2008 Vol. 27, No. 3

Display Method:
Ocean and climate sciences taking grand challenges and extraordinary opportunities: introduction to COAA 2007 special sections
ZHENG Quanan, QIAO Fangli, YANG Shi-Keng
2008, (3): 1-3.
In this universe, the earth is a unique breeding ground for living beings.It bares the evolutions, sustains the survival and enriches the development of human species.
A modification to the Munk wind-driven ocean circulation theory
ZHANG Qinghua, QU Yuanyuan, CHEN Shuiming
2008, (3): 4-10.
In order to fulfill the no-slip condition at the western and eastern boundaries of the ocean basin, introduced "effective wind stress", which has much larger spatial variations towards the boundaries than in the ocean interior.The effective wind stress can thus be decomposed into spatially slow-varying and fast varying components.Careful scale analysis on the classical Munk wind-driven ocean circulation theory, which consists of the interior Sverdrup flow and the western boundary current but of no eastern boundary current, shows that the wind stress curl appearing in the Sverdrup equation must have negligible spatial variations.In the present model the spatially slow-varying component of the wind stress appears in the Sverdrup equation, and the spatially fast-varying component becomes the forcing term of the boundary equations.As a result, in addition to the classical Munk solution the present model has an extra term at the western boundary which (Northern Hemisphere) increases the northward transport as well as the southward return transport, and has a term at the eastern boundary corresponding to the eastern boundary current.
Surface current field and seasonal variability in the Kuroshio and adjacent regions derived from satellite-tracked drifter data
HU Xiaomin, XIONG Xuejun, QIAO Fangli, GUO Binghuo, LIN Xiaopei
2008, (3): 11-29.
The multiyear averaged surface current field and seasonal variability in the Kuroshio and adjacent regions are studied.The data used are trajectories and (1/4)° latitude by (1/4)° longitude mean currents derived from 323 Argos drifters deployed by Chinese institutions and world ocean circulation experiment from 1979 to 2003.The results show that the Kuroshio surface path adapts well to the western boundary topography and exhibits six great turnings.The branching occurs frequently near anticyclonic turnings rather than near cyclonic ones.In the Luzon Strait, the surface water intrusion into the South China Sea occurs only in fall and winter.The Kuroshio surface path east of Taiwan, China appears nearly as straight lines in summer, fall, and winter, when anticyclonic eddies coexist on its right side;while the path may cyclonically turning in spring when no eddy exists.The Kuroshio intrusion northeast of Taiwan often occurs in fall and winter, but not in summer.The running direction, width and velocity of the middle segment of the Kuroshio surface currents in the East China Sea vary seasonally.The northward intrusion of the Kuroshio surface water southwest of Kyushu occurs in spring and fall, but not in summer.The northmost position of the Kuroshio surface path southwest of Kyushu occurs in fall, but never goes beyond 31°N.The northward surface current east of the Ryukyu Islands exists only along Okinawa-Amami Islands from spring to fall.In particular, it appears as an arm of an anticyclonic eddy in fall.
The role of surface waves in the ocean mixed layer
QIAO Fangli, YANG Yongzeng, XIA Changshui, YUAN Yeli
2008, (3): 30-37.
Previously, most ocean circulation models have overlooked the role of the surface waves.As a result, these models have produced insufficient vertical mixing, with an under-prediction of the mixing layer (ML) depth and an over-prediction of the sea surface temperature (SST), particularly during the summer season.As the ocean surface layer determines the lower boundary conditions of the atmosphere, this deficiency has severely limited the performance of the coupled ocean-atmospheric models and hence the climate studies.To overcome this shortcoming, a new parameterization for the wave effects in the ML model that will correct this systematic error of insufficient mixing.The new scheme has enabled the mixing layer to deepen, the surface excessive heating to be corrected, and an excellent agreement with observed global climatologic data.The study indicates that the surface waves are essential for ML formation, and that they are the primer drivers of the upper ocean dynamics;therefore, they are critical for climate studies.
On generation source sites of internal waves in the Luzon Strait
ZHENG Quanan, SONG Y Tony, LIN Hui, HU Xiaomin, MENG Junmin, WANG Dan
2008, (3): 38-50.
