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1995 Vol. 12, No. 4

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Three-dimensional Global Scale Permanent-wave Solutions of the Nonlinear Quasigeostrophic Potential Vorticity Equation and Energy Dispersion
H.L. Kuo
1995, 12(4): 387-404. doi: 10.1007/BF02657001
The three-dimensional nonlinear quasi-geostrophic potential vorticity equation is reduced to a linear form in the stream function in spherical coordinates for the permanent wave solutions consisting of zonal wavenumbers from 0 to n and rn vertical components with a given degree n. This equation is solved by treating the coefficient of the Coriolis parameter square in the equation as the eigenvalue both for sinusoidal and hyperbolic variations in vertical direction. It is found that these solutions can represent the observed long term flow patterns at the surface and aloft over the globe closely. In addition, the sinusoidal vertical solutions with large eigenvalue G are trapped in low latitude, and the scales of these trapped modes are longer than 10 deg. lat. even for the top layer of the ocean and hence they are much larger than that given by the equatorial β-plane solutions. Therefore such baroclinic disturb-ances in the ocean can easily interact with those in the atmosphere.Solutions of the shallow water potential vorticity equation are treated in a similar manner but with the effective depth H = RT / g taken as limited within a small range for the atmosphere.The propagation of the flow energy of the wave packet consisting of more than one degree is found to be along the great circle around the globe both for barotropic and for baroclinic flows in the atmosphere.
The Dynamical Influence of Land-Sea Contrast and Sea Surface Temperature on Intraseasonal Oscillation in Tropical Atmosphere
Yang Yan, Zhu Baozhen
1995, 12(4): 405-418. doi: 10.1007/BF02657002
An equatorial β-plane model which includes realistic non-uniform land-sea contrast and the underlying surface temperature distribution is used to simulate the 30-60 day oscillation (LFO) processes in tropical atmosphere, with emphasis on its longitude-dependent evolution and convective seesaw between Indian and the western Pacific oceans.The model simulated the twice-amplification of the disturbances over Indian and the western Pacific oceans while they are travelling eastward. It reproduced the dipole structure caused by the out-of-phase oscillation of the active centres in these two areas and the periodical transition between the phases of LFO. It is suggested that the convective seesaw is the result of interaction of the internal dynamics of tropical atmosphere with the zonally non-uniform thermal forcing from underlying surface. The convective activities are suppressed over Indonesia mari-time continents whilst they are favoured over the Indian Ocean and western Pacific warm waters, so there formed two active oscillation centres. The feedback of convection with large-scale flow slows down the propagation of disturb-ances when they are intensifying over these two areas, therefore they manifest a kind of quasi-stationary component to favor the ‘dipole’ structure. Whereas the disturbances weaken and speed up over the eastern Pacific cold water re-gion due to the interaction of sensible heating and evaporation with perturbational wind. Therefore the two major centers just show out-of-phase oscillation during onecycle around the latitudinal beltBy introducing the SST anomalies in El Ni?o and La Ni?a years into the surface temperature, we also show that they have significant influence on LFO processes. In an anomalously warm year, the LFO disturbances dissipate more slowly over the central-eastern Pacific region and can travel farther eastward; whilst in an anomalously cold year, the opposite is true.
On the Generalized Theory of Atmospheric Particle Systems
Liu Yangang
1995, 12(4): 419-438. doi: 10.1007/BF02657003
Unification is both necessary and challenging for studying atmospheric particle systems, which are polydisperse systems containing particles of different sizes and shapes. A general framework is proposed to realize the first order generalization. Within this generalized framework, (1) atmospheric particle shapes are unified into self-similar fractals; (2) a self-similar particle is characterized by various power-law relationships; (3) by combining these power-law relationships for a single particle with Shannon’s maximum entropy principle and some concepts in statis-tical mechanics, unified maximum likelihoood number size distributions are of the Weibull form for atmospheric particle systems. Frontier disciplines (e. g., scaling, fractal, chaos and hierarchy) are argued to provide potential “tools” for such unification. Several new topics are raised for future research.
Propagation of Envelope Solitons in Baroclinic Atmosphere
Tan Benkui, Yin Dongping
1995, 12(4): 439-448. doi: 10.1007/BF02657004
The propagation of finite amplitude baroclinic wave packets in the two-layer model is investigated by using the multiple-scale method. It is shown that the propagation of the wave packets can be described by the so-called unstable nonlinear Schrodinger equation which possesses envelope soliton solutions. The speeds of the solitons are in-dependent of their amplitudes, while the width of the solitons is directly proportional to their speeds but inversely pro-portional to their amplitudes.
