Local advective mechanism for interdecadal variability in circulations driven by constant surface heat fluxes in idealized basins

Idealized numerical experiments with a depth level coordinate ocean circulation model (GFDL MOM3) have been conducted to investigate the structure of interdecadal variability from thermally driven circulations. The model oceans are driven by steady surface heat fluxes in the absence of surface wind stresses. Interdecadal variability is observed, with characteristics similar to those reported in many previous studies. To explain the nature of the variability we propose a new mechanism based on two local horizontal advective processes. This overcomes the limitations in previous theories based on the interplay between global properties such as zonal and meridional temperature gradients and overturning. One of the two advective processes is a zonal flow anomaly induced by a temperature anomaly along the northern wall through geostrophy southward of the temperature anomaly. A cold (warm) anomaly along the northern wall produces a positive (negative) zonal flow anomaly that induces a warm (cold) temperature anomaly by enhancing (weakening) warm advection from the western boundary along the path of the zonal flow anomaly. The temperature and flow anomalies are transported toward the eastern boundary by the mean eastward zonal flow. When the positive (negative) zonal flow anomaly that accompanies the warm (cold) temperature anomaly encounters the eastern wall, a downwelling (upwelling) anomaly is produced. To dissipate the vorticity due to this downwelling (upwelling) anomaly, a northward (southward) flow anomaly, which is another advective process governing the variability, is generated within a frictional boundary layer next to the eastern wall. The northward (southward) flow anomaly circulates cyclonically along the perimeter of the basin while enhancing (reducing) warm advection. So does the warm (cold) temperature anomaly carried to the eastern wall by the mean zonal flow while pushing the cold (warm) anomaly that produced the positive (negative) zonal flow anomaly westward and initiating the other half cycle of the variability. During the anomalous downwelling or upwelling, the available potential energy stored in the anomalous density field is released to maintain the variability. Thus, neither barotropic nor baroclinic instability supplies energy for the variability. The anomalous vertical velocity is stronger along the northern boundary and the northern part of the eastern boundary. A shallow continental slope added along those boundaries prohibits the anomalous vertical motion and weakens variability very effectively, while one along the western boundary does not.     

吕宋海峡西部深海盆内孤立波潜标观测研究

Using a net surface heat flux （Qnet） product obtained from the objectively analyzed air-sea fluxes （OAFlux） project and the international satellite cloud climatology project （ISCCP）, and temperature from the simple ocean data assimilation （SODA）, the seasonal variations of the air-sea heat fluxes in the northwestern Pa cific marginal seas （NPMS） and their roles in sea surface temperature （SST） seasonality are studied. The seasonal variations of Qnet, which is generally determined by the seasonal cycle of latent heat flux （LH）, are in response to the advection-induced changes of SST over the Kuroshio and its extension. Two dynamic regimes are identified in the NPMS： one is the area along the Kuroshio and its extension, and the other is the area outside the Kuroshio. The oceanic thermal advection dominates the variations of SST and hence the sea-air humidity plays a primary role and explains the maximum heat losing along the Kuroshio. The heat transported by the Kuroshio leads to a longer period of heat losing over the Kuroshio and its Extension. Positive anomaly of heat content corresponds with the maximum heat loss along the Kuroshio. The oceanic advection controls the variations of heat content and hence the surface heat flux. This study will help us understand the mechanism controlling variations of the coupled ocean-atmosphere system in the NPMS. In the Kuroshio region, the ocean current controls the ocean temperature along the main stream of the Ku roshio, and at the same time, forces the air-sea fluxes.     

