关于双层泄流排沙孔进口斜门槽涡带性质的研究

从减压、常压试验发现的双层泄流排沙孔进口斜门槽的涡带现象，经二元水洞试验验证，证明它是１条气带，并解释了这条气带的成因。该成果对正确判断三门峡双层孔斜门槽导轨的破坏原因和筛选工程改善措施，具有现实指导作用。

三门峡双层泄水孔原型噪声观测研究

本文通过对三门峡双层泄水孔原型噪声观测资料的分析,澄清了在水工模型试验中未能取得一致意见的若干水力学问题,所得成果对确定三门峡双层泄水孔的改建方案有重要的现实意义。

STRUCTURAL AND EVOLUTION CHARACTERISTICS OF THE EASTERLY VORTEX OVER THE TROPICAL REGION

By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°× 2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere relating to the east-west direction shift of the subtropical anticyclone over the Western Pacific Ocean. It is shown that there exists a westward shift simultaneously between the anticyclone and the vortex locating south of it. The anticyclone retreats eastward abnormally while the easterly encounters with the westerly around the same longitudes as they move from the opposite directions. The former is an upper weather system, extending from mid-troposphere to the height of 50 hPa with the center locating on 200 hPa. The vertical thermal distribution illustrates the characteristics of being"warm in the upper layer but cold in the lower layer". The divergence effect and the vertical motion change largely within the east and west sides of the easterly vortex and ascending branch transforms to descending branch near its center.

THE MESOSCALE WAVES AND THE FORMATION OF POLYGONAL EYE WALL IN TYPHOONS

Mesoscale waves in typhoons were diagnosed by using a simulated typhoon data in this paper. Through analyzing the structure of the waves in typhoons, we found that the waves possess the mixed features of gravity incrtial waves and vortex Rossby waves. On the one hand, positive geopotential height perturbation is corresponding to negative vorticity perturbation and anticyclonic circulation. At the same time. negative geopotential height perturbation is corresponding to positive vorticity perturbation and cyclonic circulation. The maximum perturbation occurs near the radius of the maximum wind in the typhoon On the other hand, the mesoscale waves possess the features of strong convergence and divergence and ageostrophic wind. Finally, the authors presented a concept model to explain a linkage mechanism between the mesoscale waves and the formation of polygonal eye wall in the typhoon.

The South Pacific Subtropical Mode Water in the Tasman Sea

From the synopical CTD sections in the WOCE PR11 repeated cruises, the South Pacific Subtropical Mode Water (SPSTMW) has been identified in the region of the Tasman Front Extension (TFE) around 29?S to the east of Australia. In the depth range of 150-250 m, the SPSTMW appears as a thermostad with vertical temperature gradient lower than 1.6℃(100 m)-1 and a tem- perature range of 16.5-19.5℃ and as a pycnostad with PV lower than 2×10-10 m-1 s-1 and a potential density range of 25.4-26.0 kg m-3. Like the subtropical mode waters in the North Atlantic and North Pacific, the formation of the SPSTMW is associated with the convective mixing during the austral wintertime as manifested from the time series of the Argo floats. And cold water entrains into the mixed layer with the deepening mixed layer from September to the middle of October. During the wintertime formation process, mesoscale eddies prevailing in the TFE region play an important role in the SPSTMW formation, and have a great effect on the SPSTMW distribution in the next year. The deeper (shallower) mixed layer in wintertime, consistent with the depressed (uplifted) permanent thermocline, is formed by the anticyclonic (cyclonic) eddies, and the substantial mode water thicker than 50 m is mainly found in the region of the anticyclonic eddies where the permanent thermocline is deeper than 450 m.

USE OF A NEW STEERING FLOW METHOD TO PREDICT TROPICAL CYCLONE MOTION

A tropical cyclone is a kind of violent weather system that takes place in warmer tropical oceans and spins rapidly around its center and at the same time moves along surrounding flows. It is generally recognized that the large-scale circulation plays a major role in determining the movement of tropical cyclones and the effects of steering flows are the highest priority in the forecasting of tropical cyclone motion and track. This article adopts a new method to derive the steering flow and select a typical swerving track case (typhoon Dan, coded 9914) to illustrate the validity of the method. The general approach is to modify the vorticity, geostropical vorticity and divergence, investigate the change in the non-divergent stream function, geoptential and velocity potential, respectively, and compute a modified velocity field to determine the steering flow. Unlike other methods in regular use such as weighted average of wind fields or geopoential height, this method has the least adverse effects on the environmental field and could derive a proper steering flow which fits well with storm motion. Combined with other internal and external forcings, this method could have wide application in the prediction of tropical cyclone track.

