IMPACTS OF SURFACE SENSIBLE HEAT FLUXES IN THE KEY AREAS OF THE TIBETAN PLATEAU ON INTERANNUAL VARIATION OF THE SCS SUMMER MONSOON INTENSITY

The impacts of the variations of surface heat fluxes over the Tibetan Plateau (TP) and surrounding areas on the interannual variation of the South China Sea (SCS) summer monsoon intensity is analyzed using the NCEP/NCAR reanalysis monthly sensible heat flux data from 1949 to 2000 and monthly mean wind and temperature field data from 1958 to 1997.The results show that there is a distinct interdecadal trend in sensible heat over the key areas of the TP and the SCS summer monsoon intensity as well as South Asia high intensity (SAHI),the transition occurs in late 1970s.The SCS summer monsoon intensity has a significant positive correlation with the variation of surface sensible heat fluxes over the northwestern part of the TP,while it has negative correlation with the surface sensible heat fluxes in the south of the TP.During the strong SCS summer monsoon year,the vertical ascending motion in the northwestern TP is strengthened,but in the southern TP it is weakened,and the position of the South Asian high is northward,while in the weak summer monsoon year,it is in the contrary.The SAHI is closely related to variation of surface heat fluxes over the TP and surrounding areas,and there exists a negative relationship between the SCS summer monsoon intensity and SAHI.

Estimation of eddy viscosity on the South China Sea shelf with adjoint assimilation method

The eddy viscosity of the ocean is an important parameter indicating the small-scale mixing process in the oceanic interior water column. Ekman wind-driven current model and adjoint assimilation technique are used to calculate the vertical profiles of eddy viscosity by fitting model results to the observation data. The data used in the paper include observed wind data and ADCP data obtained at Wenchang Oil Rig on the SCS （the South China Sea） shelf in August 2002. Different simulations under different wind conditions are analyzed to explore how the eddy viscosity develops with varying wind field. The results show that the eddy viscosity endured gradual variations in the range of 10^-3 -10^-2 m^2 /s during the periods of wind changes. The mean eddy viscosity undergoing strong wind could rise by about 25% as compared to the value under weak wind.

Numerical simulation of the upper ocean currents in South China Sea

The upper ocean currents in the Pacific Ocean are calculated by using an ocean model with higher horizontal resolution. The large current systems in the Pacific Ocean, such as Kuroshio, Oyashio, NEC, SEC, NECC,Califomia Current and East Australia Current, are well simulated. This paper only gives the numerical simulation results of the upper ocean currents of the representative months in four seasons in the South China Sea (SCS). It showsthat the SCS branch of Kuroshio is the most important current in the northem SCS and it is not only the water resourceof the SCS warm current but also a significant part of the overall SCS circulation. There is a relatively strong northeastward flow entering the SCS through the Taiwan Strait throughout the year except for specific months. Some of thenumerical results have been confirmed by the observational evidences.

Two universal runoff yield models： SCS vs. LCM

Runoff calculation is one of the key components in the hydrological modeling. For a certain spatial scale, runoff is a very complex nonlinear process. Currently, the runoff yield model in different hydrological models is not unique. The Chinese LCM model and the American SCS model describe runoff at the macroscopic scale, taking into account the rela- tionship between total actual retention and total rainfall and having a certain similarity. In this study, by comparing the two runoff yield models using theoretical analyses and numerical simulations, we have found that： （1） the SCS model is a simple linear representation of the LCM model, and the LCM model reflects more significantly the nonlinearity of catchment runoff. （2） There are strict mathematical relationships between parameters （R, r） of the LCM model and between parameters （S） of the SCS model, respectively. Parameters （R, r） of the LCM can be determined using the research results of the SCS model parameters. （3） LCM model parameters （R, r） can be easily obtained by field experiments, while SCS parameters （S） are difficult to measure. Therefore, parameters （R, r） of the LCM model also can provide the foundation for the SCS model. （4） The SCS model has a linear relationship between the reciprocal of total actual retention and the reciprocal of total rainfall during runoff period. The one-order terms of a Taylor series expansion of the LCM model describe the same relation- ship, which is worth further study.

