THE REGIONAL AIR-SEA COUPLED OSCILLATION IN THE SOUTH CHINA SEA

This study examined the regional air sea coupled interaction in the South China Sea (SCS), based on the 1979-1995 NCEP/NCAR reanalysis data of sea surface temperature (SST) and meridional wind (V component). Singular value decomposition (SVD) and single field principal component analysis (PCA) were employed to analyse the SST and V anomalies and compare the results with each other. It was found that the leading mode of SVD explained a predominant amount of squared covariance between the SST and meridional wind V, and that the time series expansion coefficients of the first mode between SST and V from PCA and SVD resembled very much each other. This infers that the meridional wind, as an indicator of Asian monsoon, is closely related with the SST through the air sea interaction in the SCS. The spatial patterns of the first mode of SST and V exhibit ellipse shaped variance in the SCS center and a NE SW oriented main axis, which are much similar to those in winter season. These results show that the most active center for both V and SST is in the SCS, which suggests that a regional air sea coupled oscillation possibly exists there for the whole year and is noticeable especially during the winter season. So the SCS is a very important region for the forming of the Asian Monsoon and the climate of the west Pacific.

A Regional Air-Sea Coupled Model and Its Application over East Asia in the Summer of 2000

A regional air-sea coupled model, comprising the Regional Integrated Environment Model System （RIEMS） and the Princeton Ocean Model （POM） was developed to simulate summer climate features over East Asia in 2000. The sensitivity of the model＇s behavior to the coupling time interval （CTI）, the causes of the sea surface temperature （SST） biases, and the role of air-sea interaction in the simulation of precipitation over China are investigated. Results show that the coupled model can basically produce the spatial pattern of SST, precipitation, and surface air temperature （SAT） with five different CTIs respectively. Also, using a CTI of 3, 6 or 12 hours tended to produce more successful simulations than if using 1 and 24 hours. Further analysis indicates that both a higher and lower coupling frequency result in larger model biases in air-sea heat flux exchanges, which might be responsible for the sensitivity of the coupled model＇s behavior to the CTI. Sensitivity experiments indicate that SST biases between the coupled and uncoupled POM occurring over the China coastal waters were due to the mismatch of the surface heat fluxes produced by the RIEMS with those required by the POM. In the coupled run, the air-sea feedbacks reduced the biases in surface heat fluxes, compared with the uncoupled RIEMS, consequently resulted in changes in thermal contrast over land and sea and led to a precipitation increase over South China and a decrease over North China. These results agree well observations in the summer of 2000.

Seasonal and Intraseasonal Variations of East Asian Summer Monsoon Precipitation Simulated by a Regional Air-Sea Coupled Model

The performance of a regional air-sea coupled model, comprising the Regional Integrated Environment Model System （RIEMS） and the Princeton Ocean Model （POM）, in simulating the seasonal and intraseasonal variations of East Asian summer monsoon （EASM） rainfall was investigated. Through comparisons of the model results among the coupled model, the uncoupled RIEMS, and observations, the impact of air-sea coupling on simulating the EASM was also evaluated. Results showed that the regional air sea coupled climate model performed better in simulating the spatial pattern of the precipitation climatology and produced more realistic variations of the EASM rainfall in terms of its amplitude and principal EOF modes. The coupled model also showed greater skill than the uncoupled RIEMS in reproducing the principal features of climatological intraseasonal oscillation （CISO） of EASM rainfall, including its dominant period, intensity, and northward propagation. Further analysis indicated that the improvements in the simulation of the EASM rainfall climatology and its seasonal variation in the coupled model were due to better simulation of the western North Pacific Subtropical High, while the improvements of CISO simulation were owing to the realistic phase relationship between the intraseasonal convection and the underlying SST resulting from the air-sea coupling.

SIMULATION OF SUMMER CLIMATE IN CHINA DURING 1997 AND 1998 USING A REGIONAL AIR-SEA COUPLED MODEL

Using the regional air-sea coupled climate model RegCM3-POM,a series of numerical experiments are performed to simulate the summer climate in 1997 and 1998 with different coupling time steps.The results show that the coupled model has good performance on the simulation of the summer sea surface temperature(SST) in 1997 and 1998,and the simulation results of CPL1(with the coupling time step at 1 hour) are similar to those of CPL6(with the coupling time step at 6 hours).The coupled model can well simulate SST differences between 1997 and 1998.As for the simulation of the drought in 1997 and the flood in 1998,the results of CPL6 are more accurate.The coupled model can well simulate the drought in 1997 over North China,and compared with the results of the atmosphere model RegCM3,the simulation ability of the coupled model is improved.The coupling model has better ability in the simulation of the circulation in the middle and low levels,and the water vapor transportation in the coupling model is reasonable in both 1997 and 1998.RegCM3(an uncoupled model) cannot correctly simulate the transportation path differences between 1997 and 1998,but the coupled model can simulate the differences well.

