Advanced Search

1991 Vol. 8, No. 3

Display Method:
A Simple Quasi-Geostrophic Coupled Ocean-Atmosphere Model
Liu Shikuo, He Anguo
1991, 8(3): 257-271. doi: 10.1007/BF02919608
The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water mo-tion. We discuss the ocean-atmosphere coupling effect in mid-high and low latitudes separately and analyze charac-teristics of which the oscillatory periods of coupled low-frequency modes (ocean mode) vary with the coupling fre-quency and latitudinal number. This can interpret the correlation between low-frequency oscillation and ocean-at-mosphere interaction. Then from the dispersion curves of atmosphere and ocean, we reveal effect of the coupling strength on the propagation of Rossby waves. The convection mechanism between the two modes is also discussed in view of the slowly varying wave train.The results show that Newtonian cooling and Rayleigh friction play a stable rule in oceanic Rossby waves, the period of coupled low-frequency mode grows with the increment of the coupling frequency. The larger the latitudinal number is, the more rapidly it grows. When the coupling frequency tends to critical value, the oceanic Rossby waves become static. When the ocean-atmosphere coupling strength grows to some degree, the propagation of oceanic Rossby waves will become opposite to its original direction. One part of the oceanic Rossby waves is converted into atmospheric Rossby waves, the energy conversion coefficient is also solved out.
The Surface Friction and the Flow over Mountain
Wu Rongsheng
1991, 8(3): 272-278. doi: 10.1007/BF02919609
The flow over mountain is quite complicated. There are a lot of papers on this problem and a lot of progresses have been made. However, in the most of these papers, just the dynamics contributions of mountain have been ana-lysed; the effect of the friction is often neglected. Since the frictional effect is always associated with flow, especially when it flows over the mountain. The study shows that the friction is small in the magnitude but it is not a negligible effect because it changes the features of the flow. In the case of super-or sub-critical flow, there are two extremes: one maximum, one minimum of the fluid surface on the lee-side of the mountain, while in the inviscid fluid, there is just one extreme. The frictional effect should neither be too strong nor too weak to make the situation happened ac-cording to the investigation of this paper.
Preliminary Analysis of Climatic Variation during the Last 39 Years in China
Chen Longxun, Shao Yongning, Dong Min, Ren Zhenhai, Tian Guangsheng
1991, 8(3): 279-288. doi: 10.1007/BF02919610
The preliminary analysis of climatic variation in China during the last 39 years has been made in this paper. The results show that although the global climate is getting warmer, some parts of China are cooling. The warming only occurs in Northeast, North and the west part of Northwest China while the areas between about 35oN and Nanling Mountain, east of the Tibetan Plateau in China are getting cooler. The cooling centers are located in Sichuan, the south part of Shaanxi and the north part of Yunnan respectively. According to the theory of greenhouse effect, there are much precipitation at low and high latitudes and less precipitation in middle latitude. However, the precipitation in the most parts of China has been decreased, especially in North and Northwest China.
Telecorrelation of the 500 hPa Polar Circulation and El Nino / SO with the Temperature Fields in China
Shi Neng, Luo Boliang
1991, 8(3): 289-298. doi: 10.1007/BF02919611
By using the monthly data from 1951 through 1984, empirical orthogonal expansion is performed for the 500 hPa geopotential height north of 65oN and the canonical fields are clustered by fuzzy classification. It is noted that both the mean monthly polar vortex fields and the large-scale anomaly fields fall into three regimes, with those of the January mean field and the April anomaly field having characteristic features. In addition, the relationship between the time weigthing coefficients of the canonical fields and El Nino / SO is examined, showing significant anomalies in the large-scale polar anomaly fields during April and October of the year when El Nino occurs. These polar circulation anomalies have considerably influenced the temperature fields in China during April and October. Thus, we may con-clude that this is one of the most important reasons for a relatively cool April and a warm October in China during the El Nino year.
The Effects of Zonal Flow on Nonlinear Rossby Waves
Zhao Ping
1991, 8(3): 299-306. doi: 10.1007/BF02919612
In this paper, we using phase plane method have derived the stability criteria of linear and nonlinear Rossby waves under the conditions of semi-geostrophic approximation and have gotten the solutions and geostrophic vorticity of corresponding solitary Rossby waves. It is pointed out that the wave stability is connected with the distri-bution of zonal flow and when the zonal flow is different the solitary wave trough or ridge is formed.
Seasonal Characteristics and Interannual Variability of Monthly Scale Low-Frequency Oscillation in a Low-Order Global Spectral Model
Ni Yunqi, Zhang Qin, Lin Wuyin
1991, 8(3): 307-316. doi: 10.1007/BF02919613
Analysis is done of five-year low-pass filtered data by a Five-layer low-order global spectral model, indicating that although any non-seasonal external forcing is not considered in the model atmosphere, monthly-scale anomaly takes place which is of remarkable seasonality and interannual variability.Analysis also shows that for the same seasonal external forcing the model atmosphere can exhibit two climatic states, similar in the departure pattern but opposite in sign, indicating that the anomaly is but the manifestation of the adverse states, which supports the theory of multi-equilibria proposed by Charney and Devore (l979) once again.Finally, the source for the low-frequency oscillation of the global atmosphere is found to be the convective heat source / sink inside the tropical atmosphere as discussed before in our study.Therefore, the key approach to the exploration of atmospheric steady low-frequency oscillation and the associ-ated climatic effect lies in the examination of the distribution of convective heat sources / sinks and the variation in the tropical atmosphere.
