Advanced Search

1997 Vol. 14, No. 2

Display Method:
The Present Status and Future of Research of the East Asian Monsoon
Ma Henian, Ding Yihui
1997, 14(2): 125-140. doi: 10.1007/s00376-997-0015-z
The weather and climate in China are greatly affected by the East Asian monsoon. For long time the Chinese meteorologists have undertaken numerous works regarding research and prediction or the East Asian monsoon, and made great achievements that are well noted for the world and in China. In the future 5-10 years, the research on the East Asian monsoon will be strengthened and the thus obtained achievements will be gradually transferred into the operational capability, eventuallyleading to an improvement of weather and climate prediction in East Asia The present paper has firstly made an overview of the present status of research on the East Asian monsoon, il?lustrating the 4-stage developmental process of monsoon study in China and major achievements thus obtained. Then the major problems related to the study of the East Asian monsoon are scientifically indicated, and the monsoon-related ongoing and future scientific field experiments and study projects the Chinese scientists have initiated or participated are briefly described. It may be expected that a new breakthrough in the problem of the East Asian mon?soon in the future ten years will be made with these efforts and intensive research works. Finally, it is pointed out that, to accomplish this new breakthrough, a key problem is to carry out the extensive cooperation, in particular the scien?tific cooperation of the scientist across the Taiwan Strait as well as countries over the surrounding regions.
Climatology and Interannual Variability of the Southeast Asian Summer Monsoon
K.-M. Lau, Song Yang
1997, 14(2): 141-162. doi: 10.1007/s00376-997-0016-y
In this paper, results from a pilot study for the South China Sea Monsoon Experiment are reported. Based on analyses of 9 years of pentad and monthly mean data, the climatology of subseasonal features and interannual varia-bility of the Southeast Asian monsoon (SEAM) are documented. The present analysis is focused on the sudden onset of the South China Sea monsoon and its relation to the atmospheric and oceanic processes on the entire Asian mon-soon region. It is found that the onset of the SEAM occurs around mid-May, signaling the earliest stage of the entire Asian summer monsoon system. The establishment of monsoon rainfall over the South China Sea is abrupt, being accompanied by substantial changes in the large scale atmospheric circulation and sea surface temperature in the ad?jacent oceans. The onset and fluctuations of SEAM involve the interaction and metamorphosis of the large scale con?vection over the Indo-China, the South China Sea and the southern Bay of Bengal. Results show that the onset time of the SEAM differs greatly from one year to another. The delayed (advanced) onset of the monsoon may be related to basin-wide warm (cold) events of the Pacific and Indian Oceans. We also present evidence showing that the SEAM fluctuations in May may foreshadow the development of the full-scale Asian summer monsoon during the subse?quent months
Seasonal and Extraseasonal Predictions of Summer Monsoon Precipitation by Gcms
Zeng Qingcun, Yuan Chongguang, Li Xu, Zhang Ronghua, Yang Fanglin, Zhang Banglin, Lu Peisheng, Bi Xunqiang, Wang Huijun
1997, 14(2): 163-176. doi: 10.1007/s00376-997-0017-x
A semi-operational real time short-term climate prediction system has been developed in the Center of Climate and Environment Prediction Research (CCEPRE), Institute of Atmospheric Physics / Chinese Academy of Sciences. The system consists of the following components: the AGCM and OGCM and their coupling, initial conditions and initialization, practical schemes of anomaly prediction, ensemble prediction and its standard deviation, correction of GCM output, and verification of prediction. The experiences of semi-operational real-time prediction by using this system for six years 1989-1994) and of hindcasting for 1980-1989 are reported. It is shown that in most cases large positive and negative anomalies of summer precipitation resulting in disastrous climate events such as severe flood or drought over East Asia can be well predicted for two seasons in advance, although the quantitatively statistical skill scores are only satisfactory due to the difficulty in correctly predicting the signs of small anomalies. Some methods for removing the systematic errors and introducing corrections to the GCM output arc suggested. The sensitivity of pre-diction to the initial conditions and the problem of ensemble prediction are also discussed in the paper
Peculiar Temporal Structure of the South China Sea Summer Monsoon
Bin Wang, Renguang Wu
1997, 14(2): 177-194. doi: 10.1007/s00376-997-0018-9
