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。     

北极海冰的年代际转型与中国冻雨年代际变化的关系

基于1961-2013年HadISST海冰密集度资料,定义了北极海冰的季节性融冰指数,结果显示近几十年来北极季节性融冰范围呈显著的上升趋势,并分别在20世纪70年代末和90年代中期存在显著的年代际转型,相应地,中国冻雨发生频数总体上呈现出显著的减少趋势,但也存在显著的年代际转型。在20世纪70年代末之前,北极季节性融冰范围较小但显著增长,中国冻雨频数年际变化振幅较大,且主要受巴伦支海、喀拉海海冰的影响;20世纪70年代末至90年代中期北极季节性融冰范围维持振荡特征,没有显著的线性趋势,中国冻雨频数变化振幅减小,与北极海冰相关较弱,主要相关因子为北大西洋及北太平洋海表温度变化;而90年代中期以后,北极海冰融化加快,特别是2007年以后,季节性融冰范围大大增加,而中国冻雨频数处于低发时段,其变化与太平洋扇区海冰及堪察加半岛附近海温呈显著负相关,季节性融冰的显著区域也从东西伯利亚海逆时针旋转向波弗特海-加拿大群岛北部扩张,同时向北极中央区扩张。不同年代影响冻雨的海温或海冰关键海区不同,产生特定的大气环流异常响应,进而影响到我国冻雨。     

基于卫星数据的北极海冰变化分析

海冰是极地气候系统重要组成部分。基于1982—2004年的卫星反照率、海冰密集度数据,选取了7个北极海域(分别位于格陵兰海、巴伦支海、喀拉海、拉普捷夫海、东西伯利亚海及以北海域、楚科奇海及以北海域和波弗特海及以北海域)进行了研究。对比分析发现,两数据区域平均序列相关性比较高,最低相关系数为0.51,最高相关系数为0.94。格陵兰海海域和巴伦支海海域夏季海表反照率、海冰密集度较低,多为无冰海面;喀拉海域、拉普捷夫海域、东西伯利亚海及以北海域6月份海表反照率、海冰密集度较高,7、8月份海冰加速融化,海冰密集度下降明显;楚科奇海及以北海域、波弗特海及以北海域夏季海表反照率、海冰密集度较高。7个海域海表反照率、海冰密集度均呈现下降趋势,西部的楚科奇海及以北海域、波弗特海及以北海域下降速度最快,巴伦支海海域下降速度最慢。海表反照率和海冰总量的减少,对气候演变有着重要影响。     

北极中央区海冰密集度与云量相关性分析

本文使用海冰密集度以及低云、中云、高云的日平均数据,借助滑动相关分析方法,研究了北极中央区海冰密集度与云量之间的相关性,分析了海冰与云的相互作用机制。研究表明,在春季海冰融化季节(4、5月)、秋季海冰冻结季节(10、11月),低云与海冰密集度之间表现为较好的负相关,表明在这段时间内冰区海面蒸发强烈,对低云的形成有重要贡献。在10月和11月,中云与海冰密集度也有很好的负相关,表明秋季低云可以通过抬升形成中云。高云与海冰密集度之间并没有明显的相关性,可能原因:一方面海冰的空间分布对高云无影响,另一方面,高云主要影响到达的短波辐射,从而影响海冰的融化和冻结速度,与海冰厚度有直接显著的关系,而与海冰密集度的关系不明显。此外,在海冰密集度与低云存在较好负相关的情况下会出现某些年份相关性不好的情况,我们的研究发现这是北极中央区与周边海区发生了海冰交换或云交换的结果。     

中国江南地区降水异常的年际变化与北极海冰密集度异常的相关分析及其机理研究

本文选取最近二十年(1998—2017年)中国江南地区降水和北极海冰为研究对象,分析了年际时间尺度上中国江南地区降水异常与北极海冰异常的关系,并进一步通过研究关键区附近罗斯贝长波(Rossby长波)的波射线路径和中国中纬度地区波作用通量的传播异常,揭示了北极海冰通过Rossby波大气桥的调制作用影响江南地区降水的可能机制。结果表明:夏、秋季东西伯利亚海与巴芬湾的海冰密集度异常与次年中国江南地区降水异常存在显著的正相关关系。其影响机制是:关键海区海冰异常和北极放大能够激发Rossby波列型遥相关从北极关键区向中国中纬度地区传播,而关键区附近的Rossby波扰动能量在夏、秋季比冬、春季更容易传播至中国中纬度地区,并最终通过上下游遥相关效应引发中纬度副热带西风急流异常和急流入口区右侧江南地区的环流和降水异常,当海冰偏多时西风急流加强,江南地区对流不稳定发展,降水偏多。     

