小波周期频率分析及其应用于热带西太平洋对流变化研究

本文给出使用正交和连续小波变换（ＷＴ）以确定在综合的和实际的资料中的周期成倍和时间频率局地化。首先，将Ｈａａｒ小波分析应用于综合时间序列，由一简化的非线性动力系统一阶二次微分方程推导得出；第二，根据高分辨率日本静止卫星红外（ＩＲ）辐射资料，将复合Ｍｏｒｌｅｔ小波用于研究热带对流的时间频率局地化。综合时间序列的Ｈａａｒ小波表明在一个周期成倍序列中多种频率的存在和明确的区分，周期成倍过程产生了中间频率的多重性，当振荡位相处于较低频率时，随时间的不均匀性可证明这一点，小波变换也能探测由周期成倍的分叉造成的高阶次谐波的极微弱的信号，由传统付氏分析看这些信号是不能测定，或被认为统计上无意义。红外辐射资料的Ｍｏｒｌｅｔ小波变换表明在频率和时间二者上确定的多种时间尺度，红外资料分为湿期和干期二种状态，湿期有活跃的多种时间尺度，半日、日、几日及季内的尺度各有其结构，特别是在一个广泛的季内周期的湿位相中以天气尺度变化为主。这些不仅与以前用其它方法所发现的相一致，而且更为详尽，不同时间尺度间相互作用的振荡中的频率锁定关系指出，天气尺度的和季内变化都可以是混合振荡（由于热带大气及若干外力如太阳辐射的年或日变化等自我激发振荡造成的?

基于高分辨率OLR资料的青藏高原和南亚地区夏季对流日变化特征

利用2004-2017年静止气象卫星Kalpana-1的高分辨率(空间分辨率0.25°×0.25°,时间分辨3 h一次,每天8个时次)射出长波辐射(Outgoing Longwave Radiation,OLR)资料,分析了青藏高原和南亚地区夏季对流的日变化特征,并结合ERA-Interim分析资料和中国常规降水观测资料对2006年和2007年的对流活动异常、垂直速度异常、降水异常三者的联系进行研究。结果表明:(1)青藏高原和南亚地区夏季6-9月有非常明显的对流活动,其中在对流活动最强的盛夏7-8月,青藏高原中部和东南部、印度半岛东北部、孟加拉湾到中南半岛都有大范围的强对流区,强度最强的对流区OLR平均最小值低于190 W·m^(-2)。(2)青藏高原和南亚地区对流活动日变化特征明显。其中青藏高原中南部、青藏高原东南部、印度半岛东北部和中南半岛南部地区都在09:00(世界时,下同)左右开始出现OLR低于210 W·m^(-2)的强对流区,在12:00左右对流活动强度达到最强,对流活动均可持续到次日凌晨。孟加拉湾东海岸全天都有明显的对流活动,在09:00和21:00的2个时次达到最强。对比青藏高原、南亚和孟加拉湾地区,青藏高原中南部地区的对流日变化最为显著,陆地区域对流日变化是一个周期,而孟加拉湾东岸地区的日变化有两个周期。(3)对比分析2006年和2007年7-8月青藏高原地区和中国西南地区的OLR异常变化与垂直速度和降水异常可以发现,高分辨率的OLR负(正)距平表示的异常强(弱)对流与异常上升(下沉)运动及异常多(少)的降水三者之间密切相关,可以用来表征青藏高原地区对流活动的变化特征,以弥补其观测资料的不足。

热带对流活动日变化的模拟研究

利用一个云分辨与海洋的耦合模式,模拟研究了热带对流活动的日变化.通过对模拟结果的分析,揭示了热带地区不同海温日变化条件下,对流活动的云物理特征.利用热带海洋与全球大气响应观测实验(TOGACOARE)的观测资料作为模式的初始与边界场,来驱动耦合模式.对热带海表温度按照其日变化幅度的大小进行了分类,分为强、弱海表温度日变化两种类型,并在此基础上进行了合成分析.结果表明:1)在弱的海表温度日变化下,云中的云冰含量大于云水含量,说明云中以层状云为主;而在强的海温日变化下,云中的云水含量大于云冰含量,说明云中以水云为主.2)强的海温日变化下,地面降水率在午后达到最大;而在弱的海表温度日变化下,地面降水率最大值出现在夜间.比较上述两者云的构成,发现其差别最大.3)比较两类(强、弱海表温度日变化)云物理过程的收支发现,在弱的海表温度日变化下水汽的凝华率远小于凝结率,更易形成冰云.