Denudation History of South China Block and Sediment Supply to Northern Margin of the South China Sea

On the basis of apatite fission track （AFT） analyses, this article aims to provide a quantitative overview of Cenozoic morphotectonic evolution and sediment supply to the northern margin of the South China Sea （SCS）. Seventeen granite samples were collected from the coast to the inland of the South China block. Plots of AFT age against sample location with respect to the coastline show a general trend of youngling age away from the coast, which implies more prolonged erosion and sediment contribution at the inland of the South China Sea during post break-up evolution. Two-stage fast erosion process, Early Tertiary and Middle Miocene, is deduced from simulated cooling histories. The first fast cooling and denudation during Early Tertiary are recorded by the samples along the coast （between 70 and 60 Ma） and the inland （between 50 and 30 Ma）, respectively. This suggests initial local erosion and deposition in the northern margin of the SCS during Early Tertiary. Fast erosion along the coast ceased since ca. 50 Ma, while it had lasted until ca. 30 Ma inland, indicating that the erosion was transferred from the local coastal zone initially toward the continental interior with unified subsidence of the northern margin, which resulted in the formation of a south-dipping topography of the continental margin. The thermal stasis in the South China block since ca. 30 Ma must define the time at which the northern margin became dynamically disconnected from the active rifting and stretching that was taking place to the south. The lower erosion rate is inconsistent with higher sedimentary rate in the Pearl River Mouth basin during Late Oligocene （ca. 25 Ma）. This indicates that the increased sedimentation in the basin is not due to the erosion of the granite belt of the South China block, but perhaps points to the westward propagation of the paleo-Pearl River drainage related to the uplift of the eastern margin of Tibet plateau and southward jumping of spreading axis of the South China Sea. The second erosion acceleration rate of the Middle Miocene （ca. 14 Ma） cooling could have been linked to the long-distance effect of uplift of the Tibet plateau or due to the enhanced East Asian monsoon.

INFLUENCES OF ANOMALOUS SUMMER MONSOON OVER THE SOUTH CHINA SEA ON CLIMATE VARIATION

Using NCEP circulation data and precipitation data in China,the influences of strong/weak summer monsoon over the South China Sea (SCS) on atmospheric circulation and climate anomalies are studied.Corresponding to the strong (weak) SCS summer monsoon,there are not only different summer precipitation patterns in eastern China,but also different atmospheric circulation patterns in the Northern Hemisphere.The anomaly of the SCS summer monsoon will excite the EPA teleconnection (wave-train) in the Northern Hemispheric atmosphere and lead to climate anomalies not only in East Asia but also in North America.It is still shown that there is interaction between the SSTA in the South China Sea and the SCS summer monsoon;but the influence of the SCS summer monsoon on SSTA in the South China Sea may be more fundamental.

The Earliest Onset Areas and Mechanism of the Tropical Asian Summer Monsoon

The multi-yearly averaged pentad meteorological fields at 850 hPa of theNCEP/NCAR reanalysis dada and the TBB fields of the Japan Meteorological Agency during 1980-1994 areanalyzed. It is found that if the pentad is taken as the time unit of the monsoon onset, then thetropical Asian summer monsoon (TASM) onsets earliest, simultaneously and abruptly over the wholearea in the Bay of Bengal (BOB), the Indo-China Peninsula (ICP), and the South China Sea (SCS), eastof 90°E, in the 27th to 28th pentads of a year (Pentads 3 to 4 in May), while it onsets later inthe India Peninsula (IP) and the Arabian Sea (AS), west of 90°E. The TASM bursts first at the southend of the IP in the 30th to 31st pentads near 10°N, and advances gradually northward to the wholearea, by the end of June. Analysis of the possible mechanism depicts that the rapid changes of thesurface sensible heat flux, air temperature, and pressure in spring and early summer in the middleto high latitudes of the East Asian continent between 100°E and 120°E are crucially responsiblefor the earliest onset of the TASM in the BOB to the SCS areas. It is their rapid changes thatinduce a continental depression to form and break through the high system of pressure originallylocated in the above continental areas. The low depression in turn introduces the southwesterly tocome into the BOB to the SCS areas, east of 90° E, and thus makes the SCS summer monsoon (SCSSM)burst out earliest in Asia. In the IP to the AS areas, west of 90° E, the surface sensible heatflux almost does not experience obvious change during April and May, which makes the tropical Indiansummer monsoon (TISM) onset later than the SCSSM by about a month. Therefore, it is concluded thatthe meridian of 90° E is the demarcation line between the South Asian summer monsoon (SASM, i.e.,the TISM) and the East Asian summer monsoon (EASM, including the SCSSM). Besides, the temporalrelations between the TASM onset and the seasonal variation of the South Asian high (SAH) arediscussed, too, and it is found that there are good relations between the monsoon onset time and theSAH center positions. When the SAH center advances to north of 20°N, the SCSSM onsets, and tonorth of 25° N, the TISM onsets at its south end. Comparison between the onset time such determinedand that with other methodologies shows fair consistency in the SCS area and some differences inthe IP area.