This effort aims to determine the generation source sites in the Luzon Strait for energetic, long-crest, transbasin internal waves (IW) observed in the northern South China Sea (NSCS).The roles of islands distributed on eastern side of the strait, Kuroshio, submarine ridges, shoaling thermocline, and strait configuration played in the IW generation are examined using the cruise data analysis, satellite data interpretation, and dynamical analysis.The islands and channels on eastern side of the strait are excluded from a list of possible IW source sites owing to their unmatched horizontal dimensions to the scale of IW crest line length, and the relative low Reynolds number.The Kuroshio has a potential to be a radiator for the long-crest IW disturbances, meanwhile, the Kuroshio west (east) wing absorbs the eastward (westward) propagating IW disturbance.Namely, the Kuroshio blockades the outside west-east propagating IW disturbances.The 3-D configuration of the Luzon Strait is characterized by a sudden, more than one order widening of the cross-section areas at the outlets on both sides, providing a favorable condition for IW type initial disturbance formation.In the Luzon Strait, the thermocline is featured by a westward shoaling all the year around, providing the dynamical conditions for the amplitude growth (declination) to the westward (eastward) propagating IW type disturbance.Thus, the west slope of western submarine ridge at the western outlet of the Luzon Strait is a high possibility source sites for energetic, long-crest, transbasin IWs in the NSCS.The interpretation results of satellite SAR images during a 13 a period from 1995 to 2007 provide the convincing evidence for the conclusions.
Internal solitary waves in the East China Sea
LI Xiaofeng, ZHAO Zhongxiang, HAN Zhen, XU Liuxiong
2008, (3): 51-59.
A European Space Agency's ENVISAT advanced synthetic aperture radar (ASAR) image covering Zhejiang coastal water in the East China Sea (ECS) was acquired on 1 August 2007.This image shows that there are about 20 coherent internal solitary wave (ISW) packets propagating southwestward toward Zhejiang coast.These ISW packets are separated by about 10 km, suggesting that these ISWs are tide-generated waves.Each ISW packet contains 5-15 wave crests.The wavelengths of the wave crests within the ISW packets are about 300 m.The lengths of the leading wave crests are about 50 km.The ISW amplitude is estimated from solving KdV equation in an ideal two-layer ocean model.It is found that the ISW amplitudes is about 8 m.Further analysis of the ASAR image and ocean stratification profiles show that the observed ISWs are depression waves.Analyzing the tidal current finds that these waves are locally generated.The wavelength and amplitude of the ECS ISW are much smaller than their counterparts in the South China Sea (SCS).The propagation speed of the ECS ISW is also an order of magnitude smaller than that of the SCS ISW.The observed ISWs in the ECS happened during a spring tide period.
Dynamical analysis of mesoscale eddy-induced ocean internal waves using linear theories
XU Qing, ZHENG Quanan, LIN Hui, LIU Yuguang, SONG Y Tony, YUAN Yeli
2008, (3): 60-69.
This study aims to explore generation mechanisms of the ocean internal wave using the dynamical analysis methods based on linear theories.Historical cruise measurements and recent synthetic aperture radar (SAR) observations of mesoscale eddies with diameter of several tens of kilometers to hundreds of kilometers show that the internal wave packets with wavelength of hundreds of meters to kilometer exist inside the mesoscale eddies.This coexistence phenomenon and inherent links between the two different scale processes are revealed in the solutions of governing equations and boundary conditions for the internal wave disturbance with a horizontally slowly variable amplitude in a cylindrical coordinate system.The theoretical solutions indicate that the instability of eddy current field provides the dynamical mechanism to internal wave generation.The derived dispersion relation indicates that the internal wave propagation is modified by the eddy current field structure.The energy equation of the internal waves clearly shows the internal wave energy increment comes from the eddy.The theoretical models are used to explain the observation of the mesoscale eddy-induced internal waves off the Norwegian coast.The two-dimensional waveform solution of the anticyclonic eddy-induced internal wave packet appears as ring-shaped curves, which contains the typical features of eddy stream lines.The comparison of theoretical solutions to the structure of the internal wave packets on SAR image shows a good agreement on the major features.