Effects of air-sea coupling on the eastward propagating boreal winter intraseasonal oscillation over the tropical Indian Ocean

The effects of air-sea coupling over the tropical Indian Ocean（TIO） on the eastward propagating boreal winter intraseasonal oscillation（MJO） are investigated by comparing a fully coupled and a partially decoupled Indian Ocean experiment using the SINTEX-F coupled model.Air-sea coupling over the TIO significantly enhances the intensity of the eastward propagations of the MJO along the5°-10°S zonal areas.The zonal asymmetry of the SST anomaly（SSTA） is responsible for the enhanced eastward propagation.A positive SSTA appears to the east of the MJO convection,which results in the boundary layer moisture convergence and positively feeds back to the MJO convection.In addition,the air-sea interaction effect on the eastward propagation of the MJO is related to the interannual variations of the TIO.Air-sea coupling enhances（reduces） the eastward-propagating spectrum during the negative Indian Ocean dipole mode and positive Indian Ocean basin mode.Such phase dependence is attributed to the role of the background mean westerly in affecting the wind-evaporation-SST feedback.Air-sea coupling（decoupling） enhances（reduces） the zonal asymmetry of the low-level specific humidity,and thus the eastward propagation spectrum of the MJO.

Air–Sea Coupling Enhances the East Asian Winter Climate Response to the Atlantic Multidecadal Oscillation

A simple air-sea coupled model, the atmospheric general circulation model （AGCM） of the National Centers for Environmental Prediction coupled to a mixed-layer slab ocean model, is employed to investigate the impact of air-sea coupling on the signals of the Atlantic Multidecadal Oscillation （AMO）. A regional coupling strategy is applied, in which coupling is switched off in the extratropical North Atlantic Ocean but switched on in the open oceans elsewhere. The coupled model is forced with warm-phase AMO SST anomalies, and the modeled responses are compared with those from parallel uncoupled AGCM experiments with the same SST forcing. The results suggest that the regionally coupled responses not only resemble the AGCM simulation, but also have a stronger intensity. In comparison, the coupled responses bear greater similarity to the observational composite anomaly. Thus, air-sea coupling enhances the responses of the East Asian winter climate to the AMO. To determine the mechanism responsible for the coupling amplification, an additional set of AGCM experiments, forced with the AMO-induced tropical SST anomalies, is conducted. The SST anomalies are extracted from the simulated AMO-induced SST response in the regionally coupled model. The results suggest that the SST anomalies contribute to the coupling amplification. Thus, tropical air-sea coupling feedback tends to enhance the responses of the East Asian winter climate to the AMO.

Analysis of Decadal Climate Variability in the Tropical Pacific by Coupled GCM

This study presents the spatial and temporal structures of the decadal variability of the Pacific from an extended control run of a coupled global climate model (GCM).The GCM used was version-g2.0 of the Flexible Global Ocean Atmosphere Land System (FGOALS-g2.0) developed at LASG/IAP.The GCM FGOALS-g2.0 re-produces similar spatial-temporal structures of sea surface temperature (SST) as observed in the Pacific decadal os-cillation (PDO) with a significant period of approximately 14 years.Correspondingly,the PDO signals were closely related to the decadal change both in the upper-ocean temperature anomalies and in the atmospheric circulation.The present results suggest that warm SST anomalies along the equator relax the trade winds,causing the SSTs to warm even more in the eastern equatorial Pacific,which is a positive feedback.Meanwhile,warm SST anomalies along the equator force characteristic off-equa-torial wind stress curl anomalies,inducing much more poleward transport of heat,which is a negative feedback.The upper-ocean meridional heat transport,which is asso-ciated with the PDO phase transition,links the equatorial to the off-equatorial Pacific Ocean,acting as a major mechanism responsible for the tropical Pacific decadal variations.Therefore,the positive and negative feedbacks working together eventually result in the decadal oscilla-tion in the Pacific.

INTERANNUAL OSCILLATION OF MERIDIONAL SEA LEVEL WIND AND ITS IMPACT ON SEA SURFACE TEMPERATURE IN THE SOUTH CHINA SEA

Analysis of COADS data(1958- 1987) showed that there is obviously interannual SST oscillation including QBO (Quasi-biennial oscillation ) and quasi-3.5 year oscilation , etc ., of the SCS (South China Sea), which is the response of the the upper mixed layer of the sea to the impact of the East Asian Monsoon anomaly . Most SST anomalies appear in the central basin of the SCS.The phase-locked phenomena linking the SST annual cycle and interannual oscillation in an important characteristic of the SCS climate . There is not only SST response to atmospheric impact , but also feedback to the air . The authors put forward a scheme of regional air-sea interaction in winter time in the SCS.

