INTERDECADAL VARIABILITY OF QUASI-BIENNIAL OSCILLATION OF STRATOSPHERIC ZONAL WIND

This study investigates the interdecadal variability of Quasi-biennial Oscillation (QBO) based on the sounding data in the stratosphere, ERA-40 and ERA-interim reanalysis data in the past 62 years. The QBO periodicity experiences a significant interdecadal variability; the longer (shorter) the mean period, the smaller (larger) the amplitude of variation is. The QBO amplitude varies in a cycle around 10 to 15 years and in an out-of-phase correlation with the period. In addition, there is an increasing trend of the QBO amplitude in 30 to 10 hPa, while a little declining trend in 70 to 40 hPa. The deviation of the QBO zonal wind extremum centers from the equator also shows interdecadal variability. The deviation location of the easterly core is generally in the reverse side to the westerly core, which means that when the easterly core is on one side of a hemisphere, the westerly core is on the other side.     

1998年夏季热带内外大气低频振荡特征分析

利用纬向平均的局地经向环流模式，对1984年南海地区4月28日～5月31日每日两个时次的局地平均经向环流进行模拟。模拟结果与观测结果吻合，反映出1984年南海夏季风形势的建立是一个经历反复的过程。此外，用诊断分析的方法通过计算各动力和热力强迫因子对季风经向环流的贡献，发现驱动1984年南海夏季风经向环流的首要因子是潜热加热项，主要由北部凝结加热，南部蒸发冷却的经向不均匀加热场分布使得潜热加热对环流的作用为正。温度垂直对流输送项的作用次之，该项的分布在南海北部的值为正、南部值近似为零，这种分布形势也使该因子能单独引起一个正季风环流。第三大因子是纬向温度平流输送项，在南海地区北部有暖平流，南部冷平流的温度平流分布形势对季风环流也起正的作用。而对季风中断期的因子分析表明：潜热加热及纬向温度平流的作用与正季风环流建立期完全相反，温度垂直对流的正作用也大大减弱。     

THE STRUCTURE OF TROPICAL CYCLONE BY TOVS AND ITS APPLICATION IN NUMERICAL WEATHER PREDICTION

The TOVS data are used to study the structure of a number of tropical cyclones for the year 2000. Differences are found to some extent between what is found and classic conceptual models in that (1) the horizontal structure is asymmetric and variable so that the low-value centers at low levels of the geopotential height field (or the high-value centers at high levels) do not necessarily coincide with the high-value centers of the temperature field; (2) the vertical structure is also variable in the allocation of the anomalies of the geopotential height field between low values at low levels and high values at high levels. It is especially noted that the centers of the anomalies are tilting at both high and low levels or the high level is only at the edge of a high-pressure zone. There is not any significant high-value anomalous center in a corresponding location with the tropical cyclone. The structure of tropical cyclone in the TOVS is also used as reference to modify the structure of typhoon BOGUS in the numerical prediction model system of tropical cyclones. It is found that the modified BOGUS performs better in coordinating with the environment and predicting the track of the tropical cyclone. The demonstration is two-fold — the structure of the typhoon BOGUS is such that it means much in the track prediction and the use of the TOVS-based tropical cyclone structure really helps in improving it. It provides the foundation for modification and evolution of typhoon BOGUS.     

热带平流层臭氧准两年周期振荡的特征及数值模拟

利用HALOE的观测资料、对热带地区平流层臭氧垂直分布的年际变化及其准两年周期振荡（QBO）进行研究，并同赤道上空平均的纬向风场的准两年周期振荡进行了模拟研究。资料分析结果表明，平流层臭氧浓度高值区的位置在南北方向上和垂直方向上的有明显的准两年周期，臭氧浓度高值中心的南北移动和上下移动又引起局地臭氧总量的周期性变化和准两年周期振荡南北半球不对称。而臭氧浓度中心位置的准两年周期变化与赤道上空平均纬向风的准两年周期振荡密切相关。资料分析还表明，赤道上空平流层中臭氧浓度QBO的位相随高度变化多次。模拟试验表明，纬向风QBO引起垂直经圈环流的变化，在平流层有三对余差环流圈。它们对O3在不同纬度和高度的输送是引起O3准两年周期振荡的重要动力原因。其中，余差环流在平流层中层（25－35km)的环流圈起着重要的作用。     

