Cui Mao-chang

Seasonality and causes of the Yellow Sea Warm Current

To study the seasonality and causes of the Yellow Sea Warm Current (YSWC) in detail, rotated empirical orthogonal function (REOF) and extended associate pattern analysis are adopted with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in the present paper. Results show that in the Yellow and East China Seas, the YSWC is a mean barotropic flow as compensation of winter-monsoon-driven surface currents, which has been directly observed. When East Asia winter monsoon weakens, so do the meridional pressure gradient of the surface seawater and the YSWC, while the transversal pressure gradient changes rather slowly that results in the YSWC left turning. In addition, there is southward mean flow compensation of summer-monsoon-driven surface currents, which actually was also directly observed.

Evaluation of daily precipitation in China from ECMWF and NCEP reanalyses

Correlation analysis, hidden period analysis and complex Morlet wavelet transform were used with daily rainfall in China from observation, ECMWF (European Centre for Medium-Range Weather Forecast) and NCEP (National Center for Environmental Prediction) reanalyses to evaluate the validation of precipitation estimates. The results showed that Fishers test and wavelet analysis, specially the latter, are useful tools for statistical analysis of daily precipitation datasets. Daily rainfall data obtained from ECMWF reanalysis are obviously better than those from NCEP reanalysis in terms of long period daily mean, local correlation, variation amplitude, fluctuation pattern and frequency. Although there is still room for improvement, ECMWF reanalysis is the best available dataset with global coverage and daily variability. In both of the reanalyzed daily mean precipitation fields, the higher estimations of Sichuan Basin rainfall are most likely caused by the topography of the basin, where small scale mountains in the southeast could not be represented by the reanalysis grid points, the typhoon and summer monsoon rainbelt could reach this region.

Seasonal and intraseasonal variations of the surface Taiwan Warm Current

To study seasonal and intraseasonal variations of the Taiwan Warm Current (TWC) in detail, Rotated Empirical Orthogonal Function (REOF) and Extended Associate Pattern Analysis (EAPA) are jointly adopted with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in the present paper. Results show that the first and second REOFs of SST in the southern East China Sea (SECS) account for 50.8% and 39.8% of the total variance. The surface TWC contains persistent (multi-year mean), seasonal and intraseasonal components. The persistent one mainly inosculates with the Kuroshio but the seasonal and intraseasonal ones are usually active only on the continental shelf. Its persistent component is produced by inertial flow of the Kuroshio, however its seasonal and intraseasonal ones seems coming from seasonal and intraseasonal oscillations of monsoon force. The seasonal one reaches its maximum in late summer, lasting about four months and the intraseasonal one takes place at any seasons, lasting more than 40 days.

Coast sea level and Asian monsoon system a downscaling exercise for Chinese coast

In this study, the authors examined the relationship between monthly sea level data and concurrent large-scale monthly mean sea level pressure and SST data for 1960 to 1990, which are reasonably well simulated by present day climate models; sea level variations due to variations of regional atmospheric forcing and oceanic circulation, are not adequately simulated by a global climate model because of insufficient spatial resolution. The authours applied a statistical “down scaling” strategy to sea level along the Chinese coast. Two interrelated processes were identified: one process is the local wind or wave set-up of water due to Asian monsoon wind anomalies; the other is the rainfall diluting effect in spring. At interdecadal time scale, the later becomes more important and most likely plays a major role in the planetary scale atmosphere-ocean interaction taking place in the eastern North Pacific.

SIMPLE ECOSYSTEM MODEL OF THE CENTRAL PART OF THE EAST CHINA SEA IN SPRING

This papers simple ecological model to simulate the ecosystem variation and the vertical carbon flux in the central part of the East China Sea in spring, inter—related the phytoplankton, zooplankton, autotrophic and heterotrophic bacterioplankton, nitrate, and dissolved organic carbon (DOC) in a run lasting 90 days. Except for DOC, because of poor observation precision, the major seasonal features of the vertical distribution for these components can be simulated by this model. The results show that spring bloom is just a short period of 1–2 weeks and that deposit carbon flux at the bottom interface is about 200 mg/m2· d in the first 20 days and then reaches its maximum of 1500 mg/m2· d about 2 months later after the spring bloom.

