大气动力学中三种Rossby波作用通量的特征差异和适用性比较

大气动力学诊断Rossby波的传播时,通常用波作用通量来表示。常用的三种波作用通量分别为Plumb波作用通量,T-N波作用通量和局地E-P通量。本文详细讨论了这三种方法的特征差异,并结合2016年1月的一次寒潮事件,比较了三种方法在该事件中的适用性。结果表明:1)Plumb波作用通量的纬向分量较大而经向分量较小,适用于振幅较小的纬向均匀的西风带Rossby长波的诊断。2)T-N波作用通量是对Plumb波作用通量的改进,经向分量得以增强,能更好地描述纬向非均匀气流中的较大振幅的西风带Rossby长波扰动。T-N波作用通量计算时,背景场取多年平均的当月气候场较合适,能更好地反映当前季节内的Rossby波传播异常。3)局地E-P通量可以诊断一段时间内天气尺度瞬变波对背景场(定常波)总的调控作用,但无法直接反映Rossby长波的逐时演变(T-N波或Plumb波作用通量则可以)。     

台风“利奇马”影响期间浙江沿海海浪特征分析

利用浮标资料,对“利奇马”影响期间浙江沿海风和海浪特征及其关系进行分析,并对欧洲中心模式预报与实况进行对比,基于模式预报分析海浪的空间结构。结果发现:(1)随着台风靠近、登陆和远离,海浪波型经历了混合浪—风浪—混合浪的变化,且最大波高越大周期越长,浙江南部沿海海浪较北部沿海更具风浪特点;(2)浪高受风速影响大,北部沿海更为明显,持续风向对浪高增大有明显作用,当风向由向岸转为与海岸线平行、或由与海岸线平行转为离岸时,浪高迅速减小,反之浪高迅速增大;(3)台风靠近和影响浙江时,有效波高与风速的等值线平行,7、8、10级风分别与巨浪、狂浪、狂涛区有很好的对应,有效波高越高,风速对波高的决定作用越明显。     

低层不稳定大气边界层中的地形阻力

采用两层大气模式,通过求解线性化大气动力学—热力学方程组,得到在上层稳定层结覆盖的不稳定大气边界层中,简单三维地形引起的地形波及其波动阻力的解析表达式。讨论了地形及大气条件对地形波及波动阻力的影响。结果表明:即使在大气低层为不稳定边界层时,三维地形引起的波动在大气动量平衡中仍可起明显作用。     

大气横波型扰动连续谱的结构

采用数值方法计算了当基本气流有垂直线性切变、 层结参数为常值时横波型扰动的谱点和谱函数, 并将数值计算的结果与理论分析作了对照和讨论。当三支波动连续谱区相互不重叠时该计算结果与理论分析完全一致, 但当发生连续谱区重叠时则须采用谱函数重组的方法来得到连续谱的结构。重组的基本原则是在波谱重叠区对计算得到的谱函数作预处理后, 再对频率相邻的谱点和谱函数进行滑动平均, 并将该滑动平均后的结果作为重组后的谱点和谱函数。分析该重组后的谱函数可知, 此时扰动结构呈现涡旋－重力惯性混合波的形式, 出现了新波型。在连续谱三波重叠区域, 该混合波的谱函数在对流层中层有涡旋波的临界层并体现了涡旋波的性质, 在对流层的上、 下层则分别有顺、 逆传重力惯性波的临界层并体现了重力惯性波的性质。     

WAVEWATCHIII模式在渤海海浪预报的应用与检验

大连黄海、渤海海浪数值预报系统采用WAVEWATCHIII模式进行海浪预报,预报产品包括48 h内浪高、周期、浪向的逐3 h预报,并对其进行检验。结果表明：WAVEWATCHIII模式对渤海中部浪高模拟较好,浪高预报TS为71.7 %,对近岸海区浪高模拟相对差些。个例的检验表明,浪高最大值模拟较好,模拟浪高最大值出现的时间与实况基本吻合,浪高变化趋势预报也较好。AVEWATCHIII模式对两个周期个例进行检验,预报误差最低可达到0.17 s,预报效果较好。     

中尺度大气波动的波谱和谱函数——数学模型和计算方法

作者得到了准二维Boussinesq方程组，并用其研究了中尺度大气波动的波谱和谱函数。在一定条件下对该方程组线性化并取标准模后，可将其初边值问题转化为矩阵的广义特征值问题来进行数值求解，这样就可知原问题波谱和谱函数的性质。当无基本流且取地转参数、层结参数为常数时，可求得其波谱和谱函数的解析解。此时该模式中仅包含有一对重力惯性内波模态，且各模态均是简谐波；模态越高，垂直波数越大则波动传播得越慢，所有的模态均为离散谱，并存在聚点。对此作者用数值解作了验算，结果表明，该数值求解方案合理可行，对不太高的模态其精度也令人满意。在无基本流然而考虑层结的垂直变化后，则一般无法求取解析解，为此进行了数值求解。这时该模式仍仅包含有一对重力惯性内波的离散谱模态，不过由于层结参数的变化，各模态结构与简谐波出现了偏差。     

