2012年8月大气环流和天气分析

2012年8月环流特征如下：北半球极涡呈单极型分布,中心略偏于东半球,强度较常年偏强;北半球高纬度环流呈5波型分布;西太平洋副热带高压较常年偏北偏西。2012年8月,全国平均气温为21．4℃,较常年同期（20．8℃）偏高0．6℃。全国平均降水量92．1mm,较常年同期（105．1mm）偏少12．4％。月内共出现8次降水过程;西北太平洋有7个热带气旋活动,有5个热带气旋登陆我国,另外,热带气旋布拉万对我国东北地区造成严重影响;江南、华南、江汉、四川盆地及新疆等地出现高温天气;19个省（市、区）遭受风雹灾害。     

2015年8月大气环流和天气分析

2015年8月环流特征如下：北半球高纬地区极涡呈偏心型分布,亚洲中高纬度为两槽一脊环流形势,槽脊强度均强于常年同期;西太平洋副热带高压强度接近常年略偏强,位置偏西、偏南。8月全国平均降水量105.1 mm,接近常年同期（105.3 mm）;全国平均气温为21.1℃,较常年同期（20.8℃）偏高0.3℃,上旬,江淮及其以南地区出现大范围持续高温。月内共出现5次主要区域性暴雨过程。8月共有4个热带气旋（风力8级以上）在西北太平洋和南海活动,其中,第13号台风苏迪罗登陆我国,台风生成和登陆个数均偏少。华北、西北地区东部及内蒙古中部等地气象干旱持续发展。全国多个省（区、市）遭受风雹灾害。     

2016年8月大气环流和天气分析

2016年8月环流特征如下：北半球极涡呈单极型分布,强度偏强;亚洲大陆中、高纬为两槽一脊型;西北太平洋副热带高压位置明显偏东偏北、强度偏弱,大陆高压偏强。8月全国平均降水93.9 mm,较常年同期（105.7 mm）偏少11.2%;全国平均气温22℃,较常年同期（20.8℃）偏高1.2℃,为1961年以来历史同期最高,全国大部地区气温偏高。月内共出现了6次主要的区域性强降水过程,其中4次是由热带气旋或热带辐合带活动引起。8月共有8个热带气旋（风力8级以上）在西北太平洋和南海海域活动,其中1604号台风妮妲和1608号台风电母登陆华南沿海。月内,我国中东部地区出现大范围持续高温天气,东北地区西部和内蒙古东部气象干旱持续。     

2011年9月大气环流和天气分析

2011年9月大气环流主要特征如下：极涡呈单极型,中心略偏向西半球,中高纬度环流呈5波形分布,槽区分别位于北太平洋东北部、北美洲东部、北大西洋北部、欧洲东部、亚洲东北部。北太平洋东北部上空500 hPa高度场上有160 gpm的负距平。西北太平洋副热带高压面积较常年同期偏小,强度偏弱,西脊点位置偏东,脊线偏北。2011年9月全国平均气温16.4℃,比常年同期（16.0℃）偏高0.4℃;全国降水量为65.0 mm,接近常年同期（65.3 mm）。月内出现了3次较明显的冷空气过程和7次降水过程,有7个台风生成,其中＂纳沙＂登陆我国,造成重大灾害。     

2018年6月大气环流和天气分析

2018年6月环流特征如下：北半球高纬地区极涡呈单极型分布且偏强,亚洲中高纬度为两槽一脊环流形势,槽脊强度均强于常年同期;西太平洋副热带高压位置明显偏东,强度略偏强;南海夏季风于6月第二候爆发,较常年偏晚3候且季风槽偏弱。6月全国平均降水量92.9 mm,较常年同期（99.3 mm）偏少6%;全国平均气温为20.9℃,较常年同期（20.0℃）偏高0.9℃。月内共出现4次主要区域性暴雨过程。6月共有3个热带气旋在西北太平洋和南海活动,其中,第四号台风艾云尼3次登陆我国。内蒙古、辽宁、河北北部等地气象干旱持续发展;下旬京津冀地区出现极端高温;全国多个省（区、市）遭受风雹灾害。     

