Total column densities of tropospheric and stratospheric trace gases in the undisturbed Arctic summer atmosphere

Ground-based FTIR measurements have been performed in the Arctic summer in July 1993 and June 1994 at 79° N to study the zenith column densities of several trace gases in the undisturbed Arctic summer atmosphere. Zenith column densities of H₂O, N₂O, HNO₃, NO₂, NO, ClONO₂, ClO, HCl, HF, COF₂, OCS, SF₆, HCN, CH₄, C₂H₆, C₂H₂, CO, O₃, CFC-12, CFC-22, and CO₂ were retrieved by line-by-line calculations. The results are compared with winter and springtime observations measured at the same site, with column densities obtained in the Antarctic summer atmosphere, and with measurements at midlatitudes. For HCl the spectra give lower total zenith columns than expected, but the ratio HF/HCl agrees well with midlatitude literature data. Measurements of ClONO₂ give low total columns in agreement with observations at midlatitudes. In the undisturbed atmosphere HCl was found to be in excess of ClONO₂. The total columns of HNO₃, N₂O and the sum of NO and NO₂ agree with summer observations in Antarctica. Results for the tropospheric trace gas C₂H₆ are higher by 250% when compared with Antarctic observations. Contrary to N₂O and CH₄ the seasonal cycle of C₂H₆ and C₂H₂ give much higher total columns in winter/spring compared to the summer observations. This is assigned to transport of polluted airmasses from mid-latitudes into the Arctic.     

Arctic hazes in summer over Greenland and the North American Arctic: II. Nature and concentrations of accumulation-mode and giant particles

Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents.     

Impact of clouds on the surface radiation balance of the Arctic Ocean

Summary The relationship between clouds and the surface radiative fluxes over the Arctic Ocean are explored by conducting a series of modelling experiments using a one-dimensional thermodynamic sea ice model. The sensitivity of radiative flux to perturbations in cloud fraction and cloud optical depth are determined. These experiments illustrate the substantial effect that clouds have on the state of the sea ice and on the surface radiative fluxes. The effect of clouds on the net flux of radiation at the surface is very complex over the Arctic Ocean particularly due to the presence of the underlying sea ice. Owing to changes in surface albedo and temperature associated with changing cloud properties, there is a strong non-linearity between cloud properties and surface radiative fluxes. The model results are evaluated in three different contexts: 1) the sensitivity of the arctic surface radiation balance to uncertainties in cloud properties; 2) the impact of interannual variability in cloud characteristics on surface radiation fluxes and sea ice surface characteristics; and 3) the impact of climate change and the resulting changes in cloud properties on the surface radiation fluxes and sea ice characteristics.With 11 Figures     

Carbon dioxide and methane in the Arctic atmosphere

Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO₂) and methane (CH₄). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH₄/ppm CO₂, a standard error of 0.6, and a correlation coefficient (r²) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.     

The Summer Arctic Boundary Layer during the Arctic Ocean Experiment 2001 (AOE-2001)

Boundary-layer measurements made from the Swedish icebreaker Oden during the Arctic Ocean Experiment 2001 (AOE-2001) are analysed. They refer mainly to ice drift in the central Arctic during the period 2–21 August 2001. On board Oden a remote sensing array with a wind profiler, cloud radar and a scanning microwave radiometer, and a regular weather station operated continuously; soundings were also released during research stations. Turbulence and profile measurements on an 18-m mast were deployed on the ice, along with two sodar systems, a microbarograph array and a tethered sounding system. Surface flux and meteorological stations were also deployed on nearby ice floes. There is a clear diurnal cycle in radiation and also in wind speed, cloud base and visibility. It is absent in temperature and humidity, probably due to the very strong control by melting/ freezing ice and snow. In the advection of warm air, latent heat of melting maintains the surface temperature at 0 °C, while with a negative energy balance the latent heat of freezing of the salty ocean water acts to maintain the surface temperature > −2 °C. The constant presence of water at the surface maintains a relative humidity close to 100%, and this is also often facilitated by an increasing specific humidity through the capping inversion, making entrainment a moisture source. This ensures cloudy conditions, with low cloud and fog prevailing most of the time. Intrusions of warm and moist air from beyond the ice edge are frequent, but the local Arctic boundary layer remains at a relatively constant temperature, and is shallow and well mixed with strong capping inversions. Power spectra of surface-layer wind speed sometimes show large variance at low frequency. A scanning radiometer provides a monitoring of the vertical thermal structure with a spatial and temporal resolution not seen before in the Arctic. There are often two inversions, an elevated main inversion and a weak surface inversion, and occasionally additional inversions occur. Enhanced entrainment across the main inversion appears to occur during frontal passages. Variance of the scanning radiometer temperatures occurs in large pulses rather than varying smoothly, and the height to the maximum variance appears to be a reasonable proxy for the boundary-layer depth.     