The Effect of Topographic Forcing on the Formation and Maintenance of Blocking
Zhang Pei, Ni Yunqi
1991, 8(3): 317-326. doi: 10.1007/BF02919614
A barotropic channel model in β-plane is used to study the effect of topographic forcing on the formation and maintenance of blocking. The approximate analytical solution of potential vorticity equation can show the main property of the whole process of blocking. It is indicated that the topographic forcing is one of the main factors caus-ing the blocking process. The results suggest that the nonlinear interaction plays a very important role in the stable “Ω” situation of blocking. The atmospheric circulation with periodic and low-frequency oscillation, perhaps, is partly caused by topographic forcing.
Blocking Distributions in the Atmosphere
Yong. L. McHall
1991, 8(3): 327-338. doi: 10.1007/BF02919615
The zonal momentum generation in forced stationary waves may exceed the requirement for momentum balance after long, if the waves do not change their patterns, This suggests that the changes in stationary wave patterns would be required by maintenance of momentum balance over the external forcings. It will be found that the low frequency anomalies like blocking regimes may produce reversed zonal momentum variations, if they happen in the observed centre areas. The zonal momentum balance in the stationary waves may be maintained effectively by alternation between the normal and blocking circulation regimes, Thus, from the point of long-term zonal momentum balance, we may explain the geographical distributions of the blocking centres and the seasonal variations in blocking areas and frequencies.
The Impact of Soil Moisture Availability upon the Partition of Net Radiation into Sensible and Latent Heat Fluxes
Ye Zhuojia, Jia Xinyuan
1991, 8(3): 339-350. doi: 10.1007/BF02919616
The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a refined soil parameterization scheme. Simulation results presented that as soil moisture availability increases, the Bowen ratio and the partition of net radiation flux into sensible and soil heat fluxes decrease. The partition of net radiation flux in-to latent heat flux, however, increases. Quantitative relationships between Bowen ratio and the partitions with soil moisture availability were also given in this study.
Monsoon Subdivisional Rainfall Dimensionality and Predictability
J. R. Kulkarni
1991, 8(3): 351-356. doi: 10.1007/BF02919617
For summer monsoon rainfall purpose India is divided into 35 subdivisions. The daily rainfall series of one such subdivision (Konkan) has been analysed using the phase space approach. Fifteen years (1959-1973) of daily rainfall data have been utilised in this study. The analysis shows that the variability is due to the existing of strange attractor of dimension about 3.8. The predictability is estimated by computing the Lyapunov characteristic exponent. The computations show that the predictability is about 8 days.
On a Class of Solitary Wave Solutions of Atmospheric Nonlinear Equations
R. Dhar, C. Guha-Roy, D. K. Sinha
1991, 8(3): 357-362. doi: 10.1007/BF02919618
In this paper, an attempt is made to study some interesting results of the coupled nonlinear equations in the at-mosphere. By introducing a phase angle function ξ, it is shown that the atmospheric equations in the presence of specific forcing exhibit the exact and explicit solitary wave solutions under certain conditions.
Variations of Atmospheric Carbon Dioxide Concentration and Greenhouse Effect at Syowa Station (69o00’S, 39o35’E), Antarctica
Qu Shaohou, Takashi Yamanouchi
1991, 8(3): 363-368. doi: 10.1007/BF02919619
On the basis of the analysis of atmospheric carbon dioxide concentration variations and the annual mean air temperature at Syowa Station, Antarctica in the period of 1984-1988, the following results are easily obtained:(1) The annual mean values of the atmospheric carbon dioxide concentration are gradually increased and equal to 342.59, 343.80, 345.15, 346.83 and 348.82 ppmv for 1984, 1985, 1986, 1987 and 1988, respectively. Its annual in-crease rates are 1.21, 1.35, 1.68 and 1.99 ppmv/yr. For 1984-1985, 1985-1986, 1986-1987 and 1987-1988, respectively and are raised year by year.The seasonal variations are observed and the maximum concentration is in spring and the minimum one is in late-summer or early-autumn.(2)The increasing tendency of the concentration of the atmospheric carbon dioxide is consistent with that of the air temperature.
On Lidar Application for Remote Sensing of the Atmosphere
Qiu Jinhuan, Lu Daren
1991, 8(3): 369-378. doi: 10.1007/BF02919620
This paper introduces some advanced subjects on lidar remote sensing of the atmosphere, emphasizing recent studies and developments in lidar application for measuring ozone, cloud, aerosol, atmospheric temperature, moisture, pressure and wind.
Relaxation Time and Conductivity at a Rural Station: Raichur
G. K. Manohar, S. S. Kandalgaonkar, S. M. Sholapurkar
1991, 8(3): 379-381. doi: 10.1007/BF03342563
An examination of decay and growth rates of electric field near the ground during total solar eclipse of 16 Febru-ary 1980 was made to study the electrical relaxation time and conductivity at Raichur. The values obtained i.e., 1320 seconds and 67.1163 10-16 mhos m-1 of the two parameters were in fair agreement with the reported ones at the rural locations.