Recent advances in regional air-sea coupled models

In this paper,we first briefly review the history of air-sea coupled models,and then introduce the current status and recent advances of regional air-sea coupled models.In particular,we discuss the core technical and scientific issues involved in the development of regional coupled models,including the coupling technique,lateral boundary conditions,the coupling with sea waves(ices),and data assimilation.Furthermore,we introduce the application of regional coupled models in numerical simulation and dynamical downscaling.Finally,we discuss the existing problems and future directions in the development of regional air-sea coupled models.

DEVELOPMENT OF A COUPLED REGIONAL AIR-SEA MODEL AND ITS NUMERICAL SIMULATION FOR SUMMER MONSOON IN 1998

A coupled regional air-sea model is developed by using the regional climate model (P-σ RCM) and the regional ocean model (POM),which is used to simulate East Asian monsoon and oceanic elements in East Asian coastal waters.The simulated surface layer oceanic elements are basically consistent with the reality and can reflect the interaction between the monsoon and the surface layer currents.The great difference with the reality is “cold drift” of the simulated surface temperature.The coupled model has certain ability to simulate the atmosphere geopotential height fields,precipitation and low-level southwest wind from May to August in 1998.It can display the process of summer monsoon onset during the third dekad of May and the evolution features after the onset.The differences between the simulation results of the coupled model and that of the single P-a RCM are shown mainly in the low-level atmosphere and the model internal regions.

Simulation of China Summer Precipitation Using a Regional Air-Sea Coupled Model

A regional air-sea coupled model based on the regional climate model（RegCM3） and the regional oceanic model POM（Princeton Ocean Model） is developed and a series of experiments are performed to verify the ability of the coupled model in simulating the summer precipitation over China from 1963 to 2002.The results show that the space correlation coefficients between the GISST（Global Ice and Sea Surface Temperature） data and the simulated SST by RegCM3-POM exceed 0.9.Compared with the uncoupled experiments,the coupled model RegCM3-POM has a better performance in simulating the mean summer（June to August） precipitation over China,and the distribution of the rainband in the coupled model is more accurate.The improvement of the rainfall simulation is significant over the Yangtze River Valley and in South China.The rainbelt intraseasonal evolution over eastern China in summer indicates that the simulation ability of RegCM3-POM is improved in comparison with the uncoupled model.The interannual summer rainfall variation over eastern China simulated by RegCM3-POM is in accordance with observation,while the spatial pattern of the interannual summer rainfall variation in the uncoupled model is inaccurate.The simulated correlation coefficient between the summer rainfall in the uncoupled model RegCM3 and observation is 0.30 over the Yangtze River Valley and 0.29 in South China.The coefficient between the rainfall in the coupled RegCM3-POM and observation is 0.48 over the Yangtze River Valley and 0.61 in South China.The RegCM3-POM has successfully simulated the correlation coefficients between summer rainfall in the Yangtze River Valley and SST anomalies of the Bay of Bengal,South China Sea,and the Kuroshio area,whereas the uncoupled model RegCM3 fails to reproduce this relationship.The study further shows that the monsoon circulation and the path of the moisture transport flux simulated by RegCM3-POM are in good agreement with the NCEP/NCAR data.

区域海气耦合模式模拟的2003年东亚夏季风季节内振荡

评估了一个区域海气耦合模式(由区域环境系统集成模式RIEMS和普林斯顿海洋模式POM组成)对2003年东亚夏季风季节内振荡(ISO)的模拟性能。通过与观测海温驱动单独大气模式结果的比较,分析了海气耦合过程对东亚夏季大气ISO模拟性能的影响。结果表明:耦合模式能够模拟出2003年中国东部地区夏季降水的气候态分布,模拟的中国东部尤其是江淮地区大气ISO活动较单独大气模式更为显著。同时,耦合模式能够较好地再现大气ISO经向上北传的传播特征,模拟的江淮流域降水处于活跃和中断期时西北太平洋地区低频降水和环流异常在强度和空间分布上较单独大气模式都更为合理。相比于单独大气模式,耦合模式对大气ISO模拟的改善,一方面与其对气候态西北太平洋副热带高压和相关对流层底层风场模拟的改善有关,另一方面与其包含海气相互作用,因而对低频降水与海温和水汽辐合位相关系模拟的改善有关。

