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1.
除了动量的局地变化和水平平流之外,本文讨论了动量垂直输送和β-效应在均质正压的Ekman边界层中的作用。利用奇异摄动方法,得到了精确到O(R_0~2)的Ekman边界层中水平风场的垂直结构和边界层顶垂直速度的解析表达式,对解的非定常和水平非均匀特征作了定性讨论。用一迭加在均匀西风气流上的园形、定常涡旋场的定量计算表明,动量垂直输送和β-效应对Ekman边界层中水平风速分布、边界层厚度及边界层顶垂直速度均有明显的影响。 相似文献
2.
本文在边界层顶垂直速度正比于地转涡度和地转风速,并与下垫面粗糙度有关的前提下,研究了边界层抽吸引起的涡度变化,在圆对称气压系统内得到了不同粗糙度情况下的涡度场和气压场的变化速率,修正了经典理论的结果。在湍流交换系数是地转风速及高度的函数的前提下,推导了地形存在时边界层顶垂直速度的公式,并用来讨论地形存在时的旋转减弱问题。 相似文献
3.
本文提出一个在中性情况下边界层数值模式中考虑背景风压场影响的方法。背景风压场的水平非均匀影响了边界层运动方程中的惯性力项及边界层的上界风速。本文把三维问题用一种线性化方法简化为一维问题，只要知道背景气压场的空间分布，即可求出考虑了背景场影响的边界层风场。 相似文献
4.
在中性正压的行星边界层中,考虑边界层顶的负随时空变化的一般情况,在的假定下,用数值方法解边界层运动方程得到风及边界层某些参数的分布。还计算了边界层顶垂直速度,发现和Charney等人的结果不同。 相似文献
5.
基于风廓线雷达的广东登陆台风边界层高度特征研究 总被引：3，自引：1，他引：2
针对8个登陆广东省的热带气旋,利用经过数据质量控制的风廓线雷达连续、高时空分辨率的风场观测数据,对热带气旋边界层特征进行了分析。研究结果表明:热带气旋边界层中切向风速大值区垂直范围越大、风速越强、持续时间越久,则热带气旋强度越大、登陆后强度维持时间越久。眼区外入流层厚度越大,入流层气流越强,热带气旋登陆后强度维持时间则越久。风廓线雷达信噪比垂直梯度对大气湍流信息有一定的指示作用,对于入流层高度在2000 m以下的热带气旋,其入流层顶所在高度与信噪比梯度最大值所在高度相近,对于入流层较为深厚的热带气旋,用信噪比垂直梯度确定的边界层高度虽接近入流层顶高,但仍有一定差距。不同特点的热带气旋其边界层高度并不相同,对于登陆后强度迅速减弱的热带气旋边界层高度在500~1000 m;登陆后强度持续时间短的热带气旋,其边界层高度约1000~2000 m;登陆后强度持续时间长的热带气旋,其边界层高度在2000 m之上,最高可达5000~7000 m。这些结果加深了对登陆台风边界层高度演变特征的认识。 相似文献
6.
提出了一个由低纬地（海）面风计算边辊层顶垂直速度的方法，得到了低纬边界层顶生趣速度的一些特征，指出了惯性项及β效应的重要作用。 相似文献
7.
利用塔克拉玛干沙漠腹地2016年7月13-14日和26-27日GPS探空和地面气象观测资料,分析了塔克拉玛干沙漠夏季晴天夜间各气象要素垂直廓线特征。结果表明:夜间(21:00至次日08:00,北京时,下同)稳定边界层的厚度达到240 m。残余混合层最大厚度与前一天对流混合层厚度相当,随时间推移其厚度到10:15损耗近三分之一,残余逆温层顶盖厚度达到400 m;在残余逆温层顶盖和稳定边界层顶附近有风速极大值出现,而07:15稳定边界层顶附近有低空急流发展,其最大风速达到10.8 m·s~(-1);夜间低空处比湿的变化趋势是先增后减小再增大的过程,其最小值为2.95 g·kg~(-1),出现在04:15的稳定边界层顶附近。残余混合层内比湿随高度略微增大;夜间逆温层对水汽通量有阻挡和聚合的作用,使其在稳定边界层顶和残余混合层顶附近出现极大值,并于07:15达到最大值。垂直水汽通量于04:15在残余混合层中下部做下沉运动、上部和残余逆温层顶盖中做上升运动;同时,夜间陆面过程中,存在较强的辐射冷却和较小的摩擦速度,这也是形成较为浅薄的夜间稳定边界层主要的热力因素和湍流动力因素。 相似文献
8.
