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1999 Vol. 16, No. 1

Display Method:
The Space and Time Features of Global SST Anomalies Studied by Complex Principal Component Analysis
Silvia Alessio, Arnaldo Longhetto, Luo Meixia
1999, 16(1): 1-23. doi: 10.1007/s00376-999-0001-8
In this paper, the variability characteristics of the global field of sea surface temperature (SST) anomaly are studied by complex principal component (c.p.c.) analysis, whose results are also com?pared with those of real p.c. analysis. The data consist of 40 years of global SST monthly averages over latitudes from 42.5oS to 67.5oN. In the spatial domain, it is found that the distribution of the first complex loading amplitude is characterized by three areas of large values: the first one in the eastern and central equatorial Pacific Ocean, the second one in the northern tropical Indian Ocean and South China Sea, the third one in the northern Pacific Ocean. As it will be explained, this pat?tern may be considered as representative of El Ni?o mode. The first complex loading phase pattern shows a stationary wave in the Pacific (also revealed by real p.c. analysis) superimposed to an oscil?lating disturbance, propagating from the Pacific to Indian or the opposite way. A subsequent cor?relation analysis among different spatial points allows revealing disturbances actually propagating westward from the Pacific to the Indian Ocean, which could therefore represent reflected Rossby waves, i.e. the west phase of the signals that propagate disturbances of thermal structure in the tropical Pacific Ocean. In the time domain, a relation between the trend of the first complex prin?cipal component and the ENSO cycle is also established.
A Study of SST Warming Trend in the Western Equatorial Pacific in a Coupled Ocean-Atmosphere-Land GCM
Liu Hui, Zhang Xuehong
1999, 16(1): 24-30. doi: 10.1007/s00376-999-0002-7
In a version of LASG coupled ocean-atmosphere-land system model, where a diurnal cycle of solar radiation is included, a rapid SST warming trend of about 2.0oC appears in the western equatorial Pacific within the first two years of an integration. An analysis reveals that the appearance of the surface westerly wind anomaly since the fifth month of the integration is responsible for the SST warming. To reduce the SST warming, the reference heat flux used in the model is then redefined according to the first 4 months, instead of the first 3 years, of a trial run. It is found that the refining of the reference heat flux is successful in avoiding the unrealistic persistent westerly wind anomaly. Consequently, the SST warming is almost com-pletely removed. It is explored that the persistent westerly wind anomaly is induced by the anomalous sur-face pressure patterns in the northern tropical and subtropical regions, which is related to the errors in the surface heat flux in the off-equatorial regions.
The Role of Diabatic Heating, Torques and Stabilities in Forcing the Radial-Vertical Circulation within Cyclones Part III: Case Study of Lee-side Cyclones
Donald R. Johnson, Zhuojian Yuan
1999, 16(1): 31-63. doi: 10.1007/s00376-999-0003-6
Two phases of extratropical cyclone development identified in previous mass and angular momentum budget studies have been confirmed through the numerical simulations of the azimuthally-averaged mass-weighted radial motion within two leeside cyclones: a Mediterranean and an Alberta cyclone. In the Mediterranean cyclone, a moist baroclinic phase is identified with inward (outward) mass and storm angular momentum transport in the lower (higher) value isentropic layers. The mass and storm angular momentum are then transported diabatically from lower to higher value isentropic layers through latent heat release. In addition, storm angular mo-mentum is transferred horizontally across the inclined isentropic surfaces by pressure stresses due to the paired negative and positive pressure torque in lower and higher value isentropic layers respectively. A dry-leeside baroclinic phase is identified in the early stage of the Alberta cyclone with inward (outward) transport of mass and angular momentum in the higher (lower) value isentropic layers. The redistribution of angular momentum is associated with the virtual transfer by torques. A transition from dry to moist phase is identified in the life cycle of the Alberta cyclone. The present numerical results show that the dominant internal physical processes responsible for forcing the inflow and outflow within the Mediterranean cyclone are associated with pressure torque and horizontal eddy angular momentum transport, while within the Alberta cyclone the dominant internal processes are associated with inertial torque and pressure torque. The transfer of angular momentum from the higher value isentropic layer to the lower value isentropic layer is due to the virtual transfer by inertial torque in the dry phase of the Alberta cyclone. The transition from dry to moist phase within the Alberta cyclone results from the decrease of positive inertial torque and the intensification of negative pressure torque in the lower value isentropic layers.
Numerical Simulations on the Explosive Cyclogenesis over the Kuroshio Current
Xu Yinlong, Zhou Mingyu
1999, 16(1): 64-76. doi: 10.1007/s00376-999-0004-5
In this paper, the Pennsylvania State University-NCAR Mesoscale Model (MM4) is used to investigate the explosive oceanic cyclone of 14-15 March 1988 over the warm Kuroshio Current. A series of numerical simulations on this cyclogenesis indicates that the favorable weather condi-tions and strong baroclinity in the low- and middle-level are essential to its explosive development. The explosive cyclogenesis occurred over a wide range of sea surface temperatures (SST’s), which was then characterized by strong baroclinity, the low-level jet (LLJ) was initially formed under the favorable atmospheric circulation and then this LLJ advected the moisture and heat northward for the explosive development of the cyclone, the LLJ played an important role in the process of cyclogenesis. Sensitivity experiments show that the latent heating was a key factor to explosive cyclogenesis, the latent heating deepened the short-wave trough, which resulted in the rapid intensification of the cyclone; while in the explosive intensification stage and continuous de-velopment stage, there was less contribution of local surface processes for the explosion of the cy?clone.
Interannual Variability of the Convective Activities Associated with the East Asian Summer Monsoon Obtained from TBB Variability
Ren Baohua, Huang Ronghui
1999, 16(1): 77-90. doi: 10.1007/s00376-999-0005-4
In this paper, the interannual variability of the convective activities associated with the East Asian summer monsoon and its association with the thermal distribution of SST anomalies in the tropical Pacific are analyzed by using the daily TBB (Temperature of Black Body at Cloud Top) dataset from 1980 to 1991. The results of composite and individual analyses of TBB anomalies show that the interannual variability of the convective activities associated with the summer monsoon in East Asia is large and has a close relation to the thermal distribution of SST anomalies in the tropical Pacific, espec?ially in the western Pacific warm pool. In the summer with ENSO-like distribution of SST anoma?lies in the tropical Pacific, the convective activities are weak around the Philippines, then the convective activities are intensified and the summer monsoon rainfall is strong in the area from the Yangtze River basin and the Huaihe River basin in China to Republic of Korea and Japan. On the contrary, in the summer with anti-ENSO-like distribution of SST anomalies in the tropical Pacific, the convective activities are strong around the Philippines, then the convective activities are weakened and the summer monsoon rainfall is weak in the area from the Yangtze River basin and the Huaihe River basin to Republic of Korea and Japan. It may be also found either from the composite analysis or from the individual analysis of TBB anomalies that the convective activities associated with the summer monsoon in East Asia have a good negative relation to that around the Philippines and a positive relation to that over the equatorial central Pacific.
The Ocean-Atmosphere Coupled Regimes and East Asian Winter Monsoon (EAWM) Activity
Bueh Cholaw, Ji Liren
1999, 16(1): 91-106. doi: 10.1007/s00376-999-0006-3
In this paper, ocean-atmosphere coupled regimes are identified on the basis of SVD analysis, cluster analysis and composite analysis. The coupled regimes in cold seasons are identified as the clusters of the ocean-atmosphere coupled states in a low dimensional phase space spanned by the first four SVD modes. Three coupled regimes are found. The first two coupled regimes reflect the ENSO episodes and the accom-panying PNA patterns. The third regime, i.e., EAWM regime, is characterized by the strong EAWM activi-ty and the specific SST anomaly. The composite analysis gives further evidences to the identification of EAWM regime and also demonstrates the dynamical process of its formation. The anomaly pattern of the tropical Pacific SSTA in the strong EAWM year differs significantly from that of the La Nina year.
