北极夏季大气垂直结构与空间分布特征

低层大气垂直物理剖面是研究大气边界层过程、模拟大气环流过程和进行天气预报的关键参数,海洋特别是北冰洋地区是气象实测资料的稀疏区甚至是空白区。因此,中国第6次北极科学考察期间(2014年7月21日至9月11日),我们使用GPS低空探空系统,对北极地区的大气垂直结构和边界层特征进行了观测实验。实地观测结果表明:(1)递减率对流层顶(LRT)和冷点对流层顶(CPT)均能准确的判断该地区对流层顶的高度和温度,NCEP再分析资料在较低纬度能够很好的反应对流层顶变化特征,但是在海冰密集的北极地区(海冰密集度达9成以上)则相对较差,所以很有必要在该区域开展探空观测研究。(2)在高空存在一个明显的低温区和高空急流,低温区和高空急流中心区的海拔高度与对流层顶高度一致;在晴天和少云天气,对流层顶高度变化不大;在多云和阴雨天气,随着纬度的升高对流层顶高度逐渐降低。在晴天和少云天气相比多云和阴雨天气,高空急流区的强度较弱,垂直和水平均范围较小。(3)CPT和高空急流的高度随着纬度有降低的趋势,75°N以北的区域降低显著;对流层垂直温度递减率随着纬度呈现出逐渐增大的趋势。(4)观测期间,在海拔3km以下均存在多个逆温层。其中风速切变在逆温层的消失或者减弱过程中起着重要作用,而在80°N以北区域,对流层顶逆温(TIL)明显小于其他区域。表明极点附近对流层与平流层之间的物质和能量交换相比其他区域更加强盛。     

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...     

北冰洋夏季的海雾

以中国首次北极科学考察采用国内外海冰、大气和海洋的先进观测设备,获得海、陆、空的同步或准同步观测资料为基础,重点研究北冰洋的海雾.发现在北冰洋大范围被海冰覆盖或冰水相间的洋面上,能够形成平流雾、辐射雾和蒸汽雾.每种海雾的特点和形成的物理机制不同.在北冰洋的南部,由于暖湿气流充分,易形成持续时间长、浓度大的平流雾;在冰盖和大浮冰块上,由于冰雪面的强辐射冷却,容易形成稳定的辐射雾;在浮冰区能够形成像开锅的蒸汽一样的蒸汽雾.指出在北冰洋形成多种海雾原因是海冰的分布及独特的物理特性造成下垫面性质的复杂化,产生的海气相互作用复杂化的结果,特别是冰雪面的反照率高,不能吸收极昼期充足的太阳辐射.冰又是热的不良导体,成为海气热交换的屏障,在浮冰区由于冰屏障的破碎,海气交换活跃.海洋以潜热的形式向大气输送热量,以蒸汽雾的形式反映出海气热交换的程度和对气候影响的一种表现形式.提出在蒸汽雾发生的过程中,海洋以感热的形式向大气输送热量.     

北冰洋浮冰区湍流通量观测试验及参数化研究

利用2008年8月21～29日我国第3次北极考察期间在北冰洋海区(84°27′N,143°37′W～85°13′N,147°20′W)冰站观测的湍流资料及相关资料,对海冰近地层湍流通量及其特征参数进行了研究.结果表明:观测期间浮冰近地层始终存在逆温和逆湿层.这与我们以前(1999年在75°N和2003年在78°N)的观...     

对流层顶研究回顾

大气急流、飞机颠簸、臭氧层顶等重要物理、化学现象均与对流层顶的位置、强度及其变动密切相关,因此在研究自由大气的气候和大气环流时,作为对流层与平流层过渡层的对流层顶是非常重要的,对流层顶研究已成为当今大气科学的研究热点之一。对近几十年来对流层顶研究领域的有关研究作了简要回顾,主要从对流层顶的分布特征、对流层顶要素变化以及对流层顶与臭氧的关系等几个方面进行综述。在此基础上,总结出对流层顶研究遇到的几个困难。     

北冰洋沉积物中浮冰碎屑含量与物源的区域变化--示踪北极地区晚第四纪大气和海洋环流格局

在用箱式和重力活塞取样器获得的岩心中 ,浮冰碎屑成分和分布可以为重建北冰洋晚更新世和全新世洋流分布格局提供有用的信息。 2 0世纪 60年代到 90年代有关北冰洋冰筏、沉积物组成和浮冰碎屑物源的研究主要集中在砾级范围内。 90年代以后许多学者开始研究细粒的浮冰碎屑成分及其物源 ( >2 50μm或2 50～ 3 0 0μm)。由于冰川冰山所携带和沉积的主要是粗粒浮冰碎屑 ,所以本次研究的重点为大于 2 mm的砾级碎屑。在现今的北冰洋 ,控制海冰和冰川冰山运动的表层洋流主要是美亚海盆中顺时针波弗特涡流和欧亚海盆中东向的绕极漂流。Bischof和Dar…     

