On the turbulence structure in the stable boundary layer over the Greenland ice sheet

Turbulence measurements from a 30 m tower in the stably stratifiedboundary layer over the Greenland ice sheet are analyzed. The observationsinclude profile and eddy-correlation measurements at various levels. Atfirst, the analysis of the turbulence data from the lowest level (2 m aboveground) shows that the linear form of the non-dimensional wind profile(m) is in good agreement with the observations for z/L <0.4, whereL represents the Obukhov length. A linear regression yieldsm=1+5.8z/L. The non-dimensional temperature profile (h) at the2m level shows no tendency to increase with increasing stability. The datafrom the upper levels of the tower are analyzed in terms of both localscaling and surface-layer scaling. The m and the h values show atendency to level off at large stability (z/>0.4) where represents the local Obukhov length. Hence, the linear form of the functions is no longer appropriate under such conditions. The bestcorrespondence to the data can be achieved when using the expression ofBeljaars and Holtslag for m and h. The vertical profiles of theturbulent fluxes, the wind velocity variances and temperature variance arealso determined. The momentum flux profile and the profiles of wind speedvariances are in general agreement with other observations if a welldeveloped low-level wind maximum occurs, and the height of this maximum isused as a height scale.     

冷空气过程对黄海东海区域海洋大气边界层结构影响的个例分析

利用一次冷空气过程的14组GPS探空数据,采用位温梯度法确定了冷空气过境前后大气边界层高度,并分析了冷空气过程对大气边界层结构的影响。结果表明：冷锋过境加大了海洋大气边界层的静力不稳定度,使边界层内对流活动增强,且锋面过后距离锋面越近的区域边界层的静力不稳定度越大;冷锋过境使边界层的平均高度升高,边界层顶处逆温梯度增大。结合ERA-Interim再分析资料,分析认为大气边界层高度与静力稳定度（海气温差）存在显著的正相关关系（相关系数达0.73）,海气温差越大,大气边界层高度越高。     

Effects of mesoscale sea-surface temperature fronts on the marine atmospheric boundary layer

A numerical modelling study is presented focusing on the effects of mesoscale sea-surface temperature (SST) variability on surface fluxes and the marine atmospheric boundary-layer structure. A basic scenario is examined having two regions of SST anomaly with alternating warm/cold or cold/warm water regions. Conditions upstream from the anomaly region have SST values equal to the ambient atmosphere temperature, creating an upstream neutrally stratified boundary layer. Downstream from the anomaly region the SST is also set to the ambient atmosphere value. When the warm anomaly is upstream from the cold anomaly, the downstream boundary layer exhibits a more complex structure because of convective forcing and mixed layer deepening upstream from the cold anomaly. An internal boundary layer forms over the cold anomaly in this case, generating two distinct layers over the downstream region. When the cold anomaly is upstream from the warm anomaly, mixing over the warm anomaly quickly destroys the shallow cold layer, yielding a more uniform downstream boundary-layer vertical structure compared with the warm-to- cold case. Analysis of the momentum budget indicates that turbulent momentum flux divergence dominates the velocity field tendency, with pressure forcing accounting for only about 20% of the changes in momentum. Parameterization of surface fluxes and boundary-layer structure at these scales would be very difficult because of their dependence on subgrid-scale SST spatial order. Simulations of similar flow over smaller scale fronts (<5 km) suggest that small-scale SST variability might be parameterized in mesoscale models by relating the effective heat flux to the strength of the SST variance.     

利用探空资料估算青藏高原及下游地区大气边界层高度

利用三个时段的探空加密试验资料,分别采用气块法和Richardson数法来估算青藏高原及下游地区的对流边界层和稳定边界层的高度特征。结果显示:(1)高原中部对流边界层结构的出现概率高于高原东侧及下游地区,而四川盆地稳定边界层结构的出现概率远高于高原和长江中游。(2)高原中部和东侧的对流边界层高度春季高而夏季低,其中高原中部的对流边界层高度高于高原东侧;四川盆地和长江中游的对流边界层高度冬季低、夏季高,而高原东侧的对流边界层高度的变化趋势则相反;四川盆地的对流边界层高度低于长江中游。(3)高原的稳定边界层高度春季高而夏季低;冬季四川盆地的稳定边界层高度高于高原东侧和长江中游,而夏季长江中游的稳定边界层高度高于高原东侧和四川盆地,冬夏差异导致的稳定边界层高度的变化幅度在长江中游最明显,四川盆地次之,而高原东侧最小。(4)高原东侧及下游地区的平均边界层高度的日变化具有相似的演变特征,平均边界层高度在白天高夜间低,而高原中部的平均边界层高度在日出左右较低,之后随时间逐渐增高,并在晚上达到最大值;高原的平均边界层高度的日变化振幅大于下游地区,且其日变化振幅随站点海拔高度的增加而增大。     