夏季赤道西印度洋对大气的强迫作用及其机制研究

基于1982—2015年高分辨率海气资料,从海表面温度(Sea Surface Temperature, SST)和海表面风速相关关系的角度研究了年际尺度上赤道印度洋的海气关系。结果表明,印度洋的海气关系具有明显区域性和季节性特征,即整个印度洋除赤道东南印度洋和赤道西印度洋SST与海表风速在夏季(7—9月)为显著正相关关系,主要表现为海洋影响大气;其他地区和月份均为负相关关系,主要表现为大气对海洋的强迫作用。回归分析发现,夏季赤道西印度洋SST异常可能通过海平面气压调整机制影响海表面风场,即海温增温使边界层空气增暖,海表面风场辐合增强;反之则相反。此外,还利用AM2.1模式进行模拟试验,试验结果成功地再现了夏季赤道西印度洋海表面温度与海表风速之间的正相关关系。     

Characteristics of carbonaceous particles in Beijing during winter and summer 2003

Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer.     

夏半年热带太平洋中部型海温异常与热带印度洋海盆模对同期中国东部降水的共同影响

利用1961—2013年NCEP/NCAR再分析资料和Had ISST月平均海表面温度资料,分析了夏半年热带太平洋中部型海温异常与热带印度洋海盆模(Indian Ocean Basin M ode,IOBM)的特征,并研究了不同位相配置时二者对同期中国东部气候的共同影响。结果表明:1)太平洋中部型海温异常指数与印度洋海盆模指数几乎相互独立。太平洋中部型海温异常与IOBM同位相变化(记为PPNN事件)和反位相变化(记为PNNP事件)时,热带印太地区海温异常分别呈三级型和偶极型分布。2)不同位相配置对中国东部地区降水异常的影响及其影响机制存在显著差异:当发生PPNN事件时,水汽从海洋性大陆(Maritime Continent,MC)地区向江淮流域输送;热带海温异常引起大气产生Gill型响应,维持了中国东部的环流异常;M C地区通过经向三圈异常垂直环流引起江淮流域降水异常增多。发生PNNP事件时,Gill型环流响应中心西移,长江流域降水偏少,水汽辐散;同时MC地区对流层低层准定常Rossby波能传播也有利于长江流域扰动的维持。这些结果对深刻认识中国东部地区夏半年降水异常成因和印度洋/太平洋海温异常不同分布的作用具有重要意义。     

Variability of summer cloudiness in the Arctic Basin

Summary The extent and thickness of clouds in the Arctic Basin varied considerably in space and time in the late springs and summers of 1977–1979. While, on the average, clouds covered two thirds or more of the basin at any one time, cloud-free episodes were particularly common from the middle of June to late July and persisted locally for several days or even weeks. The central Arctic was less cloudy than the ocean zones closer to the coast in spring, but more cloudy in summer. Most clouds were semi-transparent, allowing recognition of underlying surface features. Optically thick clouds with middle and high level tops were associated with low pressure systems and with atmospheric flows from lower latitudes at the surface and aloft. Cloud-free skies were most frequent in high pressure cells. Climate models used to assess the impact of CO₂ and other trace gases on the radiation budget in the high latitudes should account for the heterogeneity of cloud extent and thickness in the Arctic Basin.With 12 Figures     

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...     

