地形引起的重力内波的水槽实验

利用不同密度分层的盐水模拟稳定层结大气条件 ,在水槽中成功地模拟了两层大气分层流中二维山脊引起的地形波 ,得到的波动图像与线性理论模式结果在定性上基本一致     

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。     

圆形涡旋中的惯性重力内波不稳定和对称不稳定

用Boussinesq近似下的轴对称径向二维柱坐标系中的线性扰动方程组，讨论了圆形大气涡旋系统中扰动的惯性重力不稳定和对称不稳定。在环境为正压情形时，惯性重力内波不稳定的条件为#A(μj/R0)2N2+n2F2<0；当环境为斜压时，具有平行型扰动特征的惯性重力波发展的条件为Ri＊<1-[(3/2)+m]2，此时表现为对称不稳定。可见，惯性重力内波不稳定和对称不稳定都可作为台风、气旋一类圆形涡旋中扰动形成和发展的机制。     

三维非静力平衡大气中平行切变流上重力内波的不稳定及半椭圆定理

本文应用守恒型非弹性模式研究了三维非静力平衡大气中平行切变流上重力内波的不稳定，推广了Miles定理和半圆定理，得到了有限深度气层的半椭圆定理。该定理指出不稳定波的复波速被限制在相速复平面上一个内接于霍华德（Howard）半圆的半椭圆内。该半椭圆长轴重合于半圆的直径，而短轴则取决于最小Ri数、波长、波宽等因素。     

对称不稳定大气中的孤立行波精确解

通过对二维准动量无辐散、无摩擦、密度非均匀分布的层结大气中基本气流切变对非线性方程组行波解的影响问题的研究，证明：（ａ）在对称稳定（ｑ＝Ｎ２Ｆ２－Ｓ４＞０）的大气中：非线性行波解为周期解，且其周期与相应的线性周期解的周期相等；（ｂ）在对称非稳定（ｑ＝Ｎ２Ｆ２－Ｓ４≤０）的大气中：存在两类非线性行波解，其性质是由参数Ｂ决定的。Ｂ＝（Ｎ２ｓｉｎ２φ－２Ｓ２ｓｉｎφｃｏｓφ＋Ｆ２ｃｏｓ２φ）／σ２。（１）当Ｂ＞０时为周期解，且其周期与相应的线性周期解的周期相等；（２）当Ｂ≤０时为孤立波解。     

层结大气中重力惯性波的发展

应用WKB方法讨论了非均匀层结大气条件下重力惯性波的发展。分析表明,在水平方向上,当波动由层结不稳定度小的地方向不稳定度大的地方传播时,波将发展,从而修正了文献[2]的结论。     

钟形地形动力抬升和重力波传播与地形云和降水形成关系研究

地形云和降水过程在区域水循环、水资源、生态环境及气候变化中具有十分重要的作用。本文利用中尺度数值模式WRF 数值模拟试验,以及通过引入表示大气层流速度、层结稳定度和地形特征的关系参数——湿Froude 数(F_w),研究了北京2009 年5 月1 日湿条件不稳定大气层结下,地形云和降水形成过程与地形动力抬升和地形重力波传播之间的关系及形成机理。研究表明,在地形最大高度2 km、半宽10 km 的条件下,层流速度从2.5 m/s 逐步增加到25 m/s 时,对应的湿F_w 数从0.19 增加到1.81。当F_w≤1 时,地形的阻挡起主要作用,由地形抬升形成的地形云主要产生在迎风坡一侧。地形重力波主要产生在迎风坡,并向上游传播,先形成层状云,最后演变为准稳定浅对流波状云。最大降水主要发生在紧靠山顶的迎风坡一侧,但当F_w 很小时,地形云不产生降水。当F_w>1 时,地形抬升形成的云主要发生在山顶附近,而地形重力波主要形成在背风坡,并向下游方向传播,形成准稳定波状云。最大降水主要产生在紧靠山顶的背风坡一侧。另外,在弱湿条件不稳定大气层流下,地形降水主要由地形动力抬升造成的暖云微物理过程产生,地形重力波形成的波状云几乎不产生降水。     

中层大气重力波的一种激发机制及其数值模拟 I. 非地转不稳定和波结构

本文用FGGE资料分析了1979年2月—3月一次爆发性增温期间平流层环流的不稳定性，从而说明在平流层爆发性增温期间伴随产生大振幅重力波活动的原因。分析结果表明:在平流层爆发性增温期间，大气中存在着很强的并且是系统性的非地转运动，从而产生非地转不稳定。强烈的地转偏差的存在激发出大振幅重力波。我们还应用一个线性化扰动方程求得了非地转不稳定判据；并且用数值方法分析了这次爆发性增温期间基流的特征谱点和不稳定波结构。计算结果表明基流满足非地转不稳定条件，具有快波性质的波动出现了不稳定。     

中性和不稳定层结大气的孤立行波精确解

通过研究二维准动量无辐散、无摩擦层结大气非线性方程组的行波解问题证明，非线性行波解的本质属性是由参数ｂ的符号性质决定的。当ｂ＞０时，为周期解，其周期与相应的线性周期解的周期相等；当ｂ≤０时，为孤立波解。给出了一般行波解的解析表达式。并细致地研究了中性和不稳定层结大气中的孤立行波的特征，发现中性和不稳定层结大气中存在具有类似于飑线结构特征的孤立波。指出了中性和不稳定层结大气中的一般孤立行波物理量的分布特征。     