对流层垂直臭氧分布变化量对生物质燃烧响应的模拟研究

采用区域气候模式与大气化学模式相连接的模式系统,模拟研究了对流层垂直臭氧分布变化量对东南亚生物质燃烧排放源强变化的响应程度.结果表明,源区对流层臭氧垂直积分浓度对燃烧源强变化十分敏感,下游区次之.特别是在对流层的中低层影响最显著,但对源区臭氧的贡献比下游区要大得多.在对流层中高层,源区和下游区受影响程度相当.对流层低层源区臭氧增加的时间超前下游区,超前的时间随高度的增加而减小,而在对流层中层出现滞后现象,到对流层高层臭氧最大值出现的时间相同.

THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA I.40-YEAR AVERAGE

By using 40-year NCEP reanalysis daily data (1958-1997), we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea (105E ~ 120E, 5N ~ 20N, to be simplified as SCS in the text followed) pentad by pentad (5 days). According to our new definition, in the monsoon area of the SCS two of the following conditions should be satisfied: 1) At 850hPa, the southwest winds should be greater than 2m/s. 2) At 850 hPa, seq should be greater than 335K. The new definition means that the summer monsoon is the southwest winds with high temperature and high moisture. The onset of the SCS summer monsoon is defined to start when one half of the SCS area (105E ~ 120E,5N ~ 20N) is controlled by the summer monsoon. The analyzed results revealed the following: 1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May. 2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal. 3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously. 4) During the summer monsoon onset in the SCS, troughs deepen and widen quickly in the lower troposphere of the India; the subtropical high in the Western Pacific moves eastward off the SCS in the middle troposphere; the easterly advances northward over the SCS in the upper troposphere.

Seasonal variability of zonal heat advection in the mixed layer of the tropical Pacific

Zonal heat advection （ZHA） plays an important role in the variability of the thermal structure in the tropical Pacific Ocean, especially in the western Pacific warm pool （WPWP）. Using the Simple Ocean Data Assimilation （SODA） Version 2.02/4 for the period 1958-2007, this paper presents a detailed analysis of the climatological and seasonal ZHA in the tropical Pacific Ocean. Climatologically, ZHA shows a zonal- band spatial pattern associated with equatorial currents and contributes to forming the irregular eastern boundary of the WPWP （EBWP）. Seasonal variation of ZHA with a positive peak from February to July is most prominent in the Nifio3.4 region, where the EBWP is located. The physical mechanism of the seasonal cycle in this region is examined. The mean advection of anomalous temperature, anomalous advection of mean temperature and eddy advection account for 31%, 51%, and 18% of the total seasonal variations, respectively. This suggests that seasonal changes of the South Equatorial Current induced by variability of the trade winds are the dominant contributor to the anomalous advection of mean temperature and hence, the seasonality of ZHA. Heat budget analysis shows that ZHA and surface heat flux make comparable contributions to the seasonal heat variation in the Nifio3.4 region, and that ZHA cools the upper ocean throughout the calendar year except in late boreal spring. The connection between ZHA and EBWP is further explored and a statistical relationship between EBWP, ZHA and surface heat flux is established based on least squares fitting.

Sub seasonal variations of weak stratospheric polar vortex in December and its impact on Eurasian air temperature

Weak stratospheric polar vortex(WPV)events during winter months were investigated.WPV events were identified as being weakest in December,accompanied by the most dramatic increase in geopotential height over the polar region.After the onset of a December WPV event,the dynamic processes influencing Eurasian temperature can be split into two separate periods.Period I(lag of 0-25 days)is referred to as the stratosphere-troposphere interactions period,as it is mainly characterized by stratospheric signals propagating downwards.In Period I,a stratospheric negative Northern Annular Mode(NAM)pattern associated with the WPV propagates downwards,inducing a negative NAM in the troposphere.The anomalous low centers over the Mediterranean and North Pacific bring cold advection to northern Eurasia,resulting in a north-cold-south-warm dipole pattern over Eurasia.The zero line between negative and positive temperature anomalies moves southwards during days 5-20.Stratospheric cold anomalies at midlatitudes propagate downwards to high latitudes in the troposphere and contribute to the dipole structure.During PeriodⅡ(lag of 25-40 days),as downward signals from the stratosphere have vanished,the dynamic processes mainly take place within the troposphere.Specifically,a wave train is initiated from the North Atlantic region to northern Europe.The propagation of wave activity flux intensifies a cyclonic anomaly over northern Europe,which brings cold advection to Scandinavia and warm advection to central Asia.Therefore,a northwest-cold-southeast-warm dipole structure occupies Eurasia and migrates southeastwards during this period.

