细粒子污染形成灰霾天气导致广州地区能见度下降

用NCAR/NCEP1958～1997年共40年资料对南海夏季风撤退的气候特征进行了分析。8月上旬西伯利亚冷空气开始南进,由于青藏高原的阻挡作用,在我国东部大陆推进得很快,到达南海后继续向南推进,最后导致9月中旬左右南海夏季风从南海撤退。就个别年份而言,最早的撤退时间是8月中,最晚的是10月中,可以差两个月。南海夏季风撤退与建立过程是很不相同的,南海夏季风和夏季风雨带的建立都是爆发性的,在全区域几乎是同时建立,但撤退是由北向南缓慢撤退的,历时一个月左右。在撤退期间,南海降水形势变化不大,但在撤退之后,南海夏季风雨季转变为ITCZ雨季,其相应和雨区随着太阳南移向南推进。南海夏季风撤退后,南海降水30～60天振荡明显减弱,而准两周振荡仍比较活跃。     

南海夏季风撤退期的气候特征Ⅰ——40年平均

用NCAR/NCEP1958～1997年共40年资料对南海夏季风撤退的气候特征进行了分析.8月上旬西伯利亚冷空气开始南进,由于青藏高原的阻挡作用,在我国东部大陆推进得很快,到达南海后继续向南推进,最后导致9月中旬左右南海夏季风从南海撤退.就个别年份而言,最早的撤退时间是8月中,最晚的是10月中,可以差两个月.南海夏季风撤退与建立过程是很不相同的,南海夏季风和夏季风雨带的建立都是爆发性的,在全区域几乎是同时建立,但撤退是由北向南缓慢撤退的,历时一个月左右.在撤退期间,南海降水形势变化不大,但在撤退之后,南海夏季风雨季转变为ITCZ雨季,其相应和雨区随着太阳南移向南推进.南海夏季风撤退后,南海降水30～60天振荡明显减弱,而准两周振荡仍比较活跃.     

2006年东亚夏季风活动特征与我国东部雨带分布

利用1979—2006年NCEP/NCAR大气月平均资料、OLR对流和CMAP降水日平均资料,从季节平均、月平均、季节内振荡不同时间尺度分析了2006年东亚夏季风活动特征及其与雨带分布之间的联系。结果表明,2006年东亚夏季风爆发时间正常,而夏季风推进过程存在异常：前沿在华南地区和华北地区维持时间偏长、在长江流域维持时间偏短,夏季风极端北界偏北,这种推进异常与南海夏季风强度偏强有关。南海夏季风强度偏强及推进过程异常导致东亚夏季(6—8月)降水为Ⅰ类雨带分布,即长江流域降水偏少,华南、黄淮流域-朝鲜半岛-日本中南部降水偏多。从月时间尺度看,2006夏季各月都具有南海地区夏季风强度偏强、前沿位置偏北和偏东的异常趋势;西太平洋副热带高压6月偏西偏南,7、8月偏北,在这种异常形势下,长江流域6、7、8各月降水都偏少,华南地区各月以偏多为主,黄淮流域7、8月降水偏多。从季节内振荡看,2006年大气季节内振荡(ISO)纬向传播与气候平均相比具有特殊性,长江流域纬度带西传波和静止波偏弱,华南地区纬度带东传波和静止波偏强,ISO这种异常与夏季长江流域降水偏少、华南降水偏多有关。     

南海夏季风撤退的气候特征Ⅱ——年代际变化

南海地区夏季风撤退期有明显的年代际变化,与南海夏季风维持期相类似,在1970年代末期有明显的突变。所以分析工作以1978年为界,主要是将前20年情况与后20年进行对比。前20年夏季风撤退较早,撤退期降水较少,对流活动较弱;后20年则与此相反,夏季风撤退较晚,撤退期降水较多,对流活动较强。南海地区夏季风撤退期的年代际变化与PDO和太阳磁循环的气候变化比较一致。     

基于QuikSCAT资料的江淮流域旱涝年南海季风变化特征

利用2001、2003年的QuikSCAT风场和中国降水的逐日资料,分析江淮流域旱、涝年南海夏季风的演变特征及其低频分量与江淮流域降水的关系。结果表明:（1） 2001、2003年南海夏季风爆发时间相当,但2003年6月中下旬季风出现明显的中断,2001年6—7月南海季风表现出明显的由南海中南部向北部推进的过程,而2003年同时期的季风则徘徊于南海中南部地区;（2） 2001、2003年的夏季(5—9月)海表面的低频纬向风场同时都存在3对低频振荡中心,且在季风爆发后均有明显的向北传播特征,南海中部和北部表现出近乎相反的低频位相,但2001年低频振荡的强度及低频波列维持的时间均大于2003年的;（3） 根据纬向风低频振荡强中心区域的位置,在南海中部和北部分别定义了南海低频夏季风指数IM-SCS和IN-SCS,发现这两个指数与我国6—7月江淮流域的降水及青藏高原中东部降水之间均存在显著的滞后负相关关系,而与云南中部、西部及华北部分地区的降水则表现出显著的滞后正相关关系。      

