低纬平均经圈环流异常与海表温度异常关系的诊断分析

利用NCEP/NCAR的40年大气再分析资料中的月平均经向风速及垂直速度，计算了纬向平均经圈环流的质量流函数，分析了纬向平均的海表温度和纬向平均的经圈环流的气候态及异常态特征，结果表明，（1）南、北半球Hadley环流圈的共同上升支偏于赤道附近的夏半球一侧，与[SST↑-]极大值位置相对应；强下沉支位于冬半球一侧；（2）El Nino事件中低纬[SST]′是异常经圈环流产生的重要外强迫源，但其影响程度受基本气流和[SST↑-]及[SST]′的季节变化和年际差异的影响甚大。     

经圈环流对定常波传播的影响

在一般斜压大气中，基本气流中包含经圈环流时，定常波传播不仅能穿过东风带，而且明显增强。在基流含有经圈环流的情况下，北半球中纬度地形强迫可引起低纬大气的显著响应，这表明经圈环流在中低纬定常响应的相互联系中起着重要作用；北半球中纬度热力强迫可产生类似北半球夏季季风环流的波列分布，这说明经圈环流在夏季季风环流的形成中起着一定的作用；在赤道东太平洋加热强迫情况下，在冬半球可引起ＰＮＡ型的定常波传播波列，而在夏半球却没有明显的ＰＮＡ特征。这表明经圈环流对冬、夏半球的定常波传播路径有着显著的影响。     

ECMWF预报模式在不同地形方案下的系统误差检验

Wallace等的研究表明,由于引进了包络地形方案,欧洲中期天气预报中心(ECMWF)的中期天气预报有所改善。本文是上述工作的继续。所用的资料为原作者的数值试验结果。检验的对象包括纬向平均风场、温度场和经圈环流,及不同波数域中的涡旋和经圈环流对角动量的平均经向输送。结果表明,在冬季,包络地形方案对低纬地区的温度场和风场的预报略有改进,对总涡旋动量通量的模拟也较好。然而对天气尺度系统的预报和对热带对流及积云摩擦的参数化却有待更进一步改善。     

平均经圈环流质量流函数两种计算方案的比较

质量流函数(Φ)是直观、定量描述纬向平均经圈环流的物理量。用相同格点网、相同资料(1958-1998年NCEP／NCAR再分析资料)比较了迭代方案、叠加方案求得Φ在描述平均经圈环流气候态、强El Nino年异常态以及Hadley环流双层结构时的异同。比较表明，二者计算结果间不存在明显差异；但叠加方案只用v资料，计算也简单。     

季风指数及其年际变化I·环流强度指数

季风环流可以分解为经向环流和纬向环流。使用NCEP和ECMWF再分析资料,计算亚洲季风区的经向动量环流和纬向动量环流强度的季节内和年际变化,结果表明:对于南亚夏季风和东南亚-西太平洋夏季风,其各自的经向环流和纬向环流的季节内变化和年际变化存在着相当的联系,尤其东南亚-西太平洋夏季风。但南亚夏季风的经向环流和纬向环流的年际变化在不同月份有着不同的关系。对于东亚夏季风,经向环流和纬向环流变化之间的相关在季节内尺度上是线性独立的,而在年际尺度上存在一定的联系。作者指出:这种大尺度上的联系是通过科里奥利力发生作用,并且受热源调节的。同时局地的对流和辐射相互作用则在某种程度上削弱这种联系,导致在不同月份相关程度有所不同。从各季风系统的经向环流之间或纬向环流之间的线性相关看,南亚夏季风,东亚夏季风和东南亚-西太平洋夏季风是相互独立的系统。计算表明,Webster-Yang和Wang-Fan分别提出的南亚夏季风指数在描述纬向环流年际变化上较好,而在经向上勉强令人满意。Wang-Fan提出的描述东南亚-西太平洋夏季风指数,则较好地表示了该区域的经向和纬向环流的年际变化。Goswami提出的季风Hadley环流指数,以及郭其蕴、施能等提出的东亚夏季风指数则较好地描述了相应区域的经向环流圈年际变化,却无法描述相应的纬向环流圈的年际变化。通过计算还表明,NCEP再分析资料和ECMWF再分析资料在1968年以前的南亚季风区和东亚季风区存在着较大的差异。用NCEP再分析资料计算东亚季风区和南亚季风区经向动量环流圈的变率在20世纪60年代较ECMWF的偏大。用NCEP再分析资料计算施能等定义的东亚季风区指数,也较使用ECMWF再分析资料、UCAR的DS010.1及CRU的北半球海平面气压资料计算的偏大。     

