Calculation of stratosphere–troposphere exchange in East Asia cut-off lows:cases from the Lagrangian perspective

本文使用三维非绝热朗格朗日轨迹模式OFFLINE3,对春末夏初东亚地区的切断低压所主导的双向平流层-对流层交换(STE)进行定量计算。通过对10个东亚地区切断低压的识别、计算、分析,发现切断低压附近发生平流层向对流层质量通量(STT)与对流层向平流层质量通量(TST)量级相当,但是分布范围不同:STT出现在低压中心西南部,最大通量位置出现在低压中心东南,TST最大值出现在槽前,并且从低压中心向外STT与TST交替分布。从本文所取的切断低压个例而言,切断低压产生的STT质量通量量级为10-4 kg m-2 s-1,促成的STE的净输送方向为从平流层向对流层,量级为10-4 kg m-2 s-1,比全球平均STE质量通量大1–2个量级。     

2001年春季临安地区对流层臭氧异常增加的一次过程分析

2001年春季在临安(30.30°N,119.75°E)进行的臭氧垂直探测发现,从3月25到31日有一次明显的臭氧异常增加过程,其中尤以29日和30日对流层上层的臭氧异常增加最具代表性.结合分析地面及高空气象要素演变和高空位势涡度的变化表明,这是一次显著的平流层空气由上向下穿过对流层顶深入对流层的下传过程,此平流层对流层交换过程与冷空气南下的天气过程和副热带急流、极锋急流移动造成的辐合下沉运动有着密切的联系.     

东亚地区平流层、对流层交换对臭氧分布影响的模拟研究

首先将区域酸沉降模式(RADM)进行改造,加入平流层化学模块以替代对流层模块.然后用MM5单向耦合改造后的化学模式M-RADM,对东亚地区一次切断低压(2000年4月8～12日)引起的对流层顶折叠对上对流层、下平流层臭氧分布形式的影响进行模拟.结果显示:(1)随着高空槽的发展与切断,高空槽的底部及切断低压四周臭氧有显著增加.对流层顶折叠使高空臭氧向下输送,这种向下的输送可以到达对流层中部,对上对流层的臭氧影响最大.(2)模式可以成功地模拟出在北京地区探测到的臭氧垂直廓线的双峰结构.250 hPa处的臭氧分压比背景值增加近5倍.模拟表明改造后的区域化学模式M-RADM可以用于研究天气过程引起的对流层顶附近臭氧的演变情况.(3)上对流层臭氧分布形势的变化主要是由动力过程中的水平平流作用引起的,但是对流层顶附近臭氧的化学过程是不可忽略的.     

2000年北半球平流层、对流层质量交换的季节变化

用2000年NCEP资料,P坐标下Wei公式诊断北半球平流层、对流层交换的季节变化.主要结论:(1)热带西太平洋是物质由对流层向平流层输送的主要通道,并有明显的季节性东西移动.由于2000年赤道辐合带偏弱,因此秋季通量最大.(2)中高纬度地区同时存在向上、向下的通量,大尺度槽区伴随着平流层向下的输送.一年中冬春季向下的输送强,夏秋季较弱,其季节变化与大尺度环流的季节性变化一致.(3)东亚地区存在很强的平流层向下输送,且中心位置移动不大.只占北半球5.6%面积的东亚其年净交换量竟占北半球的29%,这说明东亚地区的平流层与对流层之间的质量交换对北半球平流层、对流层交换研究的重要性.     

全球穿越对流层顶质量通量的时空变化特征

利用1958—2001年44年的ECMWF再分析值资料,采用Euler算法的Wei诊断模型,计算估计了全球平流层与对流层之间穿越对流层顶的质量通量(cross-tropopause flux,即CTF),并对其时空变化特征进行了分析。结果表明:(1)全球CTF的空间分布呈纬向型,且基本与全球经向环流相配合,其中对流层顶断裂带中向下的通量形势较复杂,南半球通量交换的空间变化较均匀,北半球有多峰结构的空间变化,东亚在全球的CTF中有重要作用。(2)南北半球热带对流层顶纬向平均向上的净通量极值分别在5°S为0.873×10-4kg.m-2.s-1和10°N为0.155×10-3kg.m-2.s-1;极地对流层顶向上和向下的通量极值对应在62.5°S为0.510×10-3kg.m-2.s-1,75°S是-0.365×10-3kg.m-2.s-1,55°N为0.257×10-3kg.m-2.s-1,75°N是-0.234×10-3kg.m-2.s-1,两极向上的通量极值在87.5°S为0.355×10-3kg.m-2.s-1,90°N为0.300×10-3kg.m-2.s-1;对流层顶断裂带中向下的净通量极值在35°S是-0.416×10-3kg.m-2.s-1,35°N为-0.333×10-3kg.m-2.s-1。(3)全球的净通量变化出现非对称性的季节波动,南半球和北半球净通量的季节与年际变化趋势完全相反,全球极地对流层顶控制区域的半球年平均质量交换量为-3.55×108Tg.a-1。(4)全球平均的CTF有显著的QBO特征,南北半球的年代际变化明显,特别是20世纪70年代中期至80年代中期出现了质量通量振幅的异常突变现象。     