Some Possible Solutions of Nonlinear Internal Inertial Gravity Wave Equations in the Atmosphere

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Variations in Wave Energy and Amplitudes along the Energy Dispersion Paths of Nonstationary Barotropic Rossby Waves

The variations in the wave energy and the amplitude along the energy dispersion paths of the barotropic Rossby waves in zonally symmetric basic flow are studied by solving the wave energy equation,which expresses that the wave energy variability is determined by the divergence of the group velocity and the energy budget from the basic flow.The results suggest that both the wave energy and the amplitude of a leading wave increase significantly in the propagating region that is located south of the jet axis and enclosed by a southern critical line and a northern turning latitude.The leading wave gains the barotropic energy from the basic flow by eddy activities.The amplitude continuously climbs up a peak at the turning latitude due to increasing wave energy and enlarging horizontal scale(shrinking total wavenumber).Both the wave energy and the amplitude eventually decrease when the trailing wave continuously approaches southward to the critical line.The trailing wave decays and its energy is continuously absorbed by the basic flow.Furthermore,both the wave energy and the amplitude oscillate with a limited range in the propagating region that is located near the jet axis and enclosed by two turning latitudes.Both the leading and trailing waves neither develop nor decay significantly.The jet works as a waveguide to allow the waves to propagate a long distance.     

对流云街激发的重力波和波动阻力

大气边界层中的对流活动,可以在其上部稳定层中激发出重力波,并引起垂直动量输送,影响到对流层和平流层中的动量平衡过程.从二层模式中大气波动方程的线性解出发,得出了对流云街激发的重力波波阻解析表达式,并讨论了大气条件对波阻的影响.这些分析可有助于大气环流模式(GCM)中此类重力波波阻参数化表达式的建立和改进.     

A FLUID EXPERIMENT OF GRAVITY INTERNAL WAVE INDUCED BY TERRAIN*

The mountain wave induced by a ridge in two-layer stratified fluid has been successfull ysimulated in a tank.The wave pattern is qualitatively similar to that calculated with linear theory.     

低纬大气Kelvin波和Rossby波的非线性相互作用

利用多重尺度摄动法,对低纬大气Kelvin波和Rossby波的波包演变进行了分析,得到两波的非线性相互作用方程为耦合的非线性复系数Landau方程组。数值计算表明两波相遇将使波振幅变化,波宽变窄;两波非线性相互作用可能是低纬强烈天气突然爆发的原因之一。     

近40多年广东省的寒潮活动

利用广东省１１个代表站１９５１－１９９４年每日气温（包括日平均和日最低气温）资料,分析了广东省近４４年来寒潮活动的气候特征。首先,根据广东省气象局规定的寒潮标准,寻找出每个站所有的寒潮过程,在引基础上分析了广东寒潮的地区分布特征。其次,只要１１个代表站中１站或１站以上出现寒潮就认为是一次寒潮过程。在此条件下的统计表明,广东省在４４年中一共出现了１０３次寒潮过程,影响时间从１０月底至３月中旬,其中以     

Long-term analysis of extreme wave characteristics based on the SWAN hindcasts over the Black Sea using two different wind fields

The long-term variations of wave characteristics in the Black Sea are evaluated by using a third-generation wave model (Simulating WAves Nearshore, SWAN), forced by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim and National Centers for Environmental Prediction/Climate Forecast System Reanalysis (NCEP/CFSR) wind data, covering the period of 1979−2018. The model results were calibrated and validated with buoy measurements at seven stations along the Black Sea. The comparative study shows that the CFSR dataset predicted slightly greater significant wave heights than the ERA-Interim dataset. The greatest difference between two datasets in terms of wave characteristics was found in the northeastern part of the Black Sea. The long-term averages and the variations of long-term trends for wave characteristics show that southwestern part of the Black Sea was characterized by greater significant wave heights, longer mean wave periods and storm durations, and lower variability, while the northeastern part of the basin was characterized by lower significant wave heights, shorter mean wave periods and storm durations, and higher variability. The long-term trends indicate that the wave characteristics over the 40-year period are more likely to be exposed to higher variation on the eastern part of the Black Sea than the western part of the basin.     

我国北方500hPa春、夏季平均长波年际异常的EOF分析

利用1958—2008年全球逐日2.5°×2.5°NCEP/NCAR再分析资料,采用经验正交函数分解(EOF)和谐波分析方法对我国北方地区春、夏季平均长波进行了分析。结果表明:(1)我国北方春季平均长波主要表现为亚洲北部从咸海到日本存在一个完整的长波:巴尔喀什湖到我国罗布泊地区以长波脊活动为主,我国东北地区以长波槽活动为主,长波槽、脊的强度均呈增强趋势;夏季平均长波主要表现为乌拉尔山、贝加尔湖及鄂霍次克海地区的长波脊、槽、脊分布,蒙古国到我国北部地区多为长波槽活动,近51年来长波槽存在减弱趋势。(2)春季平均长波的距平变化主要表现为我国西北、华北地区与其上游和下游邻近地区存在反相关关系;夏季平均长波距平变化和春季相比有所东移,即我国北方大部分地区距平变化与其上游和下游地区存在反相关关系。     

