Conversion Characteristics between Barotropic and Baroclinic Circulations of the SAH in Its Seasonal Evolution

In the context of 1958–1997 NCEP/ NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and baroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, whereupon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter), the SAH is a thermal (dynamical) system, with dominant baroclinicity (barotropicity), either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the “ thermal guidance” of its baroclinic component circulation, suggesting that the component circulation precedes the system itself in variation; iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the “ dynamic steering” of its barotropic component circulation. Key words SAH (South Asia high) - Barotropic circulation - Baroclinic circulation - Seasonal variation (1)This work is supported by the National Natural Sciences Foundation of China under Grant No.49735170.

Charney’s Model—the Renowned Prototype of Baroclinic Instability—Is Barotropically Unstable As Well

The Charney model is reexamined using a new mathematical tool, the multiscale window transform(MWT), and the MWT-based localized multiscale energetics analysis developed by Liang and Robinson to deal with realistic geophysical fluid flow processes. Traditionally, though this model has been taken as a prototype of baroclinic instability, it actually undergoes a mixed one. While baroclinic instability explains the bottom-trapped feature of the perturbation, the second extreme center in the perturbation field can only be explained by a new barotropic instability when the Charney–Green number γ 1, which takes place throughout the fluid column, and is maximized at a height where its baroclinic counterpart stops functioning.The giving way of the baroclinic instability to a barotropic one at this height corresponds well to the rectification of the tilting found on the maps of perturbation velocity and pressure. Also established in this study is the relative importance of barotropic instability to baroclinic instability in terms of γ. When γ 1, barotropic instability is negligible and hence the system can be viewed as purely baroclinic;when γ 1, however, barotropic and baroclinic instabilities are of the same order;in fact, barotropic instability can be even stronger. The implication of these results has been discussed in linking them to real atmospheric processes.

Numerical Physical Mechanism and Model of Turbulent Cascades in a Barotropic Atmosphere

In a barotropic atmosphere, new Reynolds mean momentum equations including turbulent viscosity, dispersion, and instability are used not only to derive the KdV-Burgers-Kuramoto equation but also to analyze the physical mechanism of the cascades of energy and enstrophy. It shows that it is the effects of dispersion and instability that result in the inverse cascade. Then based on the conservation laws of the energy and enstrophy, a cascade model is put forward and the processes of the cascades are described.

Comparison of Flow Characteristics Around Refractive and Right-angled Groins in Barotropic and Baroclinic Conditions

Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm＇s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.

Some Aspects of the Characteristics of Monsoon Disturbances Using a Combined Barotropic－Baroclinic Model

A standing Rossby wave of wavelength 30°longitude with a finite amplitude along the meridional direction is superimposed on the zonal mean component of the monsoon flow and the stability of such a flow is examined by a quasi-geostrophic barotropic.as well as by a quasi-geostrophic combined barotropic and baroclinic model on a beta plane centered at 18°N latitude. It is found that the growth of synoptic scale disturbance increases with the amplitude of the meridional wind. The barotropic stability analysis at 700 hPa pressure level shows that there is a critical value (Umaz=11 m/s) of the maximum mean zonal wind below which the computed disturbance moves to the west due to the wave-wave superposition. For maximum mean zonal wind greater that 11m /s, the westerly wind dominates and the disturbance moves to the east. In another analysis the stability of the zonally asymmetric basic now is studied with a combined barotropic-barotropic model where cumulus heating is included. The growth rate, intensity, horizontal scale and the westward velocity of computed disturbances reasonably agree with those of observed monsoon disturbances. The fastest growing mode has a horizontal wavelength of 2000 kms and the e-folding time is about 3 days,when the meridional amplitude of the Rossby wave is 4m/ s at 700 hPa pressure level. When cumulus heating is included in the analysis the intensity of geopotential perturbation at 700 hPa disturbance is -304 m2 / s2. Energy calculations show that the kinetic energy of the mean zonal flow is the main source of energy for the perturbation to grow.It is also t'ound that the contribution of the kinetic energy of the basic Rossby wave to the growth of perturbation is more in comparison to the available potential energy.

The Solitary Wave of Barotropic Atmosphere on a Sphere

In this paper, we have investigated large scale disturbance in barotropic atmosphere on a sphere. It demonstrates that: considering nonlinear effects of interaction between waves in barotropic vorticity equation, the wave packet of the disturbance is governed by the famous equation-nonlinear Schrodinger equation. For the solitary wave, two factors are very important: one is spherical effect of the disturbance and the other is meridional shear of blocking high. In comparison with the results of local Cartesian coordinates, the former factor is the individuality of spherical soliton.

