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1990 Vol. 7, No. 3

Display Method:
The Modified Envelope Orography and the Air Flow over and around Mountains
Li Long, Zhu Baozhen
1990, 7(3): 249-260. doi: 10.1007/BF03179759
By use of the two-layer adiabatic globe spectral model and the zonally averaged climatic data of winter season as initial values, 10-day integrations are carried out based on three kinds of model topography (i.e., (1) the averaged to-pography; (2) the envelope topography; (3) the modified envelope topography). The results show that the orography of the Northern Hemisphere plays an important role in the simulation of large-scale weather patterns in winter sea-son. The simulation based on the envelope topography developed by Wallace et al. has some improvements in the Rocky Mountains area. But this scheme causes very serious horizontal expansion around the Tibetan Plateau (hereafter referred to as the TP). A modified envelope topography scheme has been worked out that increases the slope of the TP by decreasing; the horizontal expansion while keeping the maximum altitude. The results show some improve-ments of the scheme around the TP. By analysis of the mechanical effects of the large-scale orography on the currents, the different forcings of the air flow over and around the TP sad the Rocky Mountain (the RM) are investi-gated.
Preliminary Investigations on the Global Summer Monsoonal Drought Mechanics and the Latitudinal Teleconnections
M. Sankar-Rao
1990, 7(3): 261-274. doi: 10.1007/BF03179760
The question of possible teleconnections between the middle latitude general circulation and the Indian south-west monsoon was investigated in this paper. Within the framework of a simple model it was shown that there can exist such an interaction via the ultra-long Rossby waves.
Sensitivity of Medium-Range Weather Forecasts to the Use of Reference Atmosphere
Chen Jiabin, A.J. Simmons
1990, 7(3): 275-293. doi: 10.1007/BF03179761
In this paper, the authors develop the earlier work of Chen Jiabin et al. (1986). In order to reduce spectral truncation errors, the reference atmosphere has been introduced in ECMWF model, and the spectrally-represented variables, temperature, geopotential height and orography, are replaced by their deviations from the reference atmos-phere. Two modified semi- implicit schemes have been proposed to alleviate the computational instability due to the introduction of reference atmosphere. Concerning the deviation of surface geopotential height from reference atmos-phere, an exact computational formulation has been used instead of the approximate one in the earlier work. To re-duce aliasing errors in the computations of the deviation of the surface geopotential height, a spectral fit has been used slightly to modify the original Gaussian grid-point values of orography.A series of experiments has been performed in order to assess the impact of the reference atmosphere on ECMWF medium- range forecasts at the resolution T21, T42 and T63, The results we have obtained reveal that the reference atmosphere introduced in ECMWF spectral model is generally beneficial to the mean statistical scores of 1000-200 hPa height 10-day forecasts over the globe. In the Southern Hemisphere, it is a clear improvement for T21, T42 and T63 throughout the 10-day forecast period, In the Northern Hemisphere, the impact of the reference atmos-phere on anomaly correlation is positive for resolution T21, a very slightly damaging at T42 and almost neutral at T63 in the range of day 1 to day 4. Beyond the day 4 there is a clear improvement at all resolutions.
An Observational Study of the 30-50 Day Atmospheric Oscillations Part I: Structure and Propagation
Li Chongyin, Wu Peili
1990, 7(3): 294-304. doi: 10.1007/BF03179762
Features of structure and propagation of the 30 to 50 day atmospheric oscillations are investigated using the ECMWF analysis of 1980-1983. Evidence is provided to confirm the characteristics of the oscillation in the equatori-al region. Those in the mid-high latitudes, however, are revealed to be very different from the tropics and pose a strong barotropic structure. Horizontal coherence shows teleconnection patterns which can be identified as EAP and PNA. The wind field of the specified time scale of the oscillation appears as long-lived vortices and vortex pairs. Mid-latitude perturbations propagate clearly westwards, especially during the winter season. In the high latitudes, they propagate westwards in the winter but eastwards in the summer. Meridional propagations are rather different from region to region.