边界层Scorer参数对背风波波长的影响

利用一个中层Scorer参数较大,上、下层Scorer参数较小的3层背风波模型,讨论了边界层(下层)Scorer参数对背风波波长的影响。结果表明,当边界层Scorer参数减小时,波长增大,反之波长减小;当中高层的Scorer参数较小时,背风波波长对边界层的Scorer参数敏感。利用该结果结合观测事实分析后发现,由于地表加热的日变化影响了边界层的Scorer参数,故造成了背风波波长在夜间缩短,在午后增加;此外还发现,因夏季的Scorer参数要比冬季小,这可导致波长变化率在夏季比冬季更大。     

On Internal Gravity Waves Associated with the Stable Boundary Layer

The stable planetary boundary layer at the baseof the residual layer supports internalwaves that are unambiguously boundary layer incharacter. Some of these wavesare instabilities and some are neutrally stable modes, but they all have critical levelsin the residual layer. These waves exist for a broad range of conditions and should bea major component of any ducted disturbance that propagates within ninety degreesof the wind direction. The wave properties can be computed without the numericaldifficulties usually associated with critical-level systems.     

大气边界层风速脉动的分形模拟

应用曲线分数维计算方法计算大气边界层实际风速观测资料的分数维值,并根据分形理论构造出一个理论模型来模拟真实的大气边界层风速时间序列。将模拟和真实数据的一些重要的统计特征,例如方差、风速概率分布、谱密度函数和自相关函数等,进行了比较,结果表明二者具有很好的一致性。     

大气边界层和大气环境研究进展

大气边界层物理和大气环境是大气科学的重要领域,中国科学院大气物理研究所自成立以来在这一研究领域取导了丰硕的成果.作者重点介绍最近十多年来在大气边界层探测、大气边界层结构特征、大气湍流理论、城市和区域大气污染预测预报模式研究等方面取得的重要进展,并对大气边界层和大气环境研究的未来发展作了展望.     

Observations of Solitary Waves in the Stable Atmospheric Boundary Layer

Large amplitude, isolated, wave-like phenomena have been observed in the lowest 40 m of the strongly stably stratified atmospheric boundary layer overlying a coastal Antarctic ice shelf. The waves only occur when prevailing wind speeds are low. They always propagate from over the land, with phase speeds exceeding the local mean wind speed. They have wavelengths of the order of 200 m. Several examples are described and a summary of the statistical properties of these waves events is presented.     

一个中尺度模式中高分辨边界层的参数化

建立一个高分辨大气边界层模式。然后,把该模式与一个中尺度数值预报模式进行耦合并把模式计算结果与实测结果进行了对比。结果表明,该耦合模式能够模拟出大气边界层的流场、温度场和气压场的特征。     

Impact of Different Aerosols on the Evolution of the Atmospheric Boundary Layer

The present work analyzes the effect of aerosols on the evolution of the atmospheric boundary layer (ABL) over Shangdianzi in Beijing.A one-dimensional ABL model and a radiative transfer scheme are incorporated to develop the structure of the ABL.The diurnal variation of the atmospheric radiative budget,atmospheric heating rate,sensible and latent heat fluxes,surface and the 2 m air temperatures as well as the ABL height,and its perturbations due to the aerosols with different single-scattering albedo (SSA) are studied by comparing the aerosol-laden atmosphere to the clean atmosphere.The results show that the absorbing aerosols cause less reduction in surface evaporation relative to that by scatting aerosols,and both surface temperature and 2 m temperature decrease from the clean atmosphere to the aerosol-laden atmosphere.The greater the aerosol absorption,the more stable the surface layer.After 12:00 am,the 2 m temperature increases for strong absorption aerosols.In the meantime,there is a slight decrease in the 2 m temperature for purely scattering aerosols due to radiative cooling.The purely scattering aerosols decrease the ABL temperature and enhance the capping inversion,further reducing the ABL height.     

Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.     

Development of the Convective Boundary Layer Capping with a Thick Neutral Layer in Badanjilin: Observations and Simulations

In this study,the development of a convective boundary layer (CBL) in the Badanjilin region was investigated by comparing the observation data of two cases.A deep neutral layer capped a CBL that occurred on 30 August 2009.This case was divided into five sublayers from the surface to higher atmospheric elevations:surface layer,mixed layer,inversion layer,neutral layer,and sub-inversion layer.The development process of the CBL was divided into three stages:S1,S2,and S3.This case was quite different from the development of the three-layer CBL observed on 31 August 2009 because the mixed layer of the five-layer CBL (CBL5) eroded the neutral layer during S2.The specific initial structure of the CBL5 was correlated to the synoptic background of atmosphere during nighttime.The three-stage development process of the CBL5 was confirmed by six simulations using National Center for Atmospheric Research (USA) large-eddy simulation (NCAR-LES),and some of its characteristics are presented in detail.