Barrier and compensation layers in the East China Sea
CHEN Xianyao, QIAO Fangli, WANG Qin, WANG Xiuhong, YUAN Yeli
2008, (3): 70-78.
Climatology of the isothermal layer depth (ILD) and the mixed layer depth (MLD) has been produced from in-situ temperature-salinity observations in the East China Sea (ECS) since 1925.The methods applied on the global are used to compute the ILD and the MLD in the ECS with a temperature criterion ΔT=0.8℃ for the ILD, and a density criterion with a threshold Δσθ corresponding to fixed ΔT=0.8℃ for the MLD, respectively.With the derived climatology ILD and MLD, the monthly variations of the barrier layer (BL) and the compensation layer (CL) in the ECS are analyzed.The BL mainly exists in the shallow water region of the ECS during April-June with thickness larger than 15 m.From December to next March, the area along the shelf break from northeast of Taiwan Island to the northeast ECS is characterized by the CL.Two kinds of main temperature-salinity structures of the CL in this area are given.
Observations and modeling of the ice-ocean conditions in the coastal Chukchi and Beaufort Seas
JIN Meibing, WANG Jia, MIZOBATA Kohei, HU Haoguo, SHIMADA Koji
2008, (3): 79-87.
The Chukchi and Beaufort Seas include several important hydrological features:inflow of the Pacific water, Alaska coast current (ACC), the seasonal to perennial sea ice cover, and landfast ice along the Alaskan coast.The dynamics of this coupled ice-ocean system is important for both regional scale oceanography and large-scale global climate change research.A number of moorings were deployed in the area by JAMSTEC since 1992, and the data revealed highly variable characteristics of the hydrological environment.A regional high-resolution coupled ice-ocean model of the Chukchi and Beaufort Seas was established to simulate the ice-ocean environment and unique seasonal landfast ice in the coastal Beaufort Sea.The model results reproduced the Beaufort gyre and the ACC.The depth-averaged annual mean ocean currents along the Beaufort Sea coast and shelf break compared well with data from four moored ADCPs, but the simulated velocity had smaller standard deviations, which indicate small-scale eddies were frequent in the region.The model results captured the seasonal variations of sea ice area as compared with remote sensing data, and the simulated sea ice velocity showed an almost stationary area along the Beaufort Sea coast that was similar to the observed landfast ice extent.It is the combined effects of the weak oceanic current near the coast, a prevailing wind with an onshore component, the opposite direction of the ocean current, and the blocking by the coastline that make the Beaufort Sea coastal areas prone to the formation of landfast ice.
Subseasonal features of the Asian summer monsoon in the NCEP climate forecast system
2008, (3): 88-103.
The operational climate forecast system (CFS) of the US National Centers for Environmental Prediction provides climate predictions over the world, and CFS products are becoming an important source of information for regional climate predictions in many Asian countries where monsoon climate dominates.Recent studies have shown that, on monthly-to-seasonal time-scales, the CFS is highly skillful in simulating and predicting the variability of the Asian monsoon.The higher-frequency variability of the Asian summer monsoon in the CFS is analyzed, using output from a version with a spectral triangular truncation of 126 waves in horizontal and 64 sigma layers in vertical, focusing on synoptic, quasi-biweekly, and intraseasonal time-scales.The onset processes of different regional monsoon components were investigated within Asia.Although the CFS generally overestimates variability of monsoon on these time-scales, it successfully captures many major features of the variance patterns, especially for the synoptic time-scale.The CFS also captures the timing of summer monsoon onsets over India and the Indo-China Peninsula.However, it encounters difficulties in simulating the onset of the South China Sea monsoon.The success and failure of the CFS in simulating the onset of monsoon precipitation can also be seen from the associated features of simulated atmospheric circulation processes.Overall, the CFS is capable of simulating the synoptic-to-intraseasonal variability of the Asian summer monsoon with skills.As for seasonal-to-interannual time-scales shown previously, the model is expected to possess a potential for skillful predictions of the high-frequency variability of the Asian monsoon.
The effect of the wave-induced mixing on the upper ocean temperature in a climate model
HUANG Chuanjiang, QIAO Fangli, SONG Zhenya
2008, (3): 104-111.
