近42年来我国北方冬半年寒潮频次的第一模态及其与北极涛动的相关分析

This study examined wintertime （November-April） cold wave frequency （CWF） in northern China during the last 42 years and its association with Arctic Oscillation （AO） through analysis of daily mean surface temperature from 280 stations across northern China and European Centre for Medium-Range Weather Forecasts （ECMWF） 40-Year Re-analysis ERA-40 data. The leading empirical orthogonal function EOF mode of wintertime CWF （CWF-EOF1） indicates an identical signal over most northern China, with the characteristic trend of linear decline for the leading principal component （CWF-PC1）. After the linear trend is removed, remarkable inter-annual variability is found to be the dominant feature of the CWF-PC1. The regression map for sea level pressure based on CWF-PC1 corresponds to the negative phase of AO. Correlation analysis further proves that CWF-PC1 has a significant negative correlation with AO at the inter-annual time scale. The relationship between AO and global surface air temperature is also investigated in order to understand its association with cold air activity over East Asia, and it is suggested that the anomalies of atmospheric circulation in Siberia may serve as a bridge for interaction between AO and CWF in northern China during wintertime.     

Sensitivity of simulated wintertime Arctic atmosphere to vertical resolution in the ARPEGE/IFS model

The current state-of-the-art general circulation models, including several of those used by the IPCC, show considerable biases in the simulated present day high-latitude climate compared to observations and reanalysis data. These biases are most pronounced during the winter season. We here employ ideal vertical profiles of temperature and wind from turbulence-resolving simulations to perform a priori studies of the first-order eddy-viscosity closure scheme employed in the ARPEGE/IFS model. This reveals that the coarse vertical resolution (31 layers) of the model cannot be expected to realistically resolve the Arctic stable boundary layer. The curvature of the Arctic inversion and thus also the vertical turbulent-exchange processes cannot be reproduced by the coarse vertical mesh employed. To investigate how turbulent vertical exchange processes in the Arctic boundary layer are represented by the model parameterization, a simulation with high vertical resolution (90 layers in total) in the lower troposphere is performed. Results from the model simulations are validated against data from the ERA-40 reanalysis. The dependence of the surface air temperature on surface winds, surface energy fluxes, free atmosphere stability and boundary layer height is investigated. The coarse-resolution run reveals considerable biases in these parameters, and in their physical relations to surface air temperature. In the simulation with fine vertical resolution, these biases are clearly reduced. The physical relation between governing parameters for the vertical turbulent-exchange processes improves in comparison with ERA-40 data.     

交叉小波变换在区域气候分析中的应用

将交叉谱与小波变换分析方法相结合,与传统的交叉谱方法相比,交叉小波变换方法用于区域气候变化与大气环流系统之间耦合振荡行为的相关分析更具优越性,不仅可以弥补经典交叉谱分析方法存在的缺陷,而且能够发挥小波变换在时频两域都具有表征气候信号局部化特征的作用;该方法具有较强的耦合信号分辨能力,便于描述耦合信号在时频域中分布状况的优点。采用交叉小波变换分析北极涛动指数(AOI)距平与河南省月平均降水量距平、气温距平序列之间的联合统计特征及其在时频域中的相关关系,根据小波互相关系数、交叉小波凝聚谱和小波位相谱分析北极涛动对河南省气候变化的可能影响。应用结果表明:河南省降水量和气温变化与AOI之间存在着多时间尺度的显著相关振荡,年代际尺度周期上的互相关系数明显大于年际尺度周期,相关程度随耦合振荡频率的增大而减小,相关显著性取决于两者的时频域联合统计特征,时域中小波互相关系数、小波凝聚谱和小波位相谱的分布具有明显的局部化特征;说明北极涛动年际和年代际异常对河南省气候变化具有显著影响。     

夏、秋季北极海冰异常与秋、冬季青藏高原极端低温日数的关系及影响机理

利用1979~2012年青藏高原125个基本、基准站观测日最高及最低气温数据、Hadley中心月平均海冰覆盖率资料、ERA-Interim的风场、高度场等再分析资料,根据相关统计分析、合成分析等方法系统地分析了青藏高原地区秋、冬季冷昼和冷夜日数(低温日数)与关键影响海区海冰的关系及影响机理。结果表明,夏、秋季关键海区海冰偏少时,秋、冬季极地和青藏高原地区500 h Pa位势高度减小,中高纬西伯利亚地区位势高度增强,北极至青藏高原有明显由北向南波动通量,高压反气旋系统在西伯利亚地区形成与壮大,青藏高原以北风场呈现明显偏北风,Rossby波在青藏高原及其以北地区呈现由北向南波动形式,青藏高原以北的西风带地区Rossby波东传减缓,导致经向活动加强,北部冷空气易于通过气流向高原侵袭,秋、冬季青藏高原低温日数将偏多。     

中国CMIP5模式对未来北极海冰的模拟偏差

本文对中国参加CMIP5的6个气候模式对未来北极海冰的模拟情况进行了评估。通过与1979-2005年海冰的观测值以及2050年代的多模式集合平均值对比发现,中国的气候模式对海冰范围的模拟结果与CMIP5模式的平均水平存在一定差距,具体表现为：BNU-ESM和FGOALS-s2对当前海冰范围估计很好,但对温度敏感性略偏高;FIO-ESM对当前海冰范围估计很好,但由于海冰对温度的敏感性偏低,导致其模拟的未来海冰在各种RCP情景中都融化缓慢;FGOALS-g2（BCC-CSM1-1和BCC-CSM1-1-m）对当前海冰范围的模拟存在显著偏多（显著偏少）的问题,这导致其对未来海冰融化的估计也持续偏多（偏少）。中国模式对北极海冰的模拟偏差导致它们对极区地表大气温度和湿度的模拟出现偏差,并且这些极区气象要素的偏差会进一步通过动力过程传导到对秋、冬季西风带、极涡的模拟中去。研究表明：从对海冰本身的模拟以及海冰偏差带来的气候影响这两个角度看,BNU-ESM在中国模式中水平较高,但总体上中国6个气候模式在海冰分量的模拟上仍与世界平均水平存在差距,这需要中国各模式中心的持续改进。     

北冰洋中心区表层淡化层的藻类色素组成

季节性海冰融化在北冰洋中心区表层形成淡水层,影响了浮游植物的类群。研究发现岩藻黄素（Fuco,指示硅藻）是冰芯底部检测到的主要光合色素,叶黄素（Lut）和叶绿素b （Chl b）（指示绿藻）是冰水界面浓度最高的类胡萝卜素。海冰底部硅藻占据了绝对的优势,但在冰水界面藻类类群转变了以绿藻为主的结构。冰下水中,浮游植物群落随着深度的增加,由绿藻为主快速转变为以硅藻为主,盐度可能是导致这种变化的原因。     

基于HY-2A散射计数据的极区海冰范围反演方法及其评估

A sea ice extent retrieval algorithm over the polar area based on scatterometer data of HY-2A satellite has been established.Four parameters are used for distinguishing between sea ice and ocean with Fisher's linear discriminant analysis method.The method is used to generate polar sea ice extent maps of the Arctic and Antarctic regions of the full 2013–2014 from the scatterometer aboard HY-2A(HY-2A-SCAT) backscatter data.The time series of the ice mapped imagery shows ice edge evolution and indicates a similar seasonal change trend with total ice area from DMSP-F17 Special Sensor Microwave Imager/Sounder(SSMIS) sea ice concentration data.For both hemispheres,the HY-2A-SCAT extent correlates very well with SSMIS 15% extent for the whole year period.Compared with Synthetic Aperture Radar(SAR) imagery,the HY-2A-SCAT ice extent shows good correlation with the Sentinel-1 SAR ice edge.Over some ice edge area,the difference is very evident because sea ice edges can be very dynamic and move several kilometers in a single day.     

