冬季太阳11年周期活动对大气环流的影响

利用气象场的再分析资料和太阳辐射活动资料,对太阳11年周期活动影响北半球冬季(11月~3月)大气环流的过程进行了统计分析和动力学诊断.根据赤道平流层纬向风准两年振荡(QBO)的东、西风状态对太阳活动效应进行了分类讨论,结果表明：东风态QBO时,太阳活动效应主要集中在赤道平流层中、高层和南半球平流层,强太阳活动时增强的紫外辐射加热了赤道地区的臭氧层,造成平流层低纬明显增温,同时加强了南半球的Brewer-Dobson(B-D)环流,引起南极高纬平流层温度增加;而北半球中高纬的环流主要受行星波的影响,太阳活动影响很小.西风态QBO时,太阳活动效应在北半球更为重要,初冬时强太阳活动除了加热赤道地区臭氧层外,还抑制了北半球的B-D环流,造成赤道平流层温度增加和纬向风梯度在垂直方向的变化,从而改变了对流层两支行星波波导的强度;冬末时在太阳活动调制下,行星波向极波导增强,B-D环流逐渐恢复,造成北半球极地平流层明显增温,同时伴随着赤道区域温度的下降.     

ENSO对平流层气溶胶分布的影响

本文采用ONI(Oceanic Nino Index)和HALOE(Halogen Occultation Experiment)气溶胶面积密度资料,从其滞后相关性入手分析了ENSO循环对平流层气溶胶的影响,通过对滞后于El Nino和La Nina时气溶胶含量的比较探讨了ENSO强迫的影响程度,并用剩余环流及其输送量解释了平流层气溶胶变化的动力机制.结果表明:ENSO对平流层气溶胶的分布有明显影响,在赤道和低纬度上空尤为显著,El Nino发生后半年内热带平流层低层的气溶胶面积密度较平均值偏大,平流层中层的面积密度则偏小,而La Nina反之.El Nino和La Nina影响的差异显著,在分别滞后于El Nino和La Nina事件2~8个月间的60 hPa气溶胶含量差异甚至高达45%,海表温度变化1 K则在滞后半年内气溶胶面积密度的变化可达到16%.ENSO的强烈影响能够维持大约半年,两年后基本消退.热带的变化幅度明显强于中高纬度,南北半球的变化特征也有所不同.ENSO通过影响剩余环流导致气溶胶输送量发生变化,进而引起气溶胶分布出现上述差异.     

春季Hadley环流异常对夏季西北太平洋热带气旋频数影响的数值模拟试验

观测事实揭示出春季Hadley环流与夏季西北太平洋热带气旋频数之间存在显著的负相关关系.由春季Hadley环流异常引起的西北太平洋地区夏季纬向风垂直切变、大气辐合辐散等的异常变化是这一关系存在的内在原因.本文通过数值试验对这一关系的真实性进行了验证,即利用中国科学院大气物理研究所发展的9层大气环流模式（IAP9L-AGCM）模拟了春季Hadley环流异常偏强情景,并分析了该情景下影响西北太平洋热带气旋生成的环境场的响应.结果表明,在春季Hadley环流偏强情景下,夏季西北太平洋地区纬向风垂直切变幅度加大,低空大气异常辐散,高空大气异常辐合,东亚夏季风减弱,这种环流背景不利于热带气旋生成和发展,因此,西北太平洋热带气旋频数异常偏少.数值模拟结果与已有的诊断结果相吻合,进而证实了春季Hadley环流与夏季西北太平洋热带气旋频数负相关关系的存在.因此,春季Hadley环流信号可以用于西北太平洋热带气旋活动的气候预测.     

利用多年卫星测高资料研究南海上层环流季节特征

利用10年高精度卫星测高海面高异常网格资料,联合EGM96稳态海面地形模型,构成南海海域合成海面地形的时间序列,并计算了各个时期的南海表层地转流场. 利用卫星跟踪漂流浮标观测结果与相应时期南海地转流场进行对比验证,结果显示本文结果可以很好地反映南海海域一些中小尺度的环流特征. 根据南海各季节多年平均表层环流场结构,对南海环流周年变化规律和季节特征进行了初步的探讨. 研究结果表明,南海表层环流始终处在不断演变过程之中,在时间和空间上都表现出明显的多尺度特征.     

