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1993 Vol. 10, No. 1

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Numerical Study for Potential Predictability of Short-Term Anomalous Climate Change Caused by El Nino
Ni Yunqi, Lin Wuyin, Wang Wanqiu, Yuan Chongguang, Zhang Qin
1993, 10(1): 1-10. doi: 10.1007/BF02656949
Abstract:
In this paper, the two-layer IAP model with sea surface temperature anomalies in the equatorial central-eastern Pacific is used to investigate potential predictability of global short-term anomalous climate change caused by El Nino via the “switching” experiments. The experimental results show that short-term anomalous climate change in the tropics is mainly caused by instantaneous response of tropical atmosphere to SSTA in the tropics. The effective period of this kind of anomalous climate is shorter and about monthly scale. In the high latitudes, the anomalous cli-mate is mainly caused by the lag response of atmosphere to SSTA in the tropics. The strongest influence appears in the month after a half year when the SSTA in the tropics disappears. Therefore, potential predictability of short-term anomalous climate change may be reached to one year; anomalous climate change in the middle-latitudes is not only affected by instantaneous response to SSTA in the tropics, but also by lag response to that. Therefore, short-term climate change prediction with monthly time scale can be not only done by using SSTA in the tropics, but also predic-tion of short-term climate after a half year can be done and its effective predictable period may be reached to one year.
An Aridity Trend in China and Its Abrupt Feature in Association with the Global Warming
Fu Congbin
1993, 10(1): 11-20. doi: 10.1007/BF02656950
Abstract:
A distinct aridity tread in China in last 100 years is presented by applying a linear fitting to both the climate re-cords and the hydrological records, which is supported by evidence of environmental changes and seems to be associ-ated with a global warming trend during this period.The Mann Kendall Rank statistic test reveals a very interesting feature that the climate of China entered into a dry regime abruptly in about l920’s, which synchronized with the rapid warming of the global temperature at almost the same time.According to an analysis of the meridional profile of observed global zonal mean precipitation anomalies during the peak period of global warming (1930-1940), the drought occurred in whole middle latitude zone (25oN-55oN) of the Northern Hemisphere, where the most part of China is located in. Although this pattern is in good agreement with the latitude distribution of the difference of zonal mean rates of precipitation between 4 × CO2 and 1 × CO2 simu-lated by climate model (Manabe and Wetherald, 1983), more studies are required to understand the linkage between the aridity trend in China and the greenhouse effect.The EOF analysis of the Northern Hemisphere sea level pressure for the season of June to August shows an ab-rupt change of the time coefficient of its first eigenvector from positive to negative in mid-lP^s, indicating an enhancement of the subtropical high over Southeast Asia and the western Pacific after that time. This is an atmos-pheric circulation pattern that is favorable to the development of dry climate in China.
Stable and Unstable Eigensolutions of Laplace’s Tidal Equations for Zonal Wavenumber Zero
Rolf Müller
1993, 10(1): 21-40. doi: 10.1007/BF02656951
Abstract:
Laplace's tidal equations are of great importance in various fields of geophysics. Here, the special case of zonal symmetry (zonal wavenumber m = 0) is investigated, where degenerate sets of eigensolutions appear. New results are presented for the inclusion of dissipative processes and the case of unstable conditions. In both instances the (nonzero) eigenfrequencies are complex. In the latter case, additional stable (i.e. real) eigenfrequencies appear in the numerical results for the absolute value of the Lambparameter ε being larger than a critical value εc. Further, it is shown that any degeneracies are removed through the inclusion of dissipation. Moreover, asymptotic relations are derived employing the relation of Laplace's tidal equations for m = 0 to the spheroidal differential equation. The implications of these findings to numerical techniques are demonstrated and results of computations are presented.
