西南涡对流云中夹卷率的模拟研究

本文使用中尺度数值模式WRF(Weather Research and Forecasting Model)模拟了2010年7月8—9日发生在四川盆地的一次西南涡降水天气过程,并计算该过程中零度层以下对流云中的夹卷率。从云内垂直特征看:云内的含水量、垂直风速和浮力都在云底之上随高度递增,而在云顶附近随高度递减;云内的湿静力能则主要随高度递减;夹卷率在云底以上随高度递减,而在云顶附近随高度递增,但是云顶高度越高,在云顶附近的递增趋势越不明显。另外,夹卷率和云内的云水、雨水含量都呈负相关,说明夹卷抑制了对流云的发展以及地面降水。当假设被夹卷的环境空气来自云边界附近时,计算所得的夹卷率值要大于假设夹卷空气远离云边界所得值,但这两种假设中夹卷率的其他特征是类似的。从演变特征看,夹卷率总体上随时间减小,这和这段时间内对流云整体发展增高有关。     

山地对流云并合形成积层混合云的过程分析

本文利用贵阳市气象台2005和2006年5-9月的地面、高空观测和雷达资料等,分析了41次山地对流云并合形成积层混合云的降水过程.研究发现如果分散的多单体对流云若距离较近,则很可能出现大范围地跨接、合并,则有可能形成范围宽广的片状或带状云系,即积层混合云系.云系形成以后在移动的过程中,会将前方不断新生的对流单体合并,从而云系前缘强度增强,云系不断维持.整个系统的生命期往往较分散云团更长,并有可能会形成间歇性或连续性降水.本文分析了山地对流云并合形成积层混合云的一些具体特征.     

两种探空仪判别云垂直结构的对比研究

利用广东省阳江地区2010年7—8月WMO组织的国际高性能探空系统对比试验数据,对Vaisala RS92型探空仪和国产长峰探空仪的测云性能进行对比分析,并利用同步观测的Vaisala云高计和毫米波雷达数据进行了分析和验证。结果表明:两种探空仪判别的云层垂直结构都能较好地反映阳江的实际的云层情况。对于低云,两种探空仪的探测结果比较接近;对于不密实的云层,两种探空仪都会误判为多层云;对于高云,两种探空仪的判别效果均不理想,长峰探空仪还容易漏判云层。RS92探空仪探测的高云的云底和云顶的平均高度要高于长峰探空仪的探测结果。     

Electrification of thundercloud by an entrainment mechanism

Summary A time dependent model for the growth of electric field by an entrainment mechanism has been developed, in which charge separation takes place at the interface of the descending blob due to discontinuity in the conductivity either from the onset of ice process or from the evaporative depletion of small ice or water particles in cloud parcels diluted by entrainment of dry air at the cloud top. Charge generation by the entrainment mechanism may be self limiting in high electric fields. We examine the extent to which the leakage current produced by the electrical forces acting on the descending thermals influences the net charge separation caused by the entrainment mechanism. When the effect of electrical force on the descending blob is negligibly small and the fractional change in conductivity of the blob is 0.75, high electric field of the order of a few hundred kV/m can be generated within the duration of 800s. The electrical force acting on the blods, however, does set an upper limit to the growth of an electric field, and the considered mechanism can generate electric field of the order of ten kV/m within the duration of 400 to 800s, depending on the meteorological and electrical conditions. We conclude that an entrainment mechanism can account for the observed electrification of thunderstorm at the initial stages, but that it is inadequate to generate an electric field high enough to initiate lightning.With 8 Figures     

强降水过程风廓线雷达资料的极值特征

基于微波辐射计、微雨雷达、风廓线雷达和毫米波云雷达获得的高时空分辨率多源新型遥感探测资料,对上海梅雨期一次强降水过程（2020年6月15日）的大气热力、动力、云雨等垂直结构特征进行了分析。主要结论如下：（1）降水发生前一日（6月14日）上午,强西南风为上海地区输送了大量水汽,对流层中低层水汽明显增多、气温偏高,大气不稳定性增加,K指数在降水前10多个小时逐渐增至35℃甚至更高;降水之后,对流层低层气温下降、水汽减少。（2）此次降水过程云层较深厚,主要降水时段云层厚度基本都维持在12 km以上,最厚可达14 km,融化层位于约4.7 km高度。（3）降水各阶段对应的云雨结构特征差异较大。降水前期,强回波垂直方向集中在3 km以下,且时间上间歇出现;降水中期,云体融化层连续且稳定,强回波区持续出现,且垂直方向扩展至4 km及以上,雨滴下降速度稳定维持在6 m·s^-1以上;降水后期,云顶高度下降至9 km及以下,降水回波减弱,弱降水特征明显。