0801号台风风浪场和涌浪场的数值模拟

利用美国国家海洋大气总局/美国国家环境预报中心（NOAA/NCEP）发布的最新版WAV-EWATCHⅢ（version3.14）海浪模式对0801号台风＂浣熊＂进行数值模拟,并在此基础上对台风浪的发展过程和台风影响下的海面有效波高、风浪场及涌浪场的分布特征进行分析。结果表明：海面有效波高的分布和演变受台风系统强度和移动的影响;台风过程中所产生的大浪主要为风浪;涌浪场的分布与风浪场的分布几乎相反,涌浪场基本分布在远离台风中心的外围海域;涌浪场波高比风浪场波高要小。     

TESTING DRAG COEFFICIENT APPROACHES BY USING THE BUOY DATA COLLECTED IN MODERATE TO HIGH WIND UNDER FOLLOWING, CROSSING AND OPPOSING SWELL CONDITIONS

Hurricane intensity and track are strongly affected by air-sea interactions. Classified as following swells, crossing swells, and opposing swells, the observed wave height was parameterized by using the 10-m wind speed collected on 5 buoys by the National Buoy Data Center during 13 hurricane events. The path information of these 13 hurricanes was obtained from the National Hurricane Center Best Track (NHC-BT). Results show that the wave height increases exponentially with the 10-m wind speed, and the wave height reaches the maximum value, 11.2 m (8.1 m), when 10-m wind speed is 40 m s-1 under the following and crossing (opposing) swell conditions. We find that the wave steepness (the ratio of wave height to wave length) is proportional to the -2/3 power of the wave age (the ratio of wave phase velocity to 10-m wind speed). The parameterizations of friction velocity and drag coefficient are tested using the buoy data collected in moderate to high wind under following, crossing and opposing swell conditions. A wave age dependent equation for drag coefficient is found more accurate and suggested for future usage in numerical models. Further, these algorithms also suggest that wind-swell orientation needs to be considered to retrieve accurate surface drag under high winds and strong swells.     

1961-2012年黑龙江省寒潮气候特征

利用1961-2012年黑龙江省62个气象站逐日平均气温及日最低气温,定义黑龙江省单站寒潮,并着重分析了黑龙江省寒潮发生频次的时空变化特征。结果表明：近52 a黑龙江省寒潮频次明显减少,寒潮频次的多少与地形的分布特点一致,山区半山区等高寒地带发生寒潮的频次明显多于平原地区。寒潮在11月和12月发生的最多,9月最少,冬季的寒潮频次明显比春季和秋季多。近52 a春季、秋季和冬季寒潮频次基本为减少趋势,而大兴安岭地区秋季寒潮频次呈增加趋势。     

INFLUENCES OF NONUNIFORM STRATIFICATION ON WAVE RAYS OF INTERNAL GRAVITY WAVE*

In this paper the influences of nonuniform stratification on the propagating paths of internal inertial-gravity and pure gravity wave energy are discussed by using the WKB approximation method.The conditions for conservation of wave energy,generalized wave action and wave enstrophy are obtained.The necessary condition of instability for internal gravity waves and the equation governing the refraction of wave rays are derived.Two types of critical levels are given.Finally,the wave rays for different distributions of stratification are calculated by using the fourth-order Runge-Kutta method.     

地形强迫对大气长波调整的可能影响

地形作为大气的外部强迫,其动力和热力作用对波动结构演变及极端天气出现都有不能忽视的作用。本文通过数值求解考虑地形强迫的β平面正压准地转位势涡度方程,探讨了地形强迫作用对大气长波调整的可能影响,结果表明:同非线性作用和纬向非均匀基流作用一样,无基流情形下具有纬向差异的地形分布影响了大气长波结构的演变,也能强迫出大气长波调整现象。大气长波调整依赖于地形的高度和地形分布,地形越高,长波越容易出现波数的调整;地形波数越大,即地形结构复杂,越不易出现波数变化。大气长波调整还与纬度有关,纬度越高,β越小,地形强迫作用越突出,长波调整容易出现;反之,低纬度以β效应为主的线性波动不易出现波数调整。大气长波调整对波动初始波动的振幅不敏感,但依赖于波动的初始结构。此外,有基流作用时,地形强迫还是诱发定常波的重要因素,且定常波流场结构依赖于地形高度分布,与波动初始结构无关。     

INFLUENCES OF NONUNIFORM STRATIFICATION ON WAVE RAYS OF INTERNAL GRAVITY WAVE

In this paper the influences of nonuniform stratification on the propagating paths of internal inertial-gravity andpure gravity wave energy are discussed by using the WKB approximation method.The conditions for conservation ofwave energy,generalized wave action and wave enstrophy are obtained.The necessary condition of instability for inter-nal gravity waves and the equation governing the refraction of wave rays are derived.Two types of critical levels are giv-en.Finally,the wave rays for different distributions of stratification are calculated by using the fourth-orderRunge-Kutta method.