Surface heat fluxes during hot events

We selected surface flux datasets to investigate the heat fluxes during “hot events”; (HEs), defined as short-term, large-scale phenomena involving very high sea surface temperature (SST). Validation of the heat fluxes against in-situ ones, which are estimated from in-situ observation in HE sampling conditions, shows the accuracies (bias ± RMS error) of net shortwave radiation, net long wave radiation, latent heat and sensible heat fluxes are 20 ± 45.0 W m⁻², −9 ± 12.3 W m⁻², −2.3 ± 31.5 W m⁻² and 1.5 ± 5.0 W m⁻², respectively. Statistical analyses of HEs show that, during these events, net solar radiation remains high and then decreases from 246 to 220 W m⁻², while latent heat is low and then increases from 100 W m⁻² to 124 W m⁻². Histogram peaks indicate net solar radiation of 270 W m⁻² and latent heat flux of 90 W m⁻² during HEs. Further, HEs are shown to evolve in three phases: formation, mature, and ending phases. Mean heat gain (HG) in the HE formation phase of 60 W m⁻² is larger than the reasonably estimated annual mean HG range of 0–25 W m⁻² in the Indo-Pacific Warm Pool. Such large daily HG in the HE formation phase can be expected to increase SSTs and produce large amplitudes of diurnal SST variations during HEs, which have been observed by both satellite and in-situ measurements in our previous studies.     

Formation of extreme surface turbulent heat fluxes from the ocean to the atmosphere in the North Atlantic

The role of extreme surface turbulent fluxes in total oceanic heat loss in the North Atlantic is studied. The atmospheric circulation patterns enhancing ocean–atmosphere heat flux in regions with significant contributions of the extreme heat fluxes (up to 60% of the net heat loss) are analyzed. It is shown that extreme heat fluxes in the Gulf Stream and the Greenland and Labrador Seas occur in zones with maximal air pressure gradients, i.e., in cyclone–anticyclone interaction zones.     

Effective parameters for matched field geoacoustic inversion in range-dependent environments

Using the well-established technique of geoacoustic inversion, one can estimate a set of acoustic sea-bed parameters from sonar array data. Simultaneously, one can search for geometric parameters such as range, water depth, and hydrophone depth. When the technique is applied in a range-dependent environment, there is a potentially much larger set of parameters to match, unless one has perfect knowledge of the bathymetry. From the point of view of optimization, one needs to handle uncertainties in bathymetry without hugely increasing the amount of computation. A simple time-domain view (which is shown to be equivalent to the adiabatic approximation) suggests that it is sufficient to use a range-independent model with an empirical "effective" depth even when the bottom is not flat. In fact, there is a set of effective environments that will suffice; one can choose whichever is the most convenient. The success of this concept is demonstrated with some test cases from a recent Geoacoustic Inversion Techniques Workshop.     

The influence of the surface heat fluxes of the Kuroshio key-area on meiyu rainfall in the Changjiang River region

On the basis, of the surface heat fluxes of the Kuroshio key-area (26°-30°N, 125°-30°E)in March andApril, the climatologicai influence of the Kuroshio heat fluxes on meiyu rainfall in the Changjiang River (Yangtse River) region are studied. The results are concluded as follows;the surface heat fluxes of the Kuroshio key-area have certain influence on meiyu rainfall in the Changjiang River region during June and July. The correctness rates for the five stations in the Changjing River region (i. e. Wuhan, Jiujiang, Anqing,Nanjing and Shanghai)are in the range of 9/20-13/20. The surface heat fluxes influence mainly on the homogeneous rainfall pattern,the correctness rates come to 7/10-8/10 for the lower valley of the Changjiang River. The estimation expression of the meiyu rainfall for Shanghai consisting of the surface heat flux and the sea surface temperature anomaly of the Kuroshio key area agrees well with the actual meiyu rainfall condition.     

中国近海海气界面热通量的反演

应用卫星SSM/I(Special Sensor Microwave/Imager)和AVHRR(Advanced Very High Resolution Radiometer)遥感资料,使用先进的海气通量计算方法(COARE3.0),计算了中国近海海气界面的感热和潜热通量.计算结果与南海西沙(2002年5月)和文昌(2000年10~11月)实测结果进行比较发现,应用遥感资料获得的海气界面热通量与实测结果非常一致.遥感获得的感热通量和潜热通量与西沙实测结果的均方根误差分别为2.9和29.9 W/m2,与文昌实测结果的均方根误差:2000年10月分别为4.42和43.05 W/m2,2000年11月分别为4.19和40.8 W/m2.与GSSTF2的结果相比,其时空分布变化特征基本一致.根据中国近海遥感资料(1988~2000年)的感热通量的分析,其均方根误差在10.1~12.4 W/m2之间,多年平均均方根误差为11.7 W/m2.潜热通量的均方根误差在34.8~49.7 W/m2之间,多年平均均方根误差为43.2 W/m2.由此可以说明,利用遥感获得的热通量可以用来进行中国近海海气相互作用的研究以及作为我国气候预测研究的重要依据.     

