Advanced Search

1995 Vol. 12, No. 3

Display Method:
The Dynamical Effects of Divergent Wind on the Intraseasonal Variability of the East Asian Circulation
Song Yucheng, Huang Ronghui
1995, 12(3): 259-272. doi: 10.1007/BF02656976
In this paper, the dynamical effects of divergent wind on the intraseasonal variability of atmospheric circulation over East Asia are analyzed by using the function of Rossby-wave source and the energy exchanging function be-tween divergent component and rotational component of the flow.The results analyzed from the observed data show that the advection of vorticity by divergent wind caused by the heating due to the monsoon rainfall in the south to the Yangtze River and the strong convective activities around the Philippines may play an important role in the northward jump of westerly jet stream during the seasonal transition from spring circulation to summer circulation over East Asia. Due to the northward movement of the advection of vorticity by the divergent wind, the energy transformation from divergent component into rotational component can be caused over the Yellow River basin and Northwest China and will cause the intensification of the zonal flow there. Thus, the jet stream abruptly shifts northward to North China.Moreover, the analysed results also show that the advection of vorticity by divergent wind caused by the heating due to the strong convective activities around the Philippines also plays an important role in the intraseasonal varia-bility of the circulation over East Asia during the seasonal transition from summer to winter. With the southward movement of the advection of vorticity by the divergent wind, the energy transformation from divergent component into rotational component can be caused over East Asia, especially over the Yangtze-Huaihe River basin. Therefore, the jet stream gradually moves southward from North China to the Yangtze River basin.
The Interannual Variability of Climate in a Coupled Ocean-Atmosphere Model
Yu Yongqiang, Guo Yufu
1995, 12(3): 273-288. doi: 10.1007/BF02656977
In this paper, the interannual variability simulated by the coupled ocean-atmosphere general circulation model of the Institute of Atmospheric Physics (IAP CGCM) in 40 year integrations is analyzed, and compared with that by the corresponding IAP AGCM which uses the climatic sea surface temperature as the boundary condition in 25 year integrations.The mean climatic states of January and July simulated by IAP CGCM are in good agreement with that by IAP AGCM, i.e., no serious ‘climate drift’ occurs in the CGCM simulation. A comparison of the results from AGCM and CGCM indicates that the standard deviation of the monthly averaged sea level pressure simulated by IAP CGCM is much greater than that by IAP AGCM in tropical region. In addition, both Southern Oscillation (SO) and North Atlantic Oscillation (NAO) can be found in the CGCM simulation for January, but these two oscillations do not exist in the AGCM simulation.The interannual variability of climate may be classified into two types: one is the variation of the annual mean, another is the variation of the annual amplitude. The ocean-atmosphere interaction mainly increases the first type of variability. By means of the rotated EOF, the most important patterns corresponding to the two types of interannual variability are found to have different spatial and temporal characteristics.
Design and Numerical Simulation of an Arctic Ocean Circulation and Thermodynamic Sea-Ice Model
Yu Rucong, Jin Xiangze, Zhang Xuehong
1995, 12(3): 289-310. doi: 10.1007/BF02656978
In this paper, the first version of a new Arctic Ocean circulation and thermodynamic sea-ice model is presented by the authors based on the framework of a twenty-layer World Oceanic general circulation model developed by Zhang et al. in 1994, The model’s domain covers the Arctic Ocean and Greenland-Norwegian Seas with the horizon-tal resolution of 200 km × 200 km on a stereographic projection plane. In vertical, the model uses the Eta-coordinate (Sigma modified to have quasi-horizontal coordinate surfaces) and has ten unevenly-spaced layers to cover the deep-est water column of 3000 m. Two 150-year integrations of coupling the ocean circulation model with the sea-ice model have been performed with seasonally cyclic surface boundary conditions. The only difference between the two experiments is in the model’s geography. Some preliminary analyses of the experimental results have been done fo-cused on the following aspects: (1) surface layer temperature, salinity and current; (2) the "Atlantic Layer"; (3) sea-ice cover and its seasonal variation. In comparison with the available observational data, these results are accept-able with reasonable accuracy.
