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2002 Vol. 19, No. 4

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The Improvement Made by a Modified TLM in 4DVAR with a Geophysical Boundary Layer Model
Zhu Jiang, Wang Hui, Masafumi Kamachi
2002, 19(4): 563-582. doi: 10.1007/s00376-002-0001-4
The strong nonlinearity of boundary layer parameterizations in atmospheric and oceanic models can cause difficulty for tangent linear models in approximating nonlinear perturbations when the time integration grows longer. Consequently, the related 4-D variational data assimilation problems could be difficult to solve. A modified tangent linear model is built on the Mellor-Yamada turbulent closure (level 2.5) for 4-D variational data assimilation. For oceanic mixed layer model settings, the modified tangent linear model produces better finite amplitude, nonlinear perturbation than the full and simplified tangent linear models when the integration time is longer than one day. The corresponding variational data assimilation performances based on the adjoint of the modified tangent linear model are also improved compared with those adjoints of the full and simplified tangent linear models.
The Wave Train Characteristics of Teleconnection Caused by the Thermal Anomaly of the Underlying Surface of the Tibetan Plateau. Part Ⅰ: Data Analysis
Zhou Yushu, Deng Guo, Gao Shouting, Xu Xiangde
2002, 19(4): 583-593. doi: 10.1007/s00376-002-0002-3
The effect of the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring on the precipitation over the middle and lower reaches of the Yangtze River (MRYR) in the subsequent summer was investigated. Through data analysis, the influence of" strong signal" features of the three-dimensional thermal anomaly of the Plateau upon the precipitation anomaly over MRYR in the subsequent summer was revealed. This feature of the signal shows that from 0 cm to 320 cm under the surface of the ground, the soil temperature anomalies of the Tibetan Plateau manifest out of phase distribution in flood years and drought years over MRYR. In flood years over MRYR, there is a positive soil temperature anomaly in the region of the southern Tibetan Plateau (to the south of 30°N) and a negative anomaly in the region of the middle and northern Tibetan Plateau (to the north of 30°N), while in drought years the distribution of the soil temperature anomaly is opposite to the one in flood years. The maximum value of the soil temperature anomaly lies in the levels between 40 cm and 160 cm under the surface of the ground. Meanwhile, the data analysis also shows that the general circulation in the Northern Hemisphere may respond to the thermal anomaly of the Tibetan Plateau and form the propagation of a low frequency wave train with a seasonal time scale, and this wave train may affect the precipitation over MRYR in the subsequent summer.Analyses reveal that the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring is one of the key influencing factors for the subsequent summer precipitation over MRYR.
Life Cycles of Blocking Flows Associated with Synoptic-Scale Eddies: Observed Results and Numerical Experiments
Luo Dehai, Li Jianping, Huang Fei
2002, 19(4): 594-618. doi: 10.1007/s00376-002-0003-2
An observational study is presented to confirm that the life cycle of blocking associated with synoptic-scale eddies is a transfer process between dispersion and nondispersion. In addition, numerical experiments are conducted. It is found that the synoptic-scale eddies seem to play a dominant role in the amplification of blocking, while the topography effect appears to play a phase-locking role. At the same time,the synoptic eddies tend to split into two branches during the onset of blocking. This supports the observational results obtained.
Scaling the Microphysics Equations and Analyzing the Variability of Hydrometeor Production Rates in a Controlled Parameter Space
Chungu Lu, Paul Schultz, Gerald L.Browning
2002, 19(4): 619-650. doi: 10.1007/s00376-002-0004-1
A set of microphysics equations is scaled based on the convective length and velocity scales. Comparisons are made among the dynamical transport and various microphysical processes. From the scaling analysis, it becomes apparent which parameterized microphysical processes present off-scaled influences in the integration of the set of microphysics equations. The variabilities of the parameterized microphysical processes are also studied using the approach of a controlled parameter space. Given macroscopic dynamic and thermodynamic conditions in different regions of convective storms, it is possible to analyze and compare vertical profiles of these processes. Bulk diabatic heating profiles for a cumulus convective updraft and downdraft are also derived from this analysis. From the two different angles, the scale analysis and the controlled-parameter space approach can both provide an insight into and an understanding of microphysics parameterizations.
The Spring Monsoon in South China and Its Relationship to Large-Scale Circulation Features
Wang Huijun, Xue Feng, Zhou Guangqing
2002, 19(4): 651-664. doi: 10.1007/s00376-002-0005-0
In this paper, the authors define the spring monsoon in South China, and study the climatology and the interannual variation through analysis of the precipitation and the related atmospheric circulation, as revealed by the NCEP/NCAR reanalysis data. The results indicate that the spring monsoon season in South China occurs climatologically in April and May, which is supported by both seasonal and interannual variation of the atmospheric circulation and precipitation. The related atmospheric circulation is different from that during the East Asian summer or winter monsoon season. The interannual variation of the spring monsoon rainfall in South China relates primarily to the anomalous circulation over the North Pacific, which is linked with the westerly jet over North Asia and with the polar vortex. It is also connected with sea surface temperature anomalies in the Pacific. Changes in the Asian tropical atmospheric circulation has little influence on the spring monsoon in South China according to this research.