梅雨与北极涛动及平流层环流异常的关联

平流层过程如何影响气候变化是一个大家关注的科学问题,在WCRP中专门设置了一个研究子计划SPARC.本文的分析研究表明,中国的梅雨异常可能受到平流层大气环流异常的影响,而这种影响是通过北极涛动（AO）的变化来实现的.从分析和计算结果可以看到,二月份北半球30 hPa位势高度的EOF第一主分量对应着副热带和高纬度地区的显著下传异常波作用量,其第三主分量对应着极地地区的显著下传异常波作用量,这些下传的异常波作用量都对三月份AO形势的形成有明显的贡献.三月份的AO则会通过影响东亚地区夏季对流层大气的冷暖状况和环流,在长江中下游地区导致异常垂直运动和辐散辐合形势,从而影响夏季的梅雨降水.     

N2O增加对大气环境影响的模拟及其与甲烷和平流层水汽影响的比较

本文利用美国国家大气环境中心(NCAR)的二维化学、辐射和动力相互作用的模式(SOCRATES),模拟了大气中N₂O增加对O₃和温度的影响,并从化学、辐射和动力过程讨论了影响原因,此外还与大气甲烷和平流层水汽增加对大气环境的影响进行了对比.分析表明:大气中N₂O浓度增加以后,将通过化学过程引起30 km以上O₃损耗,30~40 km损耗较多;30 km以上降温明显,下平流层中低纬度地区以及对流层O₃增加并有微弱升温;30~40 km附近,北半球中高纬地区O₃减少以及降温幅度都大于南半球.对流层升温主要是N₂O和O₃增加所致,而平流层温度变化主要受O₃控制.北半球中高纬地区动力过程对温度变化的反馈较其它地区明显,这种反馈对平流层中高层北半球中高纬地区温度和O₃的变化都有明显影响.大气中甲烷增加引起的O₃损耗在45 km以上,45 km以下O₃增加.平流层水汽增加会引起40 km以上O₃减少,20~40 km大部分地区O₃增加.N₂O增加造成的O₃损耗正好位于臭氧层附近,其排放对未来O₃层恢复至关重要.N₂O增加引起下平流层15~25 km中低纬度地区有弱的升温,这与其它温室气体增加对该地区温度的影响不同,CO₂,CH₄和H₂O等增加后下平流层通常是降温.     

角度域剩余深度对剩余速度的敏感性分析

本文针对地震勘探深度域偏移速度建模研究, 利用角度域共成像点道集(ADCIGS)建立了以剩余速度为自变量, 剩余深度为目标函数的关系式, 及目标函数的梯度公式.利用导出的两个公式分别对剩余深度与剩余速度的关系进行了定量分析.通过理论分析和模型试算证明初始速度模型的误差具有方向敏感性, 即正误差较负误差对速度建模迭代收敛更敏感.利用此结论进行深度域速度建模既可以提高计算效率也可以提高建模精度.     

夏季东亚和印度热带季风环流系统动能和对流扰动的纬向传播特征

使用1980~1997年NCEP/NCAR再分析资料及日本的TBB/GMS资料讨论了亚洲季风系统中印度和东亚两个子系统中热带季风变化(扰动)源地及变化后的纬向传播特性. 18a的结果表明, 在夏季热带季风主体的5º~15ºN范围内, 东亚夏季风系统中纬向风虽然为西风, 但绝大多数动能扰动和对流扰动均起源于140º~150ºE, 向西经南海传播到孟加拉湾(90º~100ºE). 而在印度夏季风系统中, 18a中有12a动能扰动起源于阿拉伯海向东传播到孟加拉湾, 东端抵达90ºE, 其余年份并无明显东西向传播特征. 因而, 在亚洲5º~15ºN夏季风主体区域内, 虽然均由西南季风控制, 但存在传播特性相反的东亚和印度两个子系统, 两个系统交界约在90º~95ºE, 比过去提出的交界经度105ºE更偏西一些. 以上结果也表明东亚夏季风环流系统在东西方向上主要受热带西太平洋影响而不是受来自孟加拉湾的印度季风影响. 相反, 印度季风环流系统除了受阿拉伯海影响外还部分受东亚季风系统影响.     

