海冰消融背景下北极增温的季节差异及其原因探讨

运用哈德莱中心第一套海冰覆盖率(HadISST1)、欧洲中心(ERA_Interim)的温度以及NCEP第一套地表感热通量、潜热通量等资料,研究了1979—2011年33a来北极海冰消融的季节特点和空间特征,并从反照率——温度正反馈与地表感热通量、潜热通量等方面分析了海冰减少对北极增温影响的季节差异。结果表明,北极海冰在秋季和夏季的减少范围明显大于冬季和春季,而北极地表升温却在秋季和冬季最显著,夏季最为微弱,且夏季的增温趋势廓线也与秋冬季显著不同。这主要是因为夏季是融冰季,海冰融化将吸收潜热。且此时北极低空大气温度高于海表温度,海水相当于大气的冷源。随着海冰的消融,更多的热量由大气传入海洋用于融冰和加热上层海水,这使得夏季的低空大气不能显著升温。而在秋冬季,海冰凝结释放潜热,且此时低空大气温度远低于海水温度,海冰的减少使得海水将更多热量释放到大气中导致低空大气显著增暖。海水对大气的这种延迟放热机制是北极低空在夏季增温不显著而在秋冬季增温显著的主要原因。此外,秋冬季的海冰减少与北极近地面升温具有非常一致的空间分布,北冰洋东南边缘和巴伦支海北部分别是秋季和冬季海气相互作用的关键区域。     

渤海海冰特征厚度分析

通过海冰生消机理和数值试验,讨论了渤海海冰特征厚度的存在条件;对不同厚度的海冰表面温度、冰面热量收支、冰面下热传导和太阳辐射透射量进行了对比分析,分析了渤海海冰向特征冰厚的动态演化过程;在不同气温、风速、相对湿度和海洋热通量等气象和水文条件下,对渤海特征冰厚进行了计算;讨论了海冰生消的动态平衡过程,分析了1997/1998年冬季辽东湾JZ20-2海域实测冰厚与特征冰厚的相互关系。对渤海特征冰厚分析将有助于渤海海冰数值模拟工作的开展和对不同重现期设计冰厚的推算。     

2008/2009年冬季南海冷涌天气过程的海-气热通量交换及热量收支

冬季风期(11月—翌年3月)南海显著的气候特点是盛行东北季风并频繁地发生冷涌天气过程。使用2008年10月到2009年4月在西沙群岛永兴岛近海进行的海-气通量观测试验资料,分析了西沙海域冬季风期,尤其是冷涌时段的海-气通量交换和热量收支特征。结果表明:冬季风前期由于海-气温差增大,感热通量比西南季风期稍增加;潜热通量平均值与西南季风期接近;太阳总辐射明显降低,大气长波辐射减小,海洋热量净收入成为负值,使得秋季之后海面温度不断降低。冷涌期间海-气之间的感热通量高于冬季风期平均值,潜热通量大部分(1月份之前)也高于冬季风期平均值;由于潜热通量增大和太阳短波辐射减小,1月份之前的冷涌过程海洋热量净收支普遍出现较大负值,海洋失热量强于冬季风期,甚至强于2008年台风过程平均值。到了冬季后期太阳总辐射增强,海洋热量净收入转为正值,海水温度又逐渐升高。季节之间比较,观测区感热通量以冬季风期间最大,秋季次之,春季最小;而潜热通量夏季风期出现最大值,冬季次之,秋季最小。     

夏季北冰洋海冰边缘区海水温盐结构及其形成机理

利用1999年北极科学考察期间在海冰边缘区的三次考察数据，研究了北冰洋海冰边缘区的温度和盐度结构。将海冰边缘区分为机制不同的两大类，一类是暖水海冰边缘区，主要热源是外部暖水进入海冰边缘区携带的热量；另一类是冷水海冰边缘区，主要热源是太阳辐射加热。文中主要对冷水海冰边缘区进行了研究。虽然两个冷水海冰边缘区(R区与T区)温度结构不尽相同，但都存在表层以下水体中的温度极大值现象，R区的温度极大值位于20m左右，T区的位于40—50m左右的深度，可以认为是海冰边缘区的典型温度特征。作者认为，次表层暖水的热源是太阳辐射的直接加热，为此，建立了太阳加热引起海水次表层增暖的物理模型和简单的数学模型，获得了冰下海水在太阳辐射的作用下增暖的解析解。结果表明，部分太阳辐射能穿过海冰加热冰下海水，加热之初温度的极大值出现在近表层，随着时间的推移，海温极大值的位置向下移动，最终可以达到40m左右，证明了仅仅依靠太阳的短波辐射就可以形成中间暖的水层。文中阐明，开阔海水更多的是上混合层和跃层结构，冰下海水主要是次表层暖水结构；冷水海冰边缘区的海水主要带有冰下海水的特征。由于次表层暖水的形成与海冰厚度关系很大，近十几年北冰洋海冰厚度的显著减少势必加强次表层暖水，可能是北冰洋增暖的又一个重要现象，对全球气候变化有意义深远的影响。     

