The Arctic Sea Ice Thickness Change in CMIP6’s Historical Simulations

This study assesses sea ice thickness(SIT)from the historical run of the Coupled Model Inter-comparison Project Phase 6(CMIP6).The SIT reanalysis from the Pan-Arctic Ice Ocean Modeling and Assimilation System(PIOMAS)product is chosen as the validation reference data.Results show that most models can adequately reproduce the climatological mean,seasonal cycle,and long-term trend of Arctic Ocean SIT during 1979-2014,but significant inter-model spread exists.Differences in simulated SIT patterns among the CMIP6 models may be related to model resolution and sea ice model components.By comparing the climatological mean and trend for SIT among all models,the Arctic SIT change in different seas during 1979-2014 is evaluated.Under the scenario of historical radiative forcing,the Arctic SIT will probably exponentially decay at-18%(10 yr)-1 and plausibly reach its minimum(equilibrium)of 0.47 m since the 2070s.

NUMERICAL SIMULATION OF SSTA IMPACTS UPON THE INTERDECADAL VARIATION OF THE CROSS-EQUATORIAL FLOWS IN EASTERN HEMISPHERE

Impacts of regional sea surface temperature(SST)anomalies on the interdecadal variation of the cross-equatorial flows(CEFs)in Eastern Hemisphere are studied using numerical simulations with a global atmospheric circulation model(NCAR CAM3)driven with 1950-2000 monthly SSTs in different marine areas(the globe,extratropics,tropics,tropical Indian Ocean-Pacific,and tropical Pacific)and ERA-40reanalysis data.Results show that all simulations,except the one driven with extratropical SSTs,can simulate the interdecadal strengthening of CEFs around Somali,120oE,and 150oE that occurred in the midand late-1970s.Among those simulated CEFs,the interdecadal variability in Somali and its interdecadal relationship with the East Asian summer monsoon are in better agreement with the observations,suggesting that changes in the SSTs of tropical oceans,especially the tropical Pacific,play a crucial role in the interdecadal variability of CEFs in Somali.The interdecadal change of CEFs in Somali is highly associated with the interdecadal variation of tropical Pacific SST.As the interdecadal warmer(colder)SST happens in the tropical Pacific,a"sandwich"pattern of SST anomalies,i.e."+,-,+"("-,+,-"),will occur in the eastern tropical Pacific from north to south with a pair of anomalous anticyclone(cyclone)at the lower troposphere;the pair links to another pair of anomalous cyclone(anticyclone)in the tropical Indian Ocean through an atmospheric bridge,and thus strengthens(weakens)the CEFs in Somali.

NUMERICAL SIMULATION OF SOUTH CHINA SEA MONSOON ONSET BASED ON GRAPES MODEL AND EXPERIMENTS ON INITIAL MODEL FIELDS

The Global and Regional Assimilation and Prediction System (GRAPES), a limited-area regional model, was used to simulate the onset of South China Sea summer monsoon. In view of the relatively insufficient information about the initial field in simulation predictions, the Advanced Microwave Sounding Unit-B (AMSU-B) data from a NOAA satellite were introduced to improve the initial values. By directly using the 3-dimensional variational data assimilation system of GRAPES, two schemes for assimilation tests were designed. In the design, Test 1 (T1) assimilates both sounding and AMSU-B data, and Test 2 (T2) assimilates only the conventional sounding data, before applying the model in simulation forecasts. Comparative experiments showed that the model was very sensitive to initial fields and successful in reproducing the monsoon onset, allocation of high- and low-level wind fields during the pentad of onset, and the northward advancement of the monsoon and monsoon rain bands. The scheme, however, simulated rainfall and the location of the subtropical high with deviations from observations. The simulated location of the subtropical high was more westward and northward and the simulated rainfall for the South China Sea was larger and covered a broader area.

Fine-resolution simulation of surface current and sea ice in the Arctic Mediterranean Seas

A free-resolution model is developed for ocean circulation simulation in the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Chinese Academy of Sciences, and is applied to simulate surface current and sea ice variations in the Arctic Mediterranean Seas. A dynamic sea ice model in elastic-viscous-plastic rheology and a thermodynamic sea ice model are employed. A 200-year simulation is performed and a dimatological average of a 10-year period （14lst-150th） is presented with focus on sea ice concentration and surface current variations in the Arctic Mediterranean Seas. The model is able to simulate well the East Greenland Current, Beaufort Gyre and the Transpolar Drift, but the simulated West Spitsbergen Current is small and weak. In the March climatology, the sea ice coverage can be simulated well except for a bit more ice in east of Spitsbergen Island. The result is also good for the September scenario except for less ice concentration east of Greenland and greater ice concentration near the ice margin. The extra ice east of Spitsbergen Island is caused by sea ice current convergence forced by atmospheric wind stress.