Evolution of Asian Summer Monsoon and the Slowly Varying Disturbances
Lu Peisheng
1995, 12(3): 311-318. doi: 10.1007/BF02656979
The evolution of Asian summer monsoon is analyzed by means of decomposition of the atmospheric circulation into basic current and slowly varying monsoon disturbances. It is seen that the major slowly varying disturbances are two vortical couples, one located in the Indian Ocean and Indian Peninsula, and another in the Northern Hemispheric western Pacific Ocean and the East Asia. This indicates that the Asian summer monsoon consists of two branches, the Indian monsoon and the East Asian monsoon. Moreover, the analysis shows that the evolutionary processes of these two vortical couples are rather independent each other, and they all can be qualitatively interpreted by the dynamical theory of wave packet. The different stages of summer monsoon can be very well characterized by the location and in?tensity of the two vortical couples. Besides, in particular years there exists also some quasistationary wave train and its characteristics should be further analyzed.
A Nonlinear Time-lag Differential Equation Model for Predicting Monthly Precipitation
Peng Yongqing, Yan Shaojin, Wang Tongmei
1995, 12(3): 319-324. doi: 10.1007/BF02656980
This paper investigates the nonlinear prediction of monthly rainfall time series which consists of phase space con-tinuation of one-dimensional sequence, followed by least-square determination of the coefficients for the terms of the time-lag differential equation model and then fitting of the prognostic expression is made to 1951-1980 monthly rainfall datasets from Changsha station Results show that the model is likely to describe the nonlinearity of the an-nual cycle of precipitation on a monthly basis and to provide a basis for flood prevention and drought combating for the wet season.
A Study on Frontal Motion over Orography
Xiao Qingnong, Wu Rongsheng
1995, 12(3): 325-334. doi: 10.1007/BF02656981
In order to study the characteristic features of the frontal motion over mountains, a frontal model is designed in this paper. The analytical solution of the model with the assumption of semigeostrophic approximation and no fric-tion is obtained and compared with numerical solution without the assumption. It assumes that the front is a free sur-face between two fluid layers with different densities. It also assumes that the mountain and the front are indefinitely long. Therefore, the motion of such a front can be determined by the one-dimensional shallow water equation system. By making a series of experiments, we confirm the rule further that front can be retarded when climbing the mountain and accelerated when going down the mountains. We also found some interesting characteristics of frontal structure influenced by topography in addition.
Neuroid BP-type Model Applied to the Study of Monthly Rainfall Forecasting
Yan Shaojin, Peng Yongqing, Guo guang
1995, 12(3): 335-342. doi: 10.1007/BF02656982
A neuroid BP-type three-layer mapping model is used for monthly rainfall forecasting in terms of 1946-1985 Nanjing monthly precipitation records as basic sequences and the model has the form i × j = 8 × 3, K = 1; by steadily modifying the weighing coefficient, long-range monthly forecasts for January to December, 1986 are constructed and 1986 month-to-month predictions are made based on, say, the January measurement for February rainfall and so on, with mean absolute error reaching 6,07 and 5,73 mm, respectively. Also, with a different monthly initial value for June through September, 1994, neuroid forecasting is done, indicating the same result of the drought in Nanjing dur-ing the summer, an outcome that is in sharp agreement with the observation.
Tests for Individual Sulfate-Containing Particles in Urban Atmosphere in Beijin
Zhang Daizhou, Tang Xiaoyan, Qin Yu, Yasunobu Iwasaka, Gai Xiuzhen
1995, 12(3): 343-350. doi: 10.1007/BF02656983
Thin film methods and X ray energy dispersive technique were applied to analyze sulfate-containing particles in Beijing in order to examine their features and sources. Atmospheric aerosol particles were collected on electron mi-croscope meshes according to two size ranges: coarse particles (r>0.5μm) and fine particles (0.5μm≥r≥0.1μm) by using a two-stage impactor. It was found fiat more than seventy percent of the fine particles and about twenty percent of the coarse particles were sulfate-containing particles. These particles were formed mainly through heterogeneous nucleation. The element composition analyses revealed that the atmospheric aerosol particles in Beijing were domi-nated by crustal particles and construction dust.