大洋风生环流观测优化的伴随分析

提出了一种依据海洋伴随资料同化达到改进海洋观测方案的客观分析方法.针对一个"真实的海洋"进行不同空间断面(或对不同层次)的假设采样,分别将这些"不完备的观测"应用于Byran-Cox海洋环流模式的伴随系统,可以计算"不完备观测"同化以后的模式环流与"完备观测"资料同化(控制试验)得到的环流之间的距离--反演距离.由于海洋伴随资料同化所具有的局地修正效应和邻域修正效应,不同观测方案所对应的反演距离有着明显的差异.采用上述方法在一定观测代价下可以对大洋风生环流进行观测方案的优化分析.     

热带印度洋增暖对南极平流层极涡的影响

过去几十年,在全球变暖的大背景下,全球大部分海洋,特别是热带印度洋,显著增暖．同时,南极平流层极涡呈现发展加深的趋势．以前的模拟结果显示,臭氧耗损的辐射冷却效应是南极极涡加深的主导因子,但模拟的臭氧耗损单独引起的南极极涡加深比实际观测到的要强．这说明有其他因子参与影响了南极极涡的趋势变化,其作用是部分抵消臭氧耗损的影响．是否热带印度洋增暖是其中的因子之一,这个问题还不清楚．利用4个大气环流模式,通过给定理想的、与观测到的强度相当的热带印度洋增暖强迫,进行集合试验,研究了这一问题．结果表明：热带印度洋增暖有利于南半球春、夏季极地平流层增暖、南极极涡减弱,于是倾向于部分抵消臭氧耗损的辐射冷却效应．这一结果能部分解释以前的模拟发现～臭氧耗损单独导致的南极极涡加深比观测到的要强．鉴于平流层变暖不利于极地平流层冰晶云的形成、遂有利于臭氧恢复,现在的结果暗示：在全球变暖的大背景下,气候系统的内部动力调整过程将有利于南极臭氧洞的恢复．     

A numerical model of the zonal mean circulation of the middle atmosphere

The annual cycle of the zonally averaged circulation in the middle atmosphere (16–96 km) is simulated using a numerical model based on the primitive equations in log pressure coordinates. The circulation is driven radiatively by heating due to solar ultraviolet absorption by ozone and infrared cooling due to carbon dioxide and ozone (parameterized as a Newtonian cooling). Since eddy fluxes due to planetary waves are neglected in the model, the computed mean meridional circulation must be interpreted as thediabatic circulation, not as the total eulerian mean. Rayleigh friction with a short (2–4 day) time constant above 70 km is included to simulate the strong mechanical dissipation which is hypothesized to exist in the vicinity of the mesopause due to turbulence associated with gravity waves and tides near the mesopause.Computed mean winds and temperatures are in general agreement with observations for both equinox and solstice conditions. In particular, the strong mechanical damping specified near the mesopause makes it possible to simulate the cold summer and warm winter mesopause temperatures without generating excessive mean zonal winds. In addition, the model exhibits a strong semiannual cycle in the mean zonal wind at the equator, with both amplitude and vertical structure in agreement with the easterly phase of the observed equatorial semiannual oscillation.Contribution No. 497, Department of Atmospheric Sciences, University of Washington, Seattle.     

Dynamic model of mesoscale eddies. Eddy parameterization for coarse resolution ocean circulation models

In the framework of the eddy dynamic model developed in two previous papers (Dubovikov, M.S., Dynamical model of mesoscale eddies, Geophys. Astophys. Fluid Dyn., 2003, 97, 311–358; Canuto, V.M. and Dubovikov, M.S., Modeling mesoscale eddies, Ocean Modelling, 2004, 8, 1–30 referred as I–II), we compute the contribution of unresolved mesoscale eddies to the large-scale dynamic equations of the ocean. In isopycnal coordinates, in addition to the bolus velocity discussed in I–II, the mesoscale contribution to the large scale momentum equation is derived. Its form is quite different from the traditional down-gradient parameterization. The model solutions in isopycnal coordinates are transformed to level coordinates to parameterize the eddy contributions to the corresponding large scale density and momentum equations. In the former, the contributions due to the eddy induced velocity and to the residual density flux across mean isopycnals (so called Σ-term) are derived, both contributions being shown to be of the same order. As for the large scale momentum equation, as well as in isopycnal coordinates, the eddy contribution has a form which is quite different from the down-gradient expression.     