Effect of sea surface wind on the seasonal variation of sea level in the east of China seas

Sea level seasonal variations in the east of China seas from 2004 to 2006 are simulated by the advanced ROMS model. The results show similar sea level spatial features with TOPEX/Poseidon observations, with annual ranges decreasing gradually from the sea coast to the Kuroshio region. By getting rid of wind stress in ROMS model, the simulated sea level results still show obvious seasonal variations. However, the phenomenon of sea level anomaly disappears in Min Zhe Current Coastwise （MZCF） and Su Bei current coastwise （SBCF）, and the change of it from coastal area to ocean recedes. The seal level difference between Bohai, Yellow Sea （BYS） and East China Sea （ECS） becomes weaker in spring and autumn. The annual differences decrease obviously, and the gradual change of annual ranges from seacoast to the Kuroshio almost disappears. The annual ranges in BYS are nearly identical. The annual range ratio without the wind stress to with the wind stress increases gradually from the sea coast to Kuroshio region.

Relation of ice conditions to climate change in the Bohai Sea of China

The ice conditions in the Bohai Sea and the northern Huanghai Sea greatly change from year to year with winter climate. Ice only covers below 15% of the the waters during the wannest win-ter, while it covers more than 80% during the coldest winter. Ice observation and data acquisition are outlined in the paper. The ice-covered area, the position of ice edge and the ice grades give indication of the ice conditions. The local climate of the waters can be expressed by using the air temperature of the stations of Dalian and Yingkou. The variation of the ice condition indexes with the monthly mean air temperature at Dalian from 1952 to 2000 is shown, as well. The local climate and ice conditions in the waters are affected by many factors,such as, evolution of the general atmospheric circulation and the solar activity. The delayed correlation between the ice conditions and lots of the affecting factors is analysed in the paper. The ice conditions are continuously mild since the 1990s, that is relative to the tendency of the global warming. The ice condition variation of the Bohai Sea is related to the El Nino event and the sunspot period. The seasonal evolution of the ice conditions is also described in the paper.

A modified discrete element model for sea ice dynamics

Considering the discontinuous characteristics of sea ice on various scales,a modified discrete element model（DEM） for sea ice dynamics is developed based on the granular material rheology.In this modified DEM,a soft sea ice particle element is introduced as a self-adjustive particle size function.Each ice particle can be treated as an assembly of ice floes,with its concentration and thickness changing to variable sizes under the conservation of mass.In this model,the contact forces among ice particles are calculated using a viscous-elastic-plastic model,while the maximum shear forces are described with the Mohr-Coulomb friction law.With this modified DEM,the ice flow dynamics is simulated under the drags of wind and current in a channel of various widths.The thicknesses,concentrations and velocities of ice particles are obtained,and then reasonable dynamic process is analyzed.The sea ice dynamic process is also simulated in a vortex wind field.Taking the influence of thermodynamics into account,this modified DEM will be improved in the future work.

Interaction between sea ice/iceberg and ship structures: A review

For ship structural design and good maneuverability in an ice-covered sea, the local and global load of ice cover on ships should be well understood. This paper reviews the extensive work done on ice loads on ships, including： （a） Ice pressure and local load determination based on field and model tests; （b） Global ice loads on ships from full-scale field observations, model tests and numerical models under different ice conditions （level ice and pack ice） and ship operations （maneuvering and mooring）. Spe- cial attention is paid to the discrete element simulation of global ice loads on ships; and （c） Analytical solutions and numerical models of impact loads of icebergs on ships for polar navigation. Finally, research potential in these areas is discussed.

Numerical simulation of the impact of underlying surface changes on Arctic climate

Using a regional atmospheric model for Arctic climate simulation, two groups of numerical experiments were carried out to study the influence of changes in the underlying surface （land surface, sea surface, and sea ice （LS/SS/SI）） from mild ice years to severe ice years on Arctic climate. In each experiment in the same group, the initial values and lateral boundary conditions were identical. The underlying surface conditions were updated every six hours. The model was integrated for 10 a and monthly mean results were saved for analysis. Variations in annual mean surface air temperature were closely correlated with changes in LS/SS/SI, with a maximum change of more than 15 K. The impact of changes in LS/SS/SI on low-level air temperature was also evident, with significant changes seen over the ocean. However, the maximum change was less than 2 K. For air temperature above 700 hPa, the impact of LS/SS/SI changes was not significant. The distribution of annual mean sea level pressure differences was coincident with the distribution of annual mean sea ice concentration. The difference centers were located in the Barents Sea, the Kara Sea, and the East Siberian Sea, with the maximum value exceeding 3 hPa. For geopotential height, some results passed and some failed a t-test. For results passing the t-test, the area of significance did not decrease with height. There was a significant difference at high levels, with a value of 27 gpm in the difference center at 200 hPa.