A DIAGNOSIS OF THE INTERANNUAL VARIABILITY OF SEA SURFACE TEMPERATURE AND SURFACE WIND FIELD IN THE TROPICAL OCEANS AND ITS CORRELATIVE CHARACTERS WITH ENSO CYCLE

Utilizing the NCEP/NCAR reanalysis monthly datasets,and based on the filter and standarddeviation calculation,the interannual variability of sea surface temperature(SST)and 1000 hPawind field for the tropical Pacific,Indian and Atlantic Oceans is investigated for the past 20 years(1979—1998).The characters of space-time evolution in SST anomalies(SSTA)for each oceanand corresponding wind anomaly field are acquired by using rotated principal component(RPC)and linear regression analysis methods.Using the method of correlation analysis.the characters ofthree tropical oceans correlated with ENSO are investigated.The contemporary correlationbetween the SSTA in the Indian Ocean and in the equatorial eastern Pacific is positive,and there isa weak negative correlation between the SSTA in the equatorial east Atlantic Ocean and in theequatorial eastern Pacific.The lead-lag correlation analysis indicates that the SSTA in theequatorial Indian Ocean lags the dominant Pacific ENSO mode by 3 months,and the SSTA in theequatorial Atlantic Ocean leads ENSO mode by 6 months.The ENSO-correlated components intropical Indian Ocean and tropical Atlantic Ocean display much the same amount of total variance ineach ocean,i.e..14% in the Indian Ocean and 12% in the Atlantic Ocean and the maximums areall above 40%.     

EFFECTS OF VERTICAL WIND SHEAR ON TROPICAL CYCLONE INTENSITY CHANGE

The effects of vertical wind shear on tropical cyclone (TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006. First, the influence of wind shear between different vertical levels and averages in different horizontal areas are compared. The results indicate that the effect of wind shear between 200 and 850 hPa averaged within a 200–800 km annulus on TC intensity change is larger than any other calculated vertical wind shear. High-latitude and intense TCs tend to be less sensitive to the effects of VWS than low-latitude and weak TCs. TCs experience time lags between the imposition of the shear and the weakening in TC intensity. A vertical shear of 8–9 m/s (9–10 m/s) would weaken TC intensity within 60 h (48 h). A vertical shear greater than 10 m/s would weaken TC intensity within 6 h. Finally, a statistical TC intensity prediction scheme is developed by using partial least squares regression, which produces skillful intensity forecasts when potential predictors include factors related to the vertical wind shear. Analysis of the standardized regression coefficients further confirms the obtained statistical results.     

我国九大气候区降水特性及其物理成因的研究Ⅱ——我国各区降水与环流因子的关系

利用ECMWF的格点风和位势高度场资料，对1998年夏季热带内外地区大气低频振荡特征进行了分析研究。结果表明，亚洲季风区的季节内振荡非常显著。850hPa季节内振荡纬向风的经向传播揭示出南海地区的西风振荡受南北两支西风的共同影响。与长江流域特大洪涝密切相关的大气环流系统(乌拉尔阻高和西太平洋副高)对季节内振荡有较强的响应。在欧亚范围，持续性异常环流十分活跃，大气低频波的活动与环流持续异常的形成有密切的联系，季节内振荡是高低纬环流持续异常同时发生的纽带。其低频(30—60d)遥相关型的分布同江淮洪涝年的波列结构相类似。     

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES

Based on the primitive equations in polar coordinates, supposing that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure agrees with the Fujita formula, a set of equations are derived, which describe the impact of perturbations of central pressure, position of tropical cyclones, direction and velocity of movement of tropical cyclones on the wind field. It is proved that the second order approximation of the kinetic energy of tropical cyclones can be described by the equations under linear approximation. Typhoon Wipha (2007) is selected to verify the above interpretation method, and the results show that the interpretation method of the wind field could give very good results before the landfall of tropical cyclones, while making no apparent improvement after the landfall. The dynamical interpretation method in this paper is applicable to improving the forecasts of the wind field of tropical cyclones close to the coast.     

