1—3月北极涛动对北半球热带太平洋和大西洋对流活动的可能影响

利用1979—2008年日分辨率的向外长波辐射资料以及NCEP再分析资料,去除ENSO影响后,分析了1—3月北极涛动对热带太平洋和热带大西洋对流活动及降水的可能影响。结果表明北极涛动偏强(弱)时,热带太平洋和大西洋对流活动显著偏强(弱)。北半球热带大洋冬季平均向外长波辐射与北极涛动指数的相关系数存在两个显著负相关区:一个位于中太平洋区,大致包括13°—20°N、160°E—170°W;另外一个位于热带大西洋,显著区覆盖的范围大体包括5°—20°N、15°—70°W。这些区域的降水量也表现出显著的正相关。向外长波辐射、强对流面积指数、强对流强度指数、平均降水量等指标与北极涛动指数的相关均以冬季同期最高,随时间滞后相关迅速减弱。与此对应的对流层低层大气环流也有显著变化,850hPa风场的变化表现为热带太平洋有异常的气旋性环流,气旋中心区与显著强对流和降水异常区一致。而热带大西洋有显著的经向环流辐合和风切变,与异常对流和降水区吻合。海洋模式的模拟结果表明,与北极涛动有关联的海温分布,很大程度上与大气强迫有关,说明热带1—3月降水和对流活动与海温的关联较弱。北极涛动与热带太平洋、大西洋对流和降水活动之间主要是通过大气环流的变动产生联系的。     

Fundamental Framework and Experiments of the Third Generation of IAP/LASG World Ocean General Circulation Model

1.IntroductionThefirstbaroclinicoceanicgeneralcirculationmodel(OGCM)developedattheStateKeyLaboratoryofNumericalModelingforAtmosphericSciencesandGeophysicalFluidDynamics(LASG),InstituteofAtmosphericPhysics(IAP)isafour--layermodelwithitshorizontalresol...     

Fundamental framework and experiments of the third generation of IAP / LASG world ocean general circulation model

A new generation of the IAP / LASG world ocean general circulation model is designed and presented based on the previous 20-layer model, with enhanced spatial resolutions and improved parameterizations. The model uses a triangular-truncated spectral horizontal grid system with its zonal wave number of 63 (T63) to match its atmospheric counterpart of a T63 spectral atmosphere general circulation model in a planned coupled ocean-atmosphere system. There are 30 layers in vertical direction, of which 20 layers are located above 1000 m for better depicting the permanent thermocline. As previous ocean models developed in IAP / LASG, a free surface (rather than “rigid-lid” approximation) is included in this model. Compared with the 20-layer model, some more detailed physical parameterizations are considered, including the along / cross isopycnal mixing scheme adapted from the Gent-MacWilliams scheme. The model is spun up from a motionless state. Initial conditions for temperature and salinity are taken from the three-dimensional distributions of Levitus’ annual mean observation. A preliminary analysis of the first 1000-year integration of a control experiment shows some encouraging improvements compared with the twenty-layer model, particularly in the simulations of permanent thermocline, thermohaline circu?lation, meridional heat transport, etc. resulted mainly from using the isopycnal mixing scheme. However, the use of isopycnal mixing scheme does not significantly improve the simulated equatorial thermocline. A series of numerical experiments show that the most important contribution to the improvement of equatori?al thermocline and the associated equatorial under current comes from reducing horizontal viscosity in the equatorial regions. It is found that reducing the horizontal viscosity in the equatorial Atlantic Ocean may slightly weaken the overturning rate of North Atlantic Deep Water.     

