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WHAT ARE THE SEPARATRIX VALUES NAMED BY LEONTOVICH ON HOMOCLINIC BIFURCATION

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Applied Mathematics and Mechanics(English Edition) 2005年第4期26卷 457-464页

作者：骆海英李继彬 LASG Institute of Atmospheric Physics Chinese Academy of Science School of Science Kunming University of Science and TechnologyKunming 650093 P.R.China Graduate School of the Chinese Academy of Sciences Beijing 100039 P.R.China

For a given system, by using the Tkachev method which concerned with the proof of the stability of a multiple limit cycle, the exact computation formula of the third separatrix values named by Leontovich for the multiple limit cycle bifurcation was given, which was one of the main criterions for the number of limit cycles bifurcated from a homoclinic orbit and the stability of the homoclinic loop, and a computation formula for higher separatrix values was conjectured.

关键词： homoclinic bifurcation separatrix value saddle value limit cycle

Improved ENSO Forecasts by Assimilating Sea Surface Temperature Observations into an Intermediate Coupled Model

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Advances in Atmospheric Sciences 2006年第4期23卷 615-624页

作者：郑飞朱江 Rong-Hua ZHANG 周广庆 International Center for Climate and Environment Science （ICCES） Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 Earth System Science Interdisciplinary Center （ ESSIC） University of Maryland College Park Maryland USA

A simple method for initializing intermediate coupled models （ICMs） using only sea surface temperature （SST） anomaly data is comprehensively tested in two sets of hindcasts with a new ICM. In the initialization scheme, both the magnitude of the nudging parameter and the duration of the assimilation are considered, and initial conditions for both atmosphere and ocean are generated by running the coupled model with SST anomalies nudged to the observations. A comparison with the observations indicates that the scheme can generate realistic thermal fields and surface dynamic fields in the equatorial Pacific through hindcast experiments. An ideal experiment is performed to get the optimal nudging parameters which include the nudging intensity and nudging time length. Twelve-month-long hindcast experiments are performed with the model over the period 1984-2003 and the period 1997-2003. Compared with the original prediction results, the model prediction skills are significantly improved by the nudging method especially beyond a 6-month lead time during the two different periods. Potential problems and further improvements are discussed regarding the new coupled assimilation system.

关键词： ENSO intermediate coupled model prediction skill hindcast

Influence of the Mascarene High and Australian High on the Summer Monsoon in East Asia: Ensemble Simulation

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Advances in Atmospheric Sciences 2003年第5期20卷 799-809页

作者：薛峰姜大膀郎咸梅王会军 LASG Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing100029

By using a nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influence of the Mascarene high (MH) and Australian high (AH) over the southern subtropics upon the East Asian summer monsoon circulation and summer precipitation in East Asia. The use of ensemble statistics is adopted to reduce the simulation errors. The result shows that with the intensification of MH, the Somali low-level jet is significantly enhanced together with the summer monsoon circulation in the tropical Asia and western Pacific region. Furthermore, the anticyclonic anomaly in the tropical western Pacific to the east of the Philippines may induce a weak East-Asia-Pacific teleconnection pattern. In the meantime, geopotential height in the Tropics is enhanced while it is reduced over most regions of mid-high latitudes, thus the northwestern Pacific subtropical high at 500 hPa extends southwestward, resulting in more rainfall in southern China arid less rainfall in northern China. A similar anomaly pattern of the atmospheric circulation systems is found in the experiment of the intensification of AH. On the other hand, because the cross-equatorial currents associated with AH are much weaker than the Somali jet, the anomaly magnitude caused by the intensification of AH is generally weak, and the influence of AH on summer rainfall in China seems to be localized in southern China. Comparison between the two sets of experiments indicates that MH plays a crucial role in the interactions of general atmospheric circulation between the two hemispheres.

关键词： rnascarene high Australian high East Asian summer monsoon

Nonlinear balance constraints in 3DVAR data assimilation

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Science China Earth Sciences 2006年第3期49卷 331-336页

作者： ZHU Jiang YAN Changxiang International Center for Climate and Environment Sciences Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China International Center for Climate and Environment Sciences Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

In many applications of 3DVAR, the balance constraints can be considered via two main approaches: weak constraint method which adds penalty terms to the cost function; and proper defi- nition of the background error covariance matrix with non-zero cross-correlation sub-matrices. The weak constraint approach requires determining the weighting matrices of the penalty terms. The background error covariance approach does not require determining those additional weighting ma- trices. However, it is only applicable to those linear or linearized balance constraints. A novel ap- proach is proposed based on the background error covariance approach by generalizing the so-called Derber-Bouttier formulation. An assimilation experiment of estimating temperature and salinity from the sea surface dynamic height observation is given to illustrate the proposed treatments of nonlinear balance constraints.

关键词： 3DVAR, linear balance constraint, nonlinear balance constraint, background error covariance matrix, sea surface dynamic height.