NUMERICAL SIMULATION OF THE TROPICAL INTRASEASONAL OSCILLATION AND THE EFFECT OF WARM SST

An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonaloscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variables,from sever-al different regions,exhibit fluctuations with a spectral peak between 30 and 60 days.This represents a 30—60 dayoscillation in the tropical atmosphere and possesses several features which are consistent with observations.These in-clude a horizontal structure dominated by zonal wavenumber 1 and a vertical structure which is predominantlybaroclinic.The effect of warm SST (sea surface temperature) anomalies on the 30—60 day oscillation in the tropical atmos-phere is also simulated by prescribing global SST as observed in 1983.This has the effect of weakening the oscillationwhile at the same time the vertical structure becomes less baroclinic.The importance of cumulus convection to the propagational characteristics of this oscillation is demonstrated by acomparison of results based on different parameterizations for convection.In one case,where the maximum convectionover the Pacific is simulated to be too far east,the simulated 30—60 day oscillation shows evidence of westward propa-gation.In the second case,where the convection maximum is located near the observed position in the western Pacific,there is more clearly evidence of eastward propagation.Both results suggest that the location of maximum convection in the Pacific can have an important influence on thestrength,structure and propagation of the 30—60 day oscillation.     

NUMERICAL SIMULATION OF INFLUENCE OF STRATOSPHERIC METHANE ON TROPICAL WATER VAPOR AND TEMPERATURE

Climatic c haracteristics of tropical stratospheric methane have been well researched using various satellite data, and numerical simulations have furtherly conducted using chemical climatic models, while the impact of tropica1 stratospheric methane oxidation on tropical distribution of water vapor is not paid enough attention in general circulation models. Parameterization of methane oxidation is taken into account to deal with the chemical moisturizing action due to the methane oxidation in this paper. Numerical simulation and analysis of the influence of stratospheric methane on the prediction of tropical stratospheric moisture and temperature fields using general circulation model is conducted using heavy storm cases including a heavy rain in South China and a typhoon caused tropical storm. The results show obvious impact of methane oxidation on the forecasting precipitation. It is demonstrated that the stratospheric water vapor in the tropic is significantly remedied by introducing of parameterization of methane oxidation. And prediction of stratospheric temperature is accordingly modified, especially in the lower stratosphere within 30°N. The verification of monthly mean of forecast anomaly correlation(ACC) and root mean square(RMS)errors over the tropics indicated that the impact of stratospheric methane is neutral as to the forecast of geopotential height, and positive to the forecast of temperature and winds over the tropics.     

热带海表温度和低层风场的年际变率及与ENSO循环的相关特征研究

采用 NCEP/NCAR的 1 979～ 1 998年逐月平均的海表温度及 1 0 0 0 h Pa风场资料 ,进行滤波和均方差计算 ,得到了热带太平洋、印度洋、大西洋海表温度 (SST)和风场的年际变化特征。用旋转主分量 (RPC)方法和投影法对热带三大洋海表温度距平 (SSTA)进行分析 ,得到了各大洋 SSTA演变的主要时空特征和相应的距平风场特征 ;并用相关分析研究热带三大洋与ENSO相关的特征 ,得到三大洋间的同期相关关系为 :印度洋 SSTA与赤道东太平洋 SSTA成正相关 ,而赤道东大西洋 SSTA与赤道东太平洋 SSTA成弱的负相关 ;赤道印度洋在落后于赤道东太平洋 3个月左右时正相关达到最大 ,赤道大西洋在超前于赤道东太平洋 6个月左右时负相关达到最大 ;热带印度洋和大西洋与 ENSO相关的分量对各自大洋海表温度年际变化的方差贡献数值相近 ,最大在 40 %以上 ,平均解释方差分别为 1 4%和 1 2 %。     