A Further Inquiry on the Mechanism of 30-60 Day Oscillation in the Tropical Atmosphere
Li Chongyin
1993, 10(1): 41-53. doi: 10.1007/s00376-006-0016-3
Abstract:
In a simple semi-geostropic model on the equatorial β-plane, the theoretical analysis on the 30-60 day oscillation in the tropical atmosphere is further discussed based on the wave-CISK mechanism. The convection heat-ing can excite the CISK-Kelvin wave and CISK-Rossby wave in the tropical atmosphere and they are all the low-frequency modes which drive the activities of 30-60 day oscillation in the tropics. The most favorable conditions to excite the CISK-Kelvin wave and CISK-Rossby wave are indicated: There is convection heating but not very strong in the atmosphere and there is weaker disturbance in the lower troposphere.The influences of vertical shearing of basic flow in the troposphere on the 30-60 day oscillation in the tropics are also discussed.
One Possible Mechanism for the Principal Mode of Atmospheric Low-Prequency Variability in the Northern Hemisphere Winter
Wang Guomin
1993, 10(1): 54-60. doi: 10.1007/BF02656953
Abstract:
With the specified basic flow in the Northern Hemisphere winter, a study is made of the structure characteristics and mechanism of the principal mode of atmospheric low-frequency variability in terms of a linear barotropic model. Statistical and dynamical analyses of the model results indicate that the mode and the related dominant-forcing excitation zone are featured by evident spatial distribution and that the mechanism responsible for the mode bears re-lation to the zonal asymmetry of the basic flow and the associated barotropic energy conversion.
Unstable Tropical Air-Sea Interaction Waves and Their Physical Mechanisms
Zhang Renhe, Chao Jiping
1993, 10(1): 61-70. doi: 10.1007/BF02656954
Abstract:
In this paper, the tropical air-sea interaction is discussed by using a simple air-sea coupled model, in which the inertia-gravity waves are filtered off and only the equatorial Rossby waves are reserved in both the atmosphere and the ocean. There exist two kinds of air-sea interaction waves in the coupled model, that is, the high-frequency fast waves and the low-frequency slow waves. The phase speed of the fast waves is westward and the frequencies are close to those of the equatorial Rossby waves in the atmosphere. The slow waves propagate westward in the part of short wavelengths and eastward in that of long wavelengths. There exist instabilities for both the westward and eastward propagating slow waves. If the fast waves are filtered off, there is little effect on the slow waves which have great in-fluence on the long range process in the tropical air-sea coupled system. According to the tropical air-sea interaction waves we obtain here, a possible explanation to the propagating process of ENSO events is given.
Large Scale Aspects of India-China Summer Monsoon Rainfall
R. H. Kripalani, S. V. Singh
1993, 10(1): 71-84. doi: 10.1007/BF02656955
Abstract:
This study investigates the dominant modes of variability in monthly and seasonal rainfall over the India-China region mainly through Empirical Orthogonal Function (EOF) analysis. The EOFs have shown that whereas the rain-fall over India varies as one coherent zone, that over China varies in east-west oriented bands. The influence of this banded structure extends well into India.Relationship of rainfall with large scale parameters such as the subtropical ridge over the Indian and the western Pacific regions, Southern Oscillation, the Northern Hemispheric surface air temperature and stratospheric winds have also been investigated. These results show that the rainfall over the area around 40oN, 110oE over China is highly related with rainfall over India. The subtropical ridge over the Indian region is an important predictor over India as well as over the northern China legion.
Effect of Counter-Gradient in the Computation of Turbulent Fluxes of Heat and Moisture in a Regional Model
S. S. Vaidya, V. N. Lykossov, S. S. Singh
1993, 10(1): 85-94. doi: 10.1007/BF02656956
Abstract:
The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gra-dient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.
Aircraft Observations of Electrical Conductivity in Warm Clouds
P. Ernest Raj, P. C. S. Devara, A. M. Selvam, A.S.R. Murty
1993, 10(1): 95-102. doi: 10.1007/BF02656957
Abstract:
Aircraft observations of electrical conductivity and cloud microphsical, dynamical and other electrical parameters were made in warm stratocumulus and cumulus clouds forming during the summer monsoon seasons (June-September) of 1983 and 1985 in the Deccan Plateau region, India. A Gerdien type cylindrical condenser was used for the measurement of electrical conductivity. The variations in the electrical conductivity are observed to be closely associated with the updrafts and downdrafts in the cloud, liquid water content, cloud droplet charge and coro-na discharge current. The value of electrical conductivity in warm clouds is found to be in the order of 10-12 ohm-1 m-1 which is two orders higher than that observed in clear-air at cloud-base levels in some regions by other investigators.Classical static electricity concepts predict reduced conductivity values inside clouds. Cloud electrical conductivi-ty measurements, particularly in warm clouds are few and the results are contradictory. The recently identified mech-anism of vertical mixing in clouds lends support to coovective charge separation mechanism with inherent larger than clear-air values for cloud electrical conductivity and therefore consistent with the measurements reported herein.