A Parameterization of Bowen Ratio with Respect to Soil Moisture Availability
Ye Zhuojia, Roger A. Pielke
1995, 12(4): 449-474. doi: 10.1007/BF02657005
The Bowen ratio (B) is impacted by 5 environmental elements: soil moisture availability, m, the ratio of resist-ances between atmosphere and soil pores, ra/rd, atmospheric relative humidity, h, atmospheric stability, ΔT, and environment temperature. These impacts have been investigated over diverse surfaces, including bare soil, free water surface, and vegetation covered land, using an analytical approach. It was concluded that: (a) B is not a continuous function. The singularity exists at the condition αhcb=h, occurring preferably in the following conditions: weak turbulence, stable stratified stability, dry soil, and humid air, where hcb, defined by Eq.(11) is a critical variable. The existence of a singularity makes the dependence of B on the five variables very complicated. The value of B approaches being inversely proportional to m under the conditions m≥mfc (the soil capacity) and / or ra/rd→0. The proportional coefficient changes with season and latitude with relatively high values in winter and over the poles; (b) B is nearly independent of ra/rd during the day. The impact of m on B is much larger as compared to that of ra/rd on B, (c) when h increases, the absolute value of B also increases; (d) over bare soil, when the absolute surface net radiation increases, the absolute value of B will increase. The impact of RN on B is larger at night than during the day, and (e) over plant canopy, the singularity and the dependcies of B on m, ra , and h are modified as compared to that over bare soil. Also (i) during the daytime unstable condition, m exerts an even stronger impact on B, at night, however, B changes are weak in response to the change in m; (ii) the value of B is much more sensitive in response to the changes of turbulent intensity; (iii) the B response to the variation of h over a vegetation covered area is weaker; and (iv) the singularity exists at the condition hcp=h instead of αhcb=h as over bare soil, where hcp is defined by Eq.(49). The formulas derived over bare soil also hold the same when applied to free water bodies as long as they are visualized as a special soil in which the volumetric fraction of soil pore is equal to one and are fully filled with water. Finally, the above discussions, are used to briefly study the impact on the thermally induced mesoscale circulations.
A Study in Search of Interconnection between Surface Parameters and Surrounding Synoptic and Subsynoptic Features
R. Pradhan, U. K. De, P.K. Sen
1995, 12(4): 475-486. doi: 10.1007/BF02657006
The paper reveals that the variations in parameters like u*, the scaling velocity and θ*. The scaling tempera-ture during the various phases of monsoon might be linked with subsynoptic features. The rise in u* is mainly connected with the presence of lower tropospheric cyclonic vorticity over a subsynoptic scale of the site. However the variations in θ* is mainly linked with the various phases of monsoon and θ* shows a sharp rise in presence of low level convective cloud.Besides the correlation studies of u and u*, θv and θv* , θv-θv0 and θv* are undertaken. The correlation be?tween θv and θv* is poor. In other two cases correlations are good. Besides u/u* , has shown good coefficient of variation values within the ζ range.
Some Aspects of the Characteristics of Monsoon Disturbances Using a Combined Barotropic-Baroclinic Model
N. R. Parija, S. K. Dash
1995, 12(4): 487-506. doi: 10.1007/BF02657007
A standing Rossby wave of wavelength 30o 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 18oN 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 (Umax=11m/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 11 m / s, the westerly wind dominates and the disturbance moves to the east. In another analysis the stability of the zonally asymmetric basic flow is studied with a combined barotropic-baroclinic 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 disturb?ances. 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 4 m / s at 700 hPa pressure level. When cumulus heating is in?cluded in the analysis the intensity of geopotential perturbation at 700 hPa disturbance is -304 m2 / s2. Energy calcu?lations show that the kinetic energy of the mean zonal flow is the main source of energy for the perturbation to grow. It is also found 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.
Condensation Induced by Rarefaction Waves and Reflected Rarefaction Waves
Fu Yunfei, Han Zhaoyuan, Gong Minwei
1995, 12(4): 507-512. doi: 10.1007/BF02657008
In this paper, homogeneous condensation induced by unsteady rarefaction waves and reflected rarefaction waves in vapor-gas mixture was investigated experimentally. It is shown that the temperature of condensation onset during very fast unsteady expansion in vapor-gas mixture is much lower than that during equilibrium process in the atmosphere. It is of interest to indicate that the size of droplets approximates a constant, but the number density and the mass density of droplets change rapidly in the region of static flow.