北冰洋表层积雪中7Be、210Po和210Pb的分布特征

大气输送的放射性核素7Be、210Po和210Pb,可以作为研究北冰洋大气沉降通量、海洋现代沉积以及海冰中物质传输的重要示踪剂,已被广泛应用于包括气团运动、土壤侵蚀以及水系统中颗粒物循环过程的研究。本文报道了2018年北极高纬度浮冰区表层积雪中7Be、210Po和210Pb的活度特征。7Be、210Po和210Pb的比活度变化范围分别为33.6～632.68 mBq/L、36.2～87.5 mBq/L、30.9～194.49 mBq/L。本文的研究发现,北冰洋表层积雪中7Be和210Pb比活度小于中纬度大陆地区。研究区域表层积雪中7Be的比活度随着纬度的增加而增加。此外,表层积雪中210Po/210Pb活度比值范围为0.70～1.48 (平均为0.93),210Po与210Pb活度已基本达到平衡,表明积雪样品年龄可能较“老”。     

夏季北极太平洋扇区和白令海对流层结构分析

利用我国第六次—第九次北极科学考察雪龙船走航探空数据,计算北极太平洋扇区和白令海的夏季对流层高度,分析对流层内的风速、温度、水汽廓线,从而确定对流层结构,并分析各要素的垂直分布和经向分布特征。结果表明:夏季北极太平洋扇区和白令海的递减率对流层顶、冷点对流层顶平均值分别为10 003 m、10 116 m,对流层高度随纬度增加而降低。夏季北极大气对流层低层和对流层顶存在逆温,对流层顶的逆温高度和厚度随纬度增加而降低。大气可降水量与纬度呈负相关,且集中于对流层中低层。近地面的风速受地表摩擦力的影响较明显,对流层内的风速随高度增加而增大,高空急流的强度和高度随纬度增加而减小,风廓线和急流易受天气尺度过程的影响。研究结果揭示了夏季北极太平洋扇区和白令海的对流层结构,并可用于检验数值预报模式对北极大气垂直结构的预报效果、评估再分析资料描述北极大气垂直结构的能力。     

基于PHC3.0数据集的北冰洋水团分析

基于PHC3.0极地科学中心水文气候数据集(简称PHC3.0数据集)的温度和盐度资料,使用聚类分析和Bayes判别分析的方法,对北纬70°以北海域的水团结构进行了分析,在北冰洋区域划分出4个水团:北冰洋表层水(ASW)、大西洋中层水(AIW)、太平洋水(PW)和北冰洋深层水(ADW)。北冰洋表层水(ASW)遍布于欧亚海盆和加拿大海盆,以低温低盐为特征。大西洋中层水(AIW)位于约200～900m深度,在北冰洋环极边界流的作用下,其影响可达到加拿大海盆。太平洋水(PW)受经白令海峡进入北冰洋的海水影响,相对高温低盐,夏季时影响显著。北冰洋深层水(ADW)在海盆中相当均匀,几乎没有季节变化,盐度约在34.95psu,温度在加拿大海盆约为-0.3℃,欧亚海盆约为-0.7℃。     

北极浮冰面积缩小

卫星拍摄的照片表明,在1984～1992年9月期间,北冰洋浮冰的面积缩小了2%,但南极水域浮冰面积在这期间几乎没有变化。这个结论与描述近期气候变化的一系列数学预测相符。这些预测认为,大气层“温室”气体浓度     

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.     

基于海豹观测的阿拉斯加湾东部陆坡海域逆温现象及其衰退机制

利用2014年3–4月北象海豹携带的自动温盐深仪（CTD-SRDL）在阿拉斯加湾东部陆坡海域上采集到的温盐剖面数据,分析了该海域逆温现象的空间分布和演变过程。结果显示,研究海域存在明显的逆温现象,逆温幅度和逆温厚度范围分别介于0.2~1.6?C和20~280 m之间,前者沿陆坡向北幅度逐渐增大,后者在50?~58?N间往北逐渐变厚,在58?N以北海域平均厚度较薄。3月25日至4月22日,逆温层处于衰退阶段。逆温层下界温度不断下降,逆温幅度呈变弱趋势,逆温厚度呈变薄趋势。一维扩散模型模拟结果表明,湍扩散作用下,观测期间海表受热导致混合层上部位温升高,但底部仍保持低温,因此逆温层上界温度变化并不明显。次表层由于具有强的位温梯度,湍扩散导致逆温层下界温度显著降低,是观测期间逆温衰退的主要原因。湍扩散作用导致次表层水体温盐属性趋于均匀,这一过程对于阿拉斯加湾逆温现象的形成及演变研究具有重要意义。     