Tidally Induced Water Temperature Change in Artesian Wells

Water temperature observation in wells,as a precursor observation project in China,aims to capture stress-strain information during the preparation of earthquakes. The study of the water temperature tidal effect has important significance,for water temperature tidal effect is both a reflection of stress-strain in crust and an interference factor of precursor observations. With a view of thermal conditions in artesian wells,the paper holds that there are two mechanisms for interpreting tidally induced water temperature changes in artesian wells. Namely,thermal conduction mechanisms and thermal convection mechanism. The paper then derives the quantitative relationship between water temperature and tidal volumetric strain changes in an ideal artesian well. Finally,the water temperature tidal effect in the Benxi artesian well is analyzed. The results show that the water temperature tidal effect in Benxi well is the result of joint action of thermal conduction mechanism and thermal convection mechanism,in which thermal conduction mechanism plays a leading role.

Two-Quark Condensate Changes with Quark Current Mass

Using the Schwinger Dyson equation and perturbation theory,we calculate the two-quark condensates forthe light quarks u,d,strange quark s and a heavy quark c with their current masses respectively.The results show thatthe two-quark condensate will decrease when the quark mass increases,which hints the chiral symmetry may be restoredfor the heavy quarks.

平流层准两年变化对南海夏季风影响机制的探讨

利用美国大气研究中心(the National Center for Atmospheric Research,NCAR)的中层大气模式模拟了平流层准两年振荡(Quasi-Biennial Oscillation,QBO)过程对对流层顶和对流层上层的影响,并结合NCEP(the National Centers for Environmental Prediction)/NCAR、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)月平均的风场资料和实际的探空观测资料,分析了平流层QBO对南海夏季风的影响作用.结果表明:平流层QBO会引起平流层的异常经向环流并向下传播,在QBO位相的中后期和位相转换期影响到对流层顶和对流层上层,使热带和低纬度的对流层上层形成异常的经向气压梯度,最终在夏季的对流层热带地区激发出不同类型的异常环流—西风位相时,激发出与南海夏季风环流相反的异常环流,在南海地区有显著的异常下沉运动,对南海夏季风有削弱作用;东风位相时,激发出反Hadley环流型的异常环流,在南海地区有明显的异常上升气流,对南海夏季风有加强的效果.虽然QBO对南海夏季风经向环流有影响,但它并不是决定南海夏季风准两年变化的唯一因子.

Regional distribution and diurnal variation of deep convective systems over the Asian monsoon region

Using 12 years of data from the Tropical Rainfall Measuring Mission(TRMM)-based Precipitation Radar(PR),spatial and diurnal variations of deep convective systems(DCSs)over the Asian monsoon region are analyzed.The DCSs are defined by a 20 dBZ echo top extending 14 km.The spatial distribution of DCSs genesis is also discussed,with reference to the National Centers for Environmental Prediction(NCEP)reanalysis data.The results show that DCSs occur mainly over land.They concentrate in south of 20°N during the pre-monsoon season,and then move distinctly to mid-latitude regions,with the most active region on the south slope of the Himalayas during monsoon season.DCSs over the Tibetan Plateau are more frequent than those in central-eastern China,but smaller in horizontal scale and weaker in convective intensity.DCSs in central-eastern China have more robust updrafts and generate more lightning flashes than in other Asian monsoon regions.The horizontal scale of DCSs over the ocean is larger than that over the other regions,and the corresponding minimum infrared(IR)brightness temperature is lower,whereas the convective intensity is weaker.Continental DCSs are more common from noon through midnight,and DCSs over the Tibetan Plateau are more frequently from noon through evening.Oceanic DCSs frequency has a weaker diurnal cycle with dawn maximum,and diurnal variation of DCSs over the tropical maritime continent is consistent with that over the continent.