尺度自适应大气边界层参数化改进及其对一次海雾的数值模拟研究

大气边界层湍流运动是地球大气运动最重要的能量输送过程之一.当数值模式分辨率接近活跃含能湍涡长度尺度时,湍流运动被部分解析,被称为"灰色区域",传统的边界层方案不适合此时模式湍流问题的描述.为了提高模式边界层方案在包括"灰色区域"的不同网格尺度上的描述能力,适应不同分辨率模式的需要,在雷诺平均湍流理论基础上,修正Mell...     

Measurements of peroxyacetylnitrate in the marine boundary layer over the Atlantic

The atmospheric concentration of peroxyacetylnitrate (PAN) was measured during a cruise of the R.S. Polarstern from Bremerhaven (Germany) to Rio Grande do Sul (Brazil) in September/ October 1988. The measurements were made in-situ by a combination of electron capture gaschromatography with a cryogenic preconcentration step. The theoretical lower limit of detection (3) was 0.4 ppt. The mixing ratios of PAN varied by more than three orders of magnitude from 2000 ppt in the English Channel to less than 0.4 ppt south of the Azores (38° N). South of 35° N, PAN levels were below the detection limit, except at 30–31° S off the eastern coast of South America. Here, PAN mixing ratios of 10 to 100 ppt were detected in continentally influenced air masses. Detectable levels of PAN were mostly observed in air masses of continental or high northern origin. Changes in the wind directions were usually associated with substantial changes in the PAN mixing ratios.     

Diurnal Variations of Air Pollution and Atmospheric Boundary Layer Structure in Beijing During Winter 2000／2001

The diurnal variations of gaseous pollutants and the dynamical and thermodynamic structures of the atmospheric boundary layer (ABE) in the Beijing area from January to March 2001 are analyzed in this study using data from the Beijing City Air Pollution Observation Field Experiment (BECAPEX). A heavy pollution day (22 February) and a good air quality day (24 February) are selected and individually analyzed and compared to reveal the relationships between gaseous pollutants and the diurnal variations of the ABL. The results show that gaseous pollutant concentrations exhibit a double-peak-double-valley-type diurnal variation and have similar trends but with different magnitudes at different sites in Beijing. The diurnal variation of the gaseous pollutant concentrations is closely related to (with a 1-2 hour delay of) changes in the atmospheric stability and the mean kinetic energy in the ABL.     

数值模式中的大气边界层参数化方案综述

大气边界层对下垫面和自由大气之间的热量、动量和物质交换以及全球辐射的收支平衡有着非常重要的作用,数值模式中对边界层的模拟需要通过参数化方案表现出来。综述了数值模式中常用的边界层参数化方案,从闭合框架以及边界层内的重要物理过程这两个方面对各类方案进行了总结,并讨论了边界层参数化方案的发展方向。     

Vertical atmospheric structure of the late summer clear days over the east Gansu loess plateau in China

In this paper, by using the sounding data collected in LOPEX05, we have analyzed the vertical atmospheric structure and boundary layer characteristics of temperature and humidity in the late summer over the east Gansu loess plateau. The results show that the bottom of the stratosphere is at about 16 500 m and varies between 14 000 m and 18 000 m above the ground. The center of the westerly jet is located between 8300 m and 14 300 m above the ground and its direction moves between 260° and 305°. There is an ...     

一次深厚浓雾过程的边界层特征和生消物理机制

2007年12月13-14日,南京出现一次厚度达600 m、持续近14 h的浓雾过程,其中强浓雾阶段维持4 h.通过系留气球边界层探测系统、涡动协方差测量系统、雾滴尺度分布和自动气象站等外场试验资料分析了此次深厚浓雾过程的边界层结构特征和生消物理机制.结果表明,此次雾过程首先由地面辐射冷却形成贴地雾层,而后因低空平流冷却形成低云.在发展阶段,伴随低云不断下伸,贴地雾层不断抬升.在贴地雾层受到地面弱冷空气平流降温影响下,雾中微物理过程迅速发展,雾滴数密度、含水量、平均直径、最大直径等微物理参数在15 min内跃增,雾体爆发性升高,最终导致地面雾和低云上下贯通形成深厚雾层,地面能见度骤降至15 m以下.雾体爆发性增强时,地面垂直动量通量和向下长波辐射通量密度增大,净辐射趋于零.整个雾过程中,由于贴地层持续弱冷平流降温和上层雾阻碍了下层雾的辐射降温,二者的共同作用使贴地强逆温结构始终维持.     

Small-Scale Variability in the Coastal Atmospheric Boundary Layer

The influence of the main large-scale wind directions on thermally driven mesoscale circulations at the Baltic southwest coast, southeast of Sweden, is examined. The aim of the study is to highlight small-scale alterations in the coastal atmospheric boundary layer. A numerical three-dimensional mesoscale model is used in this study, which is focused on an overall behaviour of the coastal jets, drainage flows, sea breezes, and a low-level eddy-type flow in particular. It is shown that synoptic conditions, together with the moderate terrain of the southeast of Sweden (max. height h₀ 206 m), governs the coastal mesoscale dynamics triggered by the land-sea temperature difference T. The subtle nature of coastal low-level jets and sea breezes is revealed; their patterns are dictated by the interplay between synoptic airflow, coastline orientation, and T.The simulations show that coastal jets typically occur during nighttime and vary in height, intensity and position with respect to the coast; they interact with downslope flows and the background wind. For the assigned land surface temperature (varying ±8 K from the sea temperature) and the opposing constant geostrophic wind 8 m s^-1, the drainage flow is more robust to the opposing ambient flow than the sea breeze later on. Depending on the part of the coast under consideration, and the prevailing ambient wind, the sea breeze can be suppressed or enhanced, stationary at the coast or rapidly penetrating inland, locked up in phase with another dynamic system or almost independently self-evolving. A low-level eddy structure is analyzed. It is governed by tilting, divergence and horizontal advection terms. The horizontal extent of the coastal effects agrees roughly with the Rossby radius of deformation.     

Structures and characteristics of the windy atmospheric boundary layer in the South China Sea region during cold surges

An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations(period<1 min) are nearly random and isotropic with weak coherency, but the gusty wind disturbances(1 min相似文献   

Characteristics of intermittent turbulence in the upper stable boundary layer over Greenland

The experiment IGLOS (Investigation of the Greenland Boundary Layer Over Summit) was conducted in June and July 2002 in the central plateau of the Greenland inland ice. The German research aircraft Polar2, equipped with the turbulence measurement system Meteopod, was used to investigate turbulence and radiation flux profiles near research station “Summit Camp”. Aircraft measurements are combined with measurements of radiation fluxes and turbulent quantities made from a 50 m tower at Summit Camp operated by Eidgenössische Technische Hochschule (ETH) Zürich. During all six flight missions, well-developed stable boundary layers were found. Even in high-wind conditions, the surface inversion thickness did not exceed roughly 100 m. The turbulent height of the stable boundary layer (SBL) was found to be much smaller than the surface inversion thickness. Above the surface layer, significant turbulent fluxes occurred only intermittently in intervals on the order of a few kilometres. Turbulent event fraction in the upper SBL shows the same dependence on gradient Richardson number as reported for near-surface measurements. Clear-air longwave radiation divergence was always found to contribute significantly to the SBL heat budget. In low-wind cases, radiative cooling even turned out to be dominant.     

Model evaluation of the atmospheric boundary layer and mixed-layer evolution

In the present study, an attempt is made to assess the atmospheric boundary-layer (ABL) depth over an urban area, as derived from different ABL schemes employed by the mesoscale model MM5. Furthermore, the relationship of the mixing height, as depicted by the measurements, to the calculated ABL depth or other features of the ABL structure, is also examined. In particular, the diurnal evolution of ABL depth is examined over the greater Athens area, employing four different ABL schemes plus a modified version, whereby urban features are considered. Measurements for two selected days, when convective conditions prevailed and a strong sea-breeze cell developed, were used for comparison. It was found that the calculated eddy viscosity profile seems to better indicate the mixing height in both cases, where either a deep convective boundary layer develops, or a more confined internal boundary layer is formed. For the urban scheme, the incorporation of both anthropogenic and storage heat release provides promising results for urban applications.     

Measurement of IO radical concentrations in the marine boundary layer using a cavity ring-down spectrometer

An open-path cavity ring-down spectroscopy (CRDS) instrument for measurement of atmospheric iodine monoxide (IO) radicals has been tested in the laboratory and subsequently deployed in Roscoff on the north-west coast of France as part of the Reactive Halogens in the Marine Boundary Layer (RHaMBLe) project in September 2006. In situ measurements are reported of local IO mixing ratios in the marine boundary layer. To obtain these mixing ratios, accurate absorption cross sections of IO are required at the selected wavelengths used for spectroscopic measurements. Absorption cross sections at the bandheads of the IO A²Π_3/2–X²Π_3/2 (3,0) and (2,0) vibronic bands were thus verified by a combination of spectral simulation methods, inter-comparison of prior determinations of cross-sections at high and low spectral resolution, and by measurement of rates of loss of IO by its self-reaction. The performance of the open-path CRDS instrument was tested by measuring concentrations of NO₂ in ambient air, both within and outside the laboratory, with results that were in excellent agreement with a previously validated continuous wave CRDS apparatus for NO₂ detection. During the RHaMBLe campaign, the open-path CRDS instrument was located within a few metres of the shoreline and operated at wavelengths close to 435 nm to detect the absorption of light by trace levels of IO. The IO mixing ratios were obtained on two days, peaked close to low tide, and were approximately 5–10 times higher than values calculated from column densities previously reported by long-path, differential optical absorption spectroscopy (DOAS) in coastal regions. The typical detection limit of the instrument was estimated to be 10 pptv of IO, with some fluctuation around this value depending on the conditions of wind and atmospheric aerosol particles, and the total accumulation time was 30 s for each data point. The observations of relatively high concentration of IO, compared to the values previously reported by DOAS, are consistent with the concurrent observations using a LIF (Laser induced Fluorescence) instrument (Whalley et al. in press). The first such measurements of localized IO by CRDS and LIF should contribute to an improved understanding of the chemistry of halogen compounds and the formation of iodine oxide aerosol particles in the marine boundary layer.     

Detection of iodine monoxide radicals in the marine boundary layer using laser induced fluorescence spectroscopy

A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere. An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of the IO A²Π_3/2 ← X²Π_3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N₂O/CF₃I/N₂ mixtures with O₃ actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer) campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF.     

温江站夏季大气边界层垂直结构特征

利用温江观测站边界层塔和探空获取的观测资料,从地表物理量的日变化、边界层的垂直结构及逐日变化这些方面分析该站夏季边界层特征,得到以下结论:(1)地表各物理量都具有明显的日变化特征,呈现一峰一谷的演变状态,其中地表热通量、动量通量、气温以及风速的峰值皆出现在午后,谷值出现在凌晨,湿度与气温日变化是反位相的。(2)近地层低层大气气温在早晚时段,随高度的增加而上升,呈逆温状态;午间时段随高度的增加而下降。9 m以下大气在午后的比湿梯度最大。风速值随着高度的增高而增大,风切变随着高度的增高而减小。(3)探空观测的边界层垂直结构显示:夏季温江站早晚边界层大气层结稳定,而午后表现为典型的混合边界层特征。大气温/湿度差异随高度增长而降低,各个时次温/湿度的差异都主要集中边界层低层,越靠近地面大气温/湿度差异越突出。8:00的温度最低,14:00最高。14:00的大气比湿最小,2:00和20:00较大。近地层风速随高度增长较快,在离地2~300 m左右高度达到一个极值,4个时次的风速差异不大。(4)地表温度、短波辐射、感热通量对边界层的高度和降水都有一定的影响。     