Statistical analysis of surface hydrography and circulation variations in northern South China Sea

To study the variations in surface hydrography and circulation in northern South China Sea (NSCS), rotated empirical orthogonal function (REOF) and extended associate pattern analysis (EAPA) are used with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1 126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in this paper. Results show that in summer, the SCS Diluted Water Expansion (SDWE) is the most dominant factor controlling SSS variations in the NSCS. The remarkable SDWE usually begins in early July, reaches its maximum in middle August and weakens in late September. In summer fluorishing period, its low saline core is just limited between 21°N and 22°N because of strong surface anomalous anticyclonic circulation in the NSCS. In early or late stage, the anomalous anticyclonic circulation becomes weak or turns into cyclonic one, thus the weak SCS diluted water can disperse. And its influence on the SSS variations has obviously decreased. The Kuroshio intrusion is the second controlling factor, and it has the almost opposite seasonal or intraseasonal oscillations and spatial characteristics to the SDWE. Winter Kuroshio Intrusion (WKI) begins in early November and lasts about three months. Intraseasonal Kuroshio Intrusion (IKI) takes place at any seasons. The westward Ekman transport produced by the north anomaly of East Asia Monsoon (EAM) pushes warmer and more saline seawater into the NSCS through the Bashi Strait and seems to decide the intensity of seasonal and intraseasonal Kuroshio intrusions.

INTERDECADAL SEA LEVEL VARIATION AT THE JAPANESE COAST AND LARGE SCALE CLIMATE STATE

Thirty years of monthly mean anomalies of sea level (SL) at 15 Japanese coastal stations, sea surface temperature (SST) and sea level pressure (SLP) in or over the northern Pacific were analyzed by canonical correlation analysis (CCA) to study the relationship between the interdecadal SL variation and large scale climate state. Given two time-varying fields this technique identifies the pair of spacial patterns with optimally correlated time series.The results show that there are two important air-sea interactive processes in the extratropical Pacific region for the variation of the SL at the Japanese coast on interdecadal scale. One is the ocean heating or cooling of the atmosphere over the Kuroshio extension region, which results in a huge SLP anomalous vortex with planetary spacial scale big enough to change the global climate. Another is the large Kuroshio meander phenomenon controlled by the large-scale wind-stress curls one year earlier in the adjacent region of the Hawaiian Islands. The first process implies the heat stored in the ocean has a role in changing the climate. This hypothesis needs proof by air-sea coupled climate modelling in the near future.

Variability of daily precipitation in China (1980–1993): PCA and wavelet analysis of observation and ECMWF reanalysis data

In this study, principal component analysis (PCA) and complex Morlet wavelet transform were used with daily rainfall in China for the period 1980–1993 (1 May–31 Dec.) from observation and ECMWF reanalysis to study its variability and eaaluate the validation of reanalyzed precipitation. The results showed that northward movement of the summer rain belt was a wavelike propagation, which was always accompanied by rainfall breaks and could be treated as one event under time scale of about 1 month only. The first 4 EOFs accounted for 28% and 35% of total variance from observation and reanalysis, respectively, and were roughly consistent with each other. The first and third EOFs for observation mainly represented interweekly, interseasonal and interannual variations and contained some summer intraseasonal fluctuations also. The second and fourth ones mainly represented some rather strong summer intraseasonal fluctuations for a paticular year and contained interweekly, interseasonal and interannual variations also. Although there is still room for improvement, the ECMWF reanalysis is the best available dataset with global coverage and daily variability.

Combination of ECMWF reanalyzed daily rainfall and pentad CMAP in China

In this study, 16 combinations of the ECMWF (European Centre for Medium-Range Weather Forecast) reanalyzed daily rainfall and the pentad CMAP in China for the period 1980–1993 (1 May–31 Dec.) were calculated. Correlation analysis was used to roughly evaluate daily rainfall for the whole of China and a combination of RPC (rotated principal component) and wavelet analyses was applied to data on observed and combined daily rainfall to obtain a detailed evaluation of the quality of these combined datasets in 6 selected major rainfall regions of eastern China. The results showed that except for intraweekly fluctuation, the best combination was roughly similar to or accorded well with observation in the aspects of space variation patterns and long period rainfall fluctuations related to monsoon onset and serious meteorologic disasters, indicating that this combination yielded better values of long term daily mean and standard deviation through the pentad CMAP (CPC Merged Analysis of Precipitation), and can also represent rainfall fluctuations through the reanalyzed daily rainfall.

Exercise in downscaling on sea surface temperature along Chinese coast

The present study examines the relationship between observed variations of regional hydrographic elements and concurrent large-scale climatological parameters. The former were chosen as the monthly sea surface temperature along the Chinese coast; the latter were chosen as monthly mean sea level pressure and sea surface temperature for the period from 1960 to 1990, which are reasonably well simulated by present day climate models. The variations of the former, due to variations of the regional atmospheric forcing and of oceanic circulation, are not adequately simulated by a global climate model because of insufficient spatial resolution. A statistical “downscaling” strategy is applied to the former.To better understand their variation mechanism and study the relationship among the environmental parameters in a group, canonical correlation analysis with combined datasets was carried out. The results show that variations of hydrographic elements are heavily forced by the East Asian monsoon through monsoon wind and rainfall.