Nolinear waves and their barotropic stability in the tropical ocean and atmosphere

In this paper, the nonlinear waves and their barotropic stability in the tropical ocean and atmosphere are studied with the qualitative theory of the ordinary differential equation. The relationship is derived between the stability of nonlinear waves with different frequencies and the basic currents and their horizontal shear in the tropical ocean and atmosphere.

The Role of the Halted Baroclinic Mode at the Central Equatorial Pacific in El Nifn Event

The role of halted ＂baroclinic modes＂ in the central equatorial Pacific is analyzed. It is found that dominant anomaly signals corresponding to ＂baroclinic modes＂ occur in the upper layer of the equatorial Pacific, in a two-and-a-half layer oceanic model, in assimilated results of a simple OGCM and in the ADCP observation of TAO. A second ＂baroclinic mode＂ is halted in the central equatorial Pacific corresponding to a positive SST anomaly while the first ＂baroclinic mode＂ propagates eastwards in the eastern equatorial Pacific. The role of the halted second ＂baroclinic mode＂ in the central equatorial Pacific is explained by a staged ocean-atmosphere interaction mechanism in the formation of El Nifio： the westerly bursts in boreal winter over the western equatorial Pacific generate the halted second ＂baroclinic mode＂ in the central equatorial Pacific, leading to the increase of heat content and temperature in the upper layer of the central Pacific which induces the shift of convection from over the western equatorial Pacific to the central equatorial Pacific; another wider, westerly anomaly burst is induced over the western region of convection above the central equatorial Pacific and the westerly anomaly burst generates the first ＂baroclinic mode＂ propagating to the eastern equatorial Pacific, resulting in a warm event in the eastern equatorial Pacific. The mechanism presented in this paper reveals that the central equatorial Pacific is a key region in detecting the possibility of ENSO and, by analyzing TAO observation data of ocean currents and temperature in the central equatorial Pacific, in predicting the coming of an El Nino several months ahead.

Vertical Structure of Baroclinic Currents over Northern South China Sea Continental Slope

The 28.6 d time series of ADCP currents at 27 depth levels, (11,15,…,115m) which are obtained from a mooring station at the northern South China Sea continental slope, have been decomposed into barotropic and baroclinic components. The emphasis in this paper is on the analysis of the time series of baroclinic currents by means of several methods,such as the tidal harmonic analysis, the power spectra and the kinetic energy estimation.The major results are as follows: (1) In respect of the baroclinic currents, the values of several parameters first decrease and then increase with depth. These parameters include the temporal mean value of the cross-shelf component, the standard deviations, the amplitudes of K1 constituents, the mean eddy kinetic energy, as well as the significant peaks of the power spectra of the cross-shelf components. (2) The diurnal period of the baroclinic currents is dominant. The diumal tidal current rotates clockwise and the major axis of current ellipse is located along the directions of NW-SE. The vertical distribution of the phases of the diurnal constituent varies with the different water layers. Around the 67m depth level, the phase changes very much.At those layers far away from the 67m depth level, the vertical distribution of the phase is relatively stable, but with opposite phases in the upper and lower water layers. For the upper layers between the surface and 67m,the phases are around 300°; for the lower layers between 67m and 115m, the phases are around 120° .(3) The mean eddy kinetic energy of the baroclinic current is quite large, accounting for 41% of the mean kinetic energy of the measured currents. The cross-shelf component is larger than the along-shelf one. The two baroclinic current components correspond to the major and minor axes of the current ellipse of the diurnal constituent respectively. (4) The power spectra of the baroclinic currents show a singnificant period of about 24h, with 23.6h at both 19m and 99m and 24.4h at 55m. The vertical distributions of the significant spectra-peak values of the power spectra of both the crossshelf and along-shelf components of both the baroclinic currents are different. The former increases with depth, then decreases and finally increases again while the latter decreases with depth.

PRELIMINARY STUDY ON RELATIONSHIP BETWEEN DOUBLE VORTICES SELF-ORGANIZATION AND TYPHOON FORMATION IN BAROCLINIC ENVIRONMENT

The relationship between the self-organization of double vortices （SODVs） and the formation of typhoons was discussed based on six numerical experiments with the Fifth-Generation National Center for Atmospheric Research/Penn State Mesoscale Model （MM5） and further discussion was made with a real typhoon case. The results showed that there is a critical distance dc for SODVs in baroclinic atmosphere. When the distance between separated vortices is smaller than or equal to d~, the double vortices self-organize into a typhoon-like vortex with two spiral bands. But the double vortices cannot have such organization if the distance between them is larger than de. The value of dc is about 380 km in the context of ideal conditions in this paper, larger than that achieved in a barotropic model. A typical typhoon case in 2005 （Haitang） was selected to verify the above-mentioned conclusions. It was found that the SODV is one of the important and typical ways for the formation of typhoons.