不同类型和强度的东亚切断低压过程中UTLS区域臭氧变化对比分析

利用ERA-Interim高分辨率臭氧资料和NCEP再分析资料,对比分析了不同类型(浅薄型和深厚型)、不同强度(针对深厚型)的东亚切断低压过程中伴随平流层空气入侵引起的上对流层-下平流层UTLS(Upper Troposphere-Low er Stratosphere)区域臭氧变化情况,结果表明:(1)深厚型和浅薄型切断低压过程中均出现了平流层臭氧入侵现象。在300 h Pa上,存在浅薄型切断低压引起的臭氧增量与深厚型切断低压相当的情况。在垂直分布上,深厚型个例臭氧浓度升高范围集中在对流层中上层至平流层下层区域,而浅薄个例中的臭氧浓度上升只集中发生在对流层中上层。(2)切断低压引起的UTLS区域臭氧浓度高值分布范围及臭氧含量大小与系统本身强度存在一定的联系。强度较强的深厚型切断低压过程中动力学对流层顶下降深度和入侵的臭氧浓度均远大于强度较弱的深厚型切断低压。(3)在选取11年臭氧平均值和11年当月臭氧平均值分别作为距平基准进行对比分析时发现,不同类型和强度的切断低压对比结果不受不同臭氧基准态选取的影响。     

冬季北半球平流层季节内振荡与对流层季节内振荡的关系

通过平流层大气ISO与对流层大气ISO的比较分析,发现在中高纬地区平流层大气ISO与对流层大气ISO有着许多相同点.北半球冬半年平流层大气环流主要低频模态也可认为是北极涛动(AO),其空间分布的主要特征为; 高纬度地区与中低纬度地区为反位相变化,北极地区附近具有最大的变化值; 其季节内振荡的正位相对应于AO增强,负位相对应于AO减弱.北半球冬半年平流层100 hPa 和70 hPa 位势高度场的低频遥相关分析表明,北极地区(概指北纬60°N以北)和北半球其他大部分地区呈负相关,北极涛动扮演了非常重要的角色.同时,北半球冬半年平流层的主要低频波列是从欧亚大陆中部到西北太平洋,并且由纬向型低频波列(欧亚大陆-西伯利亚-太平洋)和经向型低频波列(欧亚大陆-北极-太平洋)共同构成.平流层30 hPa 和对流层500 hPa 上经过带通滤波(15～90 d)位势高度场的EOF第一主分量的形势有十分类似的特征,它们对应的时间系数序列有显著的延迟相关关系.因此可以认为,北半球平流层大气ISO的变化要先于对流层大气,在滞后35 d 左右其相关系数达到最大.大气环流模式(SAMIL)的数值模拟试验结果也表明,平流层的低频扰动可以在14 d 之后便在对流层500 hPa上激发出低频响应,其谱峰在30 d 左右.这进一步表明,通过大气季节内振荡,平流层的异常可以影响到对流层.     

春季青藏高原西北侧一次平流层臭氧向对流层传输的模拟研究

利用NCEP/NCAR FNL客观分析资料和欧洲中期天气预报中心(ECMWF)的Interim再分析资料以及臭氧监测仪(OMI)的臭氧廓线资料,结合区域大气化学模式WRF-Chem对中国春季一次高空冷槽过境引起的对流层顶折卷过程(2012年3月19—21日)进行了分析,并从平流、湍流混合、对流输送等几个方面诊断分析了平流层臭氧向对流层的传输特征和细节。结果表明,发生于青藏高原西北侧的对流层顶折卷事件,其所在位置处于热带对流层顶向中纬度对流层顶的过渡区,由于陡峭的对流层顶南北梯度,在该区域发生的平流层-对流层物质交换(STE)比对流层顶东西方向折卷引起的物质交换要强烈和持久,跨越等熵面的物质交换和湍流混合对平流层-对流层物质交换有很大的贡献。大地形对平流层-对流层物质交换过程有显著的影响,且具有明显的日变化特征。早晚时段,大地形导致的爬坡上升气流显著,抑制了平流层空气与对流层空气的混合交换。午后,大地形热力作用增强,受背风坡局地环流的影响,靠近山顶处湍流混合作用对上对流层臭氧浓度升高的贡献显著增强,且地形越高,这种效应越显著。地形的湍流混合作用在2.5 km高度以上凸显,此高度之上地形平均高度每升高100 m,湍流混合的贡献增加约1%。     