Effects on Asian Monsoon of Gigantic Qinghai-Xizang Plateau and Western Pacific Warm Pool
Zhu Qiangen, Hu Jianglin
1995, 12(3): 351-360. doi: 10.1007/BF02656984
A GCM study is performed of the effects on Asian summer monsoon initiation of the Qinghai-Xizang Plateau and western Pacific warm pool, results show that the Plateau, being a prominent sensible heat source, acts as a basic factor for the formation of the monsoon circulation; the northward transported low-latitude and low-level warm, moist flow in relation to the sensible heating experiences dynamic lifting on the south and east sides of the highland, releasing vast quantifies of latent heat through condensation, whereby the monsoon circulation pattern is further modulated; the temperature contrast between the Pacific warm pool and the Australian / marine continents serves as another basic factor for the northern SW summer monsoon genesis over the South-China Sea- the western Pacific, which, however, falls into a category of winter monsoon on a physical basis.
Numerical Study of Ural Blocking High’s Effect Upon Asian Summer Monsoon Circulation and East China Flood and Drought
He Jinhai, Zhou Xueming, Ye Rongsheng
1995, 12(3): 361-370. doi: 10.1007/BF02656985
In terms of Kuo-Qian p-sigma incorporated coordinate five-level primitive equation spheric band (70oN-30oS) model with the Ural high’s effect introduced into it as initial and boundary conditions, study is made of the high’s in-fluence on Asian summer monsoon circulation and dryness / wetness, of eastern China bated on case contrast and control experiments. Results show that as an excitation source, the blocking high produces a SE-NW stationary wavetrain with its upper-air atnicyclonic divergent circulation (just over a lower-level trough zone) precisely over the middle to lower reaches of the Changjiang River, enhancing East Asian westerly jet, a situation that contributes to perturbation growth, causing an additional secondary meridional circulation at the jet entrance, which intensifies the updraft in the monsoon area. As such, the high’s presence and its excited steady wavetrain represent the large-scale key factors and acting mechanisms for the rainstorm over the Chamgjiang-Huaihe River catchment in the eastern part of the land.
Short-term Climatic Fluctuations in North Atlantic Oscillation and Frequency of Cyclonic Disturbances over North Indian Ocean and Northwest Pacific
S. S. Dugam, S. B. Kakade
1995, 12(3): 371-376. doi: 10.1007/BF02656986
A relationship between mean sea level pressure gradient between Azores High (AH) and Icelandic Low (IL) here after called North Atlantic Oscillation Index (NAOI) and the frequency of cyclonic disturbances over North Indian Ocean is investigated using 98 years of date (1891-1988). The analysis is carried out on monthly, seasonel, annual and decadal scales. Similar studies are also done for North West Pacific ocean cyclonic disturbances. It is noticed that the number of cyclonic disturbances over North Indian Ocean during monsoon season (June-September) as well as on annual scale is significantly correlated with NAOI, However for pre (April-May) and post (October-November-December) monsoon seasons frequency of cyclonic disturbances do not bear similar relationship with NAOI. The study also shows that decadal scale variability of cyclonic disturbances during the summer monsoon over North In-dian Ocean has a remarkable correspondence with the decadal variability of NAOI.
Some Unique Characteristics of Atmospheric Interannual Variability in Rainfall Time Series over India and the United Kingdom
A. Mary Selvam, J. S. Pethkar, M. K. Kulkarni
1995, 12(3): 377-385. doi: 10.1007/BF02656987
Continuous periodogram analyses of two 50-years (1871-1920 and 1936- 1985) of summer monsoon rainfall over the Indian region and one 84-years set (1893-1976) of winter half-year rainfall over England and Wales show that the power spectra of disparate rainfall regimes follow the universal and unique inverse power law form of the sta-tistical normal distribution with the percentage contribution to total variance representating the eddy probability cor-responding to the normalized standard deviation equal to [(log L / log T50)-l] where L is the period in years and T50 the period up to which the cumulative percentage contribution to total variance is equal to 50. The above results are consistent with a recently developed non-deterministic cell dynamical system model for atmospheric flows. The im-plications or the above results for prediction of interannual variability of rainfall is discussed.