Source characteristics of O_3 and CO_2 at Mt. Waliguan Observatory,Tibetan Plateau implied by using ~7Be and ^(210)Pb

The weekly averages of near-surface ^7Be, ^210pb, 03, and CO2 concentrations at the Global Atmospheric Watch Observatory, Mt. Waliguan （101.98°E, 36.287°N, 3810 m a.s.l.）, from October 2002 to January 2004 are presented. With the establishment of the new datasets of DCCW （Differential Concentrations in Contiguous Weeks） of ^7Be,^210pb, and O3, CO2 （△^7Be, △^210pb, △O3, △CO2, respectively, the impacts of upper-level downward transports and land-surface emissions on O3 and CO2 concentrations are implied by ^7Be and ^210pb being as independent tracers. The relations among △^7Be, △^210pb, and △O3, △CO2 are examined statistically and compared. The results indicate that with the DCCWs, the interferences with the tracing significance of ^7Be and ^210Pb from the seasonal wet scavenging of atmospheric aerosol are greatly reduced, and the weighting sources of O3 or CO2 variations are more pronounced. Basically, the variability of surface O3 is controlled predominately by air mass transported from the upper atmosphere levels while the emission from the Continent Boundary Layer （CBL） has an obvious input for CO2. The relation between △^210pb and △O3 reflects that influences of CBL emission are generally positive/negative for surface O3 budget in summer/winter, and the relation of △^7Be and △CO2 also reveals that upper level downward transport has positive/negative inputs for CO2 in summer/winter. With the highly correlated relations between ^7Be and O3, a quantitative estimation is made of the stratospheric contributions to the budget of surface O3 at WLG： the monthly averages of stratospheric O3 range from 6 ×10^-9 to 8 ×10^-9 （volume mixing ratio） in April and from June to August, and 2 ×10^-9 to 4 ×10^-9 in the remaining months. For the ultimate sources of the baseline concentration of surface 03, which consist of only stratospheric transport and tropospheric photochemistry production, the contribution from stratospheric transport is estimated to be about 20 ×10^-9 from May to July, and （12-15） ×10^-9 in the remaining months, and the total relative contribution rate is about 35% to 40%.

Numerical Simulation of Clocking Effect on Blade Unsteady Aerodynamic Force in Axial Turbine

To give an insight into the clocking effect and its influence on the wake transportation and its interaction, the unsteady three-dimensional flow through a 1.5-stage axial low pressure turbine is simulated numerically by using a density-correction based, Reynolds-Averaged Navier-Stokes equations commercial CFD code. The 2nd stator clocking is applied over ten equal tangential positions. The results show that the harmonic blade number ratio is an important factor affecting the clocking effect. The clocking effect has very small influence on the turbine efficiency in this investigation. The difference between the maximum and minimum efficiency is about 0.1%. The maximum efficiency can be achieved when the 1st stator wake enters the 2nd stator passage near blade suction surface and its adjacent wake passes through the 2nd stator passage close to blade pressure surface. The minimum efficiency appears if the 1st stator wake impinges upon the leading edge of the 2nd stator and its adjacent wake of the 1st stator passes through the mid-channel in the 2nd stator. The wake convective transportation and the blade circulation variation due to its impingement on the subsequent blade are the main mechanism affecting the pressure variation in blade surface.

Effect of rib height on turbulent flow and heat transfer of kerosene in rectangular duct

The coupling effects of rib heights and fluid properties on turbulent convective heat transfer of kerosene flow through the rectangular duct on the ribbed bottom wall are studied numerically in this paper.The numerical simulation is based on the ten components surrogate model of kerosene and the Reynolds average method combined with the re-normalized group(RNG)k-εturbulence model.The turbulent vortex structures and heat transfer characteristics of kerosene flowing over rectangular ribs of different heights are obtained.The results show that three dimensional vortices are generated by the ribs,and the vortices alter local flow significantly,leading to both enhanced and reduced convective heat transfer at different locations near the ribs.In addition,it is found that with the increase of rib height,the average Nusselt number and the wall friction factor on the ribbed wall also increase.For the present study,the maximum heat transfer enhancement rate of kerosene flow is 72.16%,and the ratio of rib-to-duct height is 0.75.