夏季亚洲季风区对流层向平流层输送的源区、路径及其时间尺度的模拟研究

基于NCEP/NCAR分析资料和拉格朗日轨迹输送模式FLEXPART, 通过气块轨迹计算, 对2005年夏季亚洲季风区对流层向平流层输送 (Troposphere to Stratosphere Transport, 简称TST) 的近地层源区、 输送路径及其时间尺度问题进行了一些初步探讨。结果表明: (1) 夏季亚洲季风区TST两个主要的边界层源区, 一个是热带西太平洋地区; 另一个是青藏高原南部、 孟加拉湾以及印度半岛中北部等地区, 上述两个区域与夏季强对流的分布相一致。在对流层顶高度附近 (约16 km高度), 两个近地层源区的垂直输送贡献相当。但进一步分析发现, 穿越对流层顶高度的质量输送只有约10％能够进入20～22 km高度的平流层中, 且主要源于以青藏高原南侧为代表的南亚季风区 (约贡献75%), 这进一步强调了青藏高原及其周边区域在全球TST过程中的重要地位。 (2) 轨迹分析显示, 夏季亚洲季风区对流层进入平流层的 “入口区” 主要在 (25°N～35°N, 90°E～110°E) 区域的青藏高原及其周边区域。TST路径受对流层上层南亚高压闭合环流、 北半球副热带西风急流和赤道东风急流的共同控制。 (3) 亚洲季风区TST两个主要的过程, 一个是和夏季湿对流抬升直接联系的快速输送过程, 它可以使近地层大气在1～2天内输送到平流层中, 贡献了整个TST的10%～30%; 另一个是大气辐射加热所致的大尺度垂直输送, 该输送是一个相对的慢过程, 时间尺度一般为5～30天。此结果意味着, 源于地表的短生命周期的大气污染物可通过光化学反应过程对该区域平流层臭氧及其他大气痕量成分平衡产生重要影响。     

沙尘暴过程中沙尘对流层-平流层输送的数值模拟初步分析

在初步明确东亚沙尘气溶胶对流层-平流层输送监测事实的基础上,利用观测资料、NCEP再分析资料以及基于中尺度天气模式MM5的数值模拟方法,对一次蒙古气旋沙尘暴过程中沙尘对流层-平流层输送问题进行了初步分析.结果表明:斜压不稳定是本次蒙古气旋发展的主要强迫要素,伴随气旋发展成熟,高空切断低涡的形成引导高空急流下落并诱发对流层顶折叠和高空位涡下传.对流层顶折叠区呈漏斗状,底部达500 hPa左右.高空急流产生近似垂直的下落,并在高空切断低涡的南侧和东侧达到最强.在对流层顶折叠区周边的300-500 hPa,上升气流与低涡区偏西、偏南、偏东气流叠加,或水平横穿折叠的对流层顶,或斜升并准垂直地穿过下落的对流层顶到达平流层,且随时间的推移,空气质点能够进一步抵达平流层中部(100 hPa).轨迹分析表明,沙尘天气区对流层低层的空气质点在气旋涡旋上升气流的驱动下呈气旋式盘旋上升,并在对流层高层形成分支,一支穿过对流层顶到达平流层,并在平流层向下游进行反气旋式螺旋运动,另一支则留在对流层高层并向下游进行准水平的气旋式螺旋运动.在高空位涡下传过程中,主要产生平流层到对流层的净输送;高空位涡停止下传之后则出现对流层到平流层的净输送,且强度随时间呈指数型增长.这一特征有利于形成更强的沙尘对流层平流层输送.     

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.     

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     

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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 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.     

Editorial

As we will soon celebrate the 90th anniversary of the founding of the Chinese Meteorological Society （CMS）,Acta Meteorologica Sinica （AMS）,which was originally named as Bulletin of the Chinese Meteorological Society,has gone through 89 years of development and excitement since her first issue in July 1925.According to archived documents （CMS Editorial Committee,1925）,AMS was founded to report the research findings of Chinese meteorologists,record their recommendations for improving meteorological services,and share their common meteorological interests in order to promote the growth of AMS such that more members could be inspired to conduct atmospheric research and meteorological knowledge would be better disseminated to and benefit the general public.By upholding and carrying forward this purpose,AMS has published many highly valuable scientific papers.Some could be treated as classical articles,which have produced important influences on both domestic and international meteorological communities and the related fields.