BAROTROPIC AND BAROCLINIC PATTERNS OF ATMOSPHERIC CIRCULATIONS RELATED TO MONSOON TYPES

In the context of 1982—1994 NCEP/NCAR wind at 12-level isobaric surfaces on a global basis calculation is made of the barotropic(mass-weighed vertical mean)and baroclinic components (difference between the actual wind at each level and barotropic component)of atmospheric flow fields,followed by dealing with the distribution features of barotropic and baroelinie patterns globally in winter and summer,alongside with the classification of global monsoons according to the surface barotropic/baroclinic patterns.Evidence suggests that the seasonal variation of both components will lead to the reversal of a prevailing wind between winter and summer,thus causing a related monsoon:the baroclinie flow pattern is indicative of a thermal circulation driven by atmospheric inhomogeneous heating chiefly from land-sea thermal contrast whilst the barotropic counterpart represents the result mainly from dynamic effects,which is helpful to the understanding of monsoon nature.And further study shows that the classical monsoon regions in tropical Asia,Africa and South America fall into a baroclinic category,those in the bi-hemispherie subtropical Pacific into a barotropic type and the East Asian subtropical monsoon generated under the joint action of both the patterns falls into a mixed category.

BAROTROPIC AND BAROCLINIC ENSTROPHY EQUATIONS WITH THEIR APPLICATIONS TO A BLOCKING CIRCULATION

After the manner for studying atmospheric kinetic energy,concepts of atmospheric enstrophy (ζ~2/2)_m and barotropic and baroclinic enstrophy (ζ_m^2/2,ζ_s^2/2) are developed with their relations investigated,whereupon are established,separately,equations for the 1000- 100 hPa extent- averaged ζ_m^2/2 and ζ_s^2/2 over a limited area and on a local basis.Study shows that controlling their changes are the following factors:the terms of their fluxes (viz.,divergences).β effect,their mutual conversions,production and dissipation.Analysis is undertaken of these terms-dependent physical mechanisms for the variations in barotropic and baroclinic enstrophy and by means of the equations,calculation is conducted of the terms during the development of an Okhotsk blocking circulation,indicating that the total,harotropic and haroclinic enstrophies experience noticeable variations,from which we see that the latter two factors can really characterize the development as a whole,thus revealing the mechanisms at different stages of the circulation history.

Influence of Bottom Inclination on the Flow Structure in a Rotating Convective Layer

The formation of convective flows in a rotating cylindrical layer with an inclined bottom and free surface is studied.Convection is driven by localized cooling at the center of the upper free surface and by rim heating at the bottom near the sidewall.The horizontal temperature difference in a rotating layer leads to the formation of a convective flow with a complex structure.The mean meridional circulation,consisting of three cells,provides a strongly non-uniform differential rotation.As a result of the instability of the main cyclonic zonal flow,the train of baroclinic waves appears in the upper layer.The baroclinic waves provide most of the heat transfer in the middle radii and are responsible for strong temperature and velocity fluctuations.It is shown that the inclination of the bottom is a crucial factor for the structure of the convective cells and the dynamics of the baroclinic waves.The increase in the inclination angle leads to a significant increase in the energy of the waves.The obtained results may be important for heat and mass transfer in various geophysical and industrial systems,including transport of various additives and impurities in rotating crucibles,and crystallization processes.

Global trends of tropopause folds in recent decades

对流层顶折卷是平流层-对流层物质交换的主要机制.本研究采用三维标记方法,利用1979-2020年间的ERA5再分析数据,分析了对流层顶折卷的时空变化特征及机理.研究结果表明,全球对流层顶折卷的多年变化趋势存在明显的季节性和区域性差异.总体上,对流层顶折卷呈增加趋势,其中北半球的春季,夏季和冬季,对流层顶折卷主要沿副热带急流区呈现明显增加的趋势.进一步分析表明,对流层顶折卷发生频率的增加与大气斜压性增大导致的锋生增强有关,而经向位温梯度的增大使得次级环流增强,也可能促进了对流层顶折卷活动的增多.