基于CryoSat-2数据的2010-2017年北极海冰厚度和体积的季节与年际变化特征

北极海冰变化影响着全球物质平衡、能量交换和气候变化。本文基于CryoSat-2测高数据和OSI SAF海冰密集度及海冰类型产品，分析了2010-2017年北极海冰面积、厚度和体积的季节和年际变化特征，结合NCEP再分析资料探讨了融冰期北极气温异常和夏季风异常对海冰变化的影响。结果表明，结冰期海冰面积的增加量波动较大，海冰厚度的增加量呈明显下降趋势。融冰期海冰厚度的减小量波动较大，2013年以后融冰期海冰面积的减小量逐年增加。海冰体积的变化趋势和面积变化更相似，融冰期的减小速率大于结冰期的增加速率。融冰期北极海表面大气温度异常与海冰融化量正相关。夏季风影响海冰的辐合和辐散，在弗拉姆海峡海冰的输运过程中起关键作用，促进了北冰洋表层水向大洋深层的传输。     

融冰季节北极破碎冰区热通量的初步研究

利用航空遥感数字影像的解析结果和实测气象，海洋和海冰资料，定量研究了夏季融冰期北极破碎冰区的热通量，计算了海洋对大气的热贡献，结果表明，在北极夏季海冰融化时，短波辐射远远大于感热和潜热通量，是表面热通量的决定因素，海洋对大气的热贡献主要由长波辐射决定，在观测期间，海洋对大气的热贡献为38～104Wm^-2，这部分热量的大小与海冰的密集度有关，当海冰密集度小于0.8时，海洋对大气的热贡献随海冰密度度的增大而减小，而当海冰密集度超过0.8以后，该热通量将随海冰密集度的增大而增大。     

东亚气溶胶光学厚度时空变化特征及其对气候可能的影响

本文利用Terra卫星MODIS传感器2000—2011年550nm气溶胶光学厚度(AOD)资料,AERONET东亚站点Angstrom指数资料,以及NCEP/NCAR的2000—2011年位势高度资料,用经验正交函数分解方法(EOF)分析了近12a东亚AOD时空变化特征,同时通过研究AOD与夏季850hPa西太平洋副热带高压的关系,初步分析了AOD对气候可能产生的影响。结果表明,EOF第一模态东亚大部分地区AOD同位相变化,北方振幅最大,越往南振幅越小,17°N以南出现反位相,这在春季最显著。第二模态南北方呈明显反位相,春夏季最显著。进一步分析认为第一模态主要受沙尘气溶胶影响,第二模态主要受工业气溶胶影响。关于东亚AOD对气候可能的影响,通过东亚AOD与西太平洋副热带高压西脊点指数(IW)的相关性分析,发现4月份海上AOD对6月份IW有较明显的2个月超前相关,该相关大致以22.5°N为界,以北呈负相关,以南呈正相关。分析认为这与沙尘气溶胶及炭黑气溶胶的辐射强迫有关。     

挪威海和格陵兰海海水DMS分布特征及影响因素研究

于2012年7—9月现场测定了北极挪威海和格陵兰海区域海水二甲基硫(DMS)及其前体物质二甲巯基丙酸内盐(DMSP,分溶解态DMSPd和颗粒态DMSPp)的含量,研究了其空间分布格局及其影响因素,探讨了表层海水DMS的生物周转和去除途径。结果表明,表层海水DMS、DMSPd和DMSPp的平均浓度分别为5.36nmol/L、15.63nmol/L和96.73nmol/L,受挪威海流和北极深层水影响,表层海水二甲基硫化物浓度呈现出由低纬度向高纬度海域递减的趋势。DMSPd和DMSPp浓度与Chl a浓度均有显著的相关性,说明浮游植物生物量是影响挪威海和格陵兰海二甲基硫化物生产的重要因素。表层海水DMS生物生产和消费速率平均值分别为18.19nmol/(L·d)、15.67nmol/(L·d)。DMS微生物周转时间变化范围为0.03~1.80d,平均值为0.49d,DMS海-气周转时间是微生物消费时间的90倍,说明夏季挪威海和格陵兰海表层海水中DMS微生物消费过程是比海-气扩散更具优势的去除机制。     

