副热带东北太平洋混合层深度及其对潜沉的影响

The present climate simulations of the mixed layer depth(MLD) and the subduction rate in the subtropical Northeast Pacific are investigated based on nine of the CMIP5 models. Compared with the observation data,spatial patterns of the MLD and the subduction rate are well simulated in these models. The spatial pattern of the MLD is nonuniform, with a local maximum MLD(140 m) region centered at(28°N, 135°W) in late winter. The nonuniform MLD pattern causes a strong MLD front on the south of the MLD maximum region, controls the lateral induction rate pattern, and then decides the nonuniform distribution of the subduction rate. Due to the inter-regional difference of the MLD, we divide this area into two regions. The relatively uniform Ekman pumping has little effect on the nonuniform subduction spatial pattern, though it is nearly equal to the lateral induction in values. In the south region, the northward warm Ekman advection(–1.75×10~(–7) K/s) controls the ocean horizontal temperature advection(–0.85×10~(–7) K/s), and prevents the deepening of the MLD. In the ensemble mean, the contribution of the ocean advection to the MLD is about –29.0 m/month, offsetting the sea surface net heat flux contribution(33.9 m/month). While in the north region, the southward cold advection deepens the MLD(21.4 m/month) as similar as the heat flux(30.4 m/month). In conclusion, the nonuniform MLD pattern is dominated by the nonuniform ocean horizontal temperature advection. This new finding indicates that the upper ocean current play an important role in the variability of the winter MLD and the subduction rate.     

An assessment of the subduction rate in the CMIP6 historical experiment

Subduction process is a dynamical bridge for the exchanges of heat between the atmosphere and subsurface ocean water, which is regarded as a central proxy for the ocean climate studies. Given its key indicator in climate signals, it is of importance to examine the ability of a model to simulate the global subduction rate before investigating the climate dynamics. In this paper, we evaluated the ability of 21 climate models from Coupled Model Intercomparison Project Phase 6(CMIP6) in simulating t...     

The effect of the wave-induced mixing on the upper ocean temperature in a climate model

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.     

Identification of CO2 disposal locations in an ocean general circulation model of the North Pacific

A basinwide ocean general circulation model of the North Pacific is used to identify which location is more efficient for ocean CO2 sequestration in the North Pacific. Four injection depths at each one of fifteen locations are chosen. In terms of effectiveness index (EI) and escape factor (EF), it is clear that the effectiveness increases with increasing latitude at the end of the 50 a injection period. Sitebysite differences in the EI can be over 9% for the 1 000 m injection depth in the western North Pacific at the end of 50 a of continuous injection. The difference is much larger for the 500 m injection. The difference decreases with increasing injection depth. However, the sitebysite difference is small for the injection in the eastern North Pacific. The sequestration is more efficient for the injection in the east than in the west. For the 500 m injection depth, the difference in effectiveness between the west and the east is over 10% at the end of 50 a injection period. The largest concentration of sequestered CO2 increases with increasing injection depth. For the injection in both the western and central North Pacific, the largest exchange flux always appears to be at about 42°N, 150°E, whereas for the injection in the eastern area the large flux appears to be in the equatorial region (120°W).     

Variation of Indo-Pacific upper ocean heat content during 2001–2012 revealed by Argo

Understanding of the temporal variation of oceanic heat content(OHC) is of fundamental importance to the prediction of climate change and associated global meteorological phenomena. However, OHC characteristics in the Pacific and Indian oceans are not well understood. Based on in situ ocean temperature and salinity profiles mainly from the Argo program, we estimated the upper layer(0–750 m) OHC in the Indo-Pacific Ocean(40°S–40°N, 30°E–80°W). Spatial and temporal variability of OHC and its likely physical mechanisms are also analyzed. Climatic distributions of upper-layer OHC in the Indian and Pacific oceans have a similar saddle pattern in the subtropics, and the highest OHC value was in the northern Arabian Sea. However, OHC variabilities in the two oceans were different. OHC in the Pacific has an east-west see-saw pattern, which does not appear in the Indian Ocean. In the Indian Ocean, the largest change was around 10°S. The most interesting phenomenon is that, there was a long-term shift of OHC in the Indo-Pacific Ocean during 2001–2012. Such variation coincided with modulation of subsurface temperature/salinity. During 2001–2007, there was subsurface cooling(freshening)nearly the entire upper 400 m layer in the western Pacific and warming(salting) in the eastern Pacific. During2008–2012, the thermocline deepened in the western Pacific but shoaled in the east. In the Indian Ocean, there was only cooling(upper 150 m only) and freshening(almost the entire upper 400 m) during 2001–2007. The thermocline deepened during 2008–2012 in the Indian Ocean. Such change appeared from the equator to off the equator and even to the subtropics(about 20°N/S) in the two oceans. This long-term change of subsurface temperature/salinity may have been caused by change of the wind field over the two oceans during 2001–2012, in turn modifying OHC.     

Projections of ocean climate for northwestern Pacific Ocean

The long-term adjustment processes of atmosphere and ocean in response to gradually increased atmospheric CO2 concentration have been analyzed in 70 and 140a integrations with NCAR fully-coupled climate system model (CSM). In these experiments the CO2 concentration has been increased to double and quadruples the initial concentration, respectively. After 70a, at the time of CO2 doubling, the model predicts surface air temperature rises by 1.2 and 1.5K for the globe and the northwestern Pacific Ocean, respectively. The behavior of the quadrupling run is similar: each global and regional mean surface air temperatures increase by 2.8 and 3.0K at the time of CO2 quadrupling. From the experiments, surface air temperature changes in the northwestern Pacific Ocean will be more distinctive compared with the global average, mainly due to exceptionally large warming and sea level change near the entrance of the Kuroshio extension.     

南海浅层经向翻转环流及相关的内部水体流动

The structure of the annual-mean shallow meridional overturning circulation(SMOC) in the South China Sea(SCS) and the related water movement are investigated,using simple ocean data assimilation(SODA) outputs.The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale,which consists of downwelling in the northern SCS,a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow,with a strength of about 1×10~6 m~3/s.The formation mechanisms of its branches are studied separately.The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m.The annual-mean Ekman transport across 18°N is about 1.2×10~6 m~3/s.An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework.An annual subduction rate of about 0.66×10~6m~3/s is obtained between 17° and 20°N,of which 87% is due to vertical pumping and 13% is due to lateral induction.The subduction rate implies that the subdution contributes significantly to the downwelling branch.The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 11°N within the western boundary current before returning northward.The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents.Significant upwelling mainly occurs off the Vietnam coast in the southern SCS.An upper bound for the annual-mean net upwelling rate between 10° and 15°N is 0.7×10~6m~3/s,of which a large portion is contributed by summer upwelling,with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.     

The comparison of altimeter retrieval algorithms of the wind speed and the wave period

Recent (2007-2010) research results about ocean’s role in climate variation and change by Chinese scientists are highlighted. This paper reviews a majority contributions by Chinese scientists to the understanding of ocean variability and change. This paper starts with the results about the important role of the tropical Indian Ocean in interannual variation of the Asia summer monsoon, the effect of sea surface temperature (SST) and freshwater flux on climate variability in the Pa- cific, and interannual variability research in other oceans. Then results about ocean dynamic and thermodynamic roles in decadal climate variation are reviewed. Finally, the results about oceanic response to global warming are discussed, again showcasing ocean’s important role in climate.     

潮汐对瞬态气候响应模拟的影响研究

In this study, the impact of oceanic processes on the sensitivity of transient climate change is investigated using two sets of coupled experiments with and without tidal forcing, which are termed Exp_Tide and Exp_Control,respectively. After introducing tidal forcing, the transient climate response(TCR) decreases from 2.32 K to 1.90 K,and the surface air temperature warming at high latitudes decreases by 29%. Large ocean heat uptake efficiency and heat storage can explain the low TCR in Exp_Tide. Approximately 21% more heat is stored in the ocean in Exp_Tide(1.10×10~(24) J) than in Exp_Control(0.91×10~(24) J). Most of the large ocean warming occurs in the upper 1 000 m between 60°S and 60°N, primarily in the Atlantic and Southern Oceans. This ocean warming is closely related to the Atlantic Meridional Overturning Circulation(AMOC). The initial transport at mid-and high latitudes and the decline in the AMOC observed in Exp_Tide are both larger than those observed in Exp_Control. The spatial structures of AMOC are also different with and without tidal forcing in present experiments. The AMOC in Exp_Tide has a large northward extension. We also investigated the relationship between AMOC and TCR suggested by previous studies using the present experiments.     

Tropical cyclone genesis over the western North Pacific simulated by Coupled Model Intercomparison Project Phase 6 models

Threatening millions of people and causing billions of dollars in losses, tropical cyclones(TCs) are among the most severe natural hazards in the world, especially over the western North Pacific. However, the response of TCs to a warming or changing climate has been the subject of considerable research, often with conflicting results. In this study, the abilities of Coupled Model Intercomparison Project(CMIP) Phase 6(CMIP6) models to simulate TC genesis are assessed through historical simulation...     

Response of the mixed layer depth and subduction rate in the subtropical Northeast Pacific to global warming

The response of the mixed layer depth(MLD) and subduction rate in the subtropical Northeast Pacific to global warming is investigated based on 9 CMIP5 models. Compared with the present climate in the 9 models, the response of the MLD in the subtropical Northeast Pacific to the increased radiation forcing is spatially nonuniform, with the maximum shoaling about 50 m in the ensemble mean result. The inter-model differences of MLD change are non-negligible, which depend on the various dominated mechanisms. On the north of the MLD front, MLD shallows largely and is influenced by Ekman pumping, heat flux, and upper-ocean cold advection changes. On the south of the MLD front, MLD changes a little in the warmer climate, which is mainly due to the upper-ocean warm advection change. As a result, the MLD front intensity weakens obviously from 0.24 m/km to0.15 m/km(about 33.9%) in the ensemble mean, not only due to the maximum of MLD shoaling but also dependent on the MLD non-uniform spatial variability. The spatially non-uniform decrease of the subduction rate is primarily dominated by the lateral induction reduction(about 85% in ensemble mean) due to the significant weakening of the MLD front. This research indicates that the ocean advection change impacts the MLD spatially non-uniform change greatly, and then plays an important role in the response of the MLD front and the subduction process to global warming.     

Response of the North Pacific subtropical countercurrent and its variability to global warming

Response of the North Pacific subtropical countercurrent (STCC) and its variability to global warming is examined in a state-of-the-art coupled model that is forced by increasing greenhouse gas concentrations. Compared with the present climate, the upper ocean is more stratified, and the mixed layer depth (MLD) shoals in warmer climate. The maximum change of winter MLD appears in the Kuroshio–Oyashio extension (KOE) region, where the mean MLD is the deepest in the North Pacific. This weakens the MLD front and reduces lateral induction. As a result of the reduced subduction rate and a decrease in sea surface density in KOE, mode waters form on lighter isopycnals with reduced thickness. Advected southward, the weakened mode waters decelerate the STCC. On decadal timescales, the dominant mode of sea surface height in the central subtropical gyre represents STCC variability. This STCC mode decays as CO₂ concentrations double in the twenty-first century, owing both to weakened mode waters in the mean state and to reduced variability in mode waters. The reduced mode-water variability can be traced upstream to reduced variations in winter MLD front and subduction in the KOE region where mode water forms.     

Simulation and future projection of the mixed layer depth and subduction process in the subtropical Southeast Pacific

The present climate simulation and future projection of the mixed layer depth (MLD) and subduction process in the subtropical Southeast Pacific are investigated based on the geophysical fluid dynamics laboratory earth system model (GFDL-ESM2M). The MLD deepens from May and reaches its maximum (>160 m) near (24°S, 104°W) in September in the historical simulation. The MLD spatial pattern in September is non-uniform in the present climate, which shows three characteristics: (1) the deep MLD extends from the Southeast Pacific to the West Pacific and leads to a "deep tongue" until 135°W; (2) the northern boundary of the MLD maximum is smoothly near 18°S, and MLD shallows sharply to the northeast; (3) there is a relatively shallow MLD zone inserted into the MLD maximum eastern boundary near (26°S, 80°W) as a weak "shallow tongue". The MLD non-uniform spatial pattern generates three strong MLD fronts respectively in the three key regions, promoting the subduction rate. After global warming, the variability of MLD spatial patterns is remarkably diverse, rather than deepening consistently. In all the key regions, the MLD deepens in the south but shoals in the north, strengthing the MLD front. As a result, the subduction rate enhances in these areas. This MLD antisymmetric variability is mainly influenced by various factors, especially the potential-density horizontal advection non-uniform changes. Notice that the freshwater flux change helps to deepen the MLD uniformly in the whole basin, so it hardly works on the regional MLD variability. The study highlights that there are regional differences in the mechanisms of the MLD change, and the MLD front change caused by MLD non-uniform variability is the crucial factor in the subduction response to global warming.     

副热带东北太平洋混合层深度及潜沉率季节循环对全球变暖的响应

本文利用第五次国际耦合模式比较计划（CMIP5）中的地球系统模式（ESM2M）,结合Argo观测数据和由Ishii等整理的再分析数据集,分析现在气候背景和辐射强迫极端增强下副热带东北太平洋海域（10°～40°N,110°～160°W）混合层深度（MLD）和潜沉率的季节变化特征,研究其对全球变暖的响应。在现在气候背景下,二者最大值均出现在冬季。潜沉率的主要贡献项存在显著的季节变化差异,1?5月主要受侧向潜沉率的变化控制,6?12月则由风应力旋度导致的埃克曼抽吸速度变化主控。全球变暖后,季节循环信号的主控要素不变。但受风应力旋度等要素变化的影响,各季节的MLD减小,大值区范围收缩。由于冬季减小幅度远大于夏季,MLD季节波动幅度（振幅）显著变小。长期看,MLD呈现持续变浅的趋势,其空间不均匀性减弱引起的MLD锋面减弱是控制侧向潜沉率减弱,最终导致总潜沉率减弱的关键。由于埃克曼抽吸速度的季节变化信号对全球变暖的响应较小,因此总潜沉率在冬季受全球变暖的影响最为强烈。上述结果表明,构成潜沉率的两个关键要素对总潜沉率的贡献比例是随着季节变化而改变的:冬季MLD锋面强盛时期,侧向潜沉率的影响将显著增强。全球变暖前后二者截然不同的变化会显著改变潜沉率的季节循环振幅,可能对该区域模态水的形成和输运产生深远的影响。     

Interdecadal Variation of the Transition Zone Chlorophyll Front: A Physical-Biological Model Simulation between 1960 and 1990

The interdecadal climate variability affects marine ecosystems in both the subtropical and subarctic gyres, consequently the position of the Transition Zone Chlorophyll Front (TZCF). A three-dimensional physical-biological model has been used to study interdecadal variation of the TZCF using a retrospective analysis of a 30-year (1960–1990) model simulation. The physical-biological model is forced with the monthly mean heat flux and surface wind stress from the COADS. The modeled winter mixed layer depth (MLD) shows the largest increase between 30°N and 40°N in the central North Pacific, with a value of 40–60% higher during 1979–90 relative to 1964–75 values. The winter Ekman pumping velocity difference between 1979–90 and 1964–75 shows the largest increase located between 30°N and 45°N in the central and eastern North Pacific. The modeled winter surface nitrate difference between 1979–90 and 1964–75 shows increase in the latitudinal band between 30°N and 45°N from the west to the east (135°E–135°W), the modeled nitrate concentration is about 10 to 50% higher during the period of 1979–90 relative to 1964–75 values depending upon locations. The increase in the winter surface nitrate concentration during 1979-90 is caused by a combination of the winter MLD increase and the winter Ekman pumping enhancement. The modeled nitrate concentration increase after 1976–77 enhances primary productivity in the central North Pacific. Enhanced primary productivity after the 1976–77 climatic shift contributes higher phytoplankton biomass and therefore elevates chlorophyll level in the central North Pacific. Increase in the modeled chlorophyll expand the chlorophyll transitional zone and push the TZCF equatorward. This revised version was published online in August 2006 with corrections to the Cover Date.     

海洋的季节变化及风应力异常对海洋影响的数值试验

对一个6层5°×4°网格的全球海洋模式作了一些改进,建立了10层5°×4°网格的全球海洋模式,进行了季节变化数值模拟,积分250a,取得稳定的结果.除了高纬度海洋外,模拟的季节变化与实际观测十分接近.在此基础上,作了热带太平洋海温场对热带季风异常响应的3组敏感性实验,第1组为赤道西太平洋异常西风向东传播的试验;第2组为整个赤道太平洋风应力振荡异常试验;第3组为赤道西太平洋异常西风、东风交替向东传播的敏感性试验.模拟结果表明:(1)第1组风应力敏感性实验结果揭示出,西太平洋西风异常的向东传播的风应力异常可以产生类似厄尔尼诺的赤道东太平洋变暖;(2)第2组试验结果表明,热带太平洋风应力的局地振荡首先在中太平洋东西部激发出海温扰动,然后海温扰动分别向东太平洋和西太平洋传播,从而引起东、西太平洋海温的异常;(3)第3组试验验证风应力QBO可以产生海洋中类似的QBO振荡.     

Mixed layer depth climatology of the North Pacific based on Argo observations

A monthly mean climatology of the mixed layer depth (MLD) in the North Pacific has been produced by using Argo observations. The optimum method and parameter for evaluating the MLD from the Argo data are statistically determined. The MLD and its properties from each density profile were calculated with the method and parameter. The monthly mean climatology of the MLD is computed on a 2° × 2° grid with more than 30 profiles for each grid. Two bands of deep mixed layer with more than 200 m depth are found to the north and south of the Kuroshio Extension in the winter climatology, which cannot be reproduced in some previous climatologies. Early shoaling of the winter mixed layer between 20–30°N, which has been pointed out by previous studies, is also well recognized. A notable feature suggested by our climatology is that the deepest mixed layer tends to occur about one month before the mixed layer density peaks in the middle latitudes, especially in the western region, while they tend to coincide with each other in higher latitudes.     

Warming of intermediate water in the sea of Okhotsk since the 1950s

Okhotsk Sea Intermediate Water (OSIW), the source water for ventilation of North Pacific Intermediate Water, exhibits a multidecadal warming trend. Historical data show that OSIW temperatures increased by 0.28, 0.57, 0.31 and 0.10°C during 1955 to 2003 at potential densities of 26.8, 27.0, 27.2 and 27.4σ _θ , at depths of approximately 250, 500, 700 and 900 m, respectively. This rate of warming is much faster than that of the global ocean. This OSIW warming is likely linked to the reduced ventilation of cold Dense Shelf Water associated with brine rejection during sea ice formation.