Response of extreme precipitation to increasing extratropical cyclonic vortex frequency

Since the 2000 s,extratropical extremes have been more frequent,which are closely related to anomalies of planetary-scale and synoptic-scale systems.This study focuses on a key synoptic system,the extratropical cyclonic vortex(ECV)over land,to investigate its relations with extreme precipitation.It was found that ECVs have been more active post-2000,which has induced more extreme precipitation,and such variation is projected to persist along with increasing temperature within 1.5℃of global warming.An enhanced quasi-stationary vortex(QSV)primarily contributes to the ECV,rather than inactive synoptic-scale transient eddies(STEs).Inactive STEs respond to a decline in baroclinicity due to the tendency of the homogeneous temperature gradient.However,such conditions are helpful to widening the westerly jet belt,favoring strong dynamic processes of quasi-resonant amplification and interaction of STEs with the quasi-stationary wave,and the result favors an increasing frequency and persistence of QSVs,contributing to extreme precipitation.

THE THEORY OF MOIST POTENTIAL VORTICITY AND ITS APPLICATION IN THE DIAGNOSIS OF TYPHOON RAINFALL AND INTENSITY

This paper tests the impacts of cloud-induced mass forcing on the moist potential vorticity （MPV） anomaly associated with torrential rains caused by Typhoon No.9914 （Dan） by using fine model simulation data outputted by the Fifth-Generation NCAR / Penn State Mesoscale Model （MMS）. The diagnostic results show that the positive MPV anomaly region, which is obtained by integrating the MPV from 600 hPa to 300 hPa in the vertical, roughly coincides with the precipitation at their synchronous stages either in position or in the distribution pattem, and the maximum positive MPV area of Dan is located mainly between 600 hPa and 300 hPa, which is much higher than torrential rain cases. Further analyses also showed that the value of positive MPV anomaly increased or decreased with the development of Dan, and the positive MPV anomaly may also be served as a tracer to indicate the evolution of tropical cyclone intensity.

Influences of different forces on the bubble entrainment into a stationary Gaussian vortex

Simulations of bubble entrainment into a stationary Gaussian vortex are performed by using the combined particle tracking method(PTM)and boundary element method(BEM).Before the bubble is captured by the vortex core,oscillation and migration of the quasi-spherical nucleus are solved by using improved RP equation and the momentum theorem in the Lagrangian reference frame simultaneously,and the trajectory of the nucleus presents a kind of reduced helix shape.After captured by the vortex core,the bubble grows immediately and moves and deforms along the vortex core axis.The non-spherical evolution and deformation of the bubble is simulated by adopting a mixed Eulerian-Lagrangian method.The output of quasi-spherical stage is taken as the input of non-spherical stage,and all the behaviors of the entrained bubble can be simulated such as inception,motion,deformation and split.Numerical results agree well with published experimental data.On this basis,the influences of various factors such as viscosity,surface tension,buoyancy are studied systemically.Hopefully the results from this paper would provide some insight into the control on vortex bubble entrainment.

Mechanism for initial brows-like meso-scale vortex effects on tropical cyclone track

We used a two-dimensional quasi-geostrophic barotropic model simulation to study effects of an initial brows-like meso-scale vortex on tropical cyclone (TC) track. Our results show that the impact of each of the three foundational factors (the environ- mental current, the asymmetric structure and the asymmetric convection system) on TC track varies with time and the im- portance of each of the factors is different for the different TC motion time period. They show two kinds of the effects. One is a direct way. The asymmetric outer wind structure and the positive longitudinal wind speed averaged in radial-band (100-300) km in the period of (0-11) h are caused by the introduction of the initial brows-like meso-scale vortex, which results in TC track to turn to the north from the northwest directly. The other is an indirect influence. First, initial TC axisymmetric circula- tion becomes a non-axisyrnmetric circulation after the addition of the meso-scale vortex. The initial non-axisymmetric circula- tion experiences an axisymmetrizational process in the period of (0-11) h. Second, axisymmetrizationed TC horizontal size is enlarged after t=-12 h. Third, both the TC asymmetric structure and the TC energy dispersion induced-anticyclone are intensi- fied, which quickens the TC motion and results in the track to turn to the north indirectly. The TC motion is characterized by the unusual track under the direct and the indirect effect. The formation of the unusual track should be attributed to the com- mon effects of three factors, including the environmental flow, the TC asymmetric structure and the asymmetric convection system.

An Improved Prediction Model of Vortex Shedding Noise from Blades of Fans

The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades.An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993.In this model,for mathematical convenience,an idealized vortex street is considered.However,the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade.In the present study,a modified model is proposed based on the prediction model by Lee.The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades.Considering the effect of boundary layer separation on the location of noise source,the predicted overall sound pressure level compares favorably with the experimental data of an axial fan.In the calculation of A-weighted sound pressure level(La),considering the effect of static pressure on radiate energy,the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan.