内蒙古流动沙丘下垫面水热交换研究

利用2001年夏季的内蒙古东部流动沙丘地区大气边界层试验资料,采用空气动力学方法和涡动相关法计算动量通量、感热通量等湍流通量;分析了非平坦下垫面风速、温度廓线结构对湍流通量获取结果的影响和通量廓线关系的适用性;对比了空气动力学方法和涡动相关法获取湍流通量结果。同时,结合流动沙丘可移动、含水量多等地形和气候特征,讨论了非均匀下垫面下湍流通量获取方法。     

Estimates of diapycnal mixing in the abyssal ocean

Profiles of diapycnal eddy diffusivity to a maximum depth of 4000 meters were derived from ocean velocity and temperature microstructure data obtained in conjunction with separate experiments in the Northeast Pacific and Northeast Atlantic oceans. These profiles indicate that in the ocean interior where the internal wave field is at background intensity, the diapycnal eddy diffusivity is small (on the order of 0.1 x 10(-4) meters squared per second) and independent of depth, in apparent contradiction with large-scale budget studies. Enhanced dissipation is observed in regions of elevated internal wave energy, particularly near steeply sloping boundaries (where the eddy diffusivity estimates exceed 1 x 10(-4) meters squared per second). These results suggest that basin-averaged mixing rates may be dominated by processes occurring near the ocean boundaries.     

大涡模拟分析地表热通量对边界层对流卷的影响

本文利用1995年8月14日SCMS外场试验期间的观测资料,以及大涡模式模拟的边界层垂直速度数值实验结果,研究边界层对流卷的发展演变和地表热通量对其形式和强度的影响。对观测资料的分析表明：边界层对流卷的上升气流是暖湿气流,下沉气流则相对干冷。模拟结果显示：当有边界层对流卷存在时,地表热通量越小,对流卷的线性特征越明显,对流强度越弱;随着地表热通量的增大,组织性将减弱,对流运动发展强烈;当地表热通量值增大到维持边界层对流卷的阈值,对流卷的线性特征将消失。     

Vertical nitrate fluxes in the oligotrophic ocean

The vertical flux of nitrate across the thermocline in the upper ocean imposes a rigorous constraint on the rate of export of organic carbon from the surface layer of the sea. This export is the primary means by which the oceans can serve as a sink for atmospheric carbon dioxide. For the oligotrophic open ocean regions, which make up more than 75% of the world's ocean, the rate of export is currently uncertain by an order of magnitude. For most of the year, the vertical flux of nitrate is that due to vertical turbulent transport of deep water rich in nitrate into the relatively impoverished surface layer. Direct measurements of rates of turbulent kinetic energy dissipation, coupled with highly resolved vertical profiles of nitrate and density in the oligotrophic eastern Atlantic showed that the rate of transport, averaged over 2 weeks, was 0.14 (0.002 to 0.89, 95% confidence interval) millimole of nitrate per square meter per day and was statistically no different from the integrated rate of nitrate uptake as measured by incorporation of (15)N-labeled nitrate. The stoichiometrically equivalent loss of carbon from the upper ocean, which is the relevant quantity for the carbon dioxide and climate question, is then fixed at 0.90 (0.01 to 5.70) millimole of carbon per square meter per day. These rates are much lower than recent estimates based on in situ changes in oxygen over annual scales; they are consistent with a biologically unproductive oligotrophic ocean.     

The effects of iron fertilization on carbon sequestration in the Southern Ocean

An unresolved issue in ocean and climate sciences is whether changes to the surface ocean input of the micronutrient iron can alter the flux of carbon to the deep ocean. During the Southern Ocean Iron Experiment, we measured an increase in the flux of particulate carbon from the surface mixed layer, as well as changes in particle cycling below the iron-fertilized patch. The flux of carbon was similar in magnitude to that of natural blooms in the Southern Ocean and thus small relative to global carbon budgets and proposed geoengineering plans to sequester atmospheric carbon dioxide in the deep sea.     

测定农田蒸散的涡度相关技术

 主要介绍涡度相关技术测定湍流通量的原理,及其在农田蒸散量测定方面的国内外应用研究进展。讨论了引起涡度相关技术测定农田蒸散误差的主要原因,并分析采用涡度相关系统测定的水、热通量资料的可靠性,提出进行涡度相关技术测定资料分析时剔除异常数据和进行数据修正的方法。     

高分子减阻剂对非牛顿型流体流动特性的影响

以普兰德动量传递理论为基础,按照卡门的三层模型,通过室内模拟环道用0号柴油及加入减阻剂在圆管内的流动参数的测定,计算了非牛顿型流体管内湍流边界层的层流内层、过渡层、湍流中心的涡流粘度,涡流粘度与运动粘度比、总应力随相对位置的变化等定量参数,探讨了高分子减阻剂对非牛顿流体流动特性的影响,对湍流减阻现象的机理与增大减阻率的条件进行了定量分析.     

Volume and heat transports of the Florida current: april 1982 through august 1983

Absolute velocity and temperature profiles are used to estimate the volume transport through the Straits of Florida and, in combination with historical midbasin data, to estimate the total meridional heat flux through a section at 27 degrees N. The mean annual volume transport of the Florida Current from April 1982 through August 1983 is 30.5 (+/- 1)x 10(6) cubic meters per second. The net northward heat flux through the 27 degrees N section is 1.2 (+/- 0.1)x 10(15) watts. The volume transport is characterized by high values in the late spring and early summer and low values in the late fall and early winter. There is a similar cycle in total heat flux.     

Compensation of horizontal temperature and salinity gradients in the ocean mixed layer

Establishment of the temperature-salinity relationship in the ocean has concerned oceanographers for decades because of its importance for understanding ocean circulation. High-resolution measurements in the ocean mixed layer are used to show that temperature and salinity gradients on horizontal scales of 20 meters to 10 kilometers tend to compensate in their effect on density. These observations support the notion of a horizontal mixing in the mixed layer that depends on density gradient.     

Enhanced turbulence and energy dissipation at ocean fronts

The ocean surface boundary layer mediates air-sea exchange. In the classical paradigm and in current climate models, its turbulence is driven by atmospheric forcing. Observations at a 1-kilometer-wide front within the Kuroshio Current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude, suggesting that the front, rather than the atmospheric forcing, supplied the energy for the turbulence. The data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence. The resulting boundary layer is stratified in contrast to the classically well-mixed layer. These effects will be strongest at the intense fronts found in the Kuroshio Current, the Gulf Stream, and the Antarctic Circumpolar Current, all of which are key players in the climate system.     

Atmospheric electrical detection of organized convection

Relatively simple atmospheric electrical instrumentation carried on a small aircraft constitutes a flexible and sensitive system for detecting organized convection. Data can be obtained close to the sea surface, and low-velocity flight enhances the spatial resolution. With a slow-flying airplane or powered glider, it may be possible to trace the circulation of individual convection cells and to investigate the trajectory of air which forms cumulus clouds, one of the major unsolved problems in tropical meteorology. Since space charge near the ocean surface was found on some days to be organized on a horizontal scale equivalent to the cumulus cloud scale, this suggests that some of the air which forms maritime cumulus clouds may come from within a few meters of the ocean and that atmospheric electrical instrumentation may have the potential for tracing air from the sea surface to the clouds. Although the atmospheric electrical instrumentation technique described here cannot be used for direct measurement of air velocity, it may be possible to develop model that can be used to calculate air velocities from electric field data. Even though with the technique described here it is not possible to make direct measurements of wind velocity, airborne electric field records can provide useful information about convection by delineating patterns in the wind field and structural features of thermals (rising bodies of relatively warm air) and by making possible the remote detection of thermals (29). Future plans include attempting to trace interfaces between adjacent roll vortices from the sea surface through the depth of the mixed layer (i) by flying the aircraft parallel to the wind so as to nullify the horizontal electric field (measured between wing-tip probes) while ascending and descending along the interface between adjacent roll vortices and (ii) by measuring vertical and horizontal potential gradient variations at different flight levels (30). The sensitivity of atmospheric electrical instrumentation to the top of the mixed layer and structure within it can be used to explore another important problem in boundary layer convection-why convective cloud cover and oceanic rainfall are greater at night than during the day(31). Workers in atmospheric electricity have long recognized that their domain is strongly controlled by turbulence in the lower atmosphere, and many have believed that the most effective use of atmospheric electrical techniques to assist meteorological research would be in studying exchange processes. Reiter [see (8)] effectively extended atmospheric electrical studies of boundary layer phenomena through a height range by mounting instruments on cable cars traveling between the valley floor and mountain tops in the Alps. The airborne measurements described here extend this approach. Relating the electrical structure of the atmosphere to its dynamic structure poses an interesting problem which may contribute to our understanding of the atmosphere.     

亚热带稻田能量平衡闭合状况分析

通过采用线性回归,能量平衡比率和相对残差频率分布3种统计方法对涡度相关法通量观测的稻田能量平衡闭合状况进行了评价,并分析了能量平衡闭合程度的季节变化趋势。结果表明,在稻田生态系统中存在能量不闭合现象,年能量平衡比率为0.87,年平均不闭合程度为13%;能量平衡比率在5—8月份平均为0.85,能量不闭合程度较高;1—4月份和9—12月份平均为0.92,不闭合程度较低。在假定常规的有效能量测定正确的前提下,可以认为涡度相关测定的湍流通量可能被低估了。     

Widespread intense turbulent mixing in the Southern Ocean

Observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the Southern Ocean is remarkably intense and widespread. Mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters. This suggests that turbulent mixing in the Southern Ocean may contribute crucially to driving the upward transport of water closing the ocean's meridional overturning circulation, and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers.     

极端干旱区大气边界层厚度时间演变及其与地表能量平衡的关系

主要采用ECMWF的地表和大气产品分析了中国西北极端干旱区大气边界层厚度与地表能量通量的时间变化特征,同时,结合探空加强观测分析了大气边界层演变的可能因素.得出:西北极端干旱区大气边界层厚度呈现出季节性的年际和年代际变化,夏季大气边界层厚度呈下降趋势,春、秋季节呈现出先增加后降低的趋势,冬季以阶段性降低趋势为主,20世纪80年代是大气边界层厚度的转折时期；感热通量是极端干旱区大气边界层发展的主要热力因素；由于夏季净辐射量、地气温差、粗糙度以及风速等因子随时间演变而呈降低趋势,潜热通量呈增加趋势,导致了边界层高度形成的热力作用减弱,边界层厚度降低；同时,粗糙度和风速也是大气边界层发展的主要动力因素,由于边界层粗糙度和风速降低,促使垂直风切变减小,湍流动力作用减弱,也会导致边界层厚度降低.     

三江平原大豆田湍流热通量研究

【目的】明确大豆田地表湍流热通量变化特征及其规律,为阐明大豆田地表能量平衡奠定基础。【方法】以三江平原大豆田为研究对象,基于涡度相关数据分析大豆生长季地表湍流热通量的日变化、季节变化、地表水分平衡和地表能量分配特征及其主控因子。【结果】大豆田地表潜热和感热通量日变化均表现为明显的单峰特征。潜热通量季节变化特征明显,一般于6月下旬至7月上旬达到最大值,其与净辐射呈显著线性正相关关系,但当降水量较少时也与降水量呈显著线性正相关关系。 大豆田地表感热通量整体呈下降趋势,亦与净辐射呈显著线性正相关关系,但感热通量Hs和Hs/Rn均与降水量呈显著负相关关系。大豆生长季内降水总量明显大于蒸散总量,但降水分布不均也会使得短期内出现水分收支亏缺。2005-2007年,大豆田波文比季节变化特征不完全相同,波文比与降水量和叶面积指数均呈显著负相关关系。【结论】三江平原大豆田潜热和感热通量单峰日变化特征显著,生长季内大豆地表水分盈余。净辐射、降水量和植被发育是影响大豆田潜热和感热通量以及能量分配的主要因子。     

高粘牛顿流体输送的表观滑移流动研究

在高粘度流体输送过程中,用低粘度的流体局部置换高粘度的流体,可以降低附壁边界层的粘性从而实现管道内流体流动减阻。对管道内两种粘度流体环状流动进行了理论和计算研究,推导了滑移层厚度及流体粘度与流动流量、减阻、滑移速度等的关系式,结果表明,随着滑移层变厚,其流速的增量会减小;当滑移层较薄时,流量增否取决于两层流体粘度之比;只有控制滑移层厚度不超过一定范围输送效率才会最大;滑移速度与压差成线性关系。     

Local influences on shear-flow turbulence in the equatorial ocean

A 12-day series of 1749 profiles of turbulent kinetic energy dissipation above the equatorial undercurrent at 140 degrees west showed that, in the upper 110 meters of the ocean, the dissipation radically decreased during the solar heating period each day. Daily averages were linearly related to the local wind power. When integrated over the depth range of 10 to 110 meters, the dissipation was 10.6 ergs per square centimeter per second or 0.92 +/- 0.10 percent of the wind power, a proportion not substantially different from those found in mid-latitude surface mixed layers. These results suggest that much of the energy dissipated above the equatorial undercurrent may be extracted directly from the local wind.     

风管中颗粒物沉降速度的解析法预测模型

在分析颗粒在紊流边界层中运动机理的基础上,根据沉降速度的定义,推导出了浓度边界层微分方程及其解析解,进而得到了颗粒无量纲沉降速度的解析表达式.利用经典实验数据验证了该解析法模型的正确性.最后,对不同粒径颗粒在不同风速下的无量纲沉降速度进行了预测.预测结果表明:风速越大,颗粒的无量纲沉降速度也越大.     

From tides to mixing along the Hawaiian ridge

The cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing. We investigated this cascade along the Hawaiian Ridge using observations and numerical models. A divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models. Large internal tidal waves with peak-to-peak amplitudes of up to 300 meters occur on the ridge. Internal-wave energy is enhanced, and turbulent dissipation in the region near the ridge is 10 times larger than open-ocean values. Given these major elements in the tides-to-turbulence cascade, an energy budget approaches closure.     

Atmosphere-surface exchange measurements

The exchange of various trace species and energy at the earth's surface plays an important role in climate, ecology, and human health and welfare. Surface exchange measurements can be difficult to obtain yet are important to understand physical processes, assess environmental and global change impacts, and develop robust parameterizations of atmospheric processes. The physics and turbulent structure of the atmospheric boundary layer are reviewed as they contribute to dry surface exchange rates (fluxes). Micrometeorological, budget, and enclosure techniques used to measure or estimate surface fluxes are described, along with their respective advantages and limitations. Various measurement issues (such as site characteristics, sampling considerations, sensor attributes, and flow distortion) impact on the ability to obtain representative surface-based and airborne flux data.