Nonlinear Stability of Zonally Symmetric Quasi-geostrophic Flow
Liu Yongming
1999, 16(1): 107-118. doi: 10.1007/s00376-999-0007-2
By using the conservation laws and the method of variational principle, an improved Arnol’d’s second nonlinear stability theorem for the two-dimensional multilayer quasi-geostrophic model in periodic chan-nel is obtained.
IAP General Circulation Models: A First Step Towards Developing a Local Area Model for Weather Prediction in Nigeria
Chineke Theo Chidiezie, Li Weiping
1999, 16(1): 119-132. doi: 10.1007/s00376-999-0008-1
In an earlier study, the Atmospheric Models Intercomparison Program (AMIP) simulations of African climate using the nine-layer gridpoint atmospheric general circulation model were found to be closely relat-ed to the observed European Centre for Medium Range Weather Forecast (ECMWF) temperature data at 500 and 850 hPa. This paper presents the analysis of the simulation of African climate using the Global Ocean-Atmosphere-Land System Model (IAP/ LASG GOALS) and the nine-layer spectral general circu-lation model rhomboidally truncated at zonal wave number 15 (L9RI5) developed at the Institute of At-mospheric Physics (IAP), Chinese Academy of Sciences, Beijing. Both model simulations were not significantly different from the National Center for Environmental Prediction (NCEP) Reanalysis monthly mean data for 1989-1995 in the case of surface air temperature, sea level pressure and precipitation, with the GOALS reproducing the seasonal mean climate over Africa better. The implications of the encouraging re-sults in developing a local area model for Nigeria have been discussed. The great role of topography in the developing of general circulation models for numerical modelling of weather and climate has been stressed.
Medium Range Prediction of Summer Monsoon Activities over India vis-a-vis Their Correspondence with the Observational Features
Swati Basu, K. J. Ramesh, Z. N. Begum
1999, 16(1): 133-146. doi: 10.1007/s00376-999-0009-0
A detailed examination on various aspects of the southwest monsoon over the Indian subcon-tinent using analyses and forecasts of the NCMRWF global data assimilation and forecast system for the years 1994 and 1996 is carried out in this study. Objective procedures developed by Ramesh et al. (1996) based on the monsoon 1995 data are employed in the present work. It is found that all the deterministic features of the summer monsoon viz., the onset, its advancement, stagnation / re-vival and the withdrawal, can reasonably by prognosticated after employing the objective methodologies and monitoring daily variations of certain derived quantities from the large scale analyses and forecasts. Further, a good correspondence of the observed large scale / synoptic scale circulation features and the observed rainfall etc. with the deterministic characteristics of the sum-mer monsoon show a good prospect for real time prognosis of the important summer monsoon ac-tivities over the Indian subcontinent.
Reconstruction of the Rainfall in Rainy Season Based on Historical Drought/ Flood Grades
Xiong Anyuan, Wu Yijin, Cai Shuming
1999, 16(1): 147-153. doi: 10.1007/s00376-999-0010-7
On the basis of historical yearly drought and flood grades from A. D. 1470 to A. D. 1949, the ten-year mean precipitation in the rainy season in Wuhan district was reconstructed by means of statistical method. The reconstructing method was testified to be simple and effective.
Distribution of Surface Ozone Concentration in the Clean Areas of China and Its Possible Impact on Crop Yields
Li Xingsheng, He Zhuanshi, Fang Xiumei, Zhou Xiuji
1999, 16(1): 154-158. doi: 10.1007/s00376-999-0011-6
From August 1994 to July 1995, ozone and its precursors were measured in the clean areas of China. The results show that in the period of crop growth, hourly mean ozone concentration, ozone concentration averaged in seven hours of daytime and accumulated ozone concentration in long period have approached or overpassed the harmful level in environmental and health standard of U. S. A. and Canada.