Nonlinear local Lyapunov exponent and atmospheric predictability research

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Science China Earth Sciences 2006年第10期49卷 1111-1120页

作者： CHEN Baohua1, LI Jianping1,2 & DING Ruiqiang2 1. College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China 2. State Key Laboratory of Numerical Modeling for Atmospheric Science and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China College of Atmospheric Sciences Lanzhou University Lanzhou China State Key Laboratory of Numerical Modeling for Atmospheric Science and Geophysical Fluid Dynamics (LASG) Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China

Because atmosphere itself is a nonlinear system and there exist some problems using the linearized equations to study the initial error growth, in this paper we try to use the error nonlinear growth theory to discuss its evolution, based on which we first put forward a new concept: nonlinear local Lyapunov exponent. It is quite different from the classic Lyapunov exponent because it may characterize the finite time error local average growth and its value depends on the initial condition, initial error, variables, evolution time, temporal and spatial scales. Based on its definition and the at-mospheric features, we provide a reasonable algorithm to the exponent for the experimental data, obtain the atmospheric initial error growth in finite time and gain the maximal prediction time. Lastly, taking 500 hPa height field as example, we discuss the application of the nonlinear local Lyapunov exponent in the study of atmospheric predictability and get some reliable results: atmospheric predictability has a distinct spatial structure. Overall, predictability shows a zonal distribution. Prediction time achieves the maximum over tropics, the second near the regions of Antarctic, it is also longer next to the Arctic and in subtropics and the mid-latitude the predictability is lowest. Particularly speaking, the average prediction time near the equation is 12 days and the maximum is located in the tropical Indian, Indonesia and the neighborhood, tropical eastern Pacific Ocean, on these regions the prediction time is about two weeks. Antarctic has a higher predictability than the neighboring latitudes and the prediction time is about 9 days. This feature is more obvious on Southern Hemispheric summer. In Arctic, the predictability is also higher than the one over mid-high latitudes but it is not pronounced as in Antarctic. Mid-high latitude of both Hemispheres (30°S―60°S, 30°―60°N) have the lowest predictability and the mean prediction time is just 3―4 d. In addition, predictab

关键词： nonlinear, local, Lyapunov exponent, atmospheric predictability, maximal prediction time.

North Pacific sea ice cover, a predictor for the Western North Pacific typhoon frequency?

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Science China Earth Sciences 2007年第8期50卷 1251-1257页

作者： FAN Ke Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Department of Atmospheric Science, Yun-nan University, Kunming 650091, China Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Department of Atmospheric Science Yunnan University Kunming China

The relationship between the sea ice cover in the North Pacific and the typhoon frequency has been studied in this paper. It follows that the index for the sea ice cover in the North Pacific (ISA) both in December-January-February (DJF) and in March-April-May (MAM) is negatively correlated with annual typhoon number over the western North Pacific (TNWNP) during 1965―2004, with correlation coeffi-cients of -0.42 and -0.49 respectively (above 99% significant level). Large sea ice cover in the North Pacific tends to decrease TNWNP. Positive ISA (MAM) is associated with the tropical circulation and SST anomalies in the North Pacific, which may lead to unfavorable dynamic and thermal conditions for typhoon genesis over WNP from June to October (JJASO). The variability of the atmospheric circula-tion over the North Pacific, associated with the ISA anomaly in MAM is connected to the tropical at-mospheric circulation variability in MAM via the teleconnection wave train. Besides, as the tropical circulation has strong seasonal persistency from the MAM to JJASO, thus, the ISA in MAM-related variability of the tropical atmospheric circulation as well as the SST can affect the typhoon activity over the western North Pacific.

关键词： typhoon sea ice cover North Pacific teleconnection

Statistical characteristics of the double ridges of subtropical high in the Northern Hemisphere

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Chinese Science Bulletin 2005年第20期50卷 2336-2341页

作者： ZHAN Ruifen LI Jianping HE Jinhai State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China Department of Atmospheric Sciences Institute of Meteorology Nanjing University of Information Science and Technology Nanjing 210044 China Graduate School of the Chinese Academy of Sciences Beijing100039 China

The generality and some climatological charac- teristics of the double ridge systems of subtropical high (SH) are investigated statistically by using the daily NCEP/NCAR reanalysis data from 1958 to 1998. The results show that the SH double-ridge event is a common phenomenon in the Northern Hemisphere, with the distinct seasonal and re- gional features, that is, the majority of SH double-ridge geneses concentrate over the eastern North India Ocean- western North Pacific as well as the central North Pacific in the period from mid-July to mid-September. Especially over the western North Pacific subtropics, the SH double-ridge events are extremely active. It is found that the life cycle of most double-ridge events of western Pacific subtropical high (WPSH) is shorter but some still last longer. The WPSH dou- ble-ridge events occur most frequently from July to Septem- ber, while there is a paucity of occurrences during Novem- ber-March. Also, it is shown that the WPSH double-ridge events have a strong interannual variation with a certain periodicity which possesses a remarkably abrupt change in the mid-1970s. Additionally, the relationship between the WPSH double ridges and the meridional movement of WPSH is discussed.

关键词：亚热带高度双脊系统回归线北半球气候学

The ENSO’s Effect on Eastern China Rainfall in the Following Early Summer

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Advances in Atmospheric Sciences 2009年第2期26卷 333-342页

作者：林中达陆日宇 Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences

ENSO＇s effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the E1 Nifio peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections： One is related to the western North Pacific （WNP） anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream （AJS） in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO＇s effect on the zonal flow in the whole Northern Hemisphere. After the E1 Nifio peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.

关键词： ENSO eastern China rainfall early summer Asian jet stream western North Pacific anticyclone

Influence of the Southern Hemispheric Circulation on East-west Oscillation of the Western Pacific Subtropical High

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Chinese Science Bulletin 2005年第14期50卷 1532-1536页

作者： XUE Feng HE Juanxiong LASG Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029 China

The western Pacific subtropical high (WPSH) is a large-scale circulation system in the subtropics during the boreal summer. Since 1950's, Chinese meteorologists have done a lot of studies about WPSH and recognized its influence on summer rainfall in China[1-8]. For instance, the north-south movement of WPSH is related to the movement of the rain-belt in eastern China, and the northward jump of WPSH during mid-June and mid-July corresponds to the start and end of mei-yu over the Yangtze River valley, respectively. Besides the north-south movement, the east-west movement of WPSH is also evident. Gradually, WPSH extends westwards from its center in the form of intraseasonal oscillation.

关键词：亚热带循环系统太平洋地区降雨量