季风指数及其年际变化Ⅰ.环流强度指数

季风环流可以分解为经向环流和纬向环流.使用NCEP和ECMWF再分析资料,计算亚洲季风区的经向动量环流和纬向动量环流强度的季节内和年际变化,结果表明:对于南亚夏季风和东南亚-西太平洋夏季风,其各自的经向环流和纬向环流的季节内变化和年际变化存在着相当的联系,尤其东南亚-西太平洋夏季风.但南亚夏季风的经向环流和纬向环流的年际变化在不同月份有着不同的关系.对于东亚夏季风,经向环流和纬向环流变化之间的相关在季节内尺度上是线性独立的,而在年际尺度上存在一定的联系.作者指出:这种大尺度上的联系是通过科里奥利力发生作用,并且受热源调节的.同时局地的对流和辐射相互作用则在某种程度上削弱这种联系,导致在不同月份相关程度有所不同.从各季风系统的经向环流之间或纬向环流之间的线性相关看,南亚夏季风,东亚夏季风和东南亚-西太平洋夏季风是相互独立的系统.计算表明,Webster-Yang和Wang-Fan分别提出的南亚夏季风指数在描述纬向环流年际变化上较好,而在经向上勉强令人满意.Wang-Fan提出的描述东南亚-西太平洋夏季风指数,则较好地表示了该区域的经向和纬向环流的年际变化.Goswami提出的季风Hadley环流指数,以及郭其蕴、施能等提出的东亚夏季风指数则较好地描述了相应区域的经向环流圈年际变化,却无法描述相应的纬向环流圈的年际变化.通过计算还表明,NCEP再分析资料和ECMWF再分析资料在1968年以前的南亚季风区和东亚季风区存在着较大的差异.用NCEP再分析资料计算东亚季风区和南亚季风区经向动量环流圈的变率在20世纪60年代较ECMWF的偏大.用NCEP再分析资料计算施能等定义的东亚季风区指数,也较使用ECMWF再分析资料、UCAR的DS010.1及CRU的北半球海平面气压资料计算的偏大.     

南北两半球大气的相互作用和季风的本质

理性分析和利用NCEP/NCAR资料进行统计分析表明:大气环流的季节变化和越赤道气流即两半球的相互作用首先是由于赤道面与黄道面有交角而使太阳辐射有年变化所致,行星热对流环流是热带季风的"第一推动力",而地表面特性差异(海陆热力特性差异以及地形高度等)所导致的准定常行星波为"第二推动力".如以推动大气质量跨纬圈传输的效力来看,平均来说二推动力的功效之比为2:l.第二推动力在亚澳季风区与第一推动力合拍,使热带季风在亚澳区内最明显,而各经圈环流圈的上下及南北关联及与中高纬准定常行星波的配置则使全球范围内从低纬到高纬、从低空到高空有地域性的明显季节变化区,从而构成三度空间的全球季风系统.     

中纬度平均经圈和纬圈环流维持的物理过程(一)

本文主要从分解计算的角度,讨论中纬度平均经圈环流和纬圈环流的维持,并把动量和感热的涡动输送联系起来,说明它们之间的内在联系和统一的物理机理. 大尺度涡动输送、加强和摩擦等强迫作用不断造成纬向平均环流的热成风不平衡,而热成风调整过程又不断使不平衡向平衡调整.平均经圈环流就是在这种强迫变化和调整过程的相互作用中产生的.我们引进了一个由强迫变化决定的温度场、流场的时间变率向量M.时间变率向量M的旋度在x方向的投影等于强迫作用所造成的非热成风产生率,它也等于平均经圈环流向量的旋度在x方向的投影. 当连续方程采用B     

长江中下游地区春季连阴雨-连晴天气过程的中期振荡

本文对长江中下游地区1980年春季连阴雨-连晴天气过程及西风带、低纬赤道带和南半球天气系统的10个参数进行功率谱分析表明,它们都有准两周振荡的主要周期。交叉谱分析给出了连阴雨-连晴天气与10个参数在准两周振荡上的关联和相对振荡顺序。对连阴雨-连晴天气的时空背景纬圈及经圈环流的时空谱分析表明,纬向及经向环流振荡的两组传播波在准两周振荡上有较高的相干,经向传播超前于纬向传播。     

含经圈环流的基流的斜压不稳定

基本气流含有经圈环流的斜压不稳定充要条件为:K~2<2F和(U_sk+V_s1)~2>U_0k~2.因而,对纯经向基流也可以出现斜压不稳定。在西风基流和给定经向波数1>0情况下,正经圈环流使不稳定区域增大,反经圈环流使不稳定区域减小,而在东风基流情况下,特征相反。 含有经圈环流的基流的不稳定增长率随波数变化特征与纯纬向基流的情况有着显著的不同。     

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.     

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     

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.     

Information for Authors

正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.SUBMISSIONAll submitted     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.