A possible feedback mechanism involving the Arctic freshwater, the Arctic sea ice, and the North Atlantic Drift

Model studies point to enhanced warming and to increased freshwater fluxes to high northern latitudes in response to global warming. In order to address possible feedbacks in the ice-ocean system in response to such changes, the combined effect of increased freshwater input to the Arctic Ocean and Arctic warming--the latter manifested as a gradual melting of the Arctic sea ice--is examined using a 3-D isopycnic coordinate ocean general circulation model. A suite of three idealized experiments is carried out: one control integration, one integration with a doubling of the modern Arctic river runoff, and a third more extreme case, where the river runoff is five times the modern value. In the two freshwater cases, the sea ice thickness is reduced by 1.5-2 m in the central Arctic Ocean over a 50-year period. The modelled ocean response is qualitatively the same for both perturbation experiments: freshwater propagates into the Atlantic Ocean and the Nordic Seas, leading to an initial weakening of the North Atlantic Drift.Furthermore, changes in the geostrophic currents in the central Arctic and melting of the Arctic sea ice lead to an intensified Beaufort Gyre, which in turn increases the southward volume transport through the Canadian Archipelago. To compensate for this southward transport of mass, more warm and saline Atlantic water is carried northward with the North Atlantic Drift. It is found that the increased transport of salt into the northern North Atlantic and the Nordic Seas tends to counteract the impact of the increased freshwater originating from the Arctic, leading to a stabilization of the North Atlantic Drift.     

西北太平洋温带气旋爆发性发展的热力-动力学分析

利用天气、位涡分析和导出的Lagrangian型广义Z－O发展方程的诊断分析,考查了两个西北太平洋温带气旋爆发件发展的主要强迫机制和热力一动力空;司结构。结果表明,热力强迫对爆发性气旋发展起主要控制作用,当反映大气斜乐性的Laplacian温度平流、积云对流和湍流加热为主的热力强迫共同作用使地转相对涡度急剧增长时,气旋便出现了爆发性发展,其中积二尺度的对流加热贡献更大。Laplacian绝热冷却、大气向海洋的感热输送和摩擦效应起阻滞发展的作用,也是控制气旋衰亡的主要过程。爆发性发展启动同子因例而异,涡度平流、Laplacian温度平流和Laplacian大尺度加热均可成为主要启动因子。垂直积分平均分布和垂直结构考查进一步佐证了诊断分析的结果,并揭示了气旋爆发性发展过程中一些重要的热力-动力学分布特征。     

Design and Numerical Simulation of an Arctic Ocean Circulation and Thermodynamic Sea－Ice Model

In this paper, the first version of a new Arctic Ocean circulation and thermodynamic sea-ice model is presented by the authors based on the framework of a twenty-layer World Oceanic general circulation model developed by Zhang et al. in 1994, The model’s domain covers the Arctic Ocean and Greenland-Norwegian Seas with the horizon-tal resolution of 200 km × 200 km on a stereographic projection plane. In vertical, the model uses the Eta-coordinate (Sigma modified to have quasi-horizontal coordinate surfaces) and has ten unevenly-spaced layers to cover the deep-est water column of 3000 m. Two 150-year integrations of coupling the ocean circulation model with the sea-ice model have been performed with seasonally cyclic surface boundary conditions. The only difference between the two experiments is in the model’s geography. Some preliminary analyses of the experimental results have been done fo-cused on the following aspects: (1) surface layer temperature, salinity and current; (2) the "Atlantic Layer"; (3) sea-ice cover and its seasonal variation. In comparison with the available observational data, these results are accept-able with reasonable accuracy.     

中尺度涡旋混合参数空间变化对物理场以及CFC-11模拟的影响

本文选用中国科学院大气物理研究所全球海洋模式(LICOM),对中尺度涡旋参数化方案(GM90方案)中等密度扩散系数和等密度面厚度扩散系数(统称为涡旋扩散系数A_ρ)对物理场及CFC-11(一氟三氯甲烷)分布的影响进行了研究。本文做了两个试验,即涡旋扩散系数采用常系数方式(对照试验)和采用在非绝热层以下A_ρ随海洋浮力频率垂直变化的参数化方案(浮力试验)。模拟结果表明,依浮力频率垂直变化的方案对模式物理场的模拟能力有一定程度的提升,如南极绕极流的输送强度比常系数方案增大了约20%~30%,与观测事实更接近;浮力试验对对照试验中过强的南极中层水有一定的削弱作用,使得模式对南大洋高纬次表层位密度的模拟有一定的改善。稍有不足的是,浮力试验对南极底层水也有一定的削弱,使得2000~3000 m深度位密度模拟较常系数方案偏低。通过对CFC-11分布、存储以及输送的研究发现,次网格参数取值的不同对南大洋CFC-11模拟情况有较大影响。浮力试验加大了南北高纬CFC-11海表的吸收通量,对南极大陆周边海域向南大洋主储藏区(34°S~60°S)的CFC-11输送能力有一定的增强,使得南大洋对CFC-11储藏量增大,大部分海区与观测资料更接近。通过CFC-11断面分析,浮力试验对南大洋上层海洋位密度模拟的改善使得CFC-11垂直结构与观测更接近。     