边界层参数化方案对暴雨数值模拟的影响 总被引：16，自引：1，他引：16
选取2003年7月4-5日南京暴雨个例，采用非静力中尺度模式MM5进行模拟，着重研究了不同边界层参数化方案对雨量中心强度、雨区分布的影响。结果表明：对于不同的边界层参数化方案，垂直速度场、水汽通量散度场、涡度场、水平风场的散度以及θse场都表现出不同的特征；合理边界层方案的引入对预报效果有明显的改进；结合边界层和自由大气的动力、热力结构进行了综合分析，给出了边界层作用与自由大气动力、热力结构的配置情况。说明这种配置对暴雨的形成是至关重要的。 相似文献
9.
本文用新的边界层顶垂直速度参数化方案研究了当地形和边界层摩擦同时存在时二者对Eady波不稳定性的影响,得到了边界层层结、地面粗糙度、地形坡度的影响,还研究了摩擦和地形对一般化Eady波不稳定性的影响。 相似文献
10.
大地形上边界层流场的动力学研究 总被引：1，自引：1，他引：1
本文应用边界层气象学中Estoque数值模式关于湍流交换系数及分层的处理方法,求得了大地形存在时定常边界展方程的零、一级解析解,并用来得到大地形存在时边界层的散度场、垂直速度场,改进了前人的结果。 相似文献
11.
The vertical transport of mass at the top of the boundary layer is considered as a link between theboundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layeris studied under the consideration of the interaction between the boundary layer and free atmosphere.Thevertical motion at the top of the boundary layer is evaluated.The results show that the distinguished differ-ences of the present results from classical Ekman layer do exist and they are discussed in the paper. 相似文献
12.
边界层动力学中的Ekman动量近似 总被引：3，自引：3，他引：3
自由大气中,大气运动的基本状态是地转风,近年来发展的地转动量近似,是为了进一步研究非均匀地转流的动力学问题,然而,在边界层大气中,运动的基本状态是经典的Ekman流,所以对边界层运动来说,地转动量近似是不合适的,需作一推广。本文提出了一种所谓Ekman动量近似,它相似于自由大气中的地转动量近似,并讨论了Ekman动量近似的物理基础,对边界层的风场结构及边界屋顶部的垂直速度也作了详细分析。 相似文献
13.
在边界层动力学中，涡动粘性系数是影响边界层风场结构的一个重要参数。本文利用边界层动力学中的Ekman动量近似理论，给出了涡动粘性系数随高度缓变条件下的Ekman动量近似边界层模式解，着重讨论了边界层的风场结构、水平散度、垂直涡度以及边界层顶部的垂直速度。结果分析表明：与常值涡动粘性系数情况相比，在边界层低层随高度增加的涡动粘性系数可以导致低层边界层风速随高度迅速增加，即风速垂直切变增加，同时风速矢与地转风之间的夹角减小。惯性项作用可以导致上述作用在气旋性区域减小、而在反气旋性区域增大。随高度增加的涡动粘性系数导致水平散度绝对值、垂直涡度绝对值以及边界层顶部的垂直速度绝对值在气旋性区域减小，而在反气性旋区域增大。涡动粘性系数与惯性之间的非线性相互作用是边界层动力学中重要过程。 相似文献
14.
A range of large-eddy simulations, with differing free atmosphere stratification and zero or slightly positive surface heat flux, is investigated to improve understanding of the neutral and near-neutral, inversion-capped, horizontally homogeneous, barotropic atmospheric boundary layer with emphasis on the upper region. We find that an adjustment time of at least 16 h is needed for the simulated flow to reach a quasi-steady state. The boundary layer continues to grow, but at a slow rate that changes little after 8 h of simulation time. A common feature of the neutral simulations is the development of a super-geostrophic jet near the top of the boundary layer. The analytical wind-shear models included do not account for such a jet, and the best agreement with simulated wind shear is seen in cases with weak stratification above the boundary layer. Increasing the surface heat flux decreases the magnitude and vertical extent of the jet and leads to better agreement between analytical and simulated wind-speed profiles. Over a range of different inversion strengths and surface heat fluxes, we also find good agreement between the performed simulations and models of the equilibrium boundary-layer height, and of the budget of turbulent kinetic energy integrated across the boundary layer. 相似文献
15.