Teleconnections: Summer Monsoon over Korea and India
Baek-Jo Kim, Sung-Euii Moon, Lu Riyu, R. H. Kripalani
2002, 19(4): 665-676. doi: 10.1007/s00376-002-0006-z
This study investigates the relationship between the summer monsoon rainfall over Korea and India, by using correlation analysis and Singular Value Decomposition (SVD). Results reveal that summer monsoon rainfall over Korea is negatively (significant at the 99% level) correlated with the rainfall over the northwest and central parts of India. In addition, coupled spatial modes between the rainfall over Korea and India have been identified by the SVD analysis. The squared covariance fraction explained by the first mode is 70% and the correlation coefficient between the time coefficients of the two fields is significant at the 99% level, indicating that the coupled mode reflects a large part of the interaction between the summer monsoon rainfall over Korea and India. The first mode clearly demonstrates the existence of a significant negative correlation between the rainfall over the northwest and central parts of India and the rainfall over Korea. Possible mechanisms of this correlation are investigated by analyzing the variation of upper-level atmospheric circulation associated with the Tibetan high using NCEP/NCAR Reanalysis data.
Interannual and Decadal Variability of Landfalling Tropical Cyclones in the Southeast Coastal States of the United States
Li'an Xie, Leonard J.Pietrafesa, Kejian Wu
2002, 19(4): 677-686. doi: 10.1007/s00376-002-0007-y
The interannual variability of the At lantic tropical cyclone (TC) frequency is well known. Separately,recent studies have also suggested that a much longer, multidecadal (40-60 year) trend might be emerging from the recent increase in Atlantic TC activity. However, the overall structure of the intrinsic frequencies (or temporal modes) of Atlantic TC activity is not yet known. The focus of this study is to systematically analyze the intrinsic frequencies of Atlantic TC activity using hurricane and tropical storm landfall data collected along the southeast coast (SEC) of the United States. Based on an Empirical Mode Decomposition (EMD) analysis of the frequency of landfall TCs along the SEC from 1887-1999, we have found that Atlantic TC activity has four primary, temporal modes. The interannual and multidecadal modes reported in the published literature are two such modes. After identifying all primary modes, the relative importance of each mode and its physical cause can be analyzed. For example, the most energetic mode is the interannual mode (2-7 year period). This mode is known to be associated with the 2-7 year El Nino / La Ni na cycle. The average number of annual landfalling TCs along the SEC decreased by 24% during El Nino years, but did not show significant increase during weak and moderate La Nina years. However, intense La Nina years were generally associated with more than average landfalling TCs along the SEC. The effects of El Nino and La Nina also became more significant when only hurricanes were considered. The significance of the effects of El Nino and La Nina on landfalling TCs and hurricanes in different US southeast coastal states showed significant differences.
Identification of Coherent Structures of Turbulence at the Atmospheric Surface Layer
Li Xin, Hu Fei, Pu Yifen, M.H.Al-Jiboori, Hu Zhaoxia, Hong Zhongxiang
2002, 19(4): 687-698. doi: 10.1007/s00376-002-0008-x
A parameter-free method based on orthonormal wavelet transforms is recommended for calculating the principal time scale of coherent structures in atmospheric boundary-layer measurements. First, the atmospheric turbulent signal is decomposed into the small scate vortex that has approximate isotropy and the large scale vortex with the digital filter. Then, the large scale vortex is used to detect colterent structures with this method. The principal time scale and profile of coherent structures for velocity components (u, v, w)above rice fields are obtained. In order to testify the validity of this method, the correlation of coherent structures and non-coherent structures are also calculated.
A Comparative Analysis of Computational Stability for Linear and Non-Linear Evolution Equations
Lin Wantao, Ji Zhongzhen, Wang Bin
2002, 19(4): 699-704. doi: 10.1007/s00376-002-0009-9
For several difference schemes of linear and non-linear evolution equations, taking the one-dimensional linear and non-linear advection equations as examples, a comparative analysis for computational stability is carried out and the relationship between non-linear computational stability, the construction of difference schemes, and the form of initial values is discussed. It is proved through comparative analysis and numerical experiment that the computational stability of the difference schemes of the non-linear evolution equation are absolutely different from that of the linear evolution equation.