川南一次准正压类强对流天气的综合分析

就四川而言,相较于斜压大气中的强对流天气,准正压大气中的强对流天气出现概率低,突发性更强,监测和预报难度更大。本文基于气象站观测资料、雷达组合反射率拼图、气象卫星的TBB资料以及NCEP和ERA5再分析资料,运用天气学、卫星气象学和雷达气象学方法,对2022年8月5日四川南部地区发生的准正压类强对流天气进行了综合分析。结果表明:本次强对流天气以雷暴大风和短时强降雨为主,持续时间约2 h,其间气象要素变化剧烈;主要影响系统为高层的南亚高压、中低层的季风低压倒槽和地面热低压;高CAPE值、“上干下湿”的湿度层结、弱垂直风切变、低层辐合、高层辐散和深厚的上升运动是强对流天气出现的有利环境条件;低压倒槽前的云带在川南演变为对流云团,多中心带状雷暴群的NE段在川南演变为团状雷暴群,雷暴大风和短时强降雨与冷云中心、高TBB梯度、高反射率梯度、反射率大小及其维持时间存在较好的对应关系。

NONLINEAR SCHRODINGER EQUATION IN THE ROTATIONAL BAROTROPIC ATMOSPHERE AND ATMOSPHERIC BLOCKING

In this paper,the WKB method is used to obtain the nonlinear Schrdinger equation satisfied by nonlinear Rossby wave in the rotational barotropic atmosphere.It is found that the nonlinear Schrdinger equation has an envelope solitary wave solution under the condition 1≤m≤2(m the zonal wavenumber),and the phase speed of envelope solitary Rossby wave in the atmosphere is related to the square of its amplitude linearly,that is,the larger the amplitude of envelope solitary Rossby wave,the smaller its propagation speed.Farthermore, the blocking high and cut-off low pressures which are consistent with the observations of blocking in the atmo- sphere are obtained by calculating envelope solitary Rossby wave,and the blocking structures persist more than five days,the results demonstrate that the envelope solitary Rossby wave is a possible mechanism about the formation,maintenance and breakout of blocking in the atmosphere.

Study on Atmospheric Travelling Wave Solutions and Review of Its Present Developments

The scientific achievements of travelling waves in a barotropic atmosphere are introduced, including i) the existence conditions of periodic solutions (wavetrain solutions) and solitary wave solutions (pulse solutions), together with the solution finding methods and a series of related problems, ii) seeking solutions of monotonous wave (wave front) and of nonmonotonous travelling wave (oscillatory wave) by using phase plane shooting technique and hi) progress in the study of travelling wave solution at home and abroad. The investigation of travelling wave solutions in recent years has been found in mathematics, physics, chemistry, biology and other sciences. Over the past decade the problem has been the subject of much interest and become an important area of research. So it is no doubt of great significance to investigate the travelling wave solutions and thereby explain phenomena of weather.

Slow wave in barotropic atmosphere

In barotropic atmosphere, slow wave solution isobtained from linear primitive equation in the one dimensioncase; here the slow wave behaves very similarly to Rossbywave. The existence of the slow wave depends on the merid-ional structure of the basic flow instead of the ft effect. Thecharacter of the slow wave is almost the same as Rossbywave if the profile of basic flow is the convex function abouty.

ANALYSIS OF THE INTER-TRANSFOMATION OF EQUIVALENT BAROTROPIC AND BAROCLINIC ROSSBY WAVES

By using the low-spectral model simplified from quasi-geostrophic approximation two-level model,we obtained the result that the equivalent barotropic state is an equilibrium state of the atmosphere in that model,and discussed the conditions needed for existing the Rossby wave possessing the equivalent barotropic structure.And then we derived the oscillation equation reflecting the phase change of Rossby wave between higher and lower levels from the basic state of equivalent barotropic stationary Rossby wave,indicating the relations between the change of difference of phase at higher and lower levels and the disturbance of vertical shear,the amplitude disturbance of the part of waves of stream function and thermal wind stream function on the average level (A′ and B′).It is concluded that the inter-transformation exists between Rossby waves possessing the equivalent barotropic and baroclinic structure.

FEATURES OF VARIATION IN TOTAL,BAROTROPIC AND BAROCLINIC KINETIC ENERGY WITH THE MECHANISM EXPLORED AROUND THE 1998 SCS SUMMER MONSOON ONSET

This paper concerns atmospheric kinetic energy variation related to the onset of summer monsoon in May,1998 over the SCS (South China Sea).Results show that around the onset, noticeable conversion occurs in atmospheric total,barotropic and baroclinic kinetic energy (KE) at 300-1000 hPa;three days before the onset,total and barotropic KE are already growing markedly and baroclinic KE increases simultaneously with the onset:the monsoon's onset is associated closely to the meridional propagation of barotropic and baroclinic KE in the SCS region and study of equations of barotropie/baroclinic KE indicates that the net production term is the dominant factor for the change of the two forms of KE,the term of fluxes plays a part in weakening the energies and the conversion term is responsible for transforming barotropic into baroclinic KE.