     

The scavenging of nitrate by clouds and precipitation

A model with spectral microphysics was developed to describe the scavenging of nitrate aerosol particles and HNO₃ gas. This model was incorporated into the dynamic framework of an entraining air parcel model with which we computed the uptake of nitrate by cloud drops whose size distribution changes with time because of condensation, collision-coalescence and break-up. Significant differences were found between the scavenging behavior of nitrate and our former results on the scavenging behavior of sulfate. These reflect the following chemical and microphysical differences between the two systems:

1. nitrate particles occur in a larger size range than sulfate particles.
2. HNO₃ has a much greater solubility than SO₂ and is taken up irreversibly inside the drops in contrast to SO₂.
3. nitric acid in the cloud water is formed directly on uptake of HNO₃ gas whereas on uptake of SO₂ sulfuric acid is formed only after the reaction with oxidizing agents such as e.g., H₂O₂ or O₃.
4. nitrate resulting from uptake of HNO₃ is confined mainly to small drops, whereas sulfate resulting from uptake of SO₂ is most concentrated in the largest, oldest drops, which have had the greatest time for reaction.

Sensitivity studies showed that the nitrate concentration of small drops is significantly affected by the mass accommodation coefficient.     

Cluster Ion Reactions: Insights into Processes of Atmospheric Significance

Experimental results of ion cluster reactions withatmospherically relevant species are considered hereinto provide a unified overview of the current state ofunderstanding brought about through experimentalstudies of cluster ion reactions. This isaccomplished by first outlining the atmospheric issuesaddressed by cluster ion studies and then, summarizingthe results of numerous studies. The recent, as wellas previously published studies of cluster ionreactions, are considered in the context of gainingnew insights into the molecular details ofheterogeneous processes involving the interactions ofelectrolytes with cloud droplets, ice crystals andaerosol particles. In addition to elucidating themechanisms of these and other selected reactions andtransformations of atmospheric significance, thefindings of the uptake of acid molecules in waterclusters are shown to lead to the suggestion of a newmodel that accounts for the formation of reactioncenters involving charged sites at aqueous surfaces.     

Spatial structure of internal tidal waves generated on weak topographies

The generation of internal gravity waves by barotropic tidal flow passing over a two-dimensional topography is investigated. Rather than calculating the conversion of tidal energy, this study focuses on delineating the geometric characteristics of the spatial structure of the resulting internal wave fields (i.e., the configurations of the internal beams and their horizontal projections) which have usually been ignored. It is found that the various possible wave types can be demarcated by three characteristic frequencies: the tidal frequency, ω₀; the buoyancy frequency, N; and the vertical component of the Coriolis vector or earth's rotation, f. When different possibilities arising from the sequence of these frequencies are considered, there occur 12 kinds of wave structures in the full 3D space in contrast to the 5 kinds identified by the 2D theory. The constant wave phase lines may form as ellipses or hyperbolic lines on the horizontal plane, provided the buoyancy frequency is greater or less than the tidal frequency. The effect that stems from the consideration of the basic flow is also found, which not only serves as the reason for the occurrence of higher harmonics but also increases the wave strength in the direction of basic flow.     

Atmospheric thermic structure studied by acoustic echo sounder, boundary layer model, and direct measurements

In this work, the thermic structure of the atmospheric boundary layer is analyzed by means of direct measurements with radiosonde equipment, remote exploration with a three-monostatic Doppler sodar, and a boundary layer model of order one-and-a-half. Intercomparisons of radiosonde data, sodar data, and model results are made through the study of radiative nocturnal inversion, subsidence inversion, development and height of the mixing layer, and calculus of the temperature structure parameter. The ability of sodar to find the mixing layer height and to detect stable layers is enhanced when these layers are low enough.     

Multifractal simulations and analysis of clouds by multiplicative processes

Clouds exhibit fractal structures over wide ranges of scale. However, clouds are not geometrical objects: they are produced by highly intermittent fields (e.g. liquid water content). On the other hand, they are rarely isotropic: “texture”, stratification, as well as variable (scale-dependent) orientation of structures are common. To deal with such fractal features, we must generalise scale invariance notions beyond the (usual) geometrical self-similar (or even self-affine) notions. We outline the necessary formalism (generalised scale invariance) and show how it can be used to deal with the strongly intermittent fields which result from multiplicative (cascade-type) processes concentrating matter or energy into smaller and smaller scales leading to the appearance of multiple singularities, multiple dimensions and divergences of statistics for these fields.We illustrate these ideas with radar rain data showing first how to directly estimate the elliptical dimension characterising the stratification, and second, how to determine universal scale-independent (co-) dimension functions that characterise the distribution of the intense rain regions.     

Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian sea as revealed by MONSOON-77 data

The thermodynamic structure of the Atmospheric Boundary Layer (ABL) over the Arabian sea region has been studied with the help of 135 aerological observations obtained during MONSOON-77 in the region (10–14° N, 64–68° E) by USSR research vessels. Low-level inversions were observed over the western Arabian sea region (west of 66° E) in association with suppressed convection. The different sublayers of the ABL, viz. the mixed layer, the cloud layer and the inversion/isothermal/stable layer were identified. The low-level stability analysis indicated that in the region east of 66° E, conditions were favourable for deep convection. The thermodynamic transformation of the boundary layer after precipitation was documented.     

爆炸影响对流云发展过程的原理研究

用爆炸方法进行人工防雹是我国的一个特点,且已有很长历史了,近十年来爆炸方法在群众性试验中进一步广泛采用,出现了利用空炸炮、火箭和高炮等爆炸手段。根据某些地方多年防雹资料的初步分析,用爆炸方法进行人工防雹是有一定效果的。然而爆炸究竟对云有什么作用?它对冰雹形成过程会有什么影响?国外有人试图用“空腔作用”造成软雹来解释爆炸影响冰雹云的作用,也有人提出爆炸引起过冷水的冻结作用。但我国大量人工防雹试验指出,爆炸可以迅速引起降水,出现云洞,云体消散或转向等现象,这些现象不能用上述国外已有想法来解释。     

云中风和湍流的多普勒雷达探测

一、发展概况 微波多普勒雷达可以用来测量各类降水云系中的风和湍流的场结构,这是其他一般探测方法难以做到的。 多普勒雷达接收的是回波的频移信息。频移的大小正比于降水粒子相对于雷达射束的径向速度。从分布杂乱和运动着的大气降水粒子反射回来的信息往往是展宽了的多普     

大兴安岭火区上空云和降水微物理结构特征个例研究

1987年5月24日云物理专业考查飞机对大兴安岭火区上空的云进行了水平观测。对此次观测结果的分析与研究表明:(1)来自空间状及空间技状区域的冰粒子(25—800μm)及降水粒子(200—6400μm)平均浓度较高;而来自枝状及枝星状区域的冰和降水粒子其平均浓度较低。(2)依据不同降水粒子形态所计算出的降雪强度以空间枝状为最大。     

Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke

During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground.     

Discrimination of ice from water in clouds by optical remote sensing

Water and ice, although nearly transparent in the visible, absorb weakly in the near infrared, and spectral absorption differs for the two phases, especially in the wavelength region between 1.55 and 1.75 μm. Multiple scattering in clouds amplifies absorption, so that cloud reflectance or transmittance measurements would enable the interfence of thermodynamic phase. A ground-based near-infrared radiometer, which measures the relative spectral reflectance from sides of clouds in the wavelength range 0.63 to 1.9 μm, was built and used to obtain spectra from cumulus congestus and cumulonimbus clouds. Results from measurements in summer 1985 seem to indicate that such a ground-based technique can accurately determine the phase of clouds.     

山东省1989-2008年23架次飞机云微物理结构观测试验结果

利用山东省1989-2008年23架次秋季降水云系云结构的粒子测量系统(PMS)探测试验资料,分析了云中过冷水以及冰晶浓度的分布特征.结果表明,山东省降水云系中存在较为丰富的过冷水,最大可达0.36 g/m3,云中冰晶浓度最大可达12.8-406 L-1.对2006-2008年探测的云粒子浓度、直径及过冷水随温度变化特...     

热带气旋进入北部湾后强度增强的环流特征分析

利用NCEP／NCAR再分析资料，对1949年以来7个进入北部湾后强度突然增强的热带气旋（TC）环流背景特征及物理量场特征进行分析，结果表明，有利TC进入北部湾后强度增强的环流背景是：（1）西太平洋副热带高压稳定加强西伸，（2）热带辐合带北抬至华南沿海活动，（3）西南季风爆发处于活跃期，（4）东风波西移叠加，（5）有适度的弱冷空气侵入；对物理量场的合成分析表明，TC进入北部湾前和进入北部湾后，环流中心附近500hPa涡度变化极小，200hPa高空散度增大，500hPa垂直上升速度增大，850hPa中南半岛水汽输送量增大。