Preliminary results on relationship between thermal diffusivity and porosity of sea ice in the Antarctic

The in situ sea-ice temperature, salinity and density observed from Chinese Antarctic Zhongshan Station have been applied to calculate the vertical profile of sea ice porosity. Based on numerical method, a number of schemes on sea - ice thermal diffusivity versus porosity have been accessed and one optimized scheme is identified by an optimal control model with an advanced, distributing parameter system. For simplicity, the internal heating source item was neglected in the heat conduction equation during the identification procedure. In order to illustrate the applicability of this identified scheme, the vertical ice temperature profiles have been simulated and compared with measurements, respectively by using identified scheme and by classical thermodynamic formulae. The comparisons indicated that the scheme describing sea - ice thermal diffusivity and porosity is reasonable. In spite of a minor improvement of accuracy of results against in situ data, the identified scheme has a more physical meaning and could be used potentially in various applications.

Modified PIC Method for Sea Ice Dynamics

The sea ice cover displays various dynamical characteristics such as breakup, rafting, and ridging under external forces. To model the ice dynamic process accurately, the effective numerical modeling method should be established. In this paper, a modified particle-in-cell （PIC） method for sea ice dynamics is developed coupling the finite difference （FD） method and smoothed particle hydrodynamics （SPH）. In this method, the ice cover is first discretized into a series of lagrangian ice particles which have their own sizes, thicknesses, concentrations and velocities. The ice thickness and concentration at Eulerian grid positions are obtained by interpolation with the Gaussian function from their surrounding ice particles. The momentum of ice cover is solved with FD approach to obtain the Eulerian cell velocity, which is used to estimate the ice particle velocity with the Gaussian function also. The thickness and concentration of ice particles are adjnsted with particle mass density and smooth length, which are adjusted with the redistribution of ice particles. With the above modified PIC method, numerical simulations for ice motion in an idealized rectangular basin and the ice dynamics in the Bohai Sea are carried out. These simulations show that this modified PIC method is applicable to sea ice dynamics simulation.

Estimating sea ice albedo feedback in a regional climate modeling sensitivity experiment

Surface albedo feedback （SAF）, or sea ice albedo feedback over the Arctic Ocean, has an important effect on the Arctic climate, even though it is not the leading contributor to polar amplification. Previous model-based studies on SAF have primarily used global climate models to exploit their global coverage and favorable configurations. This study verified the capability of using regional climate models （RCMs） to investigate SAF by designing a sensitivity experinaent in terms of sea ice coverage. This study modeled two control cases of the years 1980 and 2012, as well as two sensitivity cases performed by switching the sea ice coverages in the control cases. The results proved the Weather Research and Forecast model capable of separating and quantifying the respective contributions of the atmosphere and the surface albedo to the surface radiation budget. Supported by the ALL/CLR model, the balanced surface shortwave radiation absorption was used to calculate SAF. The experiments overestimated SAF, largely because of the canceled cloud effect during model initialization. This study highlights a new possibility of designing experiments for studying climatic sensitivity and feedback using RCMs.

SIMULATION ON CLIMATIC VARIATION OF ARCTIC SEA ICE THROUGH AN ICE-OCEAN COUPLED MODEL

An ocean model developed by the Institute of Marine Research and the University of Bergen in Norway (BOM) and a state-of-the-art sea ice model developed by NCAR (CSIM4) are coupled, Considering influences of 9 major rivers,forced by the NCEP reanalysis atmospheric fields and the Levitus surface salinity,the Arctic sea ice climatic variation from January 1949 to December.1999 was simulated through the coupled model.The comparison of simulated results and observations shows that:(1)the long-term ice concentration variation tendencies are in consistent with the observations in the divisional ocean regions;(2)simulated ice thickness horizontal distribution is reasonable.Simulated ice thickness has a decreasing tendency in the central Arctic,which agrees with the submarine observations.Simulated annually maximum ice thickness is highly related to observed fast-ice thickness off the Russian coast;and (3)sea ice area/volume fluxes through the Fram Strait are in accord with the satellite-derived data.Generally,the coupled model successfully simulated the Arctic Ocean sea ice climatic variation.

基于地层‑注浆体‑管片协同作用的海底盾构隧道受力研究

为研究海底盾构隧道中浆液与围岩及管片的相互作用特性,以厦门地铁2号线海底盾构段为工程背景,采用数值模拟方法和现场实测方法,分析注浆的浆液凝固过程,重点研究浆液的抗压强度、刚度、收缩、蠕变等特性对隧道力学和变形的影响特征,以及不同地层分布、不同隧道埋深下的管片受力特征,并采用流固耦合研究海水位变化对管片受力的影响。计算研究表明:注浆材料的刚度比E1/E28对管片最终轴力和围岩压力影响小,变化幅度不超过0.885%,对地层变形影响相对较大,可通过添加剂调节凝结时间,尽量让浆液早一些凝固硬化;最终收缩应变增大,隧道内力和外侧压力降低,地层沉降增大,建议采用泌水率低的浆液,且其收缩值需控制在较小的范围内;蠕变参数取值对管片轴力影响较小,变化幅度最大不超过1.35%;收缩参数主要考虑注浆材料后期的凝固收缩,蠕变则主要考虑注浆材料前期的蠕变收缩;地层变化及隧道埋深变化对隧道管片受力影响显著,隧道拱顶若软土较厚,则不易形成有效压力拱,导致围岩压力荷载较大;半日潮对地层变形、管片受力的影响不大,总体发展趋势与静水位条件下相似。最后,监测结果表明,数值模拟与实测的管片水土压力时程变化规律基本一致。

EXPERIMENTS OF SEA ICE SIMULATION

As a substitute for the original displaced pole grids, a simple rotated spherical coordinate system was intro duced into the Community Sea Ice Model version 4（CSIM4）, which is a component of the Community Climate System Model（CCSM） of the American National Center of Atmospheric Researeh（NCAR）, to deal with the ＂pole problems＂. In the new coordinates, both the geographical North Pole and South Pole lie in the model equator and grid sizes near the polar region are more uniform. With reanalysis dataset of American National Centers for Environment Prediction （NCEP） and Levitus dataset without considering sub-mixed layer heat flux, the model was integrated for 100 years with thermodynamics proce.ss involved only in the former 49 years and both dynamic and thermodynamic processes involved in the left time. Inner consistency of model results was checked with no contradiction found. The results of last 10 years＇ model output were analyzed and it is shown that the simulated sea ice seasonal variation is rational whereas sea ice extent in the Barcnts Sea in winter is larger than that of observation, Numerical experiment on influence of sub-mixed layer heat flux was also carried out and it is shown that the sub-mixed layer heat flux can modulate seasonal variation of sea ice greatly. As a model component, the sea ice model with rotated spherical coordinates was coupled with other models （the oceanic general cir culation model is the LASG/IAP Climate System Ocean Model （LICOM） with reduced grid, other models are components of NCAR CCSM2） forming a climate system model and its preliminary results were also given briefly.

THE NUMERICAL SIMULATION OF THE ICE AGE CLIMATE

Using the lAP two-level general circulation model,the ice age July climate was simulated through the surface con- ditions of 18 000 years before present assembled by the CLIMAP Project.Comparing with the present July simulation results,the ice age atmosphere is found to have a substantially lower temperature,precipitation,and cloudiness,higher sea-level pressure,especially in the high latitude land region of the Northern Hemisphere and Antarctica.When the CO2 content is set as the modern value the climatic response is very small,which shows that the problems of CO2 sen- sitivity should be studied by means of coupled models.It is also pointed out that there are some common characteristics between CO2-induced climatic changes and the ice age surface condition-induced climatic changes,which may give us some insight into how climate responds to external forcings.

