1998年青藏高原大气低频振荡的结构特征分析

使用ＮＣＥＰ／ＮＣＡＲ再分析的逐日资料,研究了１９９８年夏季青藏高原大气低频振荡的结构特征。结果表明：不同低频频率的遥相关水平结构既有相似的波列结构,也存在相异的特征。高原主体的低频振荡为相当正压结构,低频降水一般位于低频气旋性环流及低频气流辐合带内,利用高原低频降水可提前预测江南及高原南部的低频降水活动,高原和长江中下游及东北地区的低频水存在同时加强和同时减弱的关系。     

青藏高原西部地表热通量输送的低频特征

以1997年9月-1998年10月青藏高原西部改则地区自动气象站(AWS)近地层连续观测的梯度资料为基础,计算了高原西部地面感热通量、蒸发潜热通量及地面热源强度,应用Marr小波变换重点分析了地表热通量输送以及与此相关的降水量、土壤湿度和土壤热通量的周期振荡特征.结果表明:地面感热具有明显的30～60天低频振荡,并且在夏季存在准8天的中期振荡;蒸发潜热和降水量以准双周振荡为主.土壤热通量以30～50天低频振荡为主,夏季还存在准8天的中期振荡;土壤湿度在冬季呈现明显的30～50天低频振荡,夏季则为20～30天的低频振荡.     

青藏高原夏季高层纬向风季节内振荡特征

利用1979—2019年ECMWF提供的ERA-Interim逐日再分析资料,采用Morlet小波分析、滤波及合成分析等方法,探究了青藏高原夏季对流层高层纬向风季节内振荡（IntraSeasonal Oscillation,ISO）的主要周期及其传播特征。结果表明：青藏高原夏季高层纬向风季节内振荡的主要周期为10～30 d,其强度存在明显的年际差异。在纬向风ISO强年,振荡过程持续时间长、振幅强,ISO方差中心从对流层高层向下影响到对流层中层,表现为相当正压结构。其传播在纬向上主要表现为ISO中心从高原东部3次向东传,可达西太平洋地区;经向上分别有4次自中高纬向南传播的10～30 d ISO中心与来自低纬地区的ISO中心在高原南侧汇合,其强度在高原南侧有所加强,强振荡中心可向南传播到达低纬地区。ISO的位相演变主要表现为低频反气旋和低频气旋中心在高原东部交替出现,引起东部地区上空低频东风和低频西风的强度变化。在ISO极端活跃位相,高原东部低频西风达最强。     

夏季青藏高原大气热源低频振荡与南亚高压东西振荡的关系

利用1983～2012年NCEP/NCAR逐日再分析资料对夏季青藏高原大气热源和南亚高压东西振荡的低频特征以及两者的关系进行了讨论,发现夏季青藏高原东部大气热源与南亚高压纬向运动的主要低频周期都是10～20 d。在高原东部大气热源10～20 d振荡峰值位相,青藏高原上空被低频气旋控制,高原西部被低频反气旋控制,导致南亚高压主要高压中心向西移动呈伊朗高压模态;在大气热源10～20 d振荡谷值位相,低频环流形势完全相反,青藏高原上空被低频反气旋控制,高原西部被低频气旋控制,致使南亚高压主要高压中心向东移动呈青藏高压模态。高原热力场异常导致其上空暖中心变化从而引起的高层风场变化可以解释南亚高压的东西振荡。     

新疆夏季降水偏多（少）同期环流特征分析

利用美国ＮＣＥＰ／ＮＣＡＲ全球网格点再分析资料,从大气环流角度系统地分析了１９７９～１９９５年夏季（６～８月）新疆出现降水偏多或偏少时北半球范围内平流层下部（１００ｈｐａ）和对流层中部（５００ｈｐａ）的平均环流形势。结果表明新疆夏季降水偏多或偏少同期具有各自较为显著的环流特征;最后选取１９９６年夏季和１９９８年夏季两个典型个例加以补充说明。     

1998年夏季青藏高原及其邻近地区低频降水分布和传播特征

使用１９９８年美国ＮＣＥＰ再分析的逐日资料,研究了１９９８年夏季青藏高原及其邻近地区低频降水的分布和传播特征,结果表明：青藏高原及其邻近地区的低频降水量和时间变化方差对总降水量及其变化方差均具有重要贡献,因此研究高原地区低频降水的分布、发生、发展及其传播特征具有重要意义,高原东侧的低频降水主要由东向西传播,而南侧主要由南向北传播,但很少直接进入高原。高原中南部和东南部可能是高原地区的频降水的发生源     

