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1997 Vol. 14, No. 1

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Model Study on the Interannual Variability of Asian Winter Monsoon and Its Influence
Ji Liren, Sun Shuqing, Klaus Arpe, Lennart Benglsson
1997, 14(1): 1-22. doi: 10.1007/s00376-997-0039-4
The interannual variation of Asian winter (NE) monsoon and its influence is studied using the long-term inte-gration of Max-Plank Institute ECHAM3 (T42 LI9) model The simulation well reproduces the main features of the climatological mean Asian winter monsoon and shows pronounced difference of atmospheric circulation between strong and weak winter monsoon and for the consecutive seasons to follow. Most striking is the appearance and persistence of an anomalous cyclonic flow over the western Pa?cific and enhanced Walker circulation for strong winter monsoon in agreement with the observation. The contrast in summer rainfall patterns of both East China and India can also be discerned in the simulation Comparison of three sets of experiments with different SST shows that the forcing from the anomalies or global SST makes a major contribution to the interannual variability of Asian winter monsoon and, in particular, to the interseasonal persistence of the salient features of circulation. The SSTA over the tropical western Pacific also plays an important part of its own in modulating the Walker circulation and the extratropical flow patterns The apparent effect of strong NE monsoon is to enhance the convection over the tropical western Pacific. This effect, on the one hand, leads to a strengthening of SE trades to the east and extra westerly flow to the west, thus favorable to maintaining a specific pattern of SSTA. On the other hand, the thermal forcing associated with the SSTA acts to strengthen the extratropical flow pattern which is, in turn, conducive to stronger monsoon activity The result seems to suggest a certain self-sustained regime in the air-sea system, which is characterized by two related interactions, namely the air-sea and tropical-extratropical interactions with intermittent outburst of NE cold surge as linkage There is a connection between the strength of the Asian winter monsoon and the precipitation over China in the following summer. Links between these two variabilities are mainly through SST anomalies but snow over Asia is a contributing factor as well
Notes on Extended-Range Atmospheric Prediction in the Northern Hemisphere Winter
Shingo Yamada, Shuhei Maeda, K. Gambo
1997, 14(1): 23-40. doi: 10.1007/s00376-997-0040-y
We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at 500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean (Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl-1. Uznl-2, …, Zeddy-1, Zeddy-2…, respectively. We used the data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated scores for Uznl-1, Uznl-2, Zeddy-1, Zeddy-2 and so on we found that Uznl-1 and Zeddy-1 were statistically stable and their scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl-1 and those of Zeddy-1 30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases in January and February for the period of 1984-1992. Results showed that Zeddy-1 was more predicta?ble than the other EOFs for Zeddy Considering these results, we argued that prediction of the Zeddy-1 was to be one of the main target of extended range forecasting
Teleconnection Patterns in the Northern Hemisphere Simulated by IAP GCM
Xue Feng, Zeng Qingcun
1997, 14(1): 41-48. doi: 10.1007/s00376-997-0041-x
Based on monthly mean sea level pressure and 500 hPa height data for a 20-year period simulated by IAP 2L AGCM, teleconnection patterns in the Northern Hemisphere appearing in the model are identified and compared with observations. The results show that almost all of the observed teleconnection patterns in the Northern winter can be reproduced by the model, thus these patterns exist in the atmosphere without any external anomalies. On the other hand, the simulated teleconnection patterns are more dependent on each other than the observed, i.e., they are lack of spatial orthogonality among them, therefore, it is possible that more complex patterns will appear under the action of anomalous external factors. Besides, the simulated teleconnection patterns in summer are greatly different from those in winter, in particular, its scale in summer is much less than that in winter
Adjoint Matching Condition for Parameterized Discontinuities-A Derivation Using Lagrangian-form Costfunction
Xu Qin, Qiu Chongjian
1997, 14(1): 49-52. doi: 10.1007/s00376-997-0042-9
The generalized adjoint property and adjoint matching condition for systems that contain discontinuous on / off switches are derived by a perturbation analysis of the Lagranging-form costfunction
An Economical Consistent Dissipation Operator and Its Applications to the Improvement of AGCM
Wang Bin, Ji Zhongzhen
1997, 14(1): 53-58. doi: 10.1007/s00376-997-0043-8
This paper introduces a new consistent dissipation operator. It is based on the explicit square conservation scheme and the theory of consistent dissipation. The operator makes full use of the advantages of the Leap-frog scheme, i.e., its second order time precision and its explicit solution manner. Meanwhile, it overcomes the fatal disad-vantage, the absolute instability in computations, of the scheme. When it is applied to the explicit square conservation scheme, the time precision of the scheme reaches to third order. Especially, the computational stability of this scheme is as good as the third order explicit Runge-Kutta scheme. The CPU time required in computations by the scheme is less than that required by the explicit square conservation scheme with the consistent dissipation operator constructed from the Runge-Kutta method. Therefore, the new operator is an economical one. The application of the operator to the improvement of the dynamical model of the L2IAP AGCM shows its time-saving property and its good effects
The Influence of Weakly-Nonlinear Vertical Advection on the Wind Field of PBL with Large-Scale Orography
Wang Ling, Xu Yinzi
1997, 14(1): 59-68. doi: 10.1007/s00376-997-0044-7