β涡旋的垂直结构及其对热带气旋移动的影响

应用准地转斜压模式数值模拟热带气旋的移动，分析大尺度β涡旋的水平和垂直结构及其对热带气旋移动的。研究结果表明，两β涡旋之间的准均匀流（通风气流）仍然与热带气旋的运动相关。     

晚春初夏西太平洋副高突变特征及其年际变化

根据热带印度洋和热带太平洋(22.5 S～22.5 N,42.5 E～77.5 W )1951～1995年逐月5 ×5 的海面温度距平资料,首先进行了海面温度距平的平均功率谱分析,获取赤道印度洋和赤道太平洋海面平均温度距平存在准12年和准4年的周期变化;然后,利用多维时间序列的交叉谱分析,进一步分别分析了赤道印度洋和赤道太平洋各格点上海面温度距平在准12年和准4年演变周期各格点之间的演变位相及演变落后时间,获得一些有意义的结论。     

热带印度洋和热带太平洋海温振荡规律的研究

选择1979-1993年间的热带气旋为试验个例，通过扰动热带气旋初始位置和初始结构。构造集合成员，用正压原始方程模式，进行路径集合预报试验，并初步探讨预报成员的集合方法。试验结果表明：热带气旋定位误差影响路径预报，但扰动初始位置的集合平均预报与控制试验的预报水平相接近。扰动热带气旋初始结构的集合预报试验表明，约有60％。70％个例的集合路径预报得到改进：此外，试验结果还表明，当环境引导气流较弱时，进行扰动热带气旋初始结构的集合预报，预报结果的改善较明显。     

A DIAGNOSIS OF THE INTERANNUAL VARIABILITY OF SEA SURFACE TEMPERATURE AND SURFACE WIND FIELD IN THE TROPICAL OCEANS AND ITS CORRELATIVE CHARACTERS WITH ENSO CYCLE*

Utilizing the NCEP/NCAR reanalysis monthly datasets,and based on the filter and standard deviation calculation,the interannual variability of sea surface temperature (SST) and 1000 hPa wind field for the tropical Pacific,Indian and Atlantic Oceans is investigated for the past 20 years (1979-1998).The characters of space-time evolution in SST anomalies (SSTA) for each ocean and corresponding wind anomaly field are acquired by using rotated principal component (RPC) and linear regression analysis methods.Using the method of correlation analysis.the characters of three tropical oceans correlated with ENSO are investigated.The contemporary correlation between the SSTA in the Indian Ocean and in the equatorial eastern Pacific is positive,and there is a weak negative correlation between the SSTA in the equatorial east Atlantic Ocean and in the equatorial eastern Pacific.The lead-lag correlation analysis indicates that the SSTA in the equatorial Indian Ocean lags the dominant Pacific ENSO mode by 3 months,and the SSTA in the equatorial Atlantic Ocean leads ENSO mode by 6 months.The ENSO-correlated components in tropical Indian Ocean and tropical Atlantic Ocean display much the same amount of total variance in each ocean,i.e..14% in the Indian Ocean and 12% in the Atlantic Ocean and the maximums are all above 40%.     

近海岸风速衰减特征及形成机理分析

为更好理解沿海区域近地面风速衰减规律及其内在机制并获取适用于业务观测风速数据的分析方法,通过引入内边界层厚度的发展机理,推导获得风速随离岸距离变化的数学解析拟合式。结合浙江省温州市境内一沿海区域6个自动气象站2014—2019年逐时风速观测数据应用该拟合式分析了风速随离岸距离的关系,结果表明不管是逐时风速还是逐日最大风速,其平均值均与离岸距离有着良好的负相关,并发现其衰减系数与风速有着密切关系。向岸流及离岸流的风速衰减特性均可以结合该拟合式用线性及幂数律拟合来体现,但后者可以更好地解释风速随离岸距离变化特征,并在较大风速(3～10 m/s)向岸流的背景条件下,获得合理可信的分析结果,说明该方法可以适用于近海岸区域风速观测数据的应用研究。     

EFFECTS OF VERTICAL WIND SHEAR ON INTENSITY AND STRUCTURE OF TROPICAL CYCLONE

In this study,the effect of vertical wind shear(VWS)on the intensification of tropical cyclone(TC)is investigated via the numerical simulations.Results indicate that weak shear tends to facilitate the development of TC while strong shear appears to inhibit the intensification of TC.As the VWS is imposed on the TC,the vortex of the cyclone tends to tilt vertically and significantly in the upper troposphere.Consequently,the upward motion is considerably enhanced in the downshear side of the storm center and correspondingly,the low-to mid-level potential temperature decreases under the effect of adiabatic cooling,which leads to the increase of the low-to mid-level static instability and relative humidity and then facilitates the burst of convection.In the case of weak shear,the vertical tilting of the vortex is weak and the increase of ascent,static instability and relative humidity occur in the area close to the TC center.Therefore,active convection happens in the TC center region and facilitates the enhancement of vorticity in the inner core region and then the intensification of TC.In contrast,due to strong VWS,the increase of the ascent,static instability and relative humidity induced by the vertical tilting mainly appear in the outer region of TC in the case with stronger shear,and the convection in the inner-core area of TC is rather weak and convective activity mainly happens in the outer-region of the TC.Therefore,the development of a warm core is inhibited and then the intensification of TC is delayed.Different from previous numerical results obtained by imposing VWS suddenly to a strong TC,the simulation performed in this work shows that,even when the VWS is as strong as 12 m s-1,the tropical storm can still experience rapid intensification and finally develop into a strong tropical cyclone after a relatively long period of adjustment.It is found that the convection plays an important role in the adjusting period.On one hand,the convection leads to the horizontal convergence of the low-level vorticity flux and therefore leads to the enhancement of the low-level vorticity in the inner-core area of the cyclone.On the other hand,the active ascent accompanying the convection tends to transport the low-level vorticity to the middle levels.The enhanced vorticity in the lower to middle troposphere strengths the interaction between the low-and mid-level cyclonical circulation and the upper-level circulation deviated from the storm center under the effect of VWS.As a result,the vertical tilting of the vortex is considerably decreased,and then the cyclone starts to develop rapidly.     

SEASONAL VARIATIONS OF THE TROPICAL INTRASEASONAL OSCILLATION AND ITS REPRODUCTION IN SAMIL-R_(42)L_9

Seasonal variations of the tropical intraseasonal oscillation (ISO) and relationship to seasonal variation of the climate background are studied by using NCEP/NCAR reanalysis data and output of SAMIL-R42L9. Analysis of NCEP data shows that spatial distribution of the tropical ISO has obvious seasonal variations, which are well consistent with the seasonal variation of climate background. The activity of the tropical ISO is, to a great extent, dependent on warm SST, strong convection, zonal western wind, strong precipitation and low-level moisture convergence. Main characteristics of the seasonal variations of the tropical ISO are captured by SAMIL-R42L9. Simulations of seasonal variation of climate background vary greatly with different variables. Results of SAMIL-R42L9 indicate that the seasonal variations of the tropical ISO in dynamical fields are more dependent on climate background than in heating fields and SAMIL-R42L9 cannot represent well the strong dependence of the ISO on the climate background present in NCEP/NCAR reanalysis data. It also suggests that seasonal variations of the ISO do not completely depend on that of climate background.     

热带太平洋经向风异常年际变化与海温异常的关系

运用奇异谱分析（SSA）方法对热带太平洋海温和经向风进行周期分析，结果表明太平洋海气系统存在准4年、准2年和年代际尺度的变化周期，其中准4年的变率最大。不同区域的风场，在不同时间尺度上与海温异常联系的紧密程度不同，位相的演变也有差异。文中还讨论了在准4年与准2年分量之间因风场的不同而导致的海温异常的差异。     

NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION

A time-dependent linear model on the equatorial beta plane is developed in this paper.Its verticalstructure consists of two active layers with equal density and temperature above the thermocline and aquasi-stationary layer with constant density below the thermocline.The results of nurnericat experiments show that the direct influence of heat on the equatorial ocean ismuch smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction,the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibriumand anomalous development of the ocean-almosphere circulation.