基于BP-CCA的贵州夏季降水与太平洋海温耦合关系

利用贵州83个台站1979—2011年的夏季月降水资料、海温、气压场、风场等再分析格点资料及副高指数资料,利用点相关找出影响贵州夏季降水的海温关键区及关键时段,利用变形的典型相关分析(BP-CCA)方法对贵州夏季降水与关键区海温的耦合关系进行了分析,并对海温影响贵州夏季降水的可能机制进行了探讨。结果表明:1影响贵州夏季降水的海温关键区域为北太平洋及中东赤道太平洋,其中尤以加利福尼亚冷流区、北太平洋暖流区对贵州夏季降水的影响更为重要,关键时段为上一年7-9月;2BP-CCA第一对典型相关场分析结果表明:加利福尼亚冷流区海温与贵州夏季降水呈同位相变化,而北太平洋暖流区海温与贵州夏季降水呈反相位变化,关键区海温对贵州北部降水的耦合好于南部,而对西南部的耦合最差;3前期7-9月海温与副高强度指数的相关系数分布呈EI Nino型,与副高西伸脊线指数的相关系数分布在中低纬度西太平洋呈正相关,与中东赤道太平洋呈负相关,与副高脊点的相关系数与海温和副高的强度相关分布相反,在赤道中东太平洋为负相关区,西北太平洋为正相关区,海温分布型为LA Nina型。东北太平洋及中东赤道太平洋海温异常与贵州500h Pa气压场及风场显著正相关,而西北太平洋海温与贵州地区500 h Pa气压场及风场成负相关,为典型的EI Nino型。     

Association of Indian Ocean ITCZ Variations with the Arctic Oscillation during Boreal Winter

In this study,the authors analyzed the associations between the Arctic Oscillation(AO)and the tropical Indian Ocean(TIO)intertropical convergence zone(ITCZ)in boreal winter for the period 1979–2009.A statistically significant AO-TIO ITCZ linkage was found.The ITCZ vertical air motion is significantly associated with the AO,with upward(downward)air motion corresponding to the positive(negative)AO phase.The Arabian Sea anticyclone plays a crucial role in linking the AO and the TIO ITCZ.The Arabian Sea vorticity is strongly linked to high-latitude disturbances in conjunction with jet stream waveguide effects of disturbance trapping and energy dispersion.During positive(negative)AO years,the Arabian Sea anticyclone tends to be stronger(weaker).The mean vorticity over the Arabian Sea,averaged from 850hPa to 200 hPa,has a significant negative correlation with AO(r=0.63).The anomalous anticyclone over the Arabian Sea brings stronger northeastern winds,which enhance the ITCZ after crossing the equator and result in greater-than-normal precipitation and minimum outgoing long-wave radiation.     

Drag coefficient and roughness length determinations on an Alaskan Arctic Coast during summer

Field data collected over land and water near Point Lay, Alaska, yielded determinations of the aerodynamic roughness lengths and drag coefficients over three locations on an arctic barrier island and over the Chukchi Sea. The agreement between the results over the sea and previous published results from data taken at approximately the same latitude in the Beaufort Sea is excellent.     

Predictability of Northwest Pacific climate during summer and the role of the tropical Indian Ocean

A seasonal forecast system based on a global, fully coupled ocean?Catmosphere general circulation model is used to (1) evaluate the interannual predictability of the Northwest Pacific climate during June?CAugust following El Ni?o [JJA(1)], and (2) examine the contribution from the tropical Indian Ocean (TIO) variability. The model retrospective forecast for 1983?C2006 captures major modes of atmospheric variability over the Northwest Pacific during JJA(1), including a rise in sea level pressure (SLP), an anomalous anticyclone at the surface, and a reduction in subtropical rainfall, and increased rainfall to the northeast over East Asia. The anomaly correlation coefficient (ACC) for the leading principal components (PCs) of SLP and rainfall stays above 0.5 for lead time up to 3?C4?months. The predictability for zonal wind is slightly better. An additional experiment is performed by prescribing the SST climatology over the TIO. In this run, designated as NoTIO, the Northwest Pacific anticyclone during JJA(1) weakens considerably and reduces its westward extension. Without an interactive TIO, the ACC for PC prediction drops significantly. To diagnose the TIO effect on the circulation, the differences between the two runs (Control minus NoTIO) are analyzed. The diagnosis shows that El Nino causes the TIO SST to rise and to remain high until JJA(1). In response to the higher than usual SST, precipitation increases over the TIO and excites a warm atmospheric Kelvin wave, which propagates into the western Pacific along the equator. The decrease in equatorial SLP drives northeasterly wind anomalies, induces surface wind divergence, and suppresses convection over the subtropical Northwest Pacific. An anomalous anticyclone forms in the Northwest Pacific, and the intensified moisture transport on its northwest flank causes rainfall to increase over East Asia. In the NoTIO experiment, the Northwest Pacific anticyclone weakens but does not disappear. Other mechanisms for maintaining this anomalous circulation are discussed.     