Beijing located at the junction of four major components of the Asian-Australia monsoon system (the Indian, the western North Pacific, the East Asian subtropical, and the Indonesian-Australian monsoons), the monsoon cli-mate over the South China Sea (SCS) exhibits some unique features. Evidences are presented in this paper to reveal and document the following distinctive features in the temporal structure of the SCS summer monsoon:(1) pronounced monsoon singularities in the lower tropospheric monsoon flows which include the pre-onset and withdrawal easterly surges and the southwesterly monsoon bursts at Julian pentad 34-35 (June 15-24) and pentad 46-47 (August 14-23);(2) four prominent subseasonal cycles (alternative occurrences of climatological active and break monsoons);(3) considerably larger year-to-year variations in convective activity on intraseasonal time scale compared to those over the Bay of Bengal and the Philippine Sea;(4) the redness of the climatological mean spectrum of precipitation / deep convection on synoptic to intraseasona] time scales in the central SCS;(5) a remarkable asymmetry in the seasonal transitions between summer and winter monsoons and an extremely abrupt mid-May transition (the outburst of monsoon rain and the sudden switch in tie lower troposphere winds from an easterly to a westerly regime);(6) the bi-modal interannual variation of summer monsoon onset (normal and delayed modes).In addition, the monsoon rainfall displays enormous east-west gradient over the central SCS. Possible causes for these features are discussed. A number of specific science questions concerning some of the peculiar features are raised for the forthcoming SCS monsoon experiment to address
South China Sea Warm Pool in Boreal Spring
Peter C. Chu, C.-P. Chang
1997, 14(2): 195-206. doi: 10.1007/s00376-997-0019-8
During the boreal spring of 1966, a warm-core eddy is identified in the upper South China Sea (SCS) west of the Philippines through an analysis of the U.S. Navy’s Master Oceanographic Observation Data Set. This eddy occurred before the development of the northern summer monsoon and disappeared afterward. We propose that this eddy is a result of the radiative warming during spring and the downwelling due to the anticyclonic forcing at the surface. Our hypothesis suggests an air-sea feedback scenario that may explain the development and withdrawal of the summer monsoon over the SCS. The development phase of the warm-core eddy in this hypothesis is tested by using the Princeton Ocean model
Review of the Researches on Changma and Future Observational Study (KORMEX)
Jai-Ho Oh, Won-Tae Kwon, Sang-Boom Ryoo
1997, 14(2): 207-222. doi: 10.1007/s00376-997-0020-2
Changma is the most important supplier of water resource in Korea. However, its interannual variation may cause either floods or droughts time to time in many regions of Korea. A number of studies on Changma have been done in many subjects, such as the on-set and retreat timing, duration of Changma, and its interannual variation, which may cause either wet or dry Changma, and the heavy rainfall phenomena associated with the Changma front. Also, the subjects covered the dynamical situation of Changma compared to that of Baiu and Mei-yu as a part of East Asian monsoon circulation, and relation between Changma and tropical Pacific sea-surface temperature (SST) through atmosphere-ocean interaction, etc:A numerical study is presented in this paper to check the teleconnection between the behavior of Changma front and the variation of tropical Pacific SST. The difference in the lower level streamfunction between the El Ni?o event of 1987 and the La Ni?a event of 1988 illustrates that the cross-equatorial and westerly wind crossing over the India and Indo-China peninsula were weak during the summer of 1988 compared to 1987. This may cause the drought of 1988 in East Asia by reducing moisture supply from the Indian Ocean and the south-western Pacific Even though there are numerous research activities on the Changma, our knowledge on the Changma is still lim?ited to explain the mechanism of interannual variation of Changma and to provide a proper prediction of precipita?tion due to both geographical location of Korea and its complex topography. In collaboration with the international field observational projects, such as GAME and SCSMEX, the Korea Monsoon Experiment (KORMEX) has been planned by several scientists in Korea to improve our knowledge on the atmospheric circulation and water cycle relat?ed to the East Asian monsoon and to provide necessary information to predict both short- and long-term variation of rainfall during the Changing season
Regional and Synoptic-scale Features Associated with Inactive Periods of the Summer Monsoon over South China
C. H. So, Johnny C. L. Chan
1997, 14(2): 223-230. doi: 10.1007/s00376-997-0021-1
This paper presents an observational study of the physical processes responsible for the inactive period (break) of the summer monsoon over South China (SC). The break of the rnonsoon is defined by using the rainfall data over Hong Kong Meteorological parameters provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1985-1990 are examined. Daily values of each parameter for the six years are then compo-sited each day for the period of 5 days before to 1 day after the break It is found that several days before the break, changes opposite to those occurred during the onset and active pe?riods begin to take place. This suggests that a feedback mechanism is present which tends to restore the atmosphere to a more stable state. This mechanism may be initiated by the formation of convective clouds during the onset and ac?tive periods. These clouds then reduce the solar radiation to the ground, leading to a gradual drop in the temperature. This drop, together with the cooling of the atmosphere due to the large amounts of rainfall, causes the pressure over the SC region to become higher, which in turn induces a westward extension of the subtropical ridge. The decrease in temperature over SC may also shift the location of the heat source to the west, which leads to a concomitant westward shift of the convergence of the southerlies and results in less moisture-laden air reaching the SC region. The atmos?phere then becomes unfavourable for heavy convection and therefore a break starts