A mechanistic model of isopycnal diffusion in the ocean

A two-dimensional (xz) box ocean model, is formulated to examine the mechanistic role of isopycnal diffusion (i.e. diffusion along a constant density surface) as compared to that of horizontal/vertical diffusion. A large-scale surface temperature anomaly forces a steady solution. The presence of isopycnal diffusion substantially increases the vertical penetration in the steady state: the vertical heat flux is increased by an order of magnitude in some locations. The time scale of the transient response is also modified, and the nature of this response is scale dependent. It is thus not possible in general to reproduce the transient response with isopycnal diffusion by adjusting diffusitives in a lateral diffusion formulation. Implications of the results to climate modelling are considered.     

任意正交曲线坐标系下的海洋模式动力框架的发展与评估

本文发展了一个可以适用于任意水平正交曲线坐标系的海洋模式动力框架,并将其应用于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的气候系统海洋模式LICOM2.0（LASG/IAP Climate system Ocean Model,version2.0）。在经纬网格坐标系下,新的动力框架与LICOM2.0原有的动力框架模拟结果完全一致。基于新的动力框架,海洋模式可采用能够准确描述北冰洋地形的三极网格,克服了LICOM2.0经纬网格版本必须将北极点处理为孤岛的缺陷,从而显著改进了模式对于北冰洋环流和北大西洋经圈翻转流函数（AMOC）的模拟能力。此外,引进三极网格还可以避免模式网格距随纬度增加而急剧减小带来的计算不稳定,在LICOM2.0的三极网格版本中,模式不需要采用任何空间滤波方案仍然能够保证计算的稳定性,从而与LICOM2.0的经纬网格版本相比,极大地提高了模式的并行效率,这一点在当水平分辨率提高到0.1度时表现得尤为明显,海洋模式的并行加速比可以从经纬网格版本的5.8左右提高到三极网格版本的15.0左右。     

A special MJO event with a double Kelvin wave structure

The second Madden–Julian Oscillation (MJO) event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (DYNAMO/CINDY2011) exhibi ted an unusual double rainband structure. Using a wavenumber-frequency spectral filtering method, we unveil that this double rainband structure arises primarily from the Kelvin wave component. The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean, being in the range of convectively coupled Kelvin wave phase speeds. The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells, with low-level westerly (easterly) and high (low) pressure anomalies to the west (east) of the convective centers, and opposite wind and pressure anomalies in the upper troposphere. Such a zonal wind–pressure phase relationship is consistent with the equatorial free-wave dynamics. While the free-atmospheric circulation was dominated by the first baroclinic mode vertical structure, moisture and vertical motion in the boundary layer led the convection.The convection and circulation structures derived based on the conventional MJO filter show a different characteristic. For example, the phase speed is slower (about 5.9 degree per day), and there were no double convective branches. This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique.     

POSSIBLE IMPACTS OF MADDEN-JULIAN OSCILLATION ON THE SEVERE RAIN-SNOW WEATHER IN CHINA DURING NOVEMBER 2009

Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors.MJO is very active over the Indian Ocean in November 2009.Especially,it maintains 9 days in MJO phase 3,just corresponding to the two strongest rain-snow processes.Composites of MJO events show that when the MJO convective center is located over the Indian Ocean,the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China,which is consistent with the situation in November of 2009.Atmospheric circulation anomalies of mid-and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection.When the MJO is over the Indian Ocean,it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid-and higher-latitudes.Meanwhile,the western Pacific subtropical high is stronger and more westward than normal,and a significant convective belt appears over eastern East Asia.All these circulation anomalies shown in the composite result also appeared in the observations in November 2009,which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics.Besides the zonal circulation anomalies,the MJO convection can also lead to meridional circulation anomalies.When the MJO convection is located over the Indian Ocean,the western Pacific is dominated by anomalous descending motion,and the eastern East Asia is controlled by strong convergence and ascending motion.Therefore,an anomalous meridional circulation is formed between the tropics and middle latitudes,enhancing the northward transportation of low-level moisture.It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.     