2015年7月大气环流和天气分析

2015年7月环流特征如下：北半球极涡呈多极型,中高纬西风呈5波型分布。西太平洋副热带高压强度偏强。7月全国平均降水量88.7 mm,较常年同期偏少26.5%,为1951年来历史同期最少;全国平均气温为22.1℃,较常年同期偏高0.2℃。月内共出现7次主要降水过程,多站出现极端日降水量。7月共有5个热带气旋在西北太平洋和南海活动,生成个数与常年同期基本持平,并有2个台风(莲花和灿鸿)在我国登陆。新疆出现持续高温天气;华北、黄淮等地出现气象干旱;全国24个省（区、市）遭受风雹灾害。     

2014年7月大气环流和天气分析

提2014年7月环流特征如下：北半球高纬地区为单一极涡,中高纬地区呈5波型分布,巴尔喀什湖附近低槽和东亚大槽强度均较常年偏强;西北太平洋副热带高压带呈东西带状分布,强度与常年同期相当。7月全国平均降水量115．0 mm,较常年同期（120．6 mm）偏少4．6％;全国平均气温为22．3℃,较常年同期（21．9℃）偏高0．4℃。月内共出现8次强降水过程,多站出现极端日降水量。7月共有5个热带气旋（风力8级以上）在西北太平洋和南海活动,生成个数较常年偏多,并有“威马逊”、“麦德姆”2个热带气旋登陆。华南、江南等地出现持续高温天气,全国87个气象观测站发生极端高温事件,74站发生极端日降水量事件。     

2011年7月大气环流和天气分析

2011年7月环流特征如下：北半球高纬度地区极涡呈多极型分布,西太平洋副热带高压较常年偏弱,欧亚中高纬盛行纬向环流,多短波槽活动。7月,全国平均降水量为105.8 mm,较常年同期（115.9mm）偏少8.7%。全国平均气温为22.1℃,较常年同期（21.4℃）偏高0.7℃。月内,我国主要天气气候事件有：全国共出现7次强降水过程,但没有发生大范围持续性的严重洪涝灾害;4个热带气旋生成但只有一个登陆我国;新疆、内蒙占西部、江南、华南、江汉、江淮、黄淮、华北等地相继出现高温天气。     

2019年9月大气环流和天气分析

2019年9月环流特征如下:北半球极涡呈单极型分布,强度偏弱;亚洲大陆中高纬为两槽一脊型;西北太平洋副热带高压明显偏西、偏强。9月全国平均降水量62.4 mm,较常年同期(65.3 mm)偏少4%;全国平均气温为17.7℃,较常年同期(16.6℃)偏高1.1℃。月内共出现了4次主要的区域性强降水过程,其中2次降水活动与台风有关。共有6个台风在西北太平洋和南海海域活动,无台风登陆我国。月内,华西秋雨南区开始偏早,影响显著;长江中下游气象干旱持续发展;江南、华南北部和华北部分地区出现高温天气;黑龙江、内蒙占等多地遭受风雹灾害;黑龙江和内蒙古部分地区遭低温冷冻灾害。     

2010年8月大气环流和天气分析

2010年8月大气环流主要特征如下:极涡呈单极型,中心略偏于东半球。北半球高纬度环流呈4波型分布,欧洲西北部、新地岛附近为低于-40 gpm负距平所控制。西北太平洋副热带高压面积较常年同期偏大,强度显著偏强,位置异常偏西。2010年8月,全国平均气温为21.4℃,比常年同期(20.3℃)偏高1.1℃。全国平均降水量为108.1 mm,比常年同期(102.6 mm)偏多5.5 mm。月内出现了14次降水过程,共有5个热带风暴生成,其中1008号热带风暴南川在福建登陆。江淮、江南、华南北部、重庆、四川东部及新疆南部等地高温日数异常偏多。     

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.     

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.     

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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     

A Brief Introduction to Marine Meteorological Science Experiment Base at Bohe Town,Maoming City,Guangdong Province

<正>With the support of specialized funds for national science institutions,the Guangzhou Institute of Tropical and Marine Meteorology,China Meteorological Administration set up in October 2008 an experiment base for marine meteorology and a number of observation systems for the coastal boundary layer,air-sea flux,marine environmental elements,and basic meteorological elements at Bohe town,Maoming city,Guangdong province,in the northern part of the South China Sea.     

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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 AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences