Seasonal variation of global stratosphere-troposphere mass exchange

By Wei formula in pressure coordinate, the stratosphere-troposphere mass exchange (STME) is diagnosed globally for 44 years from 1958 to 2001 using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis datasets. Regions of mass flux into the stratosphere are found over Indonesia, bay of Bangladesh and the mid-west coast of South Africa. Compensating mass outflow from the stratosphere appears mainly over mid-latitudes near large-scale troughs. Upward and downward transport of mass at the middle and high latitudes accompany with each other. Mass flux into troposphere is stronger in autumn and winter than in spring and summer. Strong downward mass flux into the troposphere occurs in eastern Asia the whole year with nearly stable sites. Although the area of eastern Asia accounts for only 5.6% of that of the northern hemisphere (NH), its net mass exchange reaches 15.83% of that of the NH, which means that research on STME of eastern Asia is greatly important to that of the NH and even the global areas. Air across the tropopause enters more from stratosphere to troposphere than that from troposphere to stratosphere, which is possibly related with systematic bias of the assimilated datasets and with persistent rise of the tropopause height. Contributions of the mass exchange and the mass flux exchange in the NH and southern hemisphere (SH) on their latitudes increase from equator to pole, with larger contributions in the NH. Mass exchange and mass flux exchange per areas at high latitudes are larger than that at low latitudes, which means greater mass exchange efficiency at high latitudes.     

Mass exchange between stratosphere and trotosphere over the Tibetan Plateau and its surroundings

Using NCEP dataset we calculate the exchange of mass across the thermal tropopause by the Wei's method from 1978 to 1997 over the Tibetan Plateau and its surroundings. We also calculate the annual variation of aerosol and ozone of 100 hPa level with the monthly SAGE dataset from July 1988 to December 1993. Results indicate that ( i ) the mass from troposphere to stratosphere is magistral station in summer over the Tibetan Plateau and its surroundings. The air transport reaches the summit in midsummer with two large value centers, which lie in the north of Bengal Bay and southeastern Tibetan Plateau, respectively. A large value center, which lies over the Tibetan Plateau, is smaller than that aforementioned. In winter, the mass transport is from stratosphere to troposphere, and reaches the minimum in January. ( ii ) As far as the 19-year mean cross-tropopause mass exchange from June to September is concerned, the net mass transport is 14.84x1018 kg from troposphere to stratosphere. So the area from the Tibetan Plateau to the Bengal Bay is a channel through which the mass of lower atmosphere layer gets into upper troposphere and lower stratosphere. (iii) The cross-tropopause mass may take the lower level aerosol to the tropopause. Then, the concentration of aerosol near the tropopause becomes larger, which may cause the content of ozone to reduce.     

穿越东亚不同定义对流层顶质量和臭氧通量的分析

选取动力学和热力学定义的对流层顶作为平流层和对流层之间的分界,并利用等熵坐标下的Wei公式对东亚地区穿越对流层顶的质量和臭氧通量进行了分析,结果发现对流层顶的选择对于研究平流层与对流层交换方面的作用至关重要.东亚地区质量和臭氧通量交换在整体上具有明显的年代际变化特征,1958～2001年近44a的通量交换距平变化可以分为3个比较稳定的时段:即1958～1971,1972～1985和1986～2001年.在这3个时段中,通量交换距平分布表现为"负正负"的变化趋势,说明在东亚地区质量和臭氧净通量交换情况为先增强后减弱.东亚地区平流层和对流层之间质量和臭氧交换正距平区在东北平原和华北平原附近经历了一个逐渐增强的变化过程,表明这些区域在东亚地区平流层和对流层之间的质量和臭氧通量交换中扮演着越来越重要的角色.     

利用探空资料对对流层-平流层热力结构的分析

利用16个探空站近6年的高分辨率探空资料,采用经验正交函数和数值积分等方法,分析了对流层、对流层顶和平流层下层的温度层结特征,主要得出以下结论:①对流层顶温度年变幅最小,对流层上层和平流层下层(包括对流层顶)与对流层中低层具有相反的温度变化趋势.②不同地区对流层顶高度表现为随纬度升高而降低的规律,平均每升高1°对流层顶高度下降44 m,同纬度高原地区对流层顶高度高于平原地区.③各站对流层平均温度总体表现为单峰型结构,与地面温度的季节变化特征相同,只是年较差小于地面.④对流层顶高度与对流层平均温度具有显著的正相关关系,对流层增温时对流层顶高度升高,对流层顶高度主要取决于对流层热力状况.     

大气对流层顶的臭氧时空分布变化

 利用1958~2001年的臭氧垂直分布和NCEP资料,计算出全球对流层顶的气候场,并对其空间分布、季节、年际和年代际演变进行了分析.结果表明:①对流层顶臭氧质量比呈纬向分布的特征明显,南北半球中纬度和南极为高值区,赤道和北极为低值区,且与对流层顶高度和温度场有对应关系;②从400~70 hPa的温度和臭氧质量比垂直经向剖面中,显现出对流层顶的上层和下层由于具有不同的物理和化学过程导致垂直分布存在差异;③对流层顶臭氧质量比纬向距平场的年代际变率具有不同位相的时空演变尺度,南半球的时空差异比北半球大,南极最不稳定,低纬和赤道地区幅度变化较小,但时间尺度较大;④极地各季节对流层顶的臭氧分布和高度场特征相似,低纬则与温度场分布较一致;⑤对流层顶断裂带中臭氧质量比最大值出现在春季,秋季为最小值,其对应的纬度存在明显的季节空间经向波动,夏季达到最高纬度,冬季到达最低纬度;⑥对流层顶臭氧质量比纬向距平的季节变率表现出准半年变化趋势,且两半球变化趋势相反.     

亚印太交汇区低纬上空不同层次大气臭氧的时空变化分析

 利用ECMWF 195709~200208共45a的多层臭氧质量混合比月平均资料,详细分析了亚印太交汇区(AIPO)低纬地带上空平流层、对流层各层次上臭氧浓度的分布特征.结果表明:①区域上空对流层、平流层及臭氧总量大尺度特征均显著,纬度带分布特征明显;②对流层和平流层臭氧各个季节变化趋势相反,平流层臭氧和臭氧总量各个季节变化趋势一致;同一层次夏季臭氧浓度变化趋势与其他3个季节变化趋势相反;③区域上空20~3hPa是臭氧浓度的高值区,50~30hPa臭氧平均变化幅度最大;④对流层臭氧距平变化在整个高度上较为一致,正、负距平随季节绕赤道做南、北半球摆动,且存在季节性突变;⑤赤道上空有明显从平流层上层随季节逐渐往较低层传播的臭氧正负距平现象.     

An estimation of ozone flux in a stratosphere-troposphere exchange event

A new method based on mass fluxes and observed ozone profiles was developed to estimate crosstropopause ozone flux. Using this method, we estimated the cross-tropopause ozone flux in a stratospheric-tropospheric exchange event that occurred over East Asia in March 2001.The result revealed that the ozone flux across the tropopause in this event was an order of magnitude higher than the global and hemispheric average. Compared to the traditional method using a linear relationship between ozone mixing ratio and potential vorticity near the tropopause, the cross-tropopause ozone flux evaluated with ozonesonde data was somewhat higher, although the orders of the two values were the same.     

中国冬季降水对东亚春季O3强弱信号的响应

 利用欧洲中心(ECMWF)ERA-Interim提供的1979—2013年的O₃、温度和位势高度逐月资料及国家气候中心的160站的逐月降水资料,采用EOF分析、相关分析和合成差值分析等方法,分析了东亚春季臭氧的时空变化特征及中国冬季降水对东亚春季O3强弱信号的响应.研究发现：①通过EOF分析可知,东亚春季O₃主要有3种变化特征：其一是东亚春季不同时间的O₃随着纬度的增加而增加（或减少）.其二是青藏高原是一个O₃异常信号较强的地区.其三是鄂霍次克海以西的内陆地区和中国东北部地区的春季O₃异常信号最强,且这两地区的异常信号位相相反.②东亚春季O₃强时,中国冬季降水从西到东呈现了“多-少-多-少-多-少”的分布.这种响应显著的区域位于北方和内陆地区,而中国的东南地区较弱.这就说明,东亚春季O₃对中国冬季降水是有一定的影响的.O₃是如何引起中国冬季降水出现这种波列分布的原因尚有待于进一步的研究.③选取了6个层次分别代表平流层和对流层来开展研究.从相应于O₃强弱年的温压场分析来看,北半球冬季的温度场和位势高度场的合成差值在中高纬度都呈现了波列的分布,在平流层呈“正-负-正”分布,在对流层呈“负-正-负-正-负”分布,且这种温压场对O₃变化的响应在50、100、500hPa和700hPa层次最为显著.据此推测,东亚春季O3变化会引起北半球的温度场和位势高度场的调整,从而使得中国冬季降水分布出现异常.
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对流层顶大气臭氧的季节变化研究

 采用季节划分和季节突变的概念、理论及方法,对44a(1958~2001年)的大气臭氧资料及对流层顶气压场资料进行了计算,并分析了对流层顶大气臭氧的季节变化.结果发现对流层顶大气臭氧的季节变化在全球大部分区域中的突变性都比较明显,表明对流层顶大气臭氧的季节变化受到上对流层和下平流层中多种因素的影响.通过分析还发现,利用曾庆存所定义的参数R_W(t)及有关的一些概念和方法确能很好地反映对流层顶大气臭氧的季节变化.     

Removal of chlorofluorocarbons by increased mass exchange between the stratosphere and troposphere in a changing climate

Chlorofluorocarbons (CFCs), along with bromine compounds, have been unequivocally identified as being responsible for most of the anthropogenic destruction of stratospheric ozone. With curbs on emissions of these substances, the recovery of the ozone layer will depend on their removal from the atmosphere. As CFCs have no significant tropospheric removal process, but are rapidly photolysed above the lower stratosphere, the timescale for their removal is set mainly by the rate at which air is transported from the troposphere into the stratosphere. Using a global climate model we predict that, in response to the projected changes in greenhouse-gas concentrations during the first half of the twenty-first century, this rate of mass exchange will increase by 3% per decade. This increase is due to more vigorous extra-tropical planetary waves emanating from the troposphere. We estimate that this increase in mass exchange will accelerate the removal of CFCs to an extent that recovery to levels currently predicted for 2050 and 2080 will occur 5 and 10 years earlier, respectively.     

Concentration and seasonal variation of 10Be in surface aerosols of Lhasa,Tibet

Thirty samples of total suspended particles were collected at a site in western part of Lhasa, Tibet from August 2006 to July 2007. The ¹⁰Be concentrations were determined by Accelerator Mass Spectrometer (AMS). Analysis of correlation between ¹⁰Be con-centrations and meteorological factors revealed that the wet scavenging has little effect on ¹⁰Be. ¹⁰Be can be used as a proxy of transport processes of the upper atmosphere over the Tibetan Plateau. Analysis of correlation between ¹⁰Be concentrations and NCEP reanalysis data demonstrated that higher ¹⁰Be concentrations in spring were probably caused by the atmosphere exchange from stratosphere to troposphere during February to June. Lower ¹⁰Be concentrations during August to September were consistent with the synchronous lower O₃ values, suggestive of both ¹⁰Be and O₃ were probably influenced by the atmosphere exchange from troposphere to stratosphere.     

伴随南海季风爆发热带环流演变的合成分析

为了研究伴随南海夏季风爆发的热带环流的演变,利用40 a的NCEP逐日再分析资料,采用合成分析的方法对季风爆发前后的环流形势变化进行了讨论。合成结果中重点分析了随南海季风的爆发在对流层和平流层低层的流场都有显著变化的南亚、东南亚地区。结果表明,在对流层中印度洋赤道地区,在季风爆发前有东风扰动发展成为一对南北对称的低涡,随后北边的低涡演变成孟加拉湾低槽,低槽前的西南气流不断东扩,使西太副高东撤,南海季风爆发。低涡的演变和发展是影响南海季风爆发的重要因子之一。而高层的环流形势与低层不同,伴随季风爆发高层环流的演变则更多地体现出了全球尺度的特征。     

Detection of stratospheric ozone intrusions by windprofiler radars

Stratospheric ozone attenuates harmful ultraviolet radiation and protects the Earth's biosphere. Ozone is also of fundamental importance for the chemistry of the lowermost part of the atmosphere, the troposphere. At ground level, ozone is an important by-product of anthropogenic pollution, damaging forests and crops, and negatively affecting human health. Ozone is critical to the chemical and thermal balance of the troposphere because, via the formation of hydroxyl radicals, it controls the capacity of tropospheric air to oxidize and remove other pollutants. Moreover, ozone is an important greenhouse gas, particularly in the upper troposphere. Although photochemistry in the lower troposphere is the major source of tropospheric ozone, the stratosphere-troposphere transport of ozone is important to the overall climatology, budget and long-term trends of tropospheric ozone. Stratospheric intrusion events, however, are still poorly understood. Here we introduce the use of modern windprofiler radars to assist in such transport investigations. By hourly monitoring the radar-derived tropopause height in combination with a series of frequent ozonesonde balloon launches, we find numerous intrusions of ozone from the stratosphere into the troposphere in southeastern Canada. On some occasions, ozone is dispersed at altitudes of two to four kilometres, but on other occasions it reaches the ground, where it can dominate the ozone density variability. We observe rapid changes in radar tropopause height immediately preceding these intrusion events. Such changes therefore serve as a valuable diagnostic for the occurrence of ozone intrusion events. Our studies emphasize the impact that stratospheric ozone can have on tropospheric ozone, and show that windprofiler data can be used to infer the possibility of ozone intrusions, as well as better represent tropopause motions in association with stratosphere-troposphere transport.     

平流层CH4的时空变化特征及其与O3的关系

 利用1991年10月到2005年11月的HALO₃E卫星观测资料,对全球70°S～70°N范围内平流层100hPa到1 hPa的大气CH₄混合比进行了时空特征分析.结果表明:①CH₄混合比在平流层是随高度上升而逐渐减小的.平流层中上层CH₄变化存在年循环,而平流层中下层CH₄变化存在半年振荡(SAO₃),且南半球平流层CH₄的季节变化振幅要大于北半球,特别是平流层中上层.平流层各个高度上的CH₄基本呈纬向分布,但是不同高度上分布特征有所差异;②平流层CH₄混合比变化存在3个月,10个月,准25个月和准45个月左右时间尺度的周期,但是3个月的短期变化和10个月的年循环只在1996年之前明显;③不同高度上,CH₄和O₃变化的相关关系是不同的,CH₄对O₃的破坏作用并不是存在于整个平流层,似乎是在有的高度上相关关系明显,有的高度上相关关系不明显.     

Ozone vertical variations during a typhoon derived from the OMI observations and reanalysis data

Typhoon is considered to play a key role in the dynamical exchange processes taking place between the troposphere and stratosphere. In this paper, the impact of typhoon on the ozone distribution in the upper troposphere and middle stratosphere is investigated using ozone profiles measured by Aura’s Ozone Monitoring Instrument and meteorological fields from reanalysis data. During the passage of Typhoon Hai-Tang in 2005 over the western North Pacific, low values of ozone column above 200 hPa and ozone mixing ratio between the upper troposphere and the middle stratosphere (from 200 to 50 hPa) are observed right above the typhoon’s track, a result due to the strong upward propagation of air associated with overshooting convection in typhoon. A comparative analysis of different stages of Hai-Tang suggests that in the region where typhoon has higher intensity the troposphere-to-stratosphere transport is enhanced. These results indicated that the typhoon has a significant impact on the ozone variation in the upper troposphere and the middle stratosphere.     

利用向下控制原理对Brewer-Dobson环流变化趋势的研究

 利用ERA-Interim 1979—2011年的逐日数据,通过向下控制原理研究了Brewer-Dobson(BD)环流的季节变化和年际变化.结果表明：对流层剩余环流在15°～30°间为下沉运动,在30°～50°呈上升运动,50°～极地又呈现出下沉运动,且低纬度的上升强度大于中高纬度的上升强度.平流层中环流在30°～45°间下沉,而在45°～60°间又呈上升运动,再在60°～极地间下沉.剩余环流的分布形势具有明显的季节变化特征,冬半球的环流形势要强于夏半球,春秋季期间,环流在两半球呈相对的对称形势.且穿越100hPa面上热带和热带外两半球的质量通量也具有明显的季节变化特征.在过去的33a间平流层BD环流有微弱的增强趋势.
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大气中尘埃层对电离层电场向下映射的影响

本文首先用分析解方法计算了高纬电离层对流电场向下映射,在平流层、对流层上的水平电场分布情况。地磁场作用使70km以上的电导率呈各向异性,但计算表明,这对极区对流电场向下映射的影响不大。最后,着重讨论了尘埃层使电导率大大下降对电场映射的作用。结果表明,高高度上的尘埃层能完全改变原有的映射图象,而30km以下的尘埃层影响很小。     

北半球夏季的斜压波包个例分析

利用NCEP/NCAR再分析资料,使用局地能量诊断和三维准地转波动通量等工具分析了2002年北半球夏季的一次斜压波包过程。结果表明：波包发展的能量来源主要依靠斜压转换获得,频散项对波包的影响很小;波包进入衰减期以后,波包的东侧和南侧作为垂直方向的波动源,向下传播波动通量;向下的波通量进入对流层低层气旋范围,对气旋的维持起到重要作用。     

平流层Brunt-Vaisala频率的分布特征

讨论了Brunt-Vaisala频率的重要性,并利用NCEP/NCAR再分析资料和HALOE资料分析了平流层中它的空间分布和时间变化特征.结果表明:从对流层到平流层Brunt-Vaisala频率在垂直方向上有明显的变化,特别是在低纬度地区,它在对流层向上迅速增加,在平流层向上减小;在平流层下层,它随着纬度的增加而减小,在平流层则经向分布比较均匀;在陆地上空Brunt-Vaisala频率的垂直梯度明显大于海洋上空,且出现高值中心;无论在对流层还是在平流层,Brunt-Vaisala频率冬季的值皆大于夏季的值;该频率也有准两年周期的变化.作为一个例子,我们运用实际计算出的Brunt-Vaisala频率对行星波垂直传播的影响进行了初步的讨论.     

全球对流层顶温度场演变的气候学特征分析

 利用经验正交函数分解(EOF)方法对57 a(1948~2004年)NCEP/NCAR全球对流层顶月平均温度场进行分析,并讨论了57 a的主要特征向量空间分布及其对应的时间系数的演变,结果分析表明:第1模态的时空分布特征能够较好地反映对流层顶温度场结构的分布状况,且具有明显的季节变化;南北半球的温度场的空间分布结构不太一致,南半球纬向分布较为平稳,而北半球经向和纬向活动都比较强,且有明显的温度槽脊结构;南北半球的极地对流层顶温度结构在不同的季节有不同的变化趋势;南北半球热带对流层的第1模态温度场全年具有整体一致型分布;温度场各个季节的时间系数变化具有明显的多时间尺度特征.