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2000 Vol. 17, No. 4

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Climatic Features Related to Eastern China Summer Rainfalls in the NCAR CCM3
Yu Rucong, Li Wei, Zhang Xuehong, LiuYimin, Yu Yongqiang, Liu Hailong, Zhou Tianjun
2000, 17(4): 503-518. doi: 10.1007/s00376-000-0014-9
The climatic features associated with the eastern China summer rainfalls (ECSR) are examined in the National Center for Atmospheric Research (NCAR) Community Climate Model Version 3 (CCM3) of the United States of America, and run with time-evolving sea surface temperature (SST) from September 1978 to August 1993. The CCM3 is shown to capture the salient seasonal features of ECSR. As many other cli-mate models, however, there are some unrealistic projections of ECSR in the CCM3. The most unacceptable one is the erroneously intensified precipitation center on the east periphery of the Tibetan Plateau and its northeastward extension.The artificial strong rainfall center is fairly assessed by comparing with the products of the station rainfall data. Xie and Arkin (1996) rainfall data and the European Centre for Medium-Range Weather Fore-casts (ECMWF) reanalysis (Gibson et al., 1997). The physical processes involved in the formation of the rainfall center are discussed. The preliminary conclusion reveals that it is the overestimated sensible heating over and around the Tibetan Plateau in the CCM3 that causes the heavy rainfall. The unreal strong surface sensible heating over the southeast and northeast of Tibetan Plateau favors the forming of a powerful subtropical anticyclone over the eastern China. The fake enclosed subtropical anticyclone center makes the moist southwest wind festen on the east periphery of the Tibetan Plateau and extend to its northeast. In the southeast coast of China, locating on the southeast side of the subtropical anticyclone, the southwest mon-soon is decreased and even replaced by northeast wind in some cases. In the CCM3, therefore, the precipita-tion is exaggerated on the east periphery of the Tibetan Plateau and its northeast extension and is underestimated in the southeast coast of China.
The 3D Spiral Structure Pattern in the Atmosphere
Liu Shida, Xin Guojun, Liu Shikuo, Liang Fuming
2000, 17(4): 519-524. doi: 10.1007/s00376-000-0015-8
The steady analytical solution of the perturbation equations describing the mesoscale vortex in the at-mosphere is obtained. By analyzing the 3D wind field, the 3D spiral structure in physical space for unstable stratification is found. In many respects such as the 3D distribution of pressure and vorticity fields, the mesoscale spiral vortex is very similar to typically real cyclones.
The Instability of the Vortex Sheet along the Shear Line
Gao Shouting
2000, 17(4): 525-537. doi: 10.1007/s00376-000-0016-7
The traditional Kelvin-Helmholtz notion of studying the shear instability is not suitable for the case associated with shear line with the strong wind shear in the vortex sheet. Since then, the shear instability be-comes the instability of the vortex sheet. If the velocity is induced by the vortex sheet, the inequalities (1 – Rv + Rid)> 0 and U (y,t)> U{A(t)} become the criterion of the vortex sheet instability. This criterion indicates that 1) the disposition of environment field restrains the disturbance developing along the shear line. 2) There exist multi-scale interactions in the unstable process of the shear line. The calculation of the necessary condition for the instability is also presented in this paper.
A Comparison between Numerical Simulations of Forced Local Hadley (Anti-Hadley) Circulation in East Asian and Indian Monsoon Regions
Yuan Zhuojian, Wang Tongmei, He Haiyan, Luo Huibang, Guo Yufu
2000, 17(4): 538-554. doi: 10.1007/s00376-000-0017-6
Two numerical simulations of forced local Hadley circulation are carried out based on a linear diagnostic equation to provide an insight into the mechanisms of monsoon evolution in different monsoon regions. One simulation is for the zonal mean Hadley circulation over East Asia (from95oE to 122.5oE), another over India (from 70oE to 85oE).With the NCEP / NCAR re-analysis data re-processed by Chinese Academy of Science in Beijing, the former simulation displays a dominant anti-Hadley circulation pattern over East Asia at 1200 UTC May 1, 1994. The simulated circulation pattern is consistent well enough with the circulation pattern plotted directly from the data for lack of the radiation information at each level. Although the simulation over India is not as good as that over East Asia, a dominant Hadley circulation pattern is obvious as data show. Further ana-lysis shows that the defective simulation over India is due to the presence of statically unstable condition at some grid points in the lower troposphere. This circumstance slightly violates the hydrodynamic stability cri-terion required by the elliptic diagnostic equation for the forced circulation.Since the simulations are reliable enough compared with the given data, the linear equation facilitates a systematic assessment of relative importance of each internally forcing process. The assessment shows that among the internal processes, the horizontal temperature advections account obviously for the Hadley (anti-Hadley) circulation over India (East Asia) at 1200 UTC May 1, 1994 in addition to the process associ-ated with the latent heat releasing. The calculation of latent heat energy is a little bit unreliable due to the unclear cloud physics in the convection processes and the less accurate humidity data. These preliminary results are consistent with the results of previous studies which show that the feature of the seasonal warming in the upper troposphere and the corresponding processes are part of key processes closely related to the evolution of the summer monsoon over East Asia and India.
