤其是8月;而El Niño缓慢衰减年夏季,华北降水相较其他年份偏多不明显。El Niño春季快速衰减年6—8月850 hPa上菲律宾到南海存在异常反气旋,其强度强于El Niño缓慢衰减年;El Niño春季快速衰减年8月500 hPa西太平洋副热带高压(西太副高)显著偏北,而缓慢衰减年西太副高偏北的特征不明显,而是以偏西为主;200 hPa副热带西风急流在El Niño春季快速衰减年8月显著偏北,而在El Niño缓慢衰减年中反而略偏南;El Niño春季快速衰减年6—8月沃克环流显著偏强,相比之下El Niño缓慢衰减年沃克环流偏强的特征要弱很多。上述环流异常特征为El Niño春季快速衰减年华北7—8月降水异常偏多提供了有利条件。通过近地面风场合成分析发现,春季El Niño快速衰减月前后,赤道中西太平洋异常东风爆发非常明显,而El Niño缓慢衰减年的异常东风信号较弱。春季El Niño快速衰减前印度洋对流活动非常强盛,并向海洋性大陆传播,这种对流可能通过不断激发大气波动,继而引发近地面东风爆发,最终导致El Niño出现快速衰减。     

南海秋雨气候特征分析

用台站观测逐日降水资料和热带测雨卫星观测降水资料,对我国南海地区降水季节演变特征分析发现,与我国大部分地区不同,南海地区降水季节峰值是在秋季,主要集中在8～10月,且降水量年际变化大。环流场的合成分析表明,南海地区秋季中层500 hPa有利的副高位置和低层低压系统的活动和维持是形成这一地区显著秋雨的主要原因。而由于副高的位置受热带太平洋海温影响较大,分析发现Niño3.4的海温指数对该区域降水有很好的指示意义。8～10月Niño3.4指数和同期海南岛站点平均降水量之间的相关能够达到－0.47,超前3个月 (即5～7月)的Niño3.4指数与8～10月海南岛站点平均降水量的相关亦能达到－0.43。从跨季度气候预测的角度来考虑,5～7月的Niño3.4指数可以作为预测8～10月南海秋雨的重要参考指标。     

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.     

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