WRF模式对青藏高原那曲地区大气边界层模拟适用性研究

采用WRF（Weather Research and Forecasting）模式4种边界层参数化方案对青藏高原那曲地区边界层特征进行了数值模拟,并利用"第三次青藏高原大气科学试验"在青藏高原那曲地区5个站点的观测资料对模拟结果进行验证,分析不同参数化方案在那曲地区的适用性。研究表明,YSU、MYJ、ACM2和BouLac方案对2 m气温和地表温度的模拟偏低。BouLac方案模拟的地表温度偏差较小。通过对能量平衡各分量的对比分析发现,温度模拟偏低可能是向下长波辐射模拟偏低以及感热通量和潜热通量交换过强导致的。对于边界层风、位温和相对湿度垂直结构的模拟,局地方案的模拟效果均优于非局地方案。BouLac方案对那曲地区近地层温度、边界层内位温和相对湿度的垂直分布模拟效果较好。      

偏离度法确定济南夏季对流边界层高度研究

利用济南站边界层风廓线雷达（简称WPR）观测资料,对大气折射率结构常数（简称C_n²）确定对流边界层高度（简称CBLH）的技术难点进行了研究,通过对实测C_n²数据廓线进行求导变换突出其变量特征,提出了一种确定CBLH的方法,即e指数拟合曲线的偏离度法。结果表明：经案例分析和与实测对比,证实其判断的结果与L探空实测虚位温梯度法、湿度梯度法等的判断结果总体一致,平均值分别与后两者结果相差+10.4 m、-21.8 m,最小值差-70 m、-120 m,最大值差+50 m、+80 m,与后两者的相关系数分别达0.988、0.980。不同方法对比表明,31组样本中有7组的极大值法判断结果与偏离度法、虚位温梯度法存在较大差异,在CBLH判别时偏离度法总体优于极大值法。偏离度法能够将夏季CBLH确定结果的绝对误差降至近似WPR垂直分辨率水平。     

利用COSMIC掩星资料研究青藏高原地区大气边界层高度

以往关于青藏高原边界层的研究都是基于个别站点的常规观测,对青藏高原边界层的整体性认识受限。GPS掩星资料具有测量精度高和垂直分辨率高的特性,其廓线中含有大量有价值的边界层信息。利用2007—2013年COSMIC掩星资料,通过计算大气折射率最小梯度来确定边界层高度,并用无线电探空资料对结果进行了检验。在此基础上,对青藏高原地区边界层高度的特征及其形成机制展开了研究,比较了COSMIC掩星确定的边界层高度和ERA-Int的差别,讨论了最小梯度法用于边界层研究的不确定性。结果表明:青藏高原上COSMIC掩星和无线电探空数据检测的边界层高度相关系数为0.786,平均值偏差为0.049 km,均方根误差为0.363 km,COSMIC掩星数据检测的边界层高度和无线电探空的结果非常接近。青藏高原上边界层高度呈现西高东低的分布特征,高原中西部边界层高度主要为1.8—2.3 km,而高原东部边界层为1.4—1.8 km,最大值在高原西南部。青藏高原地区边界层有明显的季节差异,冬季高原上大部分地区边界层高度超过2.0 km;春季大部分地区高度降低,但在受印度季风影响的高原南部有明显的抬升,最大值可超过3.0 km;夏季高原上边界层高度开始升高,大部分地区超过1.8 km;秋季又开始回落。青藏高原以北塔克拉玛干沙漠和高原以南印度季风活动区是两个高值区,北部的沙漠地区边界层高度在夏季最高,南部印度季风活动区在季风爆发前（4月）达到全年最大值。青藏高原中西部地区有水平风辐合以及广泛的上升运动,为边界层的发展提供了动力条件,而东部的下沉运动对边界层的发展有抑制作用。青藏高原边界层各个季节的空间分布与地表感热通量分布一致。COSMIC掩星资料确定的边界层高度和ERA-Int相比,空间分布基本一致但ERA-Int边界层高度明显偏低。当有系统性强逆温存在的时候,或者云中液态水或冰水含量较大时,用最小梯度法检测的边界层高度不确定性增加。