Numerical Experiment of Combined Infrared and Ultraviolet Radiation Remote Sensing to Determine the Profile and Total Content of Atmospheric Ozone
Cheng Minghu, Shi Guangyu, Zhou Xiuji
1990, 7(3): 305-319. doi: 10.1007/BF03179763
A new remote sensing method is described to determine the vertical distribution and total content of atmospheric ozone. The method combines surface infrared, satellite infrared and ultraviolet channels. The width of the infrared channels is 0.01 cm-1, less than Lorentz half-width at the earth’s surface, rather than the present width, because these channels can obtain information about variations in the ozone profile below the profile main-peak. The numerical experiments show that the method has a satisfactory precision in determining total ozone content, just about 1 percent error, and vertical distribution from the earth to 65 km space. In addition, some semi-analysis functions for calculating backscattered ultraviolet and a relaxation equation are described in this paper.
Numerical Study for Characteristic Change of Asian Summer Monsoon Circulation and Its Influence Mechanism during the El Nino Period
Ni Yunqi, Lin Yuanbi
1990, 7(3): 320-330. doi: 10.1007/BF03179764
In this paper, the relation between Asian summer monsoon circulation and sea surface temperature anomalies over equatorial central-eastern Pacific is investigated by using a global spectral model. This model has nine layers in the vertical and the model variables are represented in the horizontal as truncated expansions of the surface spherical harmonics with rhomboidal truncation at wave number 15. The model involves comparatively complete physical pro-cesses and parameterizations with mountains.Using the above model, two experimental schemes are designed, namely control case and anomalous sea surface temperature case. The above two schemes are respectively integrated for forty days and the simulated results are ob-tained from the last 30-day averaged simulations.The simulations show that positive SST anomalies over equatorial central-eastern Pacific weakens Indian mon-soon circulation, decreases precipitation in Indian sub-continent whereas it intensifies East Asian monsoon circula-tion and increases precipitation in East Asian area. All these results reflect the characteristics of Asian summer mon-soon during the El Nino period. In this paper, SST anomalies over equatorial central-eastern Pacific have a direct in-fluence on the intensity and position of subtropical high via the wave train over Northern Hemisphere, which is simi-lar to that suggested by Nitta (1987) and the wave train over Southern Hemisphere has an influence on the intensity of Mascarene high and Australia high resulting in affecting cross equatorial flow. As a result, atmospheric interior heat sources and sinks are redistributed because of the change of cross equatorial flow. And the response of atmos-phere to the new heat source and sink has a significant influence on Asian summer monsoon.
Application of the Coupled Dynamical-Radiational Model of Stratocumulus
Ye Weizuo
1990, 7(3): 331-346. doi: 10.1007/BF03179765
This paper presents some results concerning applications of the coupled dynamical-radiational model of stratocumulus Ye developed (Ye, 1990, hereafter referred to as the DRS model). Basically, calculations involved here relate to the time-integration of the DRS model to estimate some time constants associated with the boundary layer and cloud developments. To obtain cloud lifetime (CLT), the time interval from its formation to its dissipation, dif-ferent cloud instability criteria are compared, the mechanism for dissipating cloud are discussed, and thereby two new criteria for judging whether cloud can maintain are established. Following these criteria, the sensitivities of CLT to parameters such as the air-sea temperature difference, subsidence, and surface wind are estimated. The main inter-esting results about the sensitivities of the forming time (CFT) are a stable environment, such as cool sea, low wind, and strong subsidence, would prolong the existence of Sc, which has been predicted by the model calculations and strikingly tallies with statistical observations.Besides, with the DRS model and the CLT criteria, we follow a marine boundary layer, starting with clear sky, through the formation and development of clouds and rain, until their dissipation. On the whole, the model results fit the developing process of a typically stable marine boundary layer, and show some features Nicholls (1984) observed for daytime Sc.