The significant underestimation of sea surface temperature (SST) and the temperature in the upper ocean is one of common problems in present climate models.The influence of the wave-induced mixing on SST and the temperature in the upper ocean was examined based on a global climate model.The results from the model coupled with wave-induced mixing showed a significant improvement in the simulation of SST and the temperature in the upper ocean compared with those of the original model without wave effects.Although there has still a cold bias, the new simulation is much closer to the climatology, especially in the northern ocean and tropical ocean.This study indicates that some important physical processes in the accurate simulation of the ocean may be ignored in present climate models, and the wave-induced mixing is one of those factors.Thus, the wave-induced mixing (or the effect of surface waves) should be incorporated properly into climate models in order to simulate or forecast the ocean, then climate system, more accurately.
Simulation evaluation and future prediction of the IPCC-AR4 GCMs on the extreme temperatures in China
WANG Ji, JIANG Zhihong, SONG Jie, LOU Dejun
2008, (3): 112-123.
On the basis of the temperature observations during 1961-2000 in China, seven coupled general circulation models' (GCMs) extreme temperature products are evaluated supplied by the Intergovernmental Panel on Climate Change's 4th Assessment Report (IPCC-AR4).The extreme temperature indices in use are frost days (FD), growing season length (GSL), extreme temperature range (ETR), warm nights (TN90), and heat wave duration index (HWDI).Results indicate that all the seven models are capable of simulating spatial and temporal variations in temperature characteristics, and their ensemble acts more reliable than any single one.Among the seven models, GFDL-Cm2.0 and MIROC3.2 performances are much better.Besides, most of the models are able to present linear trends of the same positive/negative signs as the observations but for weaker intensities.The simulation effects are different on a nationwide basis, with 110°N as the division, east (west) of which the effects are better (worse) and the poorer over the Qinghai-Tibetan Plateau in China.The predictions for the 21st century on emissions scenarios show that except decreases in the FD and ETR, other indices display significant increasing trend, especially for the indices of HWDI and TN90, which represent the notable extreme climate.This indicates that the temperature-related climate is moving towards the extreme.In the late 21st century, the GSL and TN90 (HWDI) increase most notably in southwest China (the Qinghai-Tibetan Plateau), and the FD decrease most remarkably in the Qinghai-Tibetan Plateau, northwest and northeast of China.Apart from South China, the yearly change range of the extreme temperature is reduced in most of China.
“Trends” and variations of global oceanic evaporation data sets from remote sensing
2008, (3): 124-135.
The variability in global oceanic evaporation data sets was examined for the period 1988-2000.These data sets are satellite estimates based on bulk aerodynamic formulations and include the NASA/Goddard Space Flight Center Satellite-based Surface Turbulent Flux version 2 (GSSTF2), the Japanese-ocean flux using remote sensing observations (J-OFURO), and the Hamburg Ocean-Atmosphere Parameters and Fluxes from Satellite version 2 (HOAPS2).The National Center for Environmental Prediction (NCEP) reanalysis is also included for comparison.An increase in global average surface latent heat flux (SLHF) can be observed in all the data sets.Empirical mode decomposition (EMD) shows long-term increases that started around 1990 for all remote sensing data sets.The effect of Mt.Pinatubo eruption in 1991 is clearly evident in HOAPS2 but is independent of the long-term increase.Linear regression analyses show increases of 9.4%, 13.0%, 7.3%, and 3.9% for GSSTF2, J-OFURO, HOAPS2 and NCEP, for the periods of the data sets.Empirical orthogonal function (EOF) analyses show that the pattern of the first EOF of all data sets is consistent with a decadal variation associated with the enhancement of the tropical Hadley circulation, which is supported by other satellite observations.The second EOF of all four data sets is an ENSO mode, and the correlations between their time series and an SOI are 0.74, 0.71, 0.59, and 0.61 for GSSTF2, J-OFURO, HOAPS2, and NCEP in that order.When the Hadley modes are removed from the remote sensing data, the residue global increases are reduced to 2.2%, 7.3%, and <1% for GSSTF2, J-OFURO and HOAPS, respectively.If the ENSO mode is used as a calibration standard for the data sets, the Hadley mode is at least comparable to, if not larger than, the ENSO mode during our study period.