Linear Momentum Approximation and Frontogenesis Caused by Baroclinic Ekman Momentum Flow
He Jianzhong
1993, 10(1): 103-112. doi: 10.1007/BF02656958
Abstract:
A method of linear momentum approximation is proposed that deals with weak nonlinear problems in an ap-proximate manner. A motion of nonlinear nature is obtained in the system by assuming the motion to be in the form of linear momentum flow in the corresponding space introduced, followed by the transformation from the specified into a physical space. Significant results have been thereby derived in examining the effects of baroclinic Ekman mo-mentum flow upon Eady-type baroclinic waves and frontogenesis. Also, this technique can be applied to investigate the dynamic characteristics of the weak nonlinear boundary layer including topography, stratification and non-Ekmantype friction for gaining further insight into the influence on the boundary layer inner parameters of ter-rain, baroclinicity and inhomogeneous process so that the classic theory is revised.
A Hydrometeorological Analysis of the Severe Rainstorm of 20-22 September 1900 over the Gangetic West Bengal
P.R.Rakhecha, B.N.Mandal, A.K.Kulkarni, R.B.Sangam
1993, 10(1): 113-120. doi: 10.1007/BF02656959
Abstract:
A hydrometeorological study is made of the September, 1900 severe rainstorm which led up to the record rain-falls over Gangetic West Bengal with subsequent disastrous flooding in the Damodar and the Hooghly rivers. The spatial extent of the rainstorm for different durations has been examined by constructing the isohyetal patterns based on rainfall records of stations affected by the storm. Areal rainfalls for 1,2 and 3-day periods are calculated and the values have been compared with similar values from other major rainstorms of the region. The comparison revealed that the September, 1900 rainstorm was the heaviest for 1,2 and 3-day durations for all the areas. The storm contrib-uted rainfalls of 33.0 cm, 52.0 cm and 62.0 cm over an area of 10,000 km2 in 1,2 and 3 days respectively. This rainstorm could, therefore, be considered as an important input in flood and design storm studies in the Gangetic West Bengal region. A relationship between point to areal rainfall has also been developed with a view to evaluate areal PMP estimates.
Hurricane Forecasts in the FSU Models
T. N. Krishnamurti, H. S. Bedi, K. S. Yap, D. Oosterhof
1993, 10(1): 121-132. doi: 10.1007/BF02656960
Abstract:
A brief account of our studies on the hurricane forecast problem is presented here. This covers recent prediction results from the Florida State University (FSU) regional and global numerical weather prediction models. The re-gions covered are the Indian and the Pacific Oceans. The life cycle of the onset vortex (a hurricane) of the summer monsoon, typhoons over the western Pacific Ocean and tropical cyclones over the Bay of Bengal (Andhra Pradesh and the Bangladesh storms) are covered here. The essential elements in the storm formaton are the strong horizontal shear in the cyclogenetic areas, a lack of vertical shear and warn sea surface temperatures. The storm motion has a steering component largely described by the advection of vorticity by a vertically averaged layer mean wind, the recurvature of a storm appears to invoke physical processes via the advection of divergence by the divergent part of the wind especially in the outflow layers of the storm. Very high resolution global models seem to be able to handle the motion and structure during the entire life of typhoons quite reasonably. The scope for better diagnosis of the storms life cycle appears very promising in view of the realistic simulation of the life cycle.
Brief News of International Workshop on Climate Variabilities (IWCV) Held on July 13-17,1992 in Beijing
Huang Ronghui, Zhang Renhe
1993, 10(1): 133-133. doi: 10.1007/BF02656961
Abstract:
The Fourth International Symposium on Asian Monsoon Held in Japan
Wu Guoxiong
1993, 10(1): 134-134. doi: 10.1007/BF02656962
Abstract: