Impact of different ocean reanalyses on decadal climate prediction

We study the impact of three ocean state estimates (GECCO, SODA, [ECMWF]-ORA-S3) on decadal predictability in one particular forecast system, the Earth system model from the Max Planck Institute for Meteorology in Hamburg. The forecast procedure follows two steps. First, anomalies of temperature and salinity of the observational estimates are assimilated into our coupled model. Second, the assimilation runs are then used to initialize 10-year-long hindcasts/forecasts starting from each year between 1960 and 2001. The impact of the individual ocean state estimates is evaluated both by the extent to which climate variations from the ocean state estimates are adopted by the forecast system (‘fidelity’) and by the prediction skill of the corresponding hindcast experiments. The evaluation focuses on North Atlantic (NA) sea surface temperature (SST), upper-level (0–700?m) NA ocean heat content (OHC) and the Atlantic meridional overturning circulation (MOC). Regarding fidelity, correlations between observations and the assimilation runs are generally high for NA SST and NA OHC, except for NA OHC in the GECCO assimilation. MOC variations experience strong modifications when GECCO and SODA are assimilated, much less so when assimilating ORA-S3. Regarding prediction skill, when initializing with ORA-S3 and SODA, correlations with observations are high for NA OHC and moderate for NA SST. Correlations in case of GECCO, on the other hand, are high for NA SST and moderate for NA OHC. Relatively high MOC correlations between hindcasts and respective assimilation run appear in the first five years in GECCO in the tropics and subtropics and in ORA-S3 north of 50N. Correlations are largely reduced when the MOC signals are detrended. The trends in the assimilation runs are to some extent artifacts of the assimilation procedure. Hence, our potential predictabilities of the MOC are optimistic estimates of the upper limits of predictability. However, the ORA-S3 reanalysis gives the best results for our forecast system as measured by both overall fidelity of the assimilation procedure and predictions of upper-level OHC in the North Atlantic.     

Quantification of ocean-atmosphere energy exchange during super cyclone Amphan in the Bay of Bengal using Indian Ocean moored observatories

Based on the in-situ subsurface thermal and salinity measurements from the Ocean Moored buoy network for Northern Indian Ocean (OMNI) during the Super Cyclone Amphan in the Bay of Bengal during 14–18 May 2020, we have identified that the ocean-atmosphere interaction is limited to 80 m, the depth of the pycnocline. Using the OAEE-TS algorithm and dynamic changes in the sea subsurface temperature, salinity and precipitation as inputs, we have calculated the water vapor generation rates for a range of wind speeds. Based on the salinity changes, the water vapor generation rates for cyclone period-averaged wind speeds of 9, 16 and 25 m/s were 0.86, 4.33 and 11.24 kg/m²/h, respectively. For the same wind speeds, based on the Ocean Heat Content (OHC) changes, ∼76, 86 and 95 % of the OHC changes were in the form of latent heat. The identified evaporation rate parameters along with the previous study results are presented as model which could be used as inputs for ocean-atmosphere coupled models and tropical cyclone intensification studies in the Bay of Bengal.     

Influences of Freshwater from Major Rivers on Global Ocean Circulation and Temperatures in the MIT Ocean General Circulation Model

Responses of global ocean circulation and temperature to freshwater runoff from major rivers were studied by blocking regional runoff in the global ocean general circulation model(OGCM)developed at the Massachusetts Institute of Technology.Runoff into the tropical Atlantic,the western North Pacific,and the Bay of Bengal and northern Arabian Sea were selectively blocked.The blocking of river runoff first resulted in a salinity increase near the river mouths(2 practical salinity units).The saltier and,therefore,denser water was then transported to higher latitudes in the North Atlantic,North Pacific,and southern Indian Ocean by the mean currents.The subsequent density contrasts between northern and southern hemispheric oceans resulted in changes in major ocean currents.These anomalous ocean currents lead to significant temperature changes(1°C-2°C)by the resulting anomalous heat transports.The current and temperature anomalies created by the blocked river runoff propagated from one ocean basin to others via coastal and equatorial Kelvin waves.This study suggests that river runoff may be playing an important role in oceanic salinity,temperature,and circulations;and that partially or fully blocking major rivers to divert freshwater for societal purposes might significantly change ocean salinity,circulations,temperature,and atmospheric climate.Further studies are necessary to assess the role of river runoff in the coupled atmosphere-ocean system.     

“拉尼娜”非典型影响下的新疆2021/2022年冬季气温

2021/2022年冬季新疆大部气温偏高，影响新疆冷空气活动频次少，并非拉尼娜事件对新疆冬季气温的典型影响特征。成因分析表明：2021/2022年冬季北极涛动（AO）为正位相，欧亚中高纬度500 h Pa位势高度西高东低，新疆上空700 hPa南风距平优势明显。2021/2022年冬季“拉尼娜”非典型影响新疆气温的原因主要来自于东部型弱拉尼娜事件对北大西洋涛动（NAO）和亚洲极涡面积的非典型影响，而对亚洲极涡面积的非典型影响是来自东部型拉尼娜事件对冬季AO的不确定性影响，冬季AO正位相有利于新疆气温正距平。2月300 hPa区域纬向风异常偏弱，削弱了NAO正位相对新疆气温的影响；70°E以东中纬度高度场负距平是冬季气温阶段性变化的原因之一。     

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during 1963–2003. The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1,500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland–Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre intensification precedes that of the MOC by several years.     

CAS-ESM2.0 Model Datasets for the CMIP6 Flux-Anomaly-Forced Model Intercomparison Project(FAFMIP)

The second version of the Chinese Academy of Sciences Earth System Model(CAS-ESM2.0)is participating in the Flux-Anomaly-Forced Model Intercomparison Project(FAFMIP)experiments in phase 6 of the Coupled Model Intercomparison Project(CMIP6).The purpose of FAFMIP is to understand and reduce the uncertainty of ocean climate changes in response to increased CO2 forcing in atmosphere-ocean general circulation models(AOGCMs),including the simulations of ocean heat content(OHC)change,ocean circulation change,and sea level rise due to thermal expansion.FAFMIP experiments(including faf-heat,faf-stress,faf-water,faf-all,faf-passiveheat,faf-heat-NA50pct and faf-heat-NA0pct)have been conducted.All of the experiments were integrated over a 70-year period and the corresponding data have been uploaded to the Earth System Grid Federation data server for CMIP6 users to download.This paper describes the experimental design and model datasets and evaluates the preliminary results of CAS-ESM2.0 simulations of ocean climate changes in the FAFMIP experiments.The simulations of the changes in global ocean temperature,Atlantic Meridional Overturning Circulation(AMOC),OHC,and dynamic sea level(DSL),are all reasonably reproduced.     

Sensitivity of modern climate to the presence,strength and salinity of Mediterranean-Atlantic exchange in a global general circulation model

Mediterranean Outflow Water (MOW) is thought to be a key contributor to the strength and stability of Atlantic Meridional Overturning Circulation (AMOC), but the future of Mediterranean-Atlantic water exchange is uncertain. It is chiefly dependent on the difference between Mediterranean and Atlantic temperature and salinity characteristics, and as a semi-enclosed basin, the Mediterranean is particularly vulnerable to future changes in climate and water usage. Certainly, there is strong geologic evidence that the Mediterranean underwent dramatic salinity and sea-level fluctuations in the past. Here, we use a fully coupled atmosphere–ocean General Circulation Model to examine the impact of changes in Mediterranean-Atlantic exchange on global ocean circulation and climate. Our results suggest that MOW strengthens and possibly stabilises the AMOC not through any contribution towards NADW formation, but by delivering relatively warm, saline water to southbound Atlantic currents below 800 m. However, we find almost no climate signal associated with changes in Mediterranean-Atlantic flow strength. Mediterranean salinity, on the other hand, controls MOW buoyancy in the Atlantic and therefore affects its interaction with the shallow-intermediate circulation patterns that govern surface climate. Changing Mediterranean salinity by a factor of two reorganises shallow North Atlantic circulation, resulting in regional climate anomalies in the North Atlantic, Labrador and Greenland-Iceland-Norwegian Seas of ±4 °C or more. Although such major variations in salinity are believed to have occurred in the past, they are unlikely to occur in the near future. However, our work does suggest that changes in the Mediterranean’s hydrological balance can impact global-scale climate.     

A model study of the Little Ice Age and beyond: changes in ocean heat content,hydrography and circulation since 1500

The Earth System Climate Model from the University of Victoria is used to investigate changes in ocean properties such as heat content, temperature, salinity, density and circulation during 1500 to 2000, the time period which includes the Little Ice Age (LIA) (1500–1850) and the industrial era (1850–2000). We force the model with two different wind-stress fields which take into account the North Atlantic Oscillation. Furthermore, temporally varying radiative forcings due to volcanic activity, insolation changes and greenhouse gas changes are also implemented. We find that changes in the upper ocean (0–300 m) heat content are mainly driven by changes in radiative forcing, except in the polar regions where the varying wind-stress induces changes in ocean heat content. In the full ocean (0–3,000 m) the wind-driven effects tend to reduce, prior to 1700, the downward trend in the ocean heat content caused by the radiative forcing. Afterwards no dynamical effect is visible. The colder ocean temperatures in the top 600 m during the LIA are caused by changes in radiative forcing, while the cooling at the bottom is wind-driven. The changes in salinity are small except in the Arctic Ocean. The reduced salinity content in the subsurface Arctic Ocean during the LIA is a result from reduced wind-driven inflow of saline water from the North Atlantic. At the surface of the Arctic Ocean the changes in salinity are caused by changes in sea–ice thickness. The changes in density are a composite picture of the temperature and salinity changes. Furthermore, changes in the meridional overturning circulation (MOC) are caused mainly by a varying wind-stress forcing; the additional buoyancy driven changes due to the radiative forcings are small. The simulated MOC is reduced during the LIA as compared to the industrial era. On the other hand, the ventilation rate in the Southern Ocean is increased during the LIA.     

CAS-ESM2.0 Model Datasets for the CMIP6 Ocean Model Intercomparison Project Phase 1(OMIP1)

As a member of the Chinese modeling groups,the coupled ocean-ice component of the Chinese Academy of Sciences’Earth System Model,version 2.0(CAS-ESM2.0),is taking part in the Ocean Model Intercomparison Project Phase 1(OMIP1)experiment of phase 6 of the Coupled Model Intercomparison Project(CMIP6).The simulation was conducted,and monthly outputs have been published on the ESGF(Earth System Grid Federation)data server.In this paper,the experimental dataset is introduced,and the preliminary performances of the ocean model in simulating the global ocean temperature,salinity,sea surface temperature,sea surface salinity,sea surface height,sea ice,and Atlantic Meridional Overturning Circulation(AMOC)are evaluated.The results show that the model is at quasi-equilibrium during the integration of 372 years,and performances of the model are reasonable compared with observations.This dataset is ready to be downloaded and used by the community in related research,e.g.,multi-ocean-sea-ice model performance evaluation and interannual variation in oceans driven by prescribed atmospheric forcing.     

Interpreting observed northern hemisphere snow trends with large ensembles of climate simulations

Simulated variability and trends in Northern Hemisphere seasonal snow cover are analyzed in large ensembles of climate integrations of the National Center for Atmospheric Research’s Community Earth System Model. Two 40-member ensembles driven by historical radiative forcings are generated, one coupled to a dynamical ocean and the other driven by observed sea surface temperatures (SSTs) over the period 1981–2010. The simulations reproduce many aspects of the observed climatology and variability of snow cover extent as characterized by the NOAA snow chart climate data record. Major features of the simulated snow water equivalent (SWE) also agree with observations (GlobSnow Northern Hemisphere SWE data record), although with a lesser degree of fidelity. Ensemble spread in the climate response quantifies the impact of natural climate variability in the presence and absence of coupling to the ocean. Both coupled and uncoupled ensembles indicate an overall decrease in springtime snow cover that is consistent with observations, although springtime trends in most climate realizations are weaker than observed. In the coupled ensemble, a tendency towards excessive warming in wintertime leads to a strong wintertime snow cover loss that is not found in observations. The wintertime warming bias and snow cover reduction trends are reduced in the uncoupled ensemble with observed SSTs. Natural climate variability generates widely different regional patterns of snow trends across realizations; these patterns are related in an intuitive way to temperature, precipitation and circulation trends in individual realizations. In particular, regional snow loss over North America in individual realizations is strongly influenced by North Pacific SST trends (manifested as Pacific Decadal Oscillation variability) and by sea level pressure trends in the North Pacific/North Atlantic sectors.     

NUIST ESM v3 Data Submission to CMIP6

This paper introduces the experimental designs and outputs of the Diagnostic,Evaluation and Characterization of Klima(DECK),historical,Scenario Model Intercomparison Project(MIP),and Paleoclimate MIP(PMIP)experiments from the Nanjing University of Information Science and Technology Earth System Model version 3(NESM3).Results show that NESM3 reasonably simulates the modern climate and the major internal modes of climate variability.In the Scenario MIP experiment,changes in the projected surface air temperature(SAT)show robust“Northern Hemisphere(NH)warmer than Southern Hemisphere(SH)”and“land warmer than ocean”patterns,as well as an El Ni?o-like warming over the tropical Pacific.Changes in the projected precipitation exhibit“NH wetter than SH”and“eastern hemisphere gets wetter and western hemisphere gets drier”patterns over the tropics.These precipitation patterns are driven by circulation changes owing to the inhomogeneous warming patterns.Two PMIP experiments show enlarged seasonal cycles of SAT and precipitation over the NH due to the seasonal redistribution of solar radiation.Changes in the climatological mean SAT,precipitation,and ENSO amplitudes are consistent with the results from PMIP4 models.The NESM3 outputs are available on the Earth System Grid Federation nodes for data users.     

2022年汛期气候趋势预测与展望

中国是自然灾害频发的国家,气象灾害造成的损失占自然灾害造成损失的70%。2020年夏季出现超长梅雨期,长江和淮河发生洪水;2021年夏季,华北雨季开始早,结束晚,期间发生了“21·7”河南地区特大暴雨事件。这些气象灾害都对人民生命财产造成严重损失。因此,有必要提前对气候异常进行预测,以提高国家的防灾减灾能力。2022年3月,中国科学院大气物理研究所开展汛期（6～8月）的全国汛期气候趋势预测会商会。通过综合大气所各个数值模式和统计模型的结果,在未来4～6个月全球短期气候仍处在La Ni?a事件恢复到ENSO正常状态的背景下,预计2022年汛期（6～8月）,东北东部和中部、华北大部分地区、黄河中下游、东南沿海、西北地区中部、西藏大部分地区、西南地区东部和云南大部分地区降水正常略偏多,其中环渤海湾地区降水偏多2～5成,可能发生局地洪涝灾害。全国其他大部分地区降水正常略偏少,其中长江下游地区和新疆北部降水偏少2～5成。预计今年登陆台风数正常略偏多。由于未来ENSO的趋势演变具有一定的不确定性以及夏季降水受到中高纬大气环流季节内变化的影响,因此,此次汛期预测结果具有一定的不确定性。我们将根据2022年春末、夏初大气环流和海洋等因子的实际演变趋势,做进一步补充订正预测。     

Earth Summit Mission 2022: Scientific Expedition and Research on Mt. Qomolangma Helps Reveal the Synergy between Westerly Winds and Monsoon and the Resulting Climatic and Environmental Effects

“Earth summit mission 2022” is one of the landmark scientific research activities of the Second Tibetan Plateau Scientific Expedition and Research(STEP). This scientific expedition firstly used advanced technology and methods to detect vertical meteorological elements and produce forecasts for mountain climbing. The “Earth summit mission 2022”Qomolangma scientific expedition exceeded an altitude of over 8000 meters for the first time and carried out a comprehensive scientific investigation missi...     

Ocean Response to a Climate Change Heat-Flux Perturbation in an Ocean Model and Its Corresponding Coupled Model

State-of-the-art coupled general circulation models(CGCMs)are used to predict ocean heat uptake(OHU)and sealevel change under global warming.However,the projections of different models vary,resulting in high uncertainty.Much of the inter-model spread is driven by responses to surface heat perturbations.This study mainly focuses on the response of the ocean to a surface heat flux perturbation F,as prescribed by the Flux-Anomaly-Forced Model Intercomparison Project(FAFMIP).The results of ocean model were compared with those of a CGCM with the same ocean component.On the global scale,the changes in global mean temperature,ocean heat content(OHC),and steric sea level(SSL)simulated in the OGCM are generally consistent with CGCM simulations.Differences in changes in ocean temperature,OHC,and SSL between the two models primarily occur in the Arctic and Atlantic Oceans(AA)and the Southern Ocean(SO)basins.In addition to the differences in surface heat flux anomalies between the two models,differences in heat exchange between basins also play an important role in the inconsistencies in ocean climate changes in the AA and SO basins.These discrepancies are largely due to both the larger initial value and the greater weakening change of the Atlantic meridional overturning circulation(AMOC)in CGCM.The greater weakening of the AMOC in the CGCM is associated with the atmosphere–ocean feedback and the lack of a restoring salinity boundary condition.Furthermore,differences in surface salinity boundary conditions between the two models contribute to discrepancies in SSL changes.     

Performances of seven datasets in presenting the upper ocean heat content in the South China Sea

In this study, the upper ocean heat content (OHC) variations in the South China Sea (SCS) during 1993- 2006 were investigated by examining ocean temperatures in seven datasets, including World Ocean Atlas 2009 (WOA09) (climatology), Ishii datasets, Ocean General Circulation Model for the Earth Simulator (OFES), Simple Ocean Data Assimilation system (SODA), Global Ocean Data Assimilation System (GODAS), China Oceanic ReAnalysis system (CORA), and an ocean reanalysis dataset for the joining area of Asia and Indian-Pacific Ocean (AIPO1.0). Among these datasets, two were independent of any numerical model, four relied on data assimilation, and one was generated without any data assimilation. The annual cycles revealed by the seven datasets were similar, but the interannual variations were different. Vertical structures of temperatures along the 18°N, 12.75°N, and 120°E sections were compared with data collected during open cruises in 1998 and 2005-08. The results indicated that Ishii, OFES, CORA, and AIPO1.0 were more consistent with the observations. Through systematic comparisons, we found that each dataset had its own shortcomings and advantages in presenting the upper OHC in the SCS.     

2021年秋季海洋天气评述

2021年秋季(9—11月)北半球大气环流特征为:极涡整体呈单极型,中高纬环流呈5波型分布,欧亚地区西风带环流形势季节内调整大,副热带高压(以下简称“副高”)偏强,西伸明显。秋季我国近海大风过程主要由冷空气、温带气旋和热带气旋影响造成。在12次8级以上大风过程中,冷空气影响8次,温带气旋影响6次,台风影响4次。西北太平洋和南海共生成9个台风,其中5个台风进入我国近海,在东西带状分布的副高影响下,近海台风主要活跃于南部海域;全球其他海域共命名热带气旋18个。我国出现2 m以上大浪过程的日数为74 d,约占总日数的81%,大浪过程与大风过程联系密切。秋季我国近海海面温度整体偏高,随着冷空气的逐渐活跃,北部海区和沿岸海域海面降温迅速,沿岸海面温度梯度加大,我国近海海域中,海面温度梯度最大的区域出现在东海。     

North Atlantic sea surface temperatures and their relation to the North Atlantic Oscillation during the last 230?years

August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated with 2?year average resolution from a 230-year-long sediment core (Rapid 21-12B), from the Reykjanes Ridge in the subpolar North Atlantic. The results indicate a warming trend of ~0.5°C of the surface waters at the Reykjanes Ridge for the last 230?years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1°C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860?C1880 represents the warmest period during the last 230?years. The last 25?years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. The aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. The aSST record shows a negative correlation with the aNAO indicating cold aSST during the positive aNAO trend and vice versa. Results suggest that the wind driven variation in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed relationship.     

Solar activity and spatial variations of the middle troposphere at the middle and high latitudes of the Northern Hemisphere in winter

Long-term trends are observed in the spatial variability of atmospheric circulation in the 18th–23rd solar cycles in the middle troposphere at the middle and high latitudes of the Northern Hemisphere. The intensification of solar activity in the cycle chronologically coincides with the formation of the extensive anomalies of geopotential at the level of 500 hPa over the northern parts of the Atlantic and Pacific oceans. Upper-level troughs gradually move from middle to high latitudes and, having reached the Arctic Ocean, start moving back to the south. The certain synchronization in the manifestation of natural processes on the Sun and Earth enables considering the features of the spatial distribution of natural anomalies for several solar cycles as a kind of the “marker” of natural long-term fluctuations.     

Formation and pathways of North Atlantic Deep Water in a coupled ice–ocean model of the Arctic–North Atlantic Oceans

We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation. Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models, owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water) leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar convection is found in other models, we discuss broader implications.