Air-sea carbon fluxes and their controlling factors in the Prydz Bay in the Antarctic
GAO Zhongyong, CHEN Liqi, GAO Yuan
2008, (3): 136-146.
The Prydz Bay in the Antarctic is an important area in the Southern Ocean due to its unique geographic feature.It plays an important role in the carbon cycle in the Southern Ocean.To investigate the distributions of carbon dioxide in the atmosphere and surface seawater and its air-sea exchange rates in this region, the Chinese National Antarctic Research Expedition (CHINARE) had set up several sections in the Prydz Bay.Here we present the results from the CHINARE-XVI cruises were presented onboard R/V Xuelong from November 1999 to April 2000 and the main driving forces were discussed controlling the distributions of partial pressure of carbon dioxide.According to the partial pressure of carbon dioxide distributions, the Prydz Bay can be divided into the inside and outside regions.The partial pressure of carbon dioxide was low in the inside region but higher in the outside region during the measurement period.This distribution had a good negative correlation with the concentrations of chlorophylla in general, suggesting that the partial pressure of carbon dioxide was substantially affected by biological production.The results also indicate that the biological production is most likely the main driving force in the marginal ice zone in the Southern Ocean in summer.However, in the Antarctic divergence sector of the Prydz Bay (about 64°S), the hydrological processes become the controlling factor as the sea surface partial pressure of carbon dioxide is much higher than the atmospheric one due to the upwelling of the high DIC CDW, and this made the outside of Prydz Bay a source of carbon dioxide.On the basis of the calculations, the CO2 flux in January (austral summer) was -3.23 mmol/(m2·d) in the inner part of Prydz Bay, i.e., a sink of atmospheric CO2, and was 0.62 mmol/(m2·d) in the outside part of the bay, a weak source of atmospheric CO2.The average air-sea flux of CO2 in the Prydz Bay was 2.50 mmol/(m2·d).
Wind impact on pollutant transport in a shallow estuary
XU Hongzhou, LIN Jing, SHEN Jian, WANG Dongxiao
2008, (3): 147-160.
A three-dimensional numerical model, EFDC (environmental fluid dynamics code) is applied to the Pamlico River Estuary (PRE) in eastern North Carolina of the United States to examine the wind impact on pollutant age distributions and residence time.A series of model experiments representing base case, remote-wind-induced water level set-up and local winds cases are conducted.Model results indicate that the pollutant mean age and the system residence time are functions of gravitational circulation in the PRE.The system responses to remote-wind-induced water level set-up are different in different portions of the PRE.Under such condition, dissolved substances in the upstream portion of the PRE have a younger age and shorter residence time (compared with the base case), by contrast, they have a older age and longer residence time in the downstream portion of the PRE.Upriver and downriver local winds appear to have opposite impacts on pollutant age distributions.The substances are retained much longer within the PRE under upriver wind than those under downriver wind.The model results also suggest that across-river winds may lead to longer residence time through enhanced turbulence mixing, which slows down the gravitational circulation in the PRE.
Research Notes
Year aridity index patterns in northwest China and the relationship to summer North Atlantic sea surface temperature
YAN Yan, ZHAO Xinyi, ZHOU Liping
2008, (3): 161-171.
Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index variations in northwest China and summer North Atlantic sea surface temperature (SST) variations are examined for the 44 a period of 1961-2004 using singular value decomposition (SVD) analysis.Results show that the SST anomalies (SSTA) in the North Atlantic in summer reflected three basic models.The first SVD mode of SST pattern shows a dipole-like variation with the positive center located at southwest and negative center at northeast of extratropical North Atlantic.And it strongly relates to the positive trend in AI variation in northwest China.The second coupled modes display the coherent positive anomalies in extratropical North Atlantic SST and the marked opposite trend of AI variability between north and south of Xinjiang.In addition, the lag correlation analysis of the first mode of SSTA and geopotential heights at 500 hPa variations also shows that the indication of the former influencing the latter configuration, which result in higher air temperature and less precipitation when the SSTA in the North Atlantic Ocean in summer motivated Eurasian circulation of EA pattern, further to influence the wet-dry variations in northwest China by the ocean-to-atmosphere forcing.