Modelling of Ocean Shallow Convection under Fast Ice in the Arctic

Ocean convection in the Antarctic has been studied many times and has been revealed to be responsible for ice-cover reduction. In the Arctic, proof of that phenomenon has not been documented. It is believed that this phenomenon happens on a smaller scale in the Arctic when local circulation of deep warmer water melts and slows ice production. An example of this is the North Water (NOW) polynya in northern Baffin Bay. A polynya is an area of open water in an otherwise ice-covered area. As ice forms under the fast ice near the boundary of the polynya, ocean salts (brine) are ejected from the newly formed ice. This water, which has an increased concentration of salt, sinks and is replaced by warmer water from below, and this slows ice formation. In our study a coupled one-dimensional thermodynamic snow–fast ice model incorporating ocean heat flux input via a shallow convection model was used. Ice thickness was calculated using a thermodynamic model that included a current-induced entrainment model and a convection model to account for brine rejection during ice growth. Atmospheric observations from Grise Fiord and Thule and ocean profiles around the NOW polynya near these sites were used as input to the model. This purely thermodynamic study enables us to obtain ice thickness values that can be compared with qualitative observations. This modelling study compares two sites related to the NOW polynya. The results indicate that the shallow convection model simulates the reduction of fast ice near Thule but not near Grise Fiord.     

A Study of the Stable Boundary Layer Based on a Single-Column K-Theory Model

We document numerical experiments with a single-column, high-resolution model of the stable boundary layer. The model resolves the logarithmic layer, and does not require inverting the Monin–Obukhov similarity functions in order to calculate the surface fluxes. The turbulence closure is based on the K-theory approach, with a new form of stability functions of the Richardson number, evaluated by using the Surface Heat Budget of the Arctic Ocean (SHEBA) and the Cooperative Atmosphere-Surface Exchange Study (CASES-99) data. A comparison with two, high-resolution large-eddy simulation models shows very good agreement. The reported numerical experiments test the effects of shear, surface cooling, the Coriolis parameter, subsidence, and baroclinicity. The time evolution of the drag coefficient, the heat-transfer coefficient, and the cross-isobar angle is also evaluated.     

海冰覆盖度变化下北冰洋海浪研究进展

北冰洋地区海浪的生成和发展会受到海冰范围变化的显著影响.本文介绍了近年来基于浮标、潜标和走航观测,以及卫星遥感和数值模拟等方法开展的不同海冰覆盖度下北冰洋海浪的研究进展,包括海冰覆盖区海浪的传播机制等.北冰洋夏季开阔海域的平均有效波高可达3 m,在风暴期间,波弗特海有效波高可达5 m.除大西洋一侧,夏季北冰洋大部分海域...     

Weak vertical diffusion allows maintenance of cold halocline in the central Arctic

In spring preceding the record minimum summer ice cover detailed microstructure measurements were made from drifting pack ice in the Arctic Ocean, 110 km from the North Pole. Profiles of hydrography, shear, and temperature microstructure collected in the upper water column covering the core of the Atlantic Water are analyzed to determine the diapycnal eddy diffusivity, the eddy diffusivity for heat, and the turbulent flux of heat. Turbulence in the bulk of the cold halocline layer was not strong enough to generate significant buoyancy flux and mixing. Resulting turbulent heat flux across the upper cold halocline was not significantly different than zero. The results show that the low levels of eddy diffusivity in the upper cold halocline lead to small vertical turbulent transport of heat, thereby allowing the maintenance of the cold halocline in the central Arctic.     