中国近海及其邻近海域海气热通量的模式计算

应用美国宇航局Goddard地球观测系统四维资料同化系统计算和分析了近海海域感热通量和潜热通量的季节性变化规律和地理分布特征.结果表明,近海各季感热通量冬、秋季较大,春、夏季较小.其地理分布特点是冬季感热通量的分布随纬度变化十分明显,纬度越高感热通量越大,且等值线分布密集.在台湾以东、日本以南海域,感热通量等值线呈西南一东北走向.在南海海域,感热通量比周围海域略低,感热通量等值线在该海域呈一低值倒槽分布;潜热通量冬、秋季在台湾东北部、日本南部和东南部海域形成最大值区,等值线呈西南东北走向.春、夏季在黄海海域存在潜热通量的极小值区,同时春季在日本南部海域存在潜热通量的极大值区或最大值区.因为台湾以东、日本以南海域正好是黑潮流经的区域,所以此海域的热通量与黑潮有密切关系.     

Low-frequency variability of hydrometeorological fields and heat fluxes over the North Atlantic

The linear and quadratic trends of the parameters of interaction of the atmosphere with the ocean in the North Atlantic are computed according to the archival data of the Russian Hydrometeorological Center accumulated for 1957–1990. The linear trends are regarded as probable manifestations of the anthropogenic processes. At the same time, the quadratic trends are regarded as manifestations of natural low-frequency oscillations with a characteristic period of ~65 yr. The linear trends of the sea-surface temperature (SST) and the surface air temperature (SAT) are negative at high latitudes. The thermal (SST—SAT) contrasts and the deficiency of humidity E decrease over the most part of the investigated water area, thus revealing the active influence of the North Atlantic on the trends of SAT caused by the negative feedback in the system supported by the changes in the evident and latent heat fluxes. The significant quadratic trends of various hydrometeorological parameters and total heat fluxes confirm the predominance of natural variability with a period of ~65 yr in the North Atlantic. The quadratic trend of the heat fluxes is mainly caused by the quadratic trend of E. The coincidence of the phases of long-period anomalies of the SAT and E over the major part of the North Atlantic reveals the decisive role of the variability of the ocean in supporting the interdecadal oscillations in the ocean—atmosphere system.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 19–38, July–August, 2004.     

台湾海峡海表气溶胶干沉降通量研究

在已改进的Williams模型中,应用GW03海表动力学粗糙度参数化方案,考虑波浪对干沉降速率的影响,结合卫星资料和再分析资料,计算了台湾海峡海表气溶胶干沉降速率,并利用2006～2007年走航观测结果计算了台湾海峡总悬浮颗粒物的入海通量.其结果表明：台湾海峡海表气溶胶干沉降速率及总悬浮颗粒物干沉降通量具有明显的时空变化特征.台湾海峡海表气溶胶干沉降速率范围为5.83～6.17 cm/s,平均值为6.00 cm/s.其中冬季气溶胶干沉降速率最大,平均值为6.08 cm/s;夏季气溶胶干沉降速率最小,平均值为5.85 cm/s.台湾海峡气溶胶总悬浮颗粒物的干沉降通量也呈现出冬季的高[均值为7.31μg/（m2.s）],夏季的低[均值为2.23μg/（m2.s）]的特征.从空间分布上看,台湾海峡海表气溶胶干沉降速率出现1个高值中心,位于台湾海峡北部海域.总悬浮颗粒物干沉降通量出现2个高值中心和1个低值中心,分别位于台湾海峡北部海域、汕头至厦门海域和南海中北部海域.     

Volume and heat transports and material fluxes in the East China Sea during April 1994

INTRODUCTIONTherehavebeenmanystudiesandcomputationsonVToftheKuroshiointheEastChinaThisprojectwassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49476278.Asanditsvacation.Forexample,(1)basedonhydrographicobservationsatactionG(PN)f...     

Role of the Agulhas Current in Indian Ocean circulation and associated heat and freshwater fluxes

A reduced estimate of Agulhas Current transport provides the motivation to examine the sensitivity of Indian Ocean circulation and meridional heat transport to the strength of the western boundary current. The new transport estimate is 70 Sv, much smaller than the previous value of 85 Sv. Consideration of three case studies for a large, medium and small Agulhas Current transport demonstrate that the divergence of heat transport over the Indian Ocean north of 32°S has a sensitivity of 0.08 PW per 10 Sv of Agulhas transport, and freshwater convergence has a sensitivity of 0.03×10⁹ kg s⁻¹ per 10 Sv of transport. Moreover, a smaller Agulhas Current leads to a better silica balance and a smaller meridional overturning circulation for the Indian Ocean. The mean Agulhas Current transport estimated from time-series current meter measurements is used to constrain the geostrophic transport in the western boundary region in order to re-evaluate the circulation, heat and freshwater transports across 32°S. The Indonesian Throughflow is taken to be 12 Sv at an average temperature of 18°C. The constrained circulation exhibits a vertical–meridional circulation with a net northward flow below 2000 dbar of 10.1 Sv. The heat transport divergence is estimated to be 0.66 PW, the freshwater convergence to be 0.54×10⁹ kg s⁻¹, and the silica convergence to be 335 kmol s⁻¹. Meridional transports are separated into barotropic, baroclinic and horizontal components, with each component conserving mass. The barotropic component is strongly dependent on the estimated size of the Indonesian Throughflow. Surprisingly, the baroclinic component depends principally on the large-scale density distribution and is nearly invariant to the size of the overturning circulation. The horizontal heat and freshwater flux components are strongly influenced by the size of the Agulhas Current because it is warmer and saltier than the mid-ocean. The horizontal fluxes of heat and salt penetrate down to 1500 m depth, suggesting that warm and salty Red Sea Water may be involved in converting the intermediate and upper deep waters which enter the Indian Ocean from the Southern Ocean into warmer and saltier waters before they exit in the Agulhas Current.     

南海西南季风期NCEP2湍流热通量的质量分析

以5次南海现场观测试验数据(Xisha2002,Xisha2000,Xisha1998,Kexue 1和Shiyan 3)为参照,对NCEP2再分析资料中湍流热通量在南海西南季风期的精度进行了评估.结果表明NCEP2估算的潜热通量的平均值在试验Xisha2000,Xisha1998,Kexue 1和Shiyan 3期间分别高估了6(11%),2(2%),7(7%)和13W/m2(16%),而在Xisha2002试验中低估了10 W/m2(11%).在5个试验中低估的感热通量分别为7(130%),3(64%),7(170%),5(53%)和5 W/m2(72%).NCEP2与5个现场观测试验的时间序列的相关系数均没有达到95%的置信度.模式中湍流热通量损失的误差来源于基本变量和算法,基本变量中以海表温度和海面风速的误差产生的影响最大.应用COARE2.6a算法和NCEP2的基本变量重新计算的湍流热通量更加符合物理意义.     

Vertical heat and salt fluxes induced by inertia-gravity internal waves on sea shelf

Free inertia-gravity internal waves are considered in a two-dimensional vertically nonuniform flow in the Boussinesq approximation. The equation for vertical velocity amplitude includes complex factors caused by the gradient of the flow velocity component transverse to the wave-propagation direction; therefore, the eigenfunction and wave frequency are complex. It is shown that the decrement of damping (imaginary correction to the frequency) of 15-min internal waves is two orders of magnitude smaller than the wave frequency; i.e., the waves weakly damp. Vertical wave fluxes of heat and salt are nonzero due to the phase shift between fluctuations of the vertical velocity and temperature (salinity) different from π 2. The vertical component of the Stokes drift speed is also nonzero and contributed into the vertical transport.     

An evaluation of the Arctic clouds and surface radiative fluxes in CMIP6 models

To assess the performances of state-of-the-art global climate models on simulating the Arctic clouds and surface radiation balance, the 2001–2014 Arctic Basin surface radiation budget, clouds, and the cloud radiative effects(CREs) in 22 coupled model intercomparison project 6(CMIP6) models are evaluated against satellite observations. For the results from CMIP6 multi-model mean, cloud fraction(CF) peaks in autumn and is lowest in winter and spring, consistent with that from three satellite observation products(Cloud Sat-CALIPSO, CERESMODIS, and APP-x). Simulated CF also shows consistent spatial patterns with those in observations. However,almost all models overestimate the CF amount throughout the year when compared to CERES-MODIS and APP-x.On average, clouds warm the surface of the Arctic Basin mainly via the longwave(LW) radiation cloud warming effect in winter. Simulated surface energy loss of LW is less than that in CERES-EBAF observation, while the net surface shortwave(SW) flux is underestimated. The biases may result from the stronger cloud LW warming effect and SW cooling effect from the overestimated CF by the models. These two biases compensate each other,yielding similar net surface radiation flux between model output(3.0 W/m~2) and CERES-EBAF observation(6.1 W/m~2). During 2001–2014, significant increasing trend of spring CF is found in the multi-model mean,consistent with previous studies based on surface and satellite observations. Although most of the 22 CMIP6 models show common seasonal cycles of CF and liquid water path/ice water path(LWP/IWP), large inter-model spreads exist in the amounts of CF and LWP/IWP throughout the year, indicating the influences of different cloud parameterization schemes used in different models. Cloud Feedback Model Intercomparison Project(CFMIP)observation simulator package(COSP) is a great tool to accurately assess the performance of climate models on simulating clouds. More intuitive and credible evaluation results can be obtained based on the COSP model output. In the future, with the release of more COSP output of CMIP6 models, it is expected that those inter-model spreads and the model-observation biases can be substantially reduced. Longer term active satellite observations are also necessary to evaluate models' cloud simulations and to further explore the role of clouds in the rapid Arctic climate changes.     

Reconstruction of radiation fluxes at the ocean surface from NOAA satellite data

Algorithms for obtaining operative information on the fluxes of the total solar radiation and radiation balance at the ocean surface are developed and realized on the basis of satellite observations within the spectral ranges 0·725–1·1 and 10·3–11·3 m at arbitrary scanning angles. For the 10-day and monthly values, the reconstruction errors remain at the level of the accuracy of the shipboard measurements. The atlas of charts of the above parameters (grid 0·5°×0·5°) is compiled using data obtained by the RVAkademik Vernadsky in the Atlantic Ocean during 1986–1989.Translated by Mikhail M. Trufanov.     

Seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean based on WHOI flux product

The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution(WHOI) flux product.The most turbulent heat fluxes occur during winter seasons in the two hemispheres,whose centers are located at 10°~20°N and 5°～15°S respectively.In climatological ITCZ,the turbulent heat fluxes are the greatest from June to August,and in equatorial cold tongue the turbulent heat fluxes are the greatest from March to May.Seasonal variability of sensible heat flux is smaller than that of latent heat flux and mainly is dominated by the variations of air-sea temperature difference.In the region with larger climatological mean wind speed(air-sea humidity difference),the variations of air-sea humidity difference(wind speed) dominate the variability of latent heat flux.The characteristics of turbulent heat flux yielded from theory analysis and WHOI dataset is consistent in physics which turns out that WHOI's flux data are pretty reliable in the tropical Atlantic Ocean.     

Evaluation of monthly turbulent heat fluxes from WHOI analysis and NCEP reanalysis in the tropical Atlantic

1 IntroductionThe empirical and simple model studies suggestthe existence of a SST dipole mode in the tropical At-lantic which is antisymmetric about the annual-meanthe intertropical convergence zone (ITCZ) and in-volves air- sea interaction through the wind- SST-evaporation (WES) feedback (Carton, 1996; Chang etal., 1997; Zhao et al., 2003). Chang et al. (2000)found that the dominant near-surface atmospheric re-sponse in the tropical Atlantic sector primarily comesfrom the local SST f…