南海北部海面高度季节变化的机制

利用POM模式对南海环流进行了数值模拟和数值试验 ,结果表明 :南海北部SSH的变化主要应归于南海局地的动力、热力强迫和黑潮的影响 ;黑潮对南海北部SSH平均态的影响要大于对SSH异常场的影响 ;对于南海北部深水区冬季局地风应力与浮力通量的作用相反量级相同 ,黑潮对南海北部SSH的控制作用在冬季显得最重要 ,约占 50 %～ 80 % ;春季 ,夏季和秋季 ,局地风应力、浮力通量和黑潮三者都使深水区SSH上升 ,局地风应力使深水海盆SSH上升的作用约占 4 0 %～ 6 0 % ,浮力通量的作用约占 2 0 % ,黑潮的影响约占 2 0 %～ 30 % .在夏季 ,尽管南海北部深水海盆SSH达到全年最高 ,但黑潮对南海北部深水海盆SSH的贡献最小 .在广东沿岸陆架海域 ,SSH季节变化的机制与深水海盆SSH季节变化的机制不同 :春、夏季 ,局地风应力使SSH上升的作用几乎与浮力通量使SSH下降的作用相当 ;秋、冬季 ,东北季风使SSH上升的作用大于浮力通量和黑潮使SSH下降的作用 ,陆架区SSH为正 。

一个海冰气耦合模式中格陵兰海海冰年际变异及其成因的个例分析

利用一个全球海冰气耦合模式模拟结果,选取冬季年际变率最大的海冰区———格陵兰海海冰区中的一个4年海冰剧烈变化过程展开分析,试图探讨此个例过程中海冰剧烈变化的原因。结果表明,在此个例中,该区域海冰年际变异主要是由大气环流异常驱动的,海表面温度和海冰密集度变化主要是对大气环流变化的响应。海表面温度变化决定着海冰范围及海冰密集度的变化,但海冰变化时通过相变潜热的释放或吸收反过来对海表面温度变化有一定影响。

不同海域海表温度异常对西北太平洋副热带高压年代际变化影响的数值模拟研究

采用1950～2000年逐月观测的不同海域(全球、热带外、热带、热带印度洋-太平洋、热带印度洋及热带太平洋)海表温度分别驱动NCARCAM3全球大气环流模式,进行了多组长时间积分试验,对比观测资料,讨论了这些海域海表温度异常(SSTA)对西北太平洋副热带高压年代际变化的影响。结果表明:全球、热带、热带印度洋-太平洋和热带印度洋海表温度变化均对夏季西北太平洋副热带高压的年代际变化有重要作用,即在这些海域的海表温度变化影响下,西北太平洋副热带高压均在1970年代中后期发生了年代际变化,其后副高面积增大、强度增强、位置偏西、偏南,这与观测结果较一致;热带太平洋海表温度变化对夏季西北太平洋副热带高压的年代际变化也有重要作用,在其作用下,夏季西北太平洋副热带高压的强度、面积在1960年代后期发生年代际变化,南界在1970年代中后期发生年代际变化,这些时段以后副高强度增强、面积增大、偏南;热带印度洋海表温度驱动模拟的西北太平洋副热带高压变化比热带太平洋海表温度驱动模拟的副高更接近于观测结果,且年代际变化更显著,其差异的可能原因在于两区海表温度在1970年代中后期以后的年代际变化能在孟加拉湾-中国东南沿海区域强迫产生的异常环流不同,前者强迫产生出反气旋性环流异常,有利于副高的增强、面积增大和西伸,而后者强迫产生出气旋性环流异常,不利于副高的西伸;热带太平洋和热带印度洋海表温度在1970年代中后期的冷、暖年代际背景变化对夏季西北太平洋副热带高压年代际变化有重要作用;热带外海表温度变化对西北太平洋副热带高压年代际变化作用较小。

海表温度异常影响东亚夏季风年代际变化的数值模拟

采用1950—2000年逐月观测的不同海域(全球、热带外、热带、热带印度洋—太平洋、热带印度洋及热带太平洋)海表温度分别驱动NCAR CAM3全球大气环流模式,进行了多组长时间积分试验,对比ERA-40和NCEP/NCAR再分析资料,讨论了这些海域海表温度异常对东亚夏季风年代际变化的影响。数值试验结果表明:全球、热带、热带印度洋—太平洋和热带太平洋海表温度变化对东亚夏季风的年代际变化具有重要作用,均模拟出了东亚夏季风在20世纪70年代中后期发生的年代际减弱现象,以及强、弱夏季风年代夏季大气环流异常分布的显著不同,这与观测结果较一致,表明热带太平洋是影响东亚夏季风此次年代际变化的关键海区;利用热带印度洋海表温度驱动模式模拟出的东亚夏季风在20世纪70年代中后期发生年代际增强现象,即当热带印度洋海表温度年代际偏暖(冷)时,东亚夏季风年代际增强(减弱),与热带太平洋海表温度变化对东亚夏季风年代际变化的影响相反;热带太平洋海表温度年代际背景的变化对东亚夏季风在20世纪70年代中后期的年代际减弱有重要作用。