2011年春、夏季黄、东海水团与水文结构分布特征

根据2011年春季(4月)夏季(8月)两个航次调查的CTD温盐资料,获得观测期间黄、东海主要水团特征:(1)夏季黄海冷水团10℃等温线在黄海海域中部30m以深,影响范围西至122°E南至34°N,最低温度为6.2℃,比气候态平均冷水团温度低约2℃;(2)夏季冲淡水以长江口为中心,呈半圆形向外扩展,并无明显NE转向,30.00等盐线在32°N断面上东至124°E,南至29.5°N,扩展范围与往年相比偏西1°左右,而在SE方向较往年有明显延伸扩展。水文结构特征为:(1)春季,温跃层主要在南黄海中部以西,跃层强度仅为0.10—0.40℃/m;密跃层主要在长江口以东,跃层强度0.20—0.30kg/m4;(2)夏季,温跃层强度最高值在长江口东北,跃层强度达到2.41℃/m,上界深度5.5m,厚度2.5m;黄海温跃层强度普遍强于东海,主要是冷水团区域表底显著的温度差异造成;密跃层强度高值区在33°N断面西侧海区,强度达到1.38kg/m4,上界深度5.5m,厚度约为1.5m;沿长江冲淡水舌轴方向的密跃层强度为0.30—0.60kg/m4,自西向东逐渐减弱。     

Formation of electrically active layers in the atmosphere with temperature inversion

The dynamics of the electric field in the planetary boundary layer (PBL) is thoroughly studied from in situ observations of the aeroelectric field and the height profiles of the wind-velocity components in the conditions of temperature inversion and incipient convection. It is established that the formation of a layer with temperature inversion is accompanied by a positive trend in the intensity of the aeroelectric field and by the generation of short-period aeroelectric pulsations. The transfer of a spatially nonuniform space charge and the formation of electrically active layers in PBL are studied by numerical modeling. The response of the electric field to the motion of the space charges simulating the coherent structures of electrogasdynamical turbulence is investigated for the vicinity of the observation point. The key parameters of the model distributions of the space charge are analyzed. The linear dimensions of the model structures range from 20 to 500 m, and the density of the transported charge varies from 0.1 to 1 nC/m³. The layer containing the model structures is located at a height of 60–300 m. It is shown that the spatial distribution and the transfer of the space charge form the dynamical component of the aeroelectric field in the surface layer. The short-period aeroelectric pulsations are induced by the transfer of the spatially heterogeneous space charge in PBL, while the positive trend is due to the accumulation of the space charge below the inversion layer. When the inversion was recorded by a sodar, the intensity of the field at the onset of the convection increased at a rate of 100 V/(m h) on average.     

2015年7月珠江口逆温现象的观测与分析

根据珠江口2015年7月6日至17日航次的CTD（conductivity， temperature， and depth）观测结果，分析得到：珠江口附近海域存在海水的垂向逆温现象，逆温差平均值为0.42 oC，上界深度在1 m-6 m间，下界深度在3 m-10 m间，逆温层平均厚度约为4 m。根据时空分布差异的不同，逆温现象可区分为以下三种情况：（1）在狮子洋、太平水道和蕉门水道的出口汇集处，存在温、盐差异的不同水体的交互过程中，由于潮汐和径流的作用所形成的水平流场差异导致了垂向温度的逆转现象。（2）在珠江口西侧的盐度锋面区域附近，第一航段观测期间锋面内侧低盐水团的温度低于锋面外侧高盐水团约2 oC，此时可观测到逆温现象；但在同一区域的第二航段观测期间由于河口内表层水温的上升，导致了逆温现象消失。该区域盐度锋面附近的两个水团在锋面位置附近发生叠置，冲淡水覆盖于海水之上，两个水团的温、盐差异是温度逆转现象的主因。（3）香港西南侧的上升流区域与盐度锋面的相互作用导致了该区域逆温现象的产生。     

Intercomparison of GPS radiosonde soundings during the eastern tropical Indian Ocean experiment

Temperature and relative humidity profiles derived from two China-made global positioning system（GPS） radiosondes（GPS-TK and CF-06-A） during the east tropical Indian Ocean（ETIO） experiment were compared with Vaisala RS92-SGP to assess the performances of China-made radiosondes over the tropical ocean.The results show that there have relative large biases in temperature observations between the GPSTK and the RS92-SGP in the low troposphere,with a warm bias of greater than 2 K in the day and a cooling bias of 0.6 K at night.The temperature differences of the CF-06-A were small in the troposphere both in daytime and nighttime,and became large peak-to-peak fluctuations in the stratosphere.The intercomparison of the relative humidity showed that the CF-06-A had large random errors due to the limitation of sensors and the lack of correction scheme,and the GPS-TK had large systematic biases in the low troposphere which might be related to the temperature impact.GPS height measurements are clearly suitable for China-made radiosonde systems operation.At night,the CF-06-A and the GPS-TK could provide virtual potential temperature and atmospheric boundary layer height measurements of suitable quality for both weather and climate research.As a result of the intercomparison experiment,major errors in the Chinamade radiosonde systems were well indentified and subsequently rectified to ensure improving accuracy for historical and future radiosondes.     

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.