Adaptive Grid Technique Based on the Variational Principle and Its Weight Functions
Kang Hongwen, Gu Xiangqian, Liu Chongjian, Wang Pengyun
2002, 19(4): 705-718. doi: 10.1007/s00376-002-0010-3
Two computational cases that have analytic solutions are employed for studying the adaptive grid technique based on the variational principle. The results show that for the computational case of traveling shock waves the weight function, with the 2nd-order derivation terms taken into consideration, can more effectively reduce the error than one with gradient terms. For the case of cyclonic frontogenesis, weight functions only related to the gradient are unable to enhance the computational accuracy. while ones with the wind field and frontogenesis function taken into consideration can more reasonably arrange the grid. Compared with analytic solutions, the adaptive grid technique suggested in this paper can improve computational accuracy and it displays the prominent advantage of saving memory.
Symplectic-like Difference Schemes for Generalized Hamiltonian Systems
Zhao Ying, Wang Bin, Ji Zhongzhen
2002, 19(4): 719-726. doi: 10.1007/s00376-002-0011-2
The nature of infinite-dimensional Hamiltonian systems are studied for the purpose of further study on some generalized Hamiltonian systems equipped with a given Poisson bracket. From both theoretical and practical viewpoints, we summarize a general method of constructing symplectic-like difference schemes of these kinds of systems. This study provides a new algorithm for the application of the symplectic geometry method in numerical solutions of general evolution equations.
The Relationship between the Asian/Australian Monsoon and ENSO on a Quasi-Four-Year Scale
Zhu Yanfeng, Chen Longxun
2002, 19(4): 727-740. doi: 10.1007/s00376-002-0012-1
The interannual variability of tropical zonal wind and the relationship between ENSO and the Asian/Australian monsoon in different phases are discussed. Results show that the tropical zonal wind strongly couples with the central-eastern Pacific SST on a quasi-four-year scale. During the period of El Nino, the East Asian winter (summer) monsoon is weaker (stronger) and the South Asian summer monsoon is weaker than normal. Conversely, the East Asian winter (summer) monsoon is stronger (weaker) and the South Asian summer monsoon is stronger than normal during the period of La Nina. The anomalous northerly over East Asia induces an anomalous westerly over the western equatorial Pacific, which favors the appearance of positive SST anomalies in the central-eastern Pacific. The development of El Nino requires the persistence of a westerly over the central-eastern Pacific. The convergence between anomalous northerlies from the central North Pacific (not from the East Asian continent) and anomalous southerlies from Northeast Australia favors the persistence of a westerly over the central-eastern Pacific. In particular, the anomalous southerlies from Northeast Australia play a key role in the onset of strong westerly anomalies over the tropical central-eastern Pacific.
Critical Time Span and Nonlinear Action Structure of Climatic Atmosphere and Ocean
Wang Zhiren, Wu Dexing, Chen Dake, Wu Huiding, Song Xuejia, Zhang Zhanhai
2002, 19(4): 741-756. doi: 10.1007/s00376-002-0013-0
This paper studies the critical time span and the approximate nonlinear action structure of climatic atmosphere and ocean. The critical time span of the climatic atmosphere and ocean, which is related to the spatial resolution required, the strength of nonlinear action, and the calculation exactness, may represent the relative temporal scale of predictability. As far as the same characteristic spatial scale is concerned, the minimum critical time span of the ocean is about 9 times of that of atmosphere, several days or more. Usually,the stronger the nonlinear action, the shorter the critical time span with smooth changes of external forces.The approximate structure of nonlinear action of climatic atmosphere and ocean is: the nonlinear action decreases usually with increasing latitude, which is related to the role of the Coriolis force in fluid motion (forming geostrophic current); the nonlinear action changes with the anomalous cyclonic or anticyclonic circulation shear, for instance, when the strength of anomalous eastward zonal circulation is comparable to that of anomalous meridional circulation, the nonlinear action is the strongest; wind stress plus gradient forces enhance the nonlinear action, etc..
A Personal Perspective on the Further Reform of the Advances in Atmospheric Sciences
Da-Lin Zhang
2002, 19(4): 757-764. doi: 10.1007/s00376-002-0014-z
First of all, I wish to thank the Advances in Atmospheric Sciences (AAS) Editorial Board for recommending the publication of this original letter, summarizing my personal perspective on the reform of AAS,that was distributed during its 19 December 2001 Board meeting. The letter has now been significantly improved by the incorporation of many helpful comments and suggestions from extensive email discussions conducted among over 60 foreign participants, including several board members of AAS, as well as from numerous personal communications (see the acknowledgements section).
A Response to the Letter of Da-Lin Zhang
Wu Guoxiong, Wang Huijun
2002, 19(4): 765-766. doi: 10.1007/s00376-002-0015-y