热带太平洋海温异常对北极海冰的可能影响

本文利用1950-2015年间Hadley环流中心海冰和海温资料及NCEP/NCAR再分析资料,研究了热带太平洋海温异常对北极海冰的可能影响,并从大气环流和净表面热通量两个角度探讨了可能的物理机制。结果表明,在ENSO事件发展年的夏、秋季节,EP型与CP型El Niño事件与北极海冰异常的联系无明显信号。而La Niña事件期间北极海冰出现显著异常,并且EP型与CP型La Niña之间存在明显差异。EP型La Niña发生时,北极地区巴伦支海、喀拉海关键区海冰异常减少,CP型La Niña事件则对应着东西伯利亚海、楚科奇海地区海冰异常增加。在EP型La Niña发展年的夏、秋季节,热带太平洋海温异常通过遥相关波列,使得巴伦支海、喀拉海海平面气压为负异常并与中纬度气压正异常共同构成类似AO正位相的结构,形成的风场异常有利于北大西洋暖水的输入,同时造成暖平流,偏高的水汽含量进一步加强了净表面热通量收入,使得巴伦支海、喀拉海海冰异常减少。而在CP型La Niña发展年的夏季,东西伯利亚海、楚科奇海关键区受其东侧气旋式环流的影响,以异常北风分量占主导,将海冰从极点附近由北向南输送到关键区,海冰异常增加,而净表面热通量的作用较小。     

北极秋季海冰密集度与中国初冬降雨之间的关系

本文通过对中国地区实测降水及北极海冰卫星数据的分析,研究了北极秋季海冰密集度与中国初冬降雨的关系。合成分析的研究结果表明2000年之前中国南方和北方冬季降水偏少,中部降水偏多,这之后中国南方和北方冬季降水增加,中部降水减少。SVD研究结果显示,北极海冰减少使得近三十年来中国南方和北方冬季降雨呈现逐渐增多,中部地区(从青藏高原向东北方向至日本)降雨逐步减少的趋势。随着北极海冰的进一步减少,如遇合适的气候条件,南方冻雨出现的概率会加大。北极秋季海冰异常的回复过程加之冬季海冰异常的延续信号在中国、蒙古及日本北部激发一个阻塞高压,以巴伦支海/卡拉海为中心激发一个异常低压。这使得来自北冰洋大西洋扇区的冷空气南下至欧洲大陆和亚洲北部,在阻塞高压的影响下,冷空气进一步南下,进入东亚地区。这不仅使得亚洲冬季温度降低,也为中国北部降水增加提供条件。     

Sea-ice flux in the East Greenland Current

The sea-ice export out of the central Arctic through the Fram Strait is a key variable in the Arctic climate system. Satellite data provide the only basis for mapping ice features with a high spatial and temporal resolution in polar regions. An automatic drift algorithm has been employed and optimized to monitor the sea-ice drift velocity in the Greenland Sea with AVHRR data. The combination of the ice drift and the spatial ice distribution provides an insight into the ice transport processes along the coast of Greenland. The combination with sea-ice thickness measurements allows an estimation of the spatial distribution of the sea-ice mass flux. The seasonal and spatial variability of the mass flux allows further predictions of the meridional melting and freezing processes along the East Greenland Current. This investigation covers the years 1993 and 1994. Seasonal and spatial distributions of the sea-ice drift were derived. The derived absolute values in this study are in good agreement with estimates proposed by other authors.     

Dominant climate factors influencing the Arctic runoff and association between the Arctic runoff and sea ice

By using the Arctic runoff data from R-ArcticNET V4.0 and ArcticRIMS, trends of four major rivers flowing into the Arctic Ocean, whose climate factor plays an important role in determining the variability of the Arctic runoff, are investigated. The results show that for the past 30 years, the trend of the Arctic runoff is seasonally dependent. There is a significant trend in spring and winter and a significant decreasing trend in summer, leading to the reduced seasonal cycle. In spring, surface air temperature is the dominant factor influencing the four rivers. In summer, precipitation is the most important factor for Lena and Mackenzie, while snow cover is the most important factor for Yenisei and Ob. For Mackenzie, atmospheric circulation does play an important role for all the seasons, which is not the case for the Eurasian rivers. The authors further discuss the relationships between the Arctic runoff and sea ice. Significant negative correlation is found at the mouth of the rivers into the Arctic Ocean in spring, while significant positive correlation is observed just at the north of the mouths of the rivers into the Arctic in summer. In addition, each river has different relationship with sea ice in the eastern Greenland Sea.     

北极中央区经向水汽输送的主要通道

Atmospheric moisture transport plays an important role in latent heat release and hydrologic interactions in the Arctic. In recent years, with the rapid decline in sea ice, this transport has changed. Here, we calculated the vertically integrated atmospheric moisture meridional transport(AMTv) from two global reanalysis datasets, from1979–2015, and found moisture pathways into the central Arctic. Four stable pathways showed an occurrence frequency greater than 70%, and these pathways exhibited a perennial seasonal pattern in the atmosphere above the Laptev Sea Pathway(LSP), Canadian Arctic Archipelago Pathway(CAAP), both sides of the Greenland plateau. Another seasonal pathway appeared above the east of the Chukchi Sea(CSP) during the melting/freezing months(March to September). Through these pathways, AMTv contributed a total moisture exchange of60%–80%—averaged over a 75°N circle—and focused on the low troposphere. Transports across the LSP, CSP and CAAP pathways likely create an enclosed moisture route. Meridional moisture fluxes are intensified in the Pacific sector of Arctic(PSA), especially during melting/freezing months. AMTv interannual variabilities are illustrated mainly in the Laptev Sea and the east Greenland pathway. Results indicate that accompanying a tendency for a stronger Beaufort Sea High in this sea level pressure field, AMTv through PSA pathways, switched from output to input, and approximately 960 km~3 of equivalent liquid water was transferred into the central Arctic during each decade. The detrended AMTv increment is highly correlated with the rapid decline of old ice areas(correlation coefficient is –0.78) for their synchronous fluctuations in the 1980 s and the last decade.     

一个区域海洋——海冰——大气耦合模式中的北极气候偏差：年结果检验

The Coupling of three model components, WRF/PCE （polar climate extension version of weather research and forecasting model （WRF））, ROMS （regional ocean modeling system）, and CICE （community ice code）, has been implemented, and the regional atmosphere-ocean-sea ice coupled model named WRF/PCE- ROMS-CICE has been validated against ERA-interim reanalysis data sets for 1989. To better understand the reasons that generate model biases, the WRF/PCE-ROMS-CICE results were compared with those of its components, the WRF/PCE and the ROMS-CICE. There are cold biases in surface air temperature （SAT） over the Arctic Ocean, which contribute to the sea ice concentration （SIC） and sea surface temperature （SST） biases in the results of the WRF/PCE-ROMS-CICE. The cold SAT biases also appear in results of the atmo- spheric component with a mild temperature in winter and similar temperature in summer. Compared to results from the WRF/PCE, due to influences of different distributions of the SIC and the SST and inclusion of interactions of air-sea-sea ice in the WRF/PCE-ROMS-CICE, the simulated SAT has new features. These influences also lead to apparent differences at higher levels of the atmosphere, which can be thought as responses to biases in the SST and sea ice extent. There are similar atmospheric responses in feature of distribution to sea ice biases at 700 and 500 hPa, and the strength of responses weakens when the pressure decreases in January. The atmospheric responses in July reach up to 200 hPa. There are surplus sea ice ex- tents in the Greenland Sea, the Barents Sea, the Davis Strait and the Chukchi Sea in winter and in the Beau- fort Sea, the Chukchi Sea, the East Siberian Sea and the Laptev Sea in summer in the ROMS-CICE. These differences in the SIC distribution can all be explained by those in the SST distributions. These features in the simulated SST and SIC from ROMS-CICE also appear in the WRF/PCE-ROMS-CICE. It is shown that the performance of the WRF/PCE-ROMS-CICE is determined to a l     

中国东部海域大气气溶胶入海通量的研究

根据中国东部海域气溶胶浓度及分级采样资料,计算得出黄海、东海及日本以南海域沙尘气溶胶的代表元素铝(Al)每月干沉降通量分别为42.8、18.3、5.2mg/m2;其中各海域春季的干沉降通量均占全年干沉降通量的40%以上.相应每月总沉降通量分别为54.1、29.8、10.5mg/m2.渤海、黄海、东海及日本以南海域每年沙尘气溶胶总沉降通量分别为26.4、9.3、5.1、1.8g/m2.东海污染元素总沉降通量以春季最大,夏、秋季次之,冬季最小.日本以南海域锑(Sb)元素总沉降通量的季节分布为冬季最大,夏、秋季次之,秋季最小;硒(Se)元素总沉降通量的最大值出现在夏季,其他季节分布比较均匀.     