影响北欧海和楚科奇海夏季细菌丰度和生产力的因素

Abundance and production of bacterioplankton were measured in the Nordic seas and Chukchi Sea during the5 th Chinese Arctic Research Expedition in summer 2012.The results showed that average bacterial abundances ranged from 3.31×10~(11) cells/m~3 to 2.25× 10~(11)cells/m~3,and average bacterial productions(calculated by carbon)were 0.46 mg/(m~3·d) and 0.54 mg/(m~3·d) in the Nordic seas and Chukchi Sea,respectively.T-test result showed that bacterial abundances were significantly different between the Nordic seas and Chukchi Sea,however,no significant difference was observed regarding bacterial productions.Based on the slope of lg bacterial biomass versus lg bacterial production,bacterial communities in the Nordic seas and Chukchi Sea were moderately dominated by bottom-up control.Both Pearson correlation analysis and multivariable linear regression indicated that temperature had significant positive correlation with bacterial abundance in the Chukchi Sea,while no correlations with productions in both areas.Meanwhile,Chl a had positive correlations with both bacterial abundance and production in these two regions.As the temperature and Chl a keep changing in the future,we suggest that both bacterial abundance and production been hanced in the Chukchi Sea but weaken in the Nordic seas,though the enhancement will not be dramatic as a result of higher pressure of predation and viral lysis.     

北极海洋沉积物细菌和古菌群落结构分析

This study was to investigate bacterial and archaeal community structure of pan-Arctic Ocean sediments by pyrosequencing.In total,investigation of three marine sediments revealed 15 002 bacterial and 4 362 archaeal operational taxonomic units(OTUs) at the 97% similarity level.Analysis of community structure indicated that these three samples had high bacterial and archaeal diversity.The most relatively abundant bacterial group in Samples CC1 and R05 was Proteobacteria,while Firmicutes was dominant in Sample BL03.Thaumarchaeota was the most relatively abundant archaeal phylum in Samples CC1 and R05,and the relative abundance of Thaumarchaeota was almost as high as that of Euryarchaeota in Sample BL03.These two phyla accounted for nearly 100% of the archaeal OTUs.δ-Proteobacteria and γ-Proteobacteria were the two most relatively abundant classes at Proteobacterial class level,and their relative abundance was more than 60% in Samples CC1 and R05.There were also differences in the top 10 relatively abundant bacterial and archaeal OTUs among the three samples at the 97% similarity,and only 12 core bacterial OTUs were detected.Overall,this study indicated that there were distinct microbial communities and many unique OTUs in these three samples.     

地球系统模式FIO-ESM对北极海冰的模拟和预估

评估了地球系统模式FIO-ESM(First Institute of Oceanography-Earth System Model)基于CMIP5(Coupled Model Intercomparison Project Phase 5)的历史实验对北极海冰的模拟能力,分析了该模式基于CMIP5未来情景实验在不同典型浓度路径(RCPs,Representative Concentration Pathways)下对北极海冰的预估情况。通过与卫星观测的海冰覆盖范围资料相比,该模式能够很好地模拟出多年平均海冰覆盖范围的季节变化特征,模拟的气候态月平均海冰覆盖范围均在卫星观测值±15%范围以内。FIO-ESM能够较好地模拟1979-2005年期间北极海冰的衰减趋势,模拟衰减速度为每年减少2.24×104 km2,但仍小于观测衰减速度(每年减少4.72×104 km2)。特别值得注意的是:不同于其他模式所预估的海冰一直衰减,FIO-ESM对21世纪北极海冰预估在不同情景下呈现不同的变化趋势,在RCP2.6和RCP4.5情景下,北极海冰总体呈增加趋势,在RCP6情景下,北极海冰基本维持不变,而在RCP8.5情景下,北极海冰呈现继续衰减趋势。