北欧海主要海盆海面热通量的多年变化

北欧海有暖流和寒流注入,又发生大量回流,水团特性异常复杂。由于北欧海的环流受地形控制,其水团的分布与4个海盆的分布有密切的关系。本文研究各个海盆热通量变化的差异,以研究获取对北欧海海气相互作用区域差异的认识。北欧海的热量夏季以太阳短波辐射为主,冬季以来自海洋的长波辐射、感热和潜热通量为主。海盆间的差异主要体现在格陵兰海,其变化幅度短波辐射高出50%,长波辐射高出大约40%,潜热高出大约60%,感热高出近4倍。可能的原因是,格陵兰海强烈的感热和潜热释放导致海温降低,气温也受北极冷空气的影响,形成与暖流区迥异的自然环境。过去30年发生了2次显著的热量减少事件。其中,1987年的事件很可能与冰岛的火山喷发有关,火山喷发对短波辐射的影响长达一年之久,导致感热和潜热也同步减少。1998年格陵兰海的潜热和感热明显减少,与北极海冰输出导致的海温偏低有显著关系。文章分析了4个主要海盆热通量的变化与北极涛动(AO)指数的关系。结果表明,发生在冰岛海的向下短波辐射和发生在格陵兰海的感热和潜热与AO相关度较高,体现了与AO的密切关系。这些热通量与AO指数的滑动相关系数表明,1992年以前冰岛海的短波辐射与AO的相关性非常高,而格陵兰海的感热和潜热在1993年后与AO高度相关,是值得深入研究的现象。本文的结果支持以下观点:北欧海对北极涛动的贡献主要是格陵兰海的感热和潜热释放通过冰岛低压区的上升气流影响冰岛低压的云量,从而影响到达的太阳辐射而导致大气环流的变化。

A Robustness Analysis of CMIP5 Models over the East Asia-Western North Pacific Domain

The Coupled Model Intercomparison Project （CMIP） is an international community-based infrastructure that supports climate model intercomparison, climate variability, climate prediction, and climate projection. Improving the performance of climate models over East Asia and the western North Pacific has been a challenge for the climate-modeling community. In this paper, we provide a synthesis robustness analysis of the climate models participating in CMIP-Phase 5 （CMIP5）. The strengths and weaknesses of the CMIP5 models are assessed from the perspective of climate mean state, interannual variability, past climate change during the mid-Pliocene （MP） and the last millennium, and climate projection. The added values of regional climate models relative to the driving global climate models are also assessed. Although an encouraging increase in credibility and an improvement in the simulation of mean states, interannual variability, and past climate changes are visible in the progression from CMIP3 to CMIPS, some previously noticed biases such as the ridge position of the western North Pacific subtropical high and the associated rainfall bias are still evident in CMIP5 models. Weaknesses are also evident in simulations of the interannual amplitude, such as El Nino- Southern Oscillation （ENSO）-monsoon relationships. Coupled models generally show better results than standalone atmospheric models in simulating both mean states and interannual variability. Multi-model intercomparison indicates significant uncertainties in the future projection of climate change, although precipitation increases consistently across models constrained by the Clausius-Clapeyron relation. Regional ocean-atmosphere coupled models are recommended for the dynamical downscaling of climate change oroiections over the East Asia-western North Pacific domain.

AIR-SEA COUPLING FEATURES FROM THE WARM PHASE TO THE COLD PHASE OF ENSO CYCLES IN THE SEVENTIES TO THE EIGHTIES

Using the sea surface temperature and wind anomalies(SSTA and SSWA for short)of the tropical Pacific from January 1970 to December 1989,main spatial patterns of tropical Pacific SSTA and SSWA coupling features in the transform course from the warm phase to the cold phase of El Nino-southern Oscillation(ENSO)cycles are discussed. The main conclusions are as follows:(1)air-sea coupling patterns at the mature stage of El Nino(La Nina)are main spatial ones of tropical Pacific SSWA and SSTA coupling:(2)at the mature stage of El Nino,the interaction of the anticyclonic anomaly wind,generated by the forcing of distinct meridional SSTA gradient in the Northern Hemisphere tropical central Pacific.with the California cold current and SSTA is mainly responsible for weakening of El Nino;(3)the second sea temperature increase along the South American coast in the decaying course of El Nino results from the eastward movement of the weakened positive SSTA in the tropical central-eastern Pacific forced by anomalous west wind stress:(4)La Nina results from the joint effect of Walker circulation,Ekman drift and negative SSTA in the tropical central-eastern Pacific.

STUDY ON THE AIR-SEA INTERACTION ON THE INTERANNUAL TIME SCALE IN THE SOUTH CHINA SEA

In this paper we document the correlationship between sea surface temperature (SST) and low level-winds such as sea level wind and 850 hPa wind in the South China Sea (SCS) based on COADS (1958—1987) and ECMWF objective analysis data (1973—1986).Further statistical analyses tell us that there is a fixed SCS basin mode for variations both of SST and low-level winds in the region on the interannual time scale due to air-sea interactions. A simplified,coupled model that is designed following the McCreary and Anderson's (1985) model and includes the feedback between the upper ocean and the circulation of East Asian monsoon demonstrates an interannual oscillation in the coupled air-sea system,which is similar to the observations in the SCS.