The analytical solutions of the PBL wind distribution under the equilibrium of four forces including both horizontal and vertical advections are obtained in this paper using small parameter method. Utilizing this simple PBL model, we also compute the wind spirals of a certain circular vortex over level ground and over a west-east ranged mountain, respectively. The results show that when there exsits large-scale orographic forcing, vertical advection may exert considerable influence on the wind distribution of PEL, the angle between geostrophic flow and surface wind, and the height of the top of PBL
The Influence of Tibetan Plateau on the Interannual Variability of Atmospheric Circulation over Tropical Pacific
Wu Aiming, Ni Yunqi
1997, 14(1): 69-80. doi: 10.1007/s00376-997-0045-6
An atmospheric general circulation model (AGCM) with 9 sigma levels in the vertical and rhomboidal trunction at wave number 15 in the horizontal is run for 10 years with and without the Tibetan Plateau respectively (called TP and NTP experiment). The result simulated is used to investigate the influence of the Tibetan Plateau on the interannual variability of atmospheric circulation over tropical Pacific. It is found that the spatial and temporal dis-tributions of the interannual variability of the wind field over tropical Pacific in TP experiment and those in NTP ex-periment agree with each other except for the intensity, and both of them are consistent with observations well. Fur-ther analysis shows that in El Nino period the Tibetan Plateau strengthens the intensity of El Nino event, while in La Nina period it weakens the intensity of La Nina
The Effect of Heating Anomaly on the Asian Circulation-A GCM Experiment
Wang Huijun
1997, 14(1): 81-86. doi: 10.1007/s00376-997-0046-5
A numerical experiment was done by using the IAP 9-Level AGCM to study the effects of radiation anomaly over East Asia on the Asian general circulation. The results show that the changes of Asian summer general circula-tion are remarkable in the Indian and China southwest monsoon, precipitation in India and the Yellow River and Huaihe River valley in China and area around the north Japan, the easterly anomaly of low-level zonal wind in the tropical Pacific and so on.
Comparison of Long-Term Forecasting of June-August Rainfall over Changjiang-Huaihe Valley
Jin Long, LuoYing, Lin Zhenshan
1997, 14(1): 87-92. doi: 10.1007/s00376-997-0047-4
In terms of an Artificial Neural Network (ANN) established is a long-term prediction model for June-August flood / drought in the Changjiang-Huaihe Basins and a regression forecasting expression is formulated with the aid of the same factors and sample size for comparison. Results show that the ANN is superior in predictions and fittings due to its higher self-adaptive learning recognition and nonlinear mapping especially in the years of severe flood and drought. This shows great promise in using ANN in the research of flood / drought prediction on a long-range basis
A Comparative Study of the Atmospheric Layers below First Lifting Condensation Level for Instantaneous Pre-Monsoon Thunderstorm Occurrence at Agartala (23o30’N, 91o15’E) and Ranchi (23o14’N, 85o14’E) of India
Sarbari Ghosh, Utpal Kumar De
1997, 14(1): 93-102. doi: 10.1007/s00376-997-0048-3
An attempt has been made to investigate the role of vertical wind shear, corrective instability and the thermodynamic parameter (θes - θe) below the first lifting condensation level (FLCL) in the occurrence of instanta-neous premonsoon thunderstorm over Agartala (AGT) and Ranchi (RNC) at 12 GMT Radiosonde data of 1988 have been utilized here. The study has however been confined to 1000 hPa-500 hPa range at most Here the convectively unstable layers with positive vertical wind shear upto 500 hPa have been termed as ‘Fa?vourable Layers’ (FL) and the level at which an initially stable layer turns out to be convectively unstable for the first time has been termed as ‘Transition Level’ (TL). It is observed that the changes in vertical wind shear are positive at TL at the time of occurrence of thunderstorm (TS) and the corresponding change is negative on fair-weather situa?tion Moreover, the 90% confidence interval for (θes - θe) reveals that for AGT the upper layer thermodynamic characteristic is important at the time of occurrence of TS whereas for RNC, the value of (θes - θe) at the surface is much more effective
Seasonal Variations in the Vertical Structure of Water Vapor Optical Depth in the Lower Troposphere over a Tropical Station
P. Ernest Raj, P.C.S. Devara
1997, 14(1): 103-110. doi: 10.1007/s00376-997-0062-5
Spatio-temporal variations of water vapor optical depth in the lower troposphere (450-3850 m) over Pune (18o32’N, 73o51’E, 559 m Above Mean Sea Level), India have been studied over a period of five years. The mean ver-tical structure showed that the moisture content is greatest at the lowest level and decreases with increasing altitude, except in the south-west monsoon season (June to September) when an increase upto 950 m has been found. Optical depths are maximum in the monsoon season. The increase from pre-monsoon (March-May) to monsoon season in moisture content on an average is by about 58% in the above altitude range. The temporal variations in surface Rela-tive Humidity and optical depth at 450 m show positive correlation. The amplitude of seasonal oscillation is the larg-est at 1465 m altitude. The time-height cross-sections of water vapor optical depths in the lower troposphere showed a contrast between years of good and bad monsoon.
Adjoint Sensitivity Analyses on the Anomalous Circulation Features in East Asian Summer Monsoon
Yang Yan, Li Zhijin, Ji Liren
1997, 14(1): 111-123. doi: 10.1007/s00376-997-0050-9
The concept of optimal sensitivity perturbation (OSP) is developed based on adjoint sensitivity analysis theory. The persistent anomalous features in East Asian summer monsoon system, including the Ural blocking, the Okhotsk Sea dipole blocking and the variations of subtropical high are analyzed and the OSP for each of them evaluated. The results provide us with some new insight into the most significant influential factors for these features. It also demon-strates the great potential for further applications of this method in diagnostics of atmospheric processes