On the Couplings between Chebyshev Coefficients as Derived from the Monthly Mean Geopotential Fields at 500 hPa over East Asia and the Southern Oscillation
Chen Wanlong, Chu Pao-Shin
1990, 7(3): 347-353. doi: 10.1007/BF03179766
The first six Chebyshev polynomial coefficients (i.e., A00, A01, A10, A11, A02, A20) were derived from monthly mean geopotential height over East Asia for the period 1951-1983. Spectral analysis of these coefficients reveals rela-tive maxima of power in the frequency bands of 200 months (~ 16.7 years), 25 months (the quasi-biennial oscillation), 5-6 months, and 2-3 months. Cross-spectral characteristics between Chebyshev coefficients and the Southern Oscillation Index (SOI) were also explored. Coherence spectrum for the zonal and meridional circulation index (A01 and A10) with the SOI was significant near 4 years, the QBO, and 2-3 months. Some physical explanations were offered for the spatial linkages (i.e., teleconnections) between the SO and atmospheric circulation anomalies over East Asia.
A Case Study of Warm Sector Rainbands in North China
Wang Pengyun, Xu Zixiu, Pan Zaitao
1990, 7(3): 354-365. doi: 10.1007/BF03179767
This article investigates in detail the structure, genesis and development of parallel-type warm sector rainbands from radar observations. By comparing these observations with diagnostic results from temperature, pressure, mois-ture and wind data, which are both actually observed and numerically generated by a mesoscale model, and the theo-ry of symmetric instability, it is found that the conditional symmetric instability might be responsible for the forma-tion and development of these rainbands.
Computer Identification of Multispectral Satellite Cloud Imagery
Li Jun, Zhou Fengxian
1990, 7(3): 366-375. doi: 10.1007/BF03179768
A dynamic clustering method based on multispectral satellite imagery to identify the different features is des-cribed. The channel combinations selected are for the different purposes in classification. Several cases are presented using the polar- orbiting satellite imageries.
Active-Passive Radiolocation of Dangerous Natural Phenomena
L.G. Kachurin
1990, 7(3): 376-382. doi: 10.1007/BF03179769
In nature one observes strong deviations from thermodynamic equilibrium. The most dangerous natural phenomena proceeding in a thermodynamically irreversible way, are accompanied by the initiation of nonthermal impulse radio and optical radiation, the intensity and amplitude-frequency characteristics of which may serve as a measure of irreversibility while making the passive radiolocation and simultaneously as an information characteristic of the degree of the phenomenon’s approach to the stage of maximum development.The active radiolocation of natural phenomena at the stage of thermodynamic irreversibility has a number of dis-tinct features caused by the high speed of their progress and anomalies of the dielectric properties and accordingly, ef-fective scattering area of natural radio targets.The above is the physical basis of the method proposed by the author, that of the active-passive radiolocation of dangerous natural phenomena such as thunderstorms-both naturally developing and provoked by flying vehicles or other modifying means, avalanches, landslides, catastrophic atmospheric eddies and showers, sudden destruction of sea, river and late ice and so on.Active-passive radar sounding of cloudiness presumes radical changes in the air traffic control in thunderous sit-uations in the take-off and landing areas of flying vehicles as well as along the airways.Thermodynamic irreversibility turns out to be an important factor in the process of the interaction of ice with heavy-duty icebreakers (nuclear-powered vessels) causing their anomalous corrosion. The non-thermal radio radia-tion arising at the deformation of ice cover under the pressure of an icebreaker or under the action of wind load, may be used while choosing the route and tactics of the ice-breaker’s progress, for the hydrometeorological service of oth-er sea and coastal operations. The completed investigations of the thermodynamically irreversible natural phenomena have found practical application, but their wide utilization is still ahead.The experiments of active-passive radiolocation have been carried out at the experimental proving grounds, in laboratories, in weather planes, on board an atomic-powered icebreaker. Simultaneously there have been developing the theory of thermodynamically irreversible phase transitions, in particular deformation-crystallization processes.So far, there is no generally accepted term denoting the proposed method of the active-passive radiolocation of dangerous natural phenomena (using thermodynamic irreversibility).