Heat exchange between water and ice in the Arctic Ocean

Summary The heat balance equation for the bottom surface of floating sea ice is evaluated on the basis of observations of ice temperature, water temperature, current velocity, and ablation or accretion of ice. Assuming equality of the eddy diffusivities for momentum, heat, and salt (average 24 cm² sec^–1) it is shown that the temperature gradient in the oceanic boundary layer is extremely small (averages between 2.10^–5 and 4.10^–4°C/meter) and difficult to measure directly. It is suggested that a large part of the heat transfer from the relatively warm Atlantic water to the arctic atmosphere may occur through open leads in the ice cover.

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Zusammenfassung Die Wärmebilanzgleichung für die Unterseite von schwimmendem Meereis wird an Hand von Beobachtungen der Eistemperatur, der Wassertemperatur, der Strömungsgeschwindigkeit und der Eisdickenänderung ausgewertet. Unter der Annahme gleicher Austauschkoeffizienten für Bewegungsgröße, Wärme und Salzgehalt (im Mittel 24 cm² sec^–1) ergibt sich für die ozeanische Grenzschicht ein außerordentlich kleiner Gradient der Wassertemperatur (durchschnittlich zwischen 2.10^–5 und 4.10^–4°C/Meter), der durch direkte Beobachtungen schwer nachzuweisen ist. Es ist zu vermuten, daß ein beträchtlicher Teil der Wärmeabgabe von der relativ warmen atlantischen Wassermasse an die arktische Atmosphäre durch Öffnungen in der Meereisdecke erfolgt.

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Résumé On établit l'équation du bilan thermique valable pour la surface inférieure de la glace marine dérivante. Pour ce faire, on se sert d'observations de la température de la glace, de celle de l'eau, de la vitesse du courant et des variations de l'épaisseur de la glace. En admettant que les coefficients d'échange sont les mêmes pour la quantité de mouvement, la chaleur et le taux de salinité (en moyenne 24 cm² sec^–1), il résulte pour la couche limite un gradient extrêmement faible de la température de l'eau (situé en moyenne entre 2·10^–5 et 4·10^–4°C/m); un tel gradient est difficile à prouver au moyen d'observations directes. On peut supposer qu'une partie importante de la chaleur transmise par l'eau relativement chaude de l'Atlantique à l'atmosphère arctique passe au travers des lacunes de la couche de glace recouvrant l'océan.

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Contribution 141, Department of Atmospheric Sciences, University of Washington, Seattle. This is a thesis submitted by the author in partial fulfillment of the requirements for the degree of Master of Science.     

Intercomparison of Surface Radiative Fluxes in the Arctic Ocean

Recent satellite data analysis has provided improved data sets relevant to the surface energy budget in the Arctic Ocean. In this paper, surface radiation properties in the Arctic Ocean obtained from the Surface Radiation Budget（SRB3.0） and the International Satellite Cloud Climatology Project（ISCCP-FD） during 1984– 2007 are analyzed and compared. Our analysis suggests that these datasets show encouraging agreement in basin-wide averaged seasonal cycle and spatial distribution of surface albedo; net surface shortwave and all-wave radiative fluxes; and shortwave, longwave, and all-wave cloud radiative forcings. However, a systematic large discrepancy is detected for the net surface longwave radiative flux between the two data sets at a magnitude of ~ 23 W m–2, which is primarily attributed to significant differences in surface temperature, particularly from April to June. Moreover, the largest difference in surface shortwave and all-wave cloud radiative forcings between the two data sets is apparent in early June at a magnitude of 30 W m–2.     

Arctic hazes in summer over Greenland and the North American Arctic. I: Incidence and origins

Airborne observations during August 1985 over Greenland and the North American Arctic revealed that dense, discrete haze layers were common above 850 mb. No such hazes were found near the surface in areas remote from local sources of particles. The haze layers aloft were characterized by large light-scattering coefficients due to dry particles (maximum value 1.24 × 10^–4m^–1) and relatively high total particle concentrations (maximum value 3100 cm^–3). Sulfate was the dominant ionic component of the aerosol (0.06 – 1.9 g m^–3); carbon soot was also present. Evidence for relatively fresh aerosols, accompanied by NO₂ and O₃ depletion, was found near, but not within, the haze layers. The hazes probably derived from anthropogenic sources and/or biomass burning at midlatitudes.It is hypothesized that the scavenging of particles by stratus clouds plays an important role in reducing the frequency and intensity of hazes at the surface in the Arctic in summer. Since the detection of haze layers aloft through measurements of column-integrated parameters from the surface (e.g., by lidar) cannot be carried out reliably when clouds are present, such measurements have likely underestimated the occurrence of haze layers in the Arctic, particularly in summer.