The NPO/ NAO and Interdecadal Climate Variation in China
Li Chongyin, Li Guilong
2000, 17(4): 555-561. doi: 10.1007/s00376-000-0018-5
This article discusses the interannual variation of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO), its relationship with the interdecadal climate variation in China which is associated with the climate jump in the Northern Hemisphere in the 1960’s, using the data analyses. It is clearly shown that both the amplitudes of the NAO and NPO increase obviously in the 1960’s and the main period of the oscillations changes from 3-4 years before the 1960’s to 8-15 years after the 1960’s. Therefore, interdecadal climate variation in China or the climate jump in the 1960’s is closely related to the anomalies of the NAO and NPO.
QBO Signal in Total Ozone over Tibet
Zou Han, Ji Chongping, Zhou Libo
2000, 17(4): 562-568. doi: 10.1007/s00376-000-0019-4
From data analysis of ozone satellite observation and general circulation, this article discusses the sea-sonal and interannual variations of total ozone over Tibet. Analysis has been done on Quasi-Biennial Oscillation (QBO) in interannual ozone variation over Tibet, in comparison with QBO over the tropics and non-mountain region at the same latitudes of Tibet. The fact is shown that Tibet ozone QBO has an aver-aged period of 29 months, with an averaged amplitude of 8 DU. The Tibet ozone QBO is antiphase to the stratospheric wind QBO over the tropics, i.e., when the tropics 30 hPa-wind is easterly, ozone has a surplus, and vice verse. This article also discusses the impact of atmospheric transfer on ozone QBO over Tibet.
Response of Atmospheric Low-frequency Wave to Oceanic Forcing in the Tropics
FuZuntao, Zhao Qiang, QiaoFangli, Liu Shikuo
2000, 17(4): 569-575. doi: 10.1007/s00376-000-0020-y
The effects of oceanic forcing on the atmospheric low-frequency wave (LFW for short) in the tropics are analyzed, where ocean and atmosphere are taken as an independent system, respectively. Here oceanic effects are parameterized as evaporation-wind feedback (EWF for short) and forcing of SST. Under the modulation of EWF, forcing of SST plays a different role from that without EWF. So LFWs are diabatic waves, forced by the interactions of multiple factors, in the tropics.
The Influence of Systematic Errors on the Asian Summer Monsoon Circulation
P. L. S. Rao
2000, 17(4): 576-586. doi: 10.1007/s00376-000-0021-x
The systematic errors of wind field associated with the prediction of Asian summer monsoon and their impact on the monsoon circulation have been studied in this paper. The daily operational analyses and fore-casts (up to day-5) of the National Centre for Medium Range Weather Forecasting (NCMRWF), India, over the Asian summer monsoon domain for the period June, July and August of 1995 are made use for the purpose.The systematic errors associated with the low level flow delineate, reduction in the strength of trade winds leading to weakening of cross equatorial flow as well as westerly flow over Indian Ocean. The upper level errors connote wakening of Tibetan anticyclone and reduction in the strength of return flow into the Southern Hemisphere. Further, these errors evince growing tendency with increase in the forecast period. Apart from the general underestimation of kinetic energy budget terms, the model forecasts fail to represent the transient eddies. The forecasts show increasing trend in the conversion of eddy to mean kinetic energy. These errors enfeeble Asian summer monsoon circulation with increase in the forecast period.
A New Lagrangian-Eulerian Coupling Model System
Rudklao Manonom, Lei Xiaoen, Prungchan Wongwises
2000, 17(4): 587-600. doi: 10.1007/s00376-000-0022-9
A new Lagrangiann-Eulerian coupling model system is developed to study regional air quality. The system consists of mesoscale dynamical meteorological model (MM), Monte-Carlo model (MCM), parameterized model on planetary boundary layer (PBL) turbulent statistics, dry and wet removal model, and Eulerian nonlinear chemical model (ENCM). The physical, chemical and biological processes on air pollutants are considered comprehensively. 3-D distribution laws for acidic gaseous pollutants (SO2 and NOx) emitted by Thai Mae Moh Power Plant and the secondary pollutants are studied in detail. The results simulated by the coupling model system are in good agreement with observational concentration data.
The North Atlantic Oscillation Simulated by Versions 2 and 4 of IAP/ LASG GOALS Model
Zhou Tianjun, Zhang Xuehong, Yu Yongqiang, Yu Rucong, Wang Shaowu
2000, 17(4): 601-616. doi: 10.1007/s00376-000-0023-8
The capabilities of two versions of the Global-Ocean-Atmosphere-Land-System model (i.e. GOALS-2 and GOALS-4) developed at State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), are validated in terms of the simulations of the winter North Atlantic Oscillation (NAO), which is currently the subject of considerable scientific interest. The results show that both GOALS-2 and GOALS-4 exhibit a realistic NAO signal associated with relatively reasonable spatial pat-terns of sea level pressure, surface air temperature, and precipitation. Generally speaking, the associated pat-terns of precipitation in GOALSs match better with the observation in comparison with the case of surface temperature. For the imprint of NAO on the ocean, or perhaps a coupling between the two fluids, the asso-ciated tripole patterns of the North Atlantic SST anomaly are presented distinctly in GOALS-2, for GOALS-4 however, this is not the case. Spatially, the models’ main deficiencies appear to be that the simu-lated Icelandic lows shift northward apparently, which in turn result in the blemish of GOALSs in repro-ducing the accompanied surface wind anomalies. For the interannual and even longer time scale variations of DJF sea level pressure (SLP) over the North Atlantic region. GOALSs reproduce the center with the strongest variability rationally, but the intensities are far weaker than the observation.
A Three-Dimensional Model of Transport and Diffusion of Seeding Agents within Stratus
Yu Xing, Dai Jin, Jiang Weimei, Fan Peng
2000, 17(4): 617-635. doi: 10.1007/s00376-000-0024-7
It is essential to learn the temporal and spatial concentration distributions and variations of seeding agents in cloud seeding of precipitation enhancement. A three-dimensional puff trajectory model incorpo-rating a mesoscale nonhydrostatic model has been formulated, and is applied to simulating the transporting and diffusive characteristics of multiple line sources of seeding agents within super-cooled stratus. Several important factors are taken into consideration that affect the diffusion of seeding materials such as effects of topography and vertical wind shear, temporal and spatial variation of seeding parameters and wet deposi-tion. The particles of seeding agents are assumed to be almost inert, they have no interaction with the particles of the cloud or precipitation except that they are washed out by precipitation. The model validity is demonstrated by the analyses and comparisons of model results, and checked by the sensitivity experiments of diffusive coefficients and atmospheric stratification. The advantage of this model includes not only its exact reflection of heterogeneity and unsteadiness of background fields, but also its good simulation of trans port and diffusion of multiple line sources.The horizontal diffusion rate and the horizontal transport distance have been proposed that they usual-ly were difficult to obtain in other models. In this simulation the horizontal diffusion rate is 0.82 m s-1 for average of one hour, and the horizontal average transport distance reaches 65 km after 1 h, which are closely related to the background fields.
Local Similarity Relationships of Non-Dimensional Wind and Temperature Gradient in the Tower-Layer Atmosphere over Beijing City
Al-Jiboori M. H., Xu Yumao, Qian Yongfu
2000, 17(4): 636-648. doi: 10.1007/s00376-000-0025-6
Micrometeorological data for wind and temperature from a 325 m high tower in Beijing City are analyzed by use of local similarity theory. Non-dimensional wind and temperature gradients, Фm and Фh, are determined by three techniques called, respectively, eddy-correlation, mean profiles and inertia-subrange cospectra (ISC) method for a wide range of atmospheric stratification from unstable to stable conditions. Average dissipation rate Фε of turbulent kinetic energy (TKE) is evaluated from u-spectrum, as a quantity required in the last technique. Ratio of the eddy transfer coefficients. α (= Kh / Km,), is calculated from Фm and Фh estimations. The results from various techniques are compared with each other and with some available empirical results in the tower-layer. It is shown that the empirical relationships determined by mean profiles and ISC methods in the tower-layer turbulence are in agreement with each other and with some other results.
Barotropic Interaction between Planetary- and Synoptic-Scale Waves during the Life Cycles of Blockings
Luo Dehai, Li Jianping
2000, 17(4): 649-670. doi: 10.1007/s00376-000-0026-5
In this paper, in an equivalent barotropic framework a new forced nonlinear Schroedinger equation is proposed to examine the interaction between the planetary-scale waves and the localized synoptic-scale eddies upstream. With the help of the perturbed inverse scattering transform method, nonlinear parameter equations can be derived to describe the evolution of the dipole soliton amplitude, frequency, group velocity and phase under the forcing of localized synoptic-scale eddies. The numerical solutions of these equations predict that in the interaction between the weak dipole soliton (weak incipient dipole anomaly) and the synoptic-scale eddies, only when the high-frequency eddies themselves have a moderate parameter match they can near resonantly enhance a quasi-stationary large-amplitude split flow. The instantaneous total streamfunction field (the sum of background westerly wind, envelope Rossby soliton and synoptic-scale waves) is found to be very similar to the observed Berggren-type blocking on the weather map (Berggren et al. 1149). The role of synoptic-scale eddies is to increase the amplitude of large-scale dipole anomaly flow, and to decrease its group velocity, phase velocity and zonal wavenumber so that the dipole anomaly system can be amplified and transferred from dispersive system to very weak dispersive one. This may explain why and how the synoptic-scale eddies can reinforce and maintain vortex pair block. Furthermore, it is clearly found that during the prevalence of the vortex pair block the synoptic-scale eddies are split into two branches around the vortex pair block due to the feedback of amplified dipole block.