The baroclinic circulation structure of Yellow Sea Cold Water Mass

The Yellow Sea is a semi-enclosed shallow sea with a deep trough of about 80 m. On the hy-drographic condition in the Yellow Sea, Lie[1] pointed out that it is strongly associated with winter cooling and summer heating, fresh input from rivers into the co…     

Remote sensing of the global distribution of total ozone and the inferred upper-tropospheric circulation from Nimbus IRIS experiments

The global distribution of total ozone is derived for the period April, May, June and July of 1969 from Nimbus-3 Infrared Interferometer Spectrometer (IRIS) experiment. Preliminary estimates of ozone amounts from Nimbus-4 IRIS for the same period of 1970 show similar results. The standard error of estimation of total ozone from both IRIS experiments is 6% with respect to Dobson Spectrophotometer measurements. A systematic variation in the ozone distribution from April to July in the tropical, middle and polar latitudes is observed indicating the changes in the lower stratospheric circulation.The total ozone measurements show a strong correlation with the upper tropospheric geopotential height in the extratropical latitudes. From this relationship total ozone is used as a quasi-stream function to deduce geostrophic winds at the 200 mb level over extratropical regions of the northern and southern hemispheres. These winds reveal the subtropical and polar jet streams over the globe.Allied research associates.     

Effects of a variety of Indian Ocean surface temperature anomaly patterns on the summer monsoon circulation: Experiments with the NCAR general circulation model

The time mean response of the summer monsoon circulation, as simulated by the 2.5° latitude-longitude resolution, July version of the National Center for Atmospheric Research (NCAR) General Circulation Model (GCM), to a variety of Indian Ocean surface temperature anomaly patterns is examined. In separate experiments, prescribed changes in surface temperature are imposed in the Western Arabian Sea, the Eastern Arbian Sea or the Central Indian Ocean. The influence of these anomaly patterns on the simulated summer monsoon circulation is evaluated in terms of the geographical distribution of the prescribed change response for any field of interest. This response is defined as the grid point difference between a 30-day mean from a prescribed change experiment and the ensemble average of the 30-day means from the control population for which the same set of climatological ocean surface temperatures are used in each simulation. The statistical significance of such a prescribed change response is estimated by relating the normalized response (defined as the ratio of the prescribed change response to the standard deviation of 30-day means as estimated from the finite sample of control cases) to the classical Student'st-statistic. Using this methodology, the most prominent and statistically significant features of the model's response are increased vertical velocity and precipitation over warm anomalies and typically decreased vertical velocity and precipitation in some preferred region adjacent to the prescribed change region. In the case of cold anomalies, these changes are of opposite sign. However, none of the imposed anomaly patterns produces substantial or statistically significant precipitation changes over large areas of the Indian sub-continent. The only evidence of a major nonlocal effect is found in the experiment with a large positive anomaly (+3°C) in the Central Indian Ocean. In this instance, vertical velocity and precipitation are reduced over Malaysia and a large area of the Equatorial Western Pacific Ocean. Thus, while these anomaly experiments produce only a local response (for the most part), it is hoped, as one of the purposes of the planned Monsoon Experiment (MONEX), that the necessary data will be provided to produce detailed empirical evidence on the extent to which Indian Ocean surface temperature anomalies correlate with precipitation anomalies over the Indian subcontinent—a correlation which generally does not appear in these GCM results.The National Center for Atmospheric Research is sponsored by the National Science Foundation     

用面波方法研究上扬子克拉通壳幔速度结构

本文研究采用单台法和双台法提取了穿越上扬子的基阶面波相速度和群速度频散;通过对提取的面波群速度和相速度频散进行联合反演,得到的1-D SV速度模型显示上扬子块体下地壳S波速度与典型克拉通区域相当,其上地幔顶部80~170 km深处存在高速的岩石圈盖层,较AK135模型要快2%~3%,其岩石圈厚度约为180 km.在上扬子地区,径向各向异性集中分布在300 km以浅的岩石圈与软流圈部分,其中岩石圈部分SH波比SV波波速要快2%~4%,软流圈部分SH波比SV波波速要快3%~5%;Rayleigh波相速度方位各向异性分析结果显示,上扬子块体周期为25~45 s（大致相当于30~70 km深度范围内）的Rayleigh波相速度存在1.8%~2.7%不等的方位各向异性,其快波方向介于147°~174°.我们认为上扬子块体径向各向异性集中分布在岩石圈、软流圈部分,且各向异性随深度变化, 其岩石圈部分各向异性为大陆克拉通化的遗迹,软流圈部分各向异性与现今板块运动相关.