利用卫星遥感和再分析数据刻画2017-2018年格陵兰北部罕见冰间湖事件

以90%海冰密集度为阈值，基于卫星遥感数据，2017-2018年冰季在格陵兰北部识别了两次冰间湖事件，分别出现在冬季和夏季。冬季的冰间湖事件从2018年2月20日持续至3月3日，夏季的事件从8月2日持续到9月5日。AMSR2被动微波的海冰密集度产品表明，冬季和夏季冰间湖事件对应的最低海冰密集度分别为72%和65%。两次冰间湖事件都与格陵兰北部东西气压梯度异常引起的南风加强有关，而气压梯度的异常则与对流层中部极涡的扰动有关。冬季冰间湖事件期间，相对暖和的气温和频繁出现的冰间湖，导致冬季海冰生长不持续，海冰热力增厚较小，这为夏季海冰发生破碎并形成冰间湖创造了条件。南风减弱和新冰生成是冬季冰间湖消失的主要原因。对于夏季的冰间湖，导致其消失的主要原因则是从北部输入的浮冰增加。Sentinel-1 合成孔径雷达产品相对AMSR2被动微波观测产品更加适合于应用到冰间湖事件伴随的新冰生长，这与前者具有更高的空间分辨率有关。格陵兰北部是北冰洋多年冰的聚集地，该区域被认为是北冰洋海冰的“避难所”。因此区域在2017-2018年出现罕见的冰间湖事件，对于整个北冰洋海冰的快速减少具有重要意义，也助于北冰洋海冰，尤其是多年冰的消退。     

南黄海海气热通量观测及其与OAflux数据集比较研究

2007年在南黄海进行了3个航次的热通量观测,包括长、短波辐射,近海表空气温度、湿度,风速,海表皮温等观测数据。依据计算的冬季、春季、秋季三个航次的海气热通量分析了热通量不同季节特征,南黄海海域冬季、春季和秋季平均潜热通量分别为80.7W/m2,5.6W/m2和142.1W/m2,感热通量分别为32.0W/m2,-12.5W/m2和18.9W/m2(海洋向大气传递为正)。将国际较为通用的OAflux数据集与3个季节观测数据做了逐点的比对,作为对OAflux数据集在南黄海海域的评估,结果显示:OAflux数据集热通量结果与观测数据在2006—2007年冬季最为接近,感热和潜热通量均方差是15.3W/m2和21.4W/m2。春季的潜热通量存在明显偏差,均方差为28.4W/m2。秋季的感热和潜热通量均存在显著偏差,均方差分别为20.5W/m2和57.5W/m2。导致春季偏差的主要原因是OAflux数据集和现场观测的近海表空气湿度差异,而秋季偏差则应主要归因于海表温度的偏差。     

青岛沿海风应力和海气交换研究

利用实测的海洋气象资料研究了青岛沿海海气间能通量和水汽交换情况,分析了青岛沿海40a间(1961-2000)海面风应力、海-气热通量、水汽通量的大小以及时变特征。结果表明:青岛沿海风应力冬夏季大,春秋季小,6月和12月出现峰值,分别为2.9×10-3N/m2和5.8×10-3N/m2。海面净热通量全年呈单峰变化,7月份最大,为140.4W/m2;11月份最小,为-115.0W/m2;年平均海表净热通量为23.5W/m2。海面热量收支的季节分布特征是:海面吸收的太阳短波辐射夏季大、冬季小;海表有效辐射冬季大、夏季小;海-气潜热交换季节变化呈双峰分布,极大值出现在5月和9月;海-气感热交换受海气温差控制,冬季为正,热量由海洋传向大气,夏季为负,热量由大气传向海洋。受云量影响,海面吸收的太阳短波辐射从上世纪90年代以来有所增加;海-气潜热交换的年际变化显著,40a间变动范围达33.7W/m2。海-气净热通量的年际变化也很明显,40a间变动范围达41.7W/m2,且自80年代以来呈现上升的趋势。青岛沿海年平均蒸发量大于降水量,量值分别为888.0mm和677.2mm,年平均净水汽通量为-210.8mm;蒸发量的季节分布呈双峰变化,5月和9月达极大值;多年平均7,8两个月份降水多于蒸发,其余月份蒸发多于降水。     

北极冰海耦合模式对两种不同大气再分析资料响应的分析

本文中我们比较了Climate Forecast System Reanalysis(CFSR)高分辨率的再分析数据集和低分辨率的Japanese 25-year Reanalysis Project(JRA25)再分析数据集在向下短波辐射、向下长波辐射、10m风场、近地面气温、降水、湿度上的不同,发现二者差异最大的为降水数据,其次为向下短波辐射数据、向下长波辐射数据。用这两个数据集驱动同一冰海耦合模式,CFSR强迫的海冰、北冰洋中层水和加拿大海盆温盐结构与实测相比有很大差距,等密度面上的地转流速在加拿大海盆和欧亚海盆比JRA25强迫的结果高20%,同时等密度面的深度偏深、位温偏高,在弗拉姆海峡的流通量也比海洋再分析数据Simple Ocean Data Assimilation(SODA)偏多。CFSR的向下辐射数据更加接近实测,采用此数据的敏感性实验模拟结果与实测符合的更好。对于海冰的模拟,云量起着至关重要的作用,降水带来的淡水通量通过影响大西洋入流水携带的热量进而影响到冰区。此外,CFSR过量的降水也是二者对于北冰洋温盐结构、弗拉姆海峡流通量以及地转流强度模拟产生偏差的主要原因。尽管风场的分辨率不同,在海盆尺度上对于海冰和海水温盐结构的影响并不大。     

2016年夏季北冰洋浮冰站近地层辐射和湍流通量观测

2016年8月7－14日中国第七次北极科学考察期间，在83°N附近设立的长期浮冰站开展了辐射和湍流通量观测研究。结果表明，观测期间反照率变化范围为0.64~0.92，平均反照率为0.78；基于现场观测数据评估了PW79、HIRHAM、ARCSYM和CCSM3 4种不同复杂度的反照率参数化方案在天气尺度的表现，最为复杂的CCSM3结果优于其他参数化方案，但不能体现降雪条件下的反照率快速增长。浮冰区冰雪面平均净辐射为18.10 W/m2，平均感热通量为1.73 W/m2，平均潜热通量为5.55 W/m2，海冰表面消融率为（0.30±0.22） cm/d，表明此时北冰洋浮冰正处于快速消融期。冰面的平均动量通量为0.098（kg·m/s）/（m2·s），动量通量与风速有很好的对应关系，相关系数达0.80。     

北极中央区海冰低密集度现象研究

近年，北极中央密集冰区出现海冰低密集度的异常现象。为了探讨这一现象的成因，本文使用ERA-Interim再分析资料，定义了北极中央区海冰低密集度（LCCA）指数，研究了2009-2016年的6-9月北极中央区发生的海冰低密集度现象。分析表明，研究时段内在北极中央区发生了6次明显的海冰低密集度（LCCA峰值）过程。在这些过程中，局地气温异常并不是导致海冰低密集度现象发生最主要的因素；海冰低密集度区域的形态及冰速场分布均与大气环流场相对应；在LCCA指数峰值发生前均有气旋中心出现在北冰洋70°N以北并伴随向北移动，气旋引起海冰辐散，同时所携带的较低纬度的热量导致海冰迅速融化。在6次过程中，有3次为气旋影响配合北极偶极子（DA）型环流。LCCA指数与84°N平均向北温度平流和北极中央区海冰速度散度呈正相关。在LCCA指数峰值前，温度平流对海冰低密集度区域形成的影响大于海冰辐散的影响。     

2010年马卡罗夫海盆冰站观测期间垂向热通量时间变化研究

Based on hydrographic data obtained at an ice camp deployed in the Makarov Basin by the 4th Chinese Arctic Research Expedition in August of 2010, temporal variability of vertical heat flux in the upper ocean of the Makarov Basin is investigated together with its impacts on sea ice melt and evolution of heat content in the remnant of winter mixed layer(r WML). The upper ocean of the Makarov Basin under sea ice is vertically stratified. Oceanic heat flux from mixed layer(ML) to ice evolves in three stages as a response to air temperature changes, fluctuating from 12.4 W/m2 to the maximum 43.6 W/m2. The heat transferred upward from ML can support(0.7±0.3) cm/d ice melt rate on average, and daily variability of melt rate agrees well with the observed results. Downward heat flux from ML across the base of ML is much less, only 0.87 W/m2, due to enhanced stratification in the seasonal halocline under ML caused by sea ice melt, indicating that increasing solar heat entering summer ML is mainly used to melt sea ice, with a small proportion transferred downward and stored in the r WML. Heat flux from ML into r WML changes in two phases caused by abrupt air cooling with a day lag. Meanwhile, upward heat flux from Atlantic water(AW) across the base of r WML, even though obstructed by the cold halocline layer(CHL), reaches0.18 W/m2 on average with no obvious changing pattern and is also trapped by the r WML. Upward heat flux from deep AW is higher than generally supposed value near 0, as the existence of r WML enlarges the temperature gradient between surface water and CHL. Acting as a reservoir of heat transferred from both ML and AW, the increasing heat content of r WML can delay the onset of sea ice freezing.     

海水物质平衡浮标对北冰洋中心区海冰温度与物质平衡的观测

利用中国第3次北极科学考察所布放海冰物质平衡浮标(Ice Mass-Balance buoy,IMB)的观测数据,分析了北冰洋中心区多年冰2008年8月-2009年7月温度与物质平衡的变化特征.结果表明,冰温廓线呈现明显的季节变化,秋季降温过程从海冰表面开始向冰体内部传播.海冰底部的生长/消融率受海水温度控制,随水温的...     

东南极Princess Elizabeth冰盖近地层大气参数的年变化特征

利用2002年东南极Princess Elizabeth冰盖自动气象梯度观测点获得的近地层气象资料,分析了冰盖上的感热通量、潜热通量、大气稳定度、整体输送系数及有关气象要素特征,并与中山站同期的的气象要素进行了对比分析.结果表明,由于两站的海拔高度及地理位置的差异,LGB69站的年平均气温为-25.6℃,比中山站低16.4℃,进入内陆每10km,海拔高度上升约110m,温度下降约1℃.南极内陆冰盖的湍流热通量具有明显的年变化,感热通量年平均值为-17.9W/m2,潜热通量为-0.9W/m2,年平均冷源强度(Q_h+Q_e)为-18.8W/m2,表明地表从大气吸收热量.LGB69站近地层大气以近中性层结为主,中性层结下的整体输送系数为2.6×10-3,当风速大于8m/s后,整体输送系数趋于常数.LGB69站是南极地区典型下降风区,年平均风速比中山站大2.0m/s,其下降风出现的风向频和风速均大于中山站.     

Optical properties and surface energy flux of spring fast ice in the Arctic

Over the past decades, sea ice in the polar regions has been significantly affecting local and even hemispheric climate through a positive ice albedo feedback mechanism. The role of fast ice, as opposed to drift ice, has not been well-studied due to its relatively small coverage over the earth. In this paper, the optical properties and surface energy balance of land fast ice in spring are studied using in situ observations in Barrow, Alaska. The results show that the albedo of the fast ice varied between 0.57 and 0.85 while the transmittance increased from 1.3×10?3 to 4.1×10?3 during the observation period. Snowfall and air temperature affected the albedo and absorbance of sea ice, but the transmittance had no obvious relationship with precipitation or snow cover. Net solar shortwave radiation contributes to the surface energy balance with a positive 99.2% of the incident flux, with sensible heat flux for the remaining 0.8%. Meanwhile, the ice surface loses energy through the net longwave radiation by 18.7% of the total emission, while the latent heat flux accounts for only 0.1%. Heat conduction is also an important factor in the overall energy budget of sea ice, contributing 81.2% of the energy loss. Results of the radiative transfer model reveal that the spectral transmittance of the fast ice is determined by the thickness of snow and sea ice as well as the amount of inclusions. As major inclusions, the ice biota and particulates have a significant influence on the magnitude and distribution of the spectral transmittance. Based on the radiative transfer model, concentrations of chlorophyll and particulate in the fast ice are estimated at 5.51 mg/m2 and 95.79 g/m2, which are typical values in the spring in Barrow.     

基于中国北极考察布放浮标观测和数值模拟的海冰和积雪厚度变化分析

Sea ice and the snow pack on top of it were investigated using Chinese National Arctic Research Expedition(CHINARE) buoy data.Two polar hydrometeorological drifters,known as Zeno? ice stations,were deployed during CHINARE 2003.A new type of high-resolution Snow and Ice Mass Balance Arrays,known as SIMBA buoys,were deployed during CHINARE 2014.Data from those buoys were applied to investigate the thickness of sea ice and snow in the CHINARE domain.A simple approach was applied to estimate the average snow thickness on the basis of Zeno~ temperature data.Snow and ice thicknesses were also derived from vertical temperature profile data based on the SIMBA buoys.A one-dimensional snow and ice thermodynamic model(HIGHTSI) was applied to calculate the snow and ice thickness along the buoy drift trajectories.The model forcing was based on forecasts and analyses of the European Centre for Medium-Range Weather Forecasts(ECMWF).The Zeno~ buoys drifted in a confined area during 2003–2004.The snow thickness modelled applying HIGHTSI was consistent with results based on Zeno~ buoy data.The SIMBA buoys drifted from 81.1°N,157.4°W to 73.5°N,134.9°W in 15 months during2014–2015.The total ice thickness increased from an initial August 2014 value of 1.97 m to a maximum value of2.45 m before the onset of snow melt in May 2015;the last observation was approximately 1 m in late November2015.The ice thickness based on HIGHTSI agreed with SIMBA measurements,in particular when the seasonal variation of oceanic heat flux was taken into account,but the modelled snow thickness differed from the observed one.Sea ice thickness derived from SIMBA data was reasonably good in cold conditions,but challenges remain in both snow and ice thickness in summer.     

The physical structures of snow and sea ice in the Arctic section of 150°-180°W during the summer of 2010

The physical structures of snow and sea ice in the Arctic section of 150°-180°W were observed on the basis of snow-pit, ice-core, and drill-hole measurements from late July to late August 2010. Almost all the investigated floes were first-year ice, except for one located north of Alaska, which was probably multi-year ice transported from north of the Canadian Arctic Archipelago during early summer. The snow covers over all the investigated floes were in the melting phase, with temperatures approaching 0℃ and densities of 295-398 kg/m3 . The snow covers can be divided into two to five layers of different textures, with most cases having a top layer of fresh snow, a round-grain layer in the middle, and slush and/or thin icing layers at the bottom. The first-year sea ice contained about 7%-17% granular ice at the top. There was no granular ice in the lower layers. The interior melting and desalination of sea ice introduced strong stratifications of temperature, salinity, density, and gas and brine volume fractions. The sea ice temperature exhibited linear cooling with depth, while the salinity and the density increased linearly with normalized depth from 0.2 to 0.9 and from 0 to 0.65, respectively. The top layer, especially the freeboard layer, had the lowest salinity and density, and consequently the largest gas content and the smallest brine content. Both the salinity and density in the ice basal layer were highly scattered due to large differences in ice porosity among the samples. The bulk average sea ice temperature, salinity, density, and gas and brine volume fractions were-0.8℃, 1.8, 837 kg/m3 , 9.3% and 10.4%, respectively. The snow cover, sea ice bottom, and sea ice interior show evidences of melting during mid-August in the investigated floe located at about 87°N, 175°W.     

BCC_CSM对北极海冰的模拟:CMIP5和CMIP6历史试验比较

本文利用北京气候中心气候系统模式(BCC_CSM)在最近两个耦合模式比较计划(CMIP5和CMIP6)的历史试验模拟结果，对北极海冰范围和冰厚的模拟性能进行了比较，结果表明:(1) CMIP6改善了CMIP5模拟海冰范围季节变化过大的问题，总体上更接近观测结果；(2)两个CMIP试验阶段中BCC_CSM模拟的海冰厚度都偏小，但CMIP6试验对夏季海冰厚度过薄问题有所改进。通过对影响海冰生消过程的冰面和冰底热收支的分析，我们探讨了上述模拟偏差以及CMIP6模拟结果改善的成因。分析表明，8?9月海洋热通量、向下短波辐射和反照率对模拟结果的误差影响较大，CMIP6试验在这些方面有较大改善；而12月至翌年2月，CMIP5模拟的北极海冰范围偏大主要是海洋热通量偏低所导致，CMIP6模拟的海洋热通量较CMIP5大，但北大西洋表层海流的改善才是巴芬湾附近海冰外缘线位置改善的主要原因。CMIP试验模拟的夏季海冰厚度偏薄主要是因为6?8月海洋热通量和冰面热收支都偏大，而CMIP6试验模拟的夏季海冰厚度有所改善主要是由于海洋热通量和净短波辐射的改善。海冰模拟结果的改善与CMIP6海冰模块和大气模块参数化的改进有直接和间接的关系，通过改变短波辐射、冰面反照率和海洋热通量，使BCC_CSM模式对北极海冰的模拟性能也得到有效提高。     

北冰洋浮冰站近地层参数的观测估算

利用2008年8月20～27日我国第3次北极考察队在85°N附近设立的冰站上进行的湍流通量、辐射观测所获取的相关资料,采用涡动相关法对夏季北冰洋浮冰下垫面的近地层参数进行了估算.结果显示,观测期间浮冰区冰雪面的平均感热、潜热和净辐射通量分别是0.2 W/m2,1.2 W/m2和9.9 W/m2,表明下垫面获得的大部分热...