1979-2012年北极海冰运动学特征初步分析

利用美国冰雪数据中心(NSIDC)发布的海冰速度和范围数据,本文分析了1979—2012年间北极海冰的运动学特征,以及北极海冰运动与分布范围演变之间的关系。结合欧洲中期天气预报中心(ECMWF)发布的2007和2012年高分辨率的气压场、风场数据,探讨了北极风场和气压场与海冰运动、辐散辐合和海冰面积的关系。结果表明,在1979-2012年间北极海冰平均运动速度呈显著增强的趋势,冬季海冰平均运动速度增加趋势明显强于夏季;北极、波弗特-楚科奇海域和弗拉姆海峡的冬、夏季海冰平均运动速度的增加率分别为2.1%/a和1.7%/a、2.0%/a和1.6%/a以及4.9%/a和2.2%/a。1979-2012年北极海冰平均运动速度和范围的相关性为-0.77,二者存在显著的负相关关系。北极冬季和夏季风场的长期变化趋势与海冰平均运动速度的变化趋势一致,冬季和夏季的相关系数分别为0.50和0.48。风场和气压场对海冰的运动、辐散及重新分布发挥着重要作用。2007年夏季,第234~273天波弗特海域一直被高压系统控制,波弗特涡旋加强,使得波弗特海域海冰聚集在北极中央区;顺时针的风场促使海冰向格陵兰岛和加拿大北极群岛以北聚合。2012年,白令海峡和楚科奇海域处于低压和高压系统的交界处,盛行偏北风,海冰从北极东部往西部输运,加拿大海盆的多年海冰因离岸运动而辐散,向楚科奇海域的海冰输运增加,受太平洋入流暖水影响,移入此区域的海冰加速融化,从而加剧海冰的减少。     

北极海冰变率的独特模式及其与大气强迫的关系

The spatial structure of the Arctic sea ice concentration(SIC) variability and the connection to atmospheric as well as radiative forcing during winter and summer for the 1979–2017 period are investigated. The interannual variability with different spatial characteristics of SIC in summer and winter is extracted using the empirical orthogonal function(EOF) analysis. The present study confirms that the atmospheric circulation has a strong influence on the SIC through both dynamic and thermodynamic processes, as the heat flux anomalies in summer are radiatively forced while those in winter contain both radiative and "circulation-induced" components. Thus,atmospheric fluctuations have an explicit and extensive influence to the SIC through complex mechanisms during both seasons. Moreover, analysis of a variety of atmospheric variables indicates that the primary mechanism about specific regional SIC patterns in Arctic marginal seas are different with special characteristics.     

Dimethylsulphide and dimethylsulphoniopropionate in Antarctic sea ice and their release during sea ice melting

This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP) in a variety of sea ice and seawater habitats in the Antarctic Sea Ice Zone (ASIZ) during spring and summer. Sixty-two sea ice cores of pack and fast ice were collected from twenty-seven sites across an area of the eastern ASIZ (64°E to 110°E; and the Antarctic coastline north to 62°S). Concentrations of DMS in 81 sections of sea ice ranged from < 0.3 to 75 nM, with an average of 12 nM. DMSP in 60 whole sea ice cores ranged from 25 to 796 nM and showed a negative relationship with ice thickness (y = 125x^− 0.8). Extremely high DMSP concentrations were found in 2 cores of rafted sea ice (2910 and 1110 nM). The relationship of DMSP with ice thickness (excluding rafted ice) suggests that the release of large amounts of DMSP during sea ice melting may occur in discrete areas defined by ice thickness distribution, and may produce ‘hot spots’ of elevated seawater DMS concentration of the order of 100 nM. During early summer across a 500 km transect through melting pack ice, elevated DMS concentrations (range 21–37 nM, mean 31 nM, n = 15) were found in surface seawater. This band of elevated DMS concentration appeared to have been associated with the release of sea ice DMS and DMSP rather than in situ production by an ice edge algal bloom, as chlorophyll a concentrations were relatively low (0.09–0.42 μg l^− 1). During fast ice melting in the area of Davis station, Prydz Bay, sea ice DMSP was released mostly as extracellular DMSP, since intracellular DMSP was negligible in both hyposaline brine (5 ppt) and in a melt water lens (4–5 ppt), while extracellular DMSP concentrations were as high as 149 and 54 nM, respectively in these habitats. DMS in a melt water lens was relatively high at 11 nM. During the ice-free summer in the coastal Davis area, DMS concentrations in surface seawater were highest immediately following breakout of the fast ice cover in late December (range 5–14 nM), and then remained at relatively low concentrations through to late February (< 0.3–6 nM). These measurements support the view that the melting of Antarctic sea ice produces elevated seawater DMS due to release of sea ice DMS and DMSP.