Vertical heat transports in the ocean and their effect on time-dependent climate change

In response to increasing atmospheric concentrations of greenhouse gases, the rate of time-dependent climate change is determined jointly by the strength of climate feedbacks and the efficiency of processes which remove heat from the surface into the deep ocean. This work examines the vertical heat transport processes in the ocean of the HADCM2 atmosphere–ocean general circulation model (AOGCM) in experiments with CO₂ held constant (control) and increasing at 1 per year (anomaly). The control experiment shows that global average heat exchanges between the upper and lower ocean are dominated by the Southern Ocean, where heat is pumped downwards by the wind-driven circulation and diffuses upwards along sloping isopycnals. This is the reverse of the low-latitude balance used in upwelling–diffusion ocean models, the global average upward diffusive transport being against the temperature gradient. In the anomaly experiment, weakened convection at high latitudes leads to reduced diffusive and convective heat loss from the deep ocean, and hence to net heat uptake, since the advective heat input is less affected. Reduction of deep water production at high latitudes results in reduced upwelling of cold water at low latitudes, giving a further contribution to net heat uptake. On the global average, high-latitude processes thus have a controlling influence. The important role of diffusion highlights the need to ensure that the schemes employed in AOGCMs give an accurate representation of the relevant sub-grid-scale processes. Received: 8 July 1999 / Accepted: 17 November 1999     

South Indian Ocean Rossby Waves

ABSTRACT

South Indian Ocean Rossby waves (SIO-RW) are identified in the Global Ocean Data Assimilation System (GODAS) 1.5–7?yr filtered sea surface height (SSH) time series. There is a persistent three-year oscillation in the 5°–15°S latitude band from 55° to 85°E. Field correlations show little coupling at 90°E, but as the SIO-RW undulates westward at approximately 0.19?m?s^?1 across the mid-basin, a northwest–southeast axis of warm sea surface temperatures (SSTs) and deep convection forms. Many teleconnections in earlier work are confirmed: interannual pulses of zonal wind in the eastern basin trigger the SIO-RW via anticyclonic wind stress curl. New insights derive from an understanding of links with the upper troposphere. As the SIO-RWs move westward with the onset of an El Niño in the Pacific, increased convection over the north Indian Ocean corresponds to reduced evaporation and SST warming. Mid-tropospheric heating T′?>?2°C over the northwest Indian Ocean accelerates the southern sub-tropical jet to greater than 10?m?s^?1 over the southeast Indian Ocean, reinforcing the anticyclonic vorticity. The downstream acceleration of the jet generates upper-level divergence and moist convection over the western basin, anchoring an atmospheric Rossby wave in a northwest–southeast alignment underpinned by differential propagation of the SIO-RW. As the ocean Rossby wave reaches Africa, the coupling fades and transitions. What distinguishes Indian Ocean from Pacific Ocean Rossby waves are their southern latitude and higher frequency. The tropical mid-tropospheric heating that accelerates the southern sub-tropical jet shifts westward in tandem with the SIO-RW.     