1998年南海夏季风低频振荡特征分析

利用NCEP/NCAR1998年再分析资料和SST资料，研究了南海夏季风的低频振荡特征。结果表明，南海夏季风的低频振荡对南海夏季风的爆发具有加强的作用；南海低频低层辐合（散）区对应低频降水正（负）值区；南海地区的大气低频振荡以向北、向东传播为主，南海地区低频散度在垂直方向呈现出相互补偿的特征。     

1998年南海夏季风建立前后的突变特征及爆发过程

利用南海季风试验所得到的最新资料分析了１９９８年南海夏季风建立前后的突变特征及其爆发过程,初步认定１９９８年亚洲夏季风最早（５月２３日）在南海地区建立,它是亚洲冬季风形势向夏季风形势转换的最早体现。副高从南海地区连续东撤是南海地区夏季风建立的直接过程,它的撤出有利于不稳定能量的释放,形成南海夏季风的爆发性。提出赤道印度洋地区的西风和降水向中南半岛地区扩展、华南静止锋活跃南压,这种形式的中低纬相互作     

关于东亚副热带季风和热带季风的再认识

利用NCEP/NCAR再分析数据集和CMAP(Climate Prediction Center Merged Analysis of Precipitation)降水资料, 分析了东亚副热带夏季风与热带夏季风的区别和联系, 以及两者相互作用问题, 深入讨论了东亚副热带季风的本质。分析发现东亚副热带夏季风建立早于热带夏季风, 于3月中旬已经开始建立。两者是相互独立的两个过程, 前者并非是后者向北推进的结果；相反, 前者建立后的突然南压有利于后者的爆发。副热带夏季风为渐进式建立, 但撤退迅速；热带夏季风爆发突然, 但撤退缓慢。副热带夏季风的建立以偏南风的建立为特征, 而热带夏季风的建立以偏东风向偏西风转变为特征。热带夏季风的建立时间取决于经向海陆热力差异转向, 而东亚副热带夏季风则更依赖于纬向海陆热力差异的逆转。亚洲大陆（含青藏高原）与西太平洋之间的纬向海陆热力差异的季节逆转无论对东亚副热带夏季风还是热带夏季风均有重要作用。     

大气环流的变化与南海夏季风活动的关系

通过对近20年观测资料的计算分析表明，在南海夏季风活跃与中断期，南北半球副热带西风急流和热带东风急流以及青藏高压和墨西哥高压有明显的差异。从南半球向北传播的散度场低频振荡以及从北半球高纬向南传播的西风场低频振荡等的有利位相同时传入南海并共同作用可引起南海夏季风的活跃或中断。各种低频振荡的有利位相传播到南海并发生锁相的时间决定着南海夏季风明显的活跃或中断发生的时间。     

基于MTM-SVD方法的西南地区降水季节内振荡特征分析

利用1981-2010年中国西南地区气象站点逐日降水资料以及NCEP/NCAR逐日再分析资料,使用MTM-SVD方法分析了西南地区降水的季节内振荡特征,结果表明:西南地区降水存在显著的14.4候(70天左右)振荡周期,该季节内振荡在1985年前后最强,在整个研究时段内夏季更明显。典型循环重建表明,西南地区降水的季节内振荡整体上有一个从南向北的推进过程,对OLR的分析表明,南海—西太平洋地区和孟加拉湾地区是影响西南地区降水的两个关键区。在季节内振荡尺度上影响西南地区降水的OLR异常信号首先出现在爪哇岛附近,逐渐向东传播到马鲁古群岛地区,然后北跳传播到北半球的南海—西太平洋地区和孟加拉湾地区,最后两者先后向北推进影响西南地区降水。     

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.     

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     

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.     

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.     

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.     

Information for Authors

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.     

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.     

INFORMATION FOR AUTHORS

正Aims Scope Advances in Atmospheric Sciences(AAS)is an international journal on the dynamics,physics,and chemistry of the atmosphere and ocean with papers across the full range of the atmospheric sciences,co-published bimonthly by Science Press and Springer.The journal includes Articles,Note and Correspondence,and Letters.Contributions from all over the world are welcome.