热带对流活动与长江中下游和华北地区夏季旱涝的关系

利用ＯＬＰ资料,结合ＮＣＥＰ／ＮＣＡＲ再分析资料,研究了长江中下游、华北地区旱、涝年热带对流活动特征,着重讨论了ＩＴＣＺ位置、季节内低频振荡与两地区旱、涝气候异常的联系,结果发现：１月赤道太平洋上对流活动的异常与夏季两地区旱涝有密切的关系,冬季赤道太平洋对流活动东强西弱（东弱西强）,则对应夏季长江中下游地区易偏涝（旱）,华北地区锡偏旱（涝）;ＩＴＣＺ的位置异常偏南（北）时,夏季长江中下游地区易偏涝     

夏季东亚副热带西风急流的季节内变化及其与我国东部降水的关系

利用ERA-interim再分析资料和中国降水观测数据,分析了夏季东亚副热带西风急流的季节内变化以及对我国降水的可能影响,结果表明:亚洲地区夏季200 hPa纬向风在空间上主要表现为南北振荡和东西振荡特征,在时间上具有10～40 d的周期;在低频尺度(10～40 d)上,纬向风异常由西北先向东传播,到达东亚地区后再向南传播;伴随低频纬向风季节内演变,高原以北的急流中心向东和东南移动,急流轴也呈现南北振荡的特征;降水异常对200 hPa风场低频振荡有显著响应,在东亚地区,低频纬向风与低频降水南移,降水在黄淮地区出现,并逐渐移至长江及其以南地区;急流附近的低频西(东)风异常在其南侧形成负(正)切变涡度,对应我国东部地区位势高度的升高(降低),使得南亚高压东伸(西退),从而使我国东部雨带的位置发生显著变化。     

中高纬度垂直环流的低频振荡与华北地区夏季干旱初探

用国家气象中心１９９２年６月１０日至７月２３日Ｔ４２中期数值预报模式格点资料，分析了中高纬度夏季垂直环流的低频振荡。发现中高纬度纬向垂直环流与热带纬向环流不同存在着２０－４０天的局地低频振荡，在热带季风中断时，３５－４５°Ｎ范围内中高纬度纬向垂直环流主要表现为１２０°Ｅ附近区域内下沉气流加强。初步探讨了中高纬度地区经圈环流的低频振荡，所选范围为１００－１２０°Ｅ平均低频经向环流，热带季风中断时，下沉气流在３０－４０°Ｎ区域内加强。通过对中高纬度地区垂直环而的低频振荡的分析，探讨了中高纬度地区垂直环流的低频振荡与华北地区夏季干旱的可能联系。由于热带季风中断时，主要降雨带位于我国江淮一带，此时垂直环流表现为在对流层低层２８°Ｎ左右范围内为上升运动区，在３５－４５°Ｎ区域附近内下沉气流加强，即我国华北地区上空盛行下沉气流，对应于该地区干旱、少雨。     

1997—1998年青藏高原大气低频振荡及对降水影响

利用1979—1998年NCEP/DOE逐日再分析资料和国家气象信息中心的常规观测站资料,研究了1997/1998年冬季、1998年夏季青藏高原 (简称高原) 季风的低频振荡特征,研究夏季高原和周边区域高低层大气低频环流系统的配置及其与我国降水的联系。结果表明:1997/1998年冬季和1998年夏季,高原季风不仅表现出很强的30~60 d的周期振荡特征,还伴随有较强的准双周低频振荡;相应区域对流层上层200 hPa上的环流系统则是30~60 d为主的周期变化。1998年夏季,高原地面气压也存在两个频带的低频振荡变化,且其强度存在明显的经向变化,即自南向北30~60 d低频振荡信号有逐渐减弱趋势,准双周信号则呈增强趋势。对30~60 d的低频信号而言,高原夏季风低频信号较强 (弱) 时,高原地面表现为低频低 (高) 压环流系统,在同纬度带的我国东部地区和西太平洋沿岸,是较强的低频北 (南) 风和低 (高) 压环流系统;相应地,在80°~90°E之间,自孟加拉湾到我国西北中部地区,是低频反气旋-气旋-反气旋的经向低频波列;受低频环流系统影响,高原东部、长江中下游地区降水偏多 (少)、川西高原、云南西南部降水偏少 (多)。     

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