Hongrong SHI Hongbin CHEN Xiang&# ao XIA Xuehua FAN Jinqiang ZHANG Jun LI Chao LING 《大气科学进展》2017,34(6):783-790
Using radiosonde measurements from 26 July to 30 July 2014 at Baiqi over the Inner Mongolia grassland of China, the vertical structure of shallow cumulus(SCu) clouds and associated environmental conditions were investigated. The cloud base height and the cloud top height of SCu was 3.4 km and 5 km, respectively. The temperature of the SCu layer was less than 0℃. The horizontal advection of specific humidity was smaller than the vertical transport in the atmosphere below 5 km.Above 5 km, the thermodynamic structure of the atmosphere remained stable. At the interface of the cloud layer and free air atmosphere, there was obvious wind shear and a temperature inversion(~2.9℃). Comparisons of environmental parameters associated with cumulus congestus, rain and clear days, showed that the formation of SCu was characterized by a higher Bowen ratio(high sensible heat flux and low latent heat flux), which indicated intensive turbulence in the boundary layer. The formation of SCu was associated with the boundary layer height exceeding the lifting condensation level. The maintenance of SCu was likely associated with the lower convective available potential energy, weak wind shear, and weak subsidence of the synoptic system, which did not favor the dramatic vertical development of SCu and thereby the transformation of SCu to cumulus congestus. 相似文献
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17.
The analytical results of the previous paper(Wu,1989)are used to study the properties of vertical veloc-ity distribution at the top of the boundary layer.The relative position of a jet like geostrophic flow and el-lipse-shaped orography will affect the characteristic feature of vertical motion at the top of the boundary layerwhen the contributions of friction and orography are taken into consideration simultaneously. 相似文献
18.
Wu Rongsheng 《大气科学进展》1985,2(1):1-7
In this paper, the influences of orography on the boundary layer flow with the approximation of geostrophic momentum are studied. The wind velocity at the lower boundary will not always be zero when the orography exists. So the structure of the boundary layer flow, as well as the vertical velocity at the top of the boundary layer, is affected. There are three factors affecting the vertical motion at the top of the boundary layer: lifting due to orography; divergence due to Ekman flow, and advection of the geostrophic momentum. These effects and the features of the flow within the boundary layer are discussed in detail. 相似文献
19.
R.L. Raddatz 《大气与海洋》2013,51(4):399-419
Abstract This paper describes a 1‐D agroclimatic model of the atmosphere/crop‐soil interface. Vertical profiles of wind, potential temperature and water vapour are constructed twice daily for the overnight‐low and maximum temperature times by combining 1200 and 0000 UTC upper‐air standard‐level grid‐point data with climatological observations. The vertical structure of the atmospheric boundary layer has a surface constant‐flux layer that is usually topped by a mixed layer by day but not at night. The crop‐soil boundary layer consists of a shallow top‐zone and a growing root‐zone. Vegetation cover and root depth depend upon crop type and phenological stage. Water‐balance accounting tracks the moisture contents of both the top‐ and root‐zones. Evapotranspiration or the vertical flux of water vapour in the atmospheric boundary layer is tied to the evolution of the crop‐soil boundary layer. The model was calibrated using field data from the Regional Evaporation Study's primary site in an agricultural area of central Saskatchewan. The evolution of 1991's wheat‐soil boundary layer from the crop's heading to ripe stages was then successfully simulated at two additional sites in the same geographical area. 相似文献
20.
In considering the weak non-linear effect, and using the small parameter expansion method, the analyt-ical expressions of the wind distribution within PBL (planetary boundary layer) and the vertical velocity at the top of the PBL are obtained when the PBL is divided into three layers and different eddy transfer coefficients K are adopted for the three layers. The conditions of barotropy and neutrality for the PBL are extended to that of baroclinity and non-neutral stratification. An example of a steady circular vortex is used to display the characteristics of the horizontal wind within the PBL and the vertical velocity at the top of the PBL. Some new results have been obtained, indicating that the magnitude of the speed in the lower height calculated by the present model is larger than that by the model in which k is a constant within the whole boundary layer, for example, in the classical Ekman boundary layer model and the model by Wu (1984). The angle between the wind at the top of the PBL and the wind near the surface calculated by the present model is less than that calculated by the single K model. These results are in agreement with the observations. 相似文献