The climatic response of the Arctic Ocean to Soviet river diversions

A numerical model is constructed to evaluate the effect of river diversions on the circulation of the Arctic Ocean, including the climatically important response in the extent of sea ice. The ocean model solves the primitive equations of motion in finite-difference form for the irregular geometry of the Arctic Ocean and Greenland/Norwegian Sea, using 110 km horizontal grid spacing and up to 13 unevenly spaced levels in the vertical. Annual mean atmospheric conditions and river discharges are specified from observations. The presence of sea ice is diagnosed on the basis of model ocean temperature; and the effects of sea ice on the surface fluxes of momentum, heat, and salt are included in a simplified way. Lateral exchanges at the southernmost boundary are held near observed values but respond to circulation changes in the Greenland/Norwegian Sea. Three equilibrium solutions are obtained by eighty-year integrations from simple initial conditions: the first with inflow from all rivers, the second with one-third of the inflow diverted from four major rivers (the Ob, Yenesei, Dvina, and Pechora), and the third with total diversion from those rivers. The middle case corresponds to maximal diversions which are either planned or envisioned by the Soviet Union over the next fifty years, whereas the final extreme case is run in the event that model sensitivity is low relative to that of nature.The control integration gives a good simulation of known water masses and currents. In the Central Arctic, for example, the model correctly predicts a strong shallow halocline, a relatively warm intermediate layer of Atlantic origin, and a temperature jump across the deep Lomonosov Ridge. The overall pattern of surface salinity and the margin of the pack ice are also properly simulated.When runoff into the marginal Kara and Barents Seas is diverted, either in part or in full, almost no effect on the halocline results in the Central Arctic. In particular, deep convection does not develop in the Eurasian Basin, the possibility of which was suggested by Aagaard and Coachman (1975). The vertical stability within the two marginal seas is considerably decreased by the total diversion of four rivers, but not to the point of convective overturning. The surface currents in this area change to confine the water with increased salinity to the shelf region. At deeper levels, an increased salinity tongue spreads into the deep basins of the ice-free Greenland/Norwegian Sea, where existing deep convection is slightly enhanced. As a result, there is some additional heat loss from the Atlantic layer before it enters the Central Arctic. The ice extent remains nearly the same as before within the Kara and Barents Seas. In fact, since modified bottom currents over the continental shelf bring in less heat from the Greenland Sea, an increased thickness of sea ice may result there, in spite of reduced vertical stability. These model responses are generally in agreement with those suggested by Micklin (1981) and by Soviet investigations of the effect of river diversions. These annualmean results should be regarded as tentative, pending confirmation by studies which include the seasonal cycles of runoff and atmospheric forcing.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Spatial differences in seasonal variation of the upper-tropospheric jet stream in the Northern Hemisphere and its thermal dynamic mechanism

NCEP/NCAR reanalysis daily data from 1951 to 2008 are used in this study to reveal the spatial-asymmetric features in the seasonal variation of the upper-tropospheric jet stream (UTJS) and its thermal dynamic forcing mechanism. The jet occurrence percentage distribution of the UTJS demonstrates a spiral-like pattern in winter, but it is quasi-annular in summer. The jet occurrence percentage in the Eastern Hemisphere is larger than that in the Western Hemisphere, and its maximum area is located further south. The polar front jet stream (PJS) and subtropical jet stream (SJS) can be distinguished over the Northern Africa and Asian regions, whereas only one jet stream can be observed over the Western Pacific and Atlantic Ocean. Furthermore, a single peak pattern is found in the seasonal variation of the SJS occurrence frequency with the highest jet occurrence appearing in winter and the lowest in summer, while a double peak pattern is observed in the seasonal variation of the PJS occurrence, i.e., the jet occurrence reaches its peaks in autumn and spring for the PJS. Based on the thermal wind theory, air temperature gradient and atmospheric baroclinicity are calculated and compared with the jet occurrence variation to explore the thermal dynamic forcing mechanism for the UTJS variation. In addition, synoptic-scale transports of eddy heat and momentum are also calculated. The results indicate that the SJS variation is primarily determined by the air temperature gradient and atmospheric baroclinicity, while the PJS variation is under great influence of the transport of eddy heat and momentum over Northern Africa and East Asia. The UTJS variation over the area from 140E to 70W cannot be well individually explained by the air temperature gradient and atmospheric baroclinicity. Further analysis indicates that UTJS variation over this area is largely under control of combined effect of the transport of eddy heat and momentum as well as the atmospheric baroclinicity.     

Diagnostic simulations of the summer circulation in the Canadian arctic archipelago

Abstract

Gridded fields of potential temperature and salinity, interpolated to the time of minimal ice coverage, are constructed for the Canadian Arctic Archipelago based on archived data. In order to overcome the large variations in the horizontal coverage of the observations, the gridding is performed in an iterative procedure where the horizontal correlation scales depend on the data coverage as well as on the flow field. The mean flow corresponding to the temperature and salinity fields are calculated with a diagnostic numerical ocean model. The simulations show that the relative flow through the different straits depends on the elevation difference from the Arctic Ocean to Baffin Bay, and on the density distribution and baroclinic pressure gradients. A 5‐cm increase in the Arctic‐Baffin elevation difference can double the transport. Mean values of the summer flow are a total transport of 0.9 Sv, with 34% flowing through Barrow Strait, 20% through Jones Sound, and 46% through Nares Strait.