Seasonal Transition of Summer Rainy Season over Indochina and Adjacent Monsoon Region
Jun Matsumoto
1997, 14(2): 231-245. doi: 10.1007/s00376-997-0022-0
The mean onset and withdrawal of summer rainy season over the Indochina Peninsula were investigated using 5-day averaged rainfall data (1975-87). The mean seasonal transition process during onset and retreat phases in Indochina, India and the South China Sea is also examined using 5-day mean OLR (1975-87) and 850 hPa wind (1980-88) date. It was found that the onset of summer rainy season begins earlier in the inland region of Indochina (Thailand) in late April to early May than in the coastal region along the Bay of Bengal. This early onset of rainy sea-son is due to pre-monsoon rain under the mid-latitude westerly wind regime. The full summer monsoon circulation begins to establish in mid-May, causing active convective activity both over the west coast of Indochina and the cen-tral South China Sea. In case of withdrawal, the earliest retreat of summer rainy season is found in the central northern part of Indochina in late September. The wind field, on the other hand, already changes to easterlies in the northern South China Sea in early September. This easterly wind system covers the eastern part of Indochina where post-monsoon rain is still active. In late October, the wind field turns to winter time situation, but post monsoon rain still continues in the southern part of the Indochina Peninsula until late November
Evolution of Intraseasonal Oscillation over the Tropical Western Pacific / South China Sea and Its Effect to the Summer Precipitation in Southern China
Li Chongyin, Li Guilong
1997, 14(2): 246-254. doi: 10.1007/s00376-997-0023-z
In this paper, the evolution of intraseasonal oscillation over the South China Sea and tropical western Pacific area and its effect to the summer rainfall in the southern China are studied based on the ECMWF data and TBB data) analyses. A very low-frequency waves exist in the tropics and play an important role in dominating intraseasonal oscillation and lead to special seasonal variation of intraseasonal oscillation over the South China Sea / tropical western Pacific area. The intraseasonal oscillation (convection) over the South China Sea and tropical western Pacific area is closely related to the summer rainfall (convection) in the southern China. Their relationship seems to be a seesaw feature, and this relationship resulting from the different pattern of convection in those two re-gions is caused by the different type of local meridional circulation
The South China Sea Monsoon Experiment (SCSMEX) Implementation Plan
Ding Yihui, Chao Qingchen, Zhang Yan, Gan Zijun, Zhang Xiuzhi
1997, 14(2): 255-270. doi: 10.1007/s00376-997-0024-y
The Sooth China Sea monsoon is not only a main component of Asian monsoon system, but also plays an im-portant role in the weather and climate over the surrounding areas and the globe. However, because of the insufficient observation data, it is self evident that the large-scale field experiment over SCS is very important to deepen under-standing East Asian monsoon. In this paper, the composite experiment, modelling and data assimilation, especially the atmospheric observation, oceanic observation, air-sea interface observational network as well as satellite observa-tion are introduced in detail
Interannual and Interdecadal Variations in Heat Content of the Upper Ocean of the South China Sea
He Youhai, Guan Cuihua, Gan Zijun
1997, 14(2): 271-276. doi: 10.1007/s00376-997-0025-x
The vertically averaged temperature (TAV) from surface to 100 m depth of the South China Sea for the period 1959-1988 is analyzed. The results indicate that there is a significant long-term variability from interannual to interdecadal scales in the heat content in the upper ocean. The heat content of the upper ocean of the South China Sea increases evidently in the El Nino year. TAV anomaly in the ocean was negative from the end of 1950’s to early l970’s, and then changed to positive. The changes of TAV of the ocean are closely related to ENSO events, the Asian winter monsoon and the tropical atmospheric circulation anomalies.
Observational Study on the Onset of the South China Sea Southwest Monsoon
Yan Junyue
1997, 14(2): 277-287. doi: 10.1007/s00376-997-0026-9
Based on the long-term marine ship observation data, records of meteorological stations and High-Reflective Cloud (HRC) data by satellite remote sensing, this paper has studied the circulation patterns and variability in ele-ments during onset and the established periods of the South China Sea (SCS) southwest (SW) monsoon, The averaged date of the onset SW monsoon in the SCS occurs in the middle of May climatologically. The corresponding date for the northern part is little earlier (May 12) and those for the southern parts are little later (May 20), The interannual range of the onset dates is about one month. Following the onset of the SW monsoon, the cloud amount and the pre-cipitation increase while the convection activities enhance over the SCS. But there is a strong spatial heterogeneity within the domain. After onset of the SW monsoon the strong convective area moves northwards, while the SCS rain band moves to the center and north. Sea surface temperature (SST) increases rapidly before the onset and the leading time is about one month. The increment of SST supplies heat and vapor for the onset. From April to May the surface heat fluxes display obvious changes, e.g., latent heat exchange and evaporation enhancement. It is one of the reasons why the SW monsoon bursts firstly in the SCS.