Characteristics of atmospheric boundary layer structure and its influencing factors under different sea and land positions in Europe

This study identifies quantitatively the dominant contributions of meteorological factors on the development of the boundary layer heights(BLH)in the European region,based on 32 years(1990-2021)of radiosonde observations.The spatial variability of the BLH is further discussed by location,by classifying recording stations as inland,coastal,or bay.We find that the BLH in Europe varies considerably from day to night and with the seasons.Nighttime BLH is higher in winter and lower in summer,with the highest BLH recorded at coastal stations.Daytime BLH at coastal stations shows a bimodal structure with peaks in spring and autumn;at inland and bay stations,daytime BLH is lower in winter and higher in summer.The daily amplitudes of BLH at the inland and bay stations are stronger than those at coastal stations.Based on our multiple linear regression analysis and our decoupling analysis of temperature and specific humidity,we report that the development of the nighttime BLH at all types of stations is strongly dominated by the variations of surface wind speed(and,at coastal stations,wind directions).The main contributors to daytime BLH are the near-surface temperature variability at most coastal and inland stations,and,at most bay stations,the variation of the near-surface specific humidity.

Determining Atmospheric Boundary Layer Height with the Numerical Differentiation Method Using Bending Angle Data from COSMIC

This paper presents a new method to estimate the height of the atmospheric boundary layer(ABL) by using COSMIC radio occultation bending angle(BA) data. Using the numerical differentiation method combined with the regularization technique, the first derivative of BA profiles is retrieved, and the height at which the first derivative of BA has the global minimum is defined to be the ABL height. To reflect the reliability of estimated ABL heights, the sharpness parameter is introduced, according to the relative minimum of the BA derivative. Then, it is applied to four months of COSMIC BA data(January, April, July, and October in 2008), and the ABL heights estimated are compared with two kinds of ABL heights from COSMIC products and with the heights determined by the finite difference method upon the refractivity data. For sharp ABL tops(large sharpness parameters), there is little difference between the ABL heights determined by different methods, i.e.,the uncertainties are small; whereas, for non-sharp ABL tops(small sharpness parameters), big differences exist in the ABL heights obtained by different methods, which means large uncertainties for different methods. In addition, the new method can detect thin ABLs and provide a reference ABL height in the cases eliminated by other methods. Thus, the application of the numerical differentiation method combined with the regularization technique to COSMIC BA data is an appropriate choice and has further application value.

HEIGHT OF ATMOSPHERIC BOUNDARY LAYER AS DETECTED BY COSMIC GPS RADIO OCCULTATION DATA

The characteristics of the atmospheric boundary layer height over the global ocean were studied based on the Constellation Observation System of Meteorology,Ionosphere and Climate(COSMIC) refractivity data from 2007 to2012.Results show that the height is much characteristic of seasonal,inter-annual and regional variation.Globally,the spatial distribution of the annual mean top height shows a symmetrical zonal structure,which is more zonal in the Southern Hemisphere than in the Northern Hemisphere.The boundary layer top is highest in the tropics and gradually decreases towards higher latitudes.The height is in a range of 3 to 3.5 km in the tropics,2 to 2.5 km in the subtropical regions,and 1 to 1.5 km or even lower in middle and high latitudes.The diurnal variation of the top height is not obvious,with the height varying from tens to hundreds of meters.Furthermore,it is different from region to region,some regions have the maximum height during 9:00 to 12:00,others at 15:00 to18:00.

New expressions for the surface roughness length and displacement height in the atmospheric boundary layer

An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness obstacles. The experiments are carried out by the use of the hot wire anemometry in the simulated atmospheric boundary layer in a wind tunnel. Based on the experimental data, a new expression for the zero-plane displacement height is proposed for the square arrays of roughness elements, which highlights the influence of free-stream speed on the roughness length. It appears that the displacement height increases with the wind speed while the surface roughness length decreases with Reynolds number increasing. It is shown that the calculation results based on the new expressions are in reasonable agreement with the experimental data.

Observation-based Estimation of Aerosol-induced Reduction of Planetary Boundary Layer Height

Radiative aerosols are known to influence the surface energy budget and hence the evolution of the planetary boundary layer. In this study, we develop a method to estimate the aerosol-induced reduction in the planetary boundary layer height （PBLH） based on two years of ground-based measurements at a site, the Station for Observing Regional Processes of the Earth System （SORPES）, at Nanjing University, China, and radiosonde data from the meteorological station of Nanjing. The observations show that increased aerosol loads lead to a mean decrease of 67.1 W m-2 for downward shortwave radiation （DSR） and a mean increase of 19.2 W m-2 for downward longwave radiation （DLR）, as well as a mean decrease of 9.6 W m-2 for the surface sensible heat flux （SHF） in the daytime. The relative variations of DSR, DLR and SHF are shown as a function of the increment of column mass concentration of particulate matter （PM2.5）. High aerosol loading can significantly increase the atmospheric stability in the planetary boundary layer during both daytime and nighttime. Based on the statistical relationship between SHF and PM2.5 column mass concentrations, the SHF under clean atmospheric conditions （same as the background days） is derived. In this case, the derived SHF, together with observed SHF, are then used to estimate changes in the PBLH related to aerosols. Our results suggest that the PBLH decreases more rapidly with increasing aerosol loading at high aerosol loading. When the daytime mean column mass concentration of PM2.5 reaches 200 mg m-2, the decrease in the PBLH at 1600 LST （local standard time） is about 450 m.

Marine Atmospheric Boundary Layers Associated with Summer Monsoon Onset over the South China Sea in 1998

The variations of the marine atmospheric boundary layer (MABL) associated with the South China Sea Summer Monsoon were examined using the Global Positioning System (GPS) sounding datasets obtained four times daily during May-June 1998 on board Research Vessels Kexue 1 and Shiyan 3. The MABL height is defined as the height at the lowest level where virtual potential temperature increases by 1 K from the surface. The results indicate that the MABL height decreased over the northern South China Sea (SCS) and remained the same over the southern SCS, as sea surface temperature (SST) fell for the northern and rose for the southern SCS after the monsoon onset. Over the northern SCS, a decrease in both the SST and the surface latent-heat flux after the onset resulted in a reduction of the MABL height as well as a decoupling of MABL from clouds. It was found that MABL height reduction corresponded to rainfall occurrence. Over the southern SCS, a probable reason for the constant increase of SST and surface heat flux was the rainfall and internal atmospheric dynamics.

边界层高度的不同诊断方法在京津冀及周边地区的适用性分析

利用2016~2021年京津冀及周边地区7个站的探空数据,分析了传统的位温梯度法、改进的位温梯度法、相对湿度梯度法、比湿梯度法和理查森数法5种大气边界层高度的诊断方法在京津冀及周边地区大气边界层高度计算的适用性。结果表明:5种方法计算的边界层高度差距在40~1000 m,传统的位温梯度法、相对湿度梯度法、比湿梯度法诊断的边界层高度普遍偏高,且存在较大的结构不确定性,理查森数法和改进的位温梯度法诊断的边界层高度偏低,前者的不确定性最小;5种方法在乐亭、北京、太原3个代表站得到的边界层高度具有明显的季节性和季节内差异,两种湿度法在乐亭呈现夏秋高、春冬低的特点,在北京和太原呈现春夏高、秋冬低的特点,其他3种方法在3个站均是春夏高、秋冬低的特点;相对湿度梯度法和比湿梯度法参数不确定性较大,传统的位温梯度法和改进的位温梯度法次之,理查森数法最小;在边界层高度计算结果月均值的时间一致性上,晚上各方法间的相关性明显高于白天,两种湿度法之间的相关系数始终最高,但与另外3种方法间的相关性均较差,理查森数法和改进的位温梯度法相关性较高,传统的位温梯度法因站点不同,与其他方法间的相关性波动较大。

中国夏季边界层高度及其主要影响因子的分区研究

中国区域下垫面复杂且边界层热力和动力影响因子众多,目前缺乏对全国范围内边界层高度及其影响因子的综合分析。本文基于2012~2016年L波段高分辨率探空资料,采用K-prototypes算法结合12个可能影响因子将中国夏季边界层高度进行了聚类分析,以探讨中国夏季边界层高度的区域性特征和主要影响因子。结果表明,中国区域100个站点08、14、20时(北京时,下同)的边界层高度均可划分为东北、东南、西北和西南4个区域。在此基础上,分析了三个不同时次不同区域边界层高度的主要影响因子,并探究这些因子影响不同热力状态下边界层发展的可能机理。结果表明:稳定边界层早(08时)、晚(20时)的发展主要受风速湍流动力作用的影响,而中午14时的发展与间歇性湍流作用密切相关。中性和对流边界层的发展在早上也主要受风速的驱动,而在中午则主要受较高地表温度和较大地表净辐射通量所引起的湍流热力作用驱动。此外,东北地区的云量和比湿、东南地区的潜热通量、西北地区的感热通量和比湿、西南地区的感热通量和土壤湿度也会通过对热力湍流的直接或间接影响,从而影响该区域中性和对流边界层的发展。晚上,由于东西时差的影响,在东部地区,风速开始成为中性和对流边界层高度的主要影响因子,而西部地区边界层高度的主要影响因子仍为热力因子。值得注意的是,北部地区的叶面积指数可以通过植被蒸腾作用改变比湿,从而影响边界层的发展;东北地区地表气压的变化可以通过影响气流的上升和下沉运动从而影响边界层的发展。

青藏高原东坡大气边界层高度变化观测研究

利用2021年2—5月和8—11月青藏高原东坡高海拔宇宙线观测站(Large High Altitude Air Shower Observatory,LHAASO)多通道微波辐射计观测的高时空分辨率温度廓线数据,并结合2021年ERA5再分析资料,分析大气边界层高度(Atmospheric Boundary Layer Height,ABLH)的日、月和季平均日变化规律。结果表明:(1)晴朗天气的ABLH具有明显的波峰波谷变化,日出后地表温度升高,ABLH也随之持续升高,最大值通常出现在午后,至18时左右迅速降低,日落之后降至最低。(2)一年之中,4月平均ABLH最大,约为1200 m,11月只有600 m。ABLH白天波动大,夜晚稳定,平均降至400 m左右。基于ERA5再分析资料反演的ABLH整体结果偏小,但具有与微波辐射计一致的变化趋势。(3)ABLH最大值出现在春季,夏季和秋季次之,冬季最小,且均在14:00—15:00达到峰值。

基于地基C波段垂直雷达的青藏高原大气边界层湍流特征研究

基于2014年7—8月那曲地区不同来源的边界层高度资料(包括C波段调频连续波垂直探测雷达(BLH_(CR))、L波段探空(BLH_(SD))、梯度塔观测及欧洲中心再分析数据集(BLH_(ERA5))),分析了边界层高度(BLH)、不同感热通量(SH)和稳定度(z/L或BLH_(CR)/L)条件下近地层和混合层湍流统计特征及湍流谱。主要结果如下:(1)BLH_(CR)、BLH_(SD)与BLH_(ERA5)互相之间有很好的相关,均方根偏差约为0.6 km。那曲地区BLH_(CR)的日变化较为明显,日较差中值为0.7—0.8 km。在北京时16时BLH_(CR)达最大,样本中值约为1.2 km。(2)随着感热通量增大,近地层垂直速度标准差(σ_(w))、温度标准差(σT)、温度与垂直速度相关系数(R_(wT))逐渐增大,σT增大速率呈线性,σ_(w)和R_(wT)的增大速率在感热通量超过一定阈值后逐渐减小。当-z/L<0.3时,σT和R_(wT)随-z/L增大迅速增大;-z/L≥0.3时增速明显趋缓。(3)混合层内湍流垂直速度方差(σ_(w)^(2))最大值出现在(0.25—0.3)×BLH_(CR)高度,平均值为1.2—1.3 m^(2)/s^(2)。强不稳定时混合层内σ_(w)^(2)略小于弱不稳定;σ_(w)^(2)平均值随感热通量增大而增大。归一化湍流垂直速度方差(σ_(w)^(2)/w_*2)随z/BLH_(CR)增大先迅速增大后逐渐减小,极大值出现在0.35×BLH_(CR)附近。(4)随着不稳定层结的增强,近地层和混合层的归一化垂直速度谱均谱峰左移,谱峰对应的归一化功率谱密度变大。强不稳定时湍流尺度变大、能量增强。

基于上海高层建筑观测冬季大气CO_(2)/CH_(4)垂直变化

采用便携式温室气体分析仪于2021年12月6日~2022年3月31日在上海中心大厦255和500m高度以及浦东新区环境监测站25m高度连续观测大气CO_(2)和CH_(4)浓度.结果表明:(1)城市中不同高度上温室气体的日变化趋势存在差异,25m高度CO_(2)和CH_(4)浓度白天低夜间高,255和500m高度的浓度则白天高夜间低.各高度处CO_(2)和CH_(4)浓度变化都明显受大气边界层高度的影响,因此城市内部温室气体浓度垂直观测中观测点高度设置要充分考虑城市大气边界层的变化特征.(2)CO_(2)和CH_(4)浓度的垂直差异受到人为活动以及气象等条件的影响,可以指征城市大气CO_(2)和CH_(4)浓度增强的局地和区域贡献.(3)各高度处(25,255,500m)CO_(2)浓度与CH_(4)浓度均显著相关,但观测高度越高所代表的浓度贡献源区越大,多种排放源的干扰使得温室气体之间的同源性变差,导致其相关性随着高度增加而降低.城市温室气体浓度的垂直观测提供了从水平方向上无法获得的独特信息,因此有必要在城市开展立体化的温室气体监测,以便更好地捕捉大气温室气体浓度的变化,从而服务于城市碳减排政策.

中国东部及西北太平洋地区边界层高度变化特征

利用19792019年ERA5逐月大气边界层高度(ABLH,Atmospheric boundary layer height)资料,采用气候态分析、距平分析、极值分析、经验正交(EOF)分析及小波分析等方法,研究了中国东部及西北太平洋区域大气边界层高度的变化特征。结果表明:(1)太阳辐射对边界层高度有重要影响,边界层高度的季节变化存在显著的海陆差异,大陆(海洋)上,夏季时边界层高度最高(低),而在冬季时最低(高)。(2)边界层高度的海陆差异随季节改变,春秋季海陆差异较小,冬夏季时最明显。(3)大陆上边界层高度极大值出现在夏半年的月份,极小值出现在冬半年的月份;海洋上的相反。(4)41年边界层高度场的EOF分析得到两个模态,第一模态表现为南北经向和海陆差异,第二模态为自西北至东南的“+-+-”相位分布,第一模态的时间系数以3~7 a的周期最显著,第二模态同时存在4~7 a和9~11 a的振荡周期。

Research Progress on Estimation of the Atmospheric Boundary Layer Height

Atmospheric boundary layer height(ABLH)is an important parameter used to depict characteristics of the planetary boundary layer(PBL)in the lower troposphere.The ABLH is strongly associated with the vertical distributions of heat,mass,and energy in the PBL,and it is a key quantity in numerical simulation of the PBL and plays an essential role in atmospheric environmental assessment.In this paper,various definitions and methods for deriving and estimating the ABLH are summarized,from the perspectives of turbulent motion,PBL dynamics and thermodynamics,and distributions of various substances in the PBL.Different methods for determining the ABLH by means of direct observation and remote sensing retrieval are reviewed,and comparisons of the advantages and disadvantages of these methods are presented.The paper also summarizes the ABLH parameterization schemes,discusses current problems in the estimation of ABLH,and finally points out the directions for possible future breakthroughs in the ABLHrelated research and application.

Vertical distribution of sand-dust aerosols and the relationships with atmospheric environment

The vertical distribution of aerosols in the troposphere is important for determining their effects on cli- mate. The vertical distribution of aerosols under different atmospheric conditions in the free troposphere was di- rectly observed using a surface micro-pulse LIDAR （MPL） and a TP/WVP-3000 microwave radiometer at the Semi-Arid Climate ＆ Environment Observatory of Lanzhou University （SACOL, 35.95~N, 104.10~E） in the western Loess Plateau, China, in the spring of 2008. The results showed two possible transportation paths of a sandstorm from May 1 to May 4 in 2008. In one path, sand-dust aerosols were transported toward the east from the Taklimakan Desert to the Badain Jaran Desert and the Tengger Desert by a westerly wind and then toward the southeast to Jingtai and Lanzhou. A weak aerosol index （AI） indicated another possible transport path toward the east from the Taklimakan Desert to the Qaidam Basin and through the Tibetan Plateau eastward to SACOL. The aerosol profile of sandstorm processes over the SACOL area displayed three patterns： a single peak distribution under stable at- mospheric conditions, indicating urban aerosol distribution; an exponential decrease under unstable atmospheric conditions in the presence of a sandstorm; and a slight change in the mixed layer during the first and last stages of the sandstorm, indicative of thorough mixing during lifting and deposition stages. Analyses of the aerosol layer height （ALH） showed that there are two types of ALH diurnal variation. The ALH during the first sandstorm stage was complex and disordered, and affected by atmospheric circulation. While the ALH had obvious diurnal variation in the other stage, the ALH and aerosol extinction coefficient （AEC） had a single peak, and was higher in the af- ternoon and lower in the morning. In the second case the ALH was in agreement with the atmospheric boundary layer height （BLH） variation. As a result of the development of the atmospheric boundary layer （ABL） during day and maintenance at night, ALH during sandstorm-free days showed obvious diurnal variations. Multiple vertical distribu- tion patterns of sand-dust aerosols will result in different climate effects; therefore, the vertical distribution patterns can be used to parameterize climate and aerosol models.

南海大气边界层高度的气候特征研究

利用1979—2020年逐时的ERA5再分析数据,研究了南海区域大气边界层高度的气候特征及其影响因子。结果表明:南海区域平均大气边界层高度为500~800 m,空间上呈中间高、四周低的分布特征。南海大气边界层高度具有显著的季节变化特征,总体按照冬季、秋季、夏季、春季依次递减,日变化较小,大部分区域边界层高度的日变化幅度小于300 m,日循环比较平缓。南海大气边界层高度显著的季节变化特征主要受海气温差、海表面风、感热通量、潜热通量和稳定度的共同影响。较大的海气温差和强风速使海表热通量增加,下垫面不稳定性增加,海气相互作用加强,湍流活动增强,导致秋冬季边界层高度较高。过去42 a南海区域年平均大气边界层高度显著增高,年平均增高率约为0.8 m/a,且边界层高度变化存在显著的季节差异。海表面温度升高、潜热通量增加以及稳定度减小有利于边界层的发展,可能是导致南海边界层高度增加的主要原因。

地基遥感联合反演大气边界层高度与ERA5再分析资料比对分析

利用北京国家综合气象探测试验基地超大城市观测试验建设的地基垂直遥感设备(激光气溶胶雷达、微波辐射计及风廓线雷达),使用2021年5—8月的观测资料,根据不同设备的探测优势以及边界层的日变化规律,利用激光气溶胶雷达、微波辐射计、风廓线雷达观测资料进行联合反演,得到全天候大气边界层高度。并将联合反演所得的边界层高度与探空资料计算及ERA5再分析资料提供的全天候大气边界层高度进行比较,发现:联合反演边界层高度与ERA5数据提供的大气边界层高度有较好的一致性;激光气溶胶雷达适用于白天对流边界层的观测,微波辐射计适用于夜间稳定边界层的观测,使用微波辐射计与风廓线雷达联合反演大气边界层高度可以改善弱降雨时单设备的反演结果;联合反演的大气边界层高度结果与单设备反演大气边界层高度均符合大气边界层的日变化规律;得到的联合反演边界层高度与探空数据计算得到的大气边界层高度差值的标准偏差为62 m,相较于ERA5数据提供的一定范围内大气边界层高度均值,联合反演边界层高度能更精准地反映更小范围内的大气边界层高度。

基于激光雷达的天津海-岸-陆地区大气边界层高度研究

利用2018年8月~2019年7月的气溶胶激光雷达观测数据对天津城市、渤海沿岸和渤海地区的大气边界层高度进行了反演,并利用无人机探空观测对激光雷达反演结果进行验证,同时结合天津大气边界层观测站、塘沽站和渤海A平台站的不同气象特征分析了大气边界层高度的分布特征及其差异产生的原因.结果表明:激光雷达和无人机观测获得的大气边界层高度具有较高一致性,在稳定、中性和不稳定层结条件下两者的相关系数分别为0.508,0.565和0.687.天津城区和塘沽地区各季节的大气边界层高度日变化规律较为一致,与各季节湍流动能和感热通量日变化规律接近,均呈单峰型分布,A平台大气边界层高度具有明显的海洋大气特征,表现为冬季高于城区和塘沽,夏季则与之相反.夏季由于海陆环流造成的热力内边界层的形成,是市区与塘沽大气边界层高度差异产生的原因之一,2019年夏季塘沽出现热力内边界层的情况下,其午后边界层高度下降约30~160m,与城区的大气边界层高度差升高约150~300m.

Measuring boundary-layer height under clear and cloudy conditions using three instruments

Boundary-layer height （BLH） under clear, altostratus and low stratus cloud conditions were measured by GPS sounding, wind profiler radar, and micro-pulse lidar during the atmospheric radiation measurement experiment from Sep. to Dec. 2008 in Shouxian, Anhui, China. Results showed that during daytime or nighttime, regardless of cloud conditions, the GPS sounding was the most accurate method for measuring BLH. Unfortunately, because of the long time gap between launchings, sounding data did not capture the diurnal evolution of the BLH. Thus, wind profile radar emerged as a promising instrument for direct and continuous measurement of the mixing height during the daytime, accurately determining BLH using the structure parameter of the electromagnetic refractive index. However, during nighttime, radar was limited by weak signal extraction and did not work well for determining the BLH of the stable boundary layer, often recording the BLH of the residual layer. While micro-pulse lidar recorded the evolution of BLH, it overestimated the BLH of the stable boundary layer. This method also failed to work under cloudy conditions because of the influence of water vapor. Future work needs to develop a method to determine BLH that combines the complimentary features of all three algorithms.

大气边界层高度确定及应用研究进展

大气边界层高度是表征边界层特征的重要参量,影响边界层内水热、物质、能量的垂直分布,也是数值模拟、环境评估中的重要参数。从湍流运动、热力作用、动力作用以及物质分布等多视角总结了大气边界层高度的定义及确定方法,回顾了采用直接观测手段和遥感手段确定大气边界层高度的不同方法,对比了大气边界层高度不同获取手段的优缺点,梳理了大气边界层高度参数化方案,探讨了大气边界层高度确定中存在的问题,并提出未来相关研究和应用可能突破方向。

北京地区PM_(10)质量浓度与边界层气象要素相关性分析

对北京市2007年观象台观测站PM10质量浓度资料、观象台气象自动站资料、风廓线资料和探空资料进行了数据分析。结果表明,在污染物源强一定的条件下,污染物的积累、稀释、扩散和清除主要取决于气象条件。近地面风速、温度、湿度、气压和边界层高度等气象条件对于可吸入颗粒物的污染程度有着很重要的影响:PM10质量浓度与地面风速、温度、湿度、气压和大气边界层高度呈显著相关性,并且相关性随季节变化明显。其中,6月PM10质量浓度与地面风速和大气边界层高度呈负相关性,而与温度呈正相关,11月则与温度成负相关;风速与PM10质量浓度之间的相关性可以用二次多项式来描述,二者呈"U"形变化。另外由11月份PM10质量浓度资料的分析表明,当月PM10质量浓度最小值对应的风速为4.1 m/s。