基于数据窗口标准差的边界层高度反演方法——以上海市为例

大气边界层具备一个重要特性,即在边界层顶部,气溶胶浓度在垂直分布上存在显著突变。利用该特性,采用主动遥感装置经过窗口平滑去除噪点后数据,提出基于梯度法改进的大气边界层高度反演方法——窗口标准偏差法。基于激光云高仪后向散射廓线数据,利用该方法反演边界层高度,在边界层高度下大气气溶胶混合均匀时,反演结果较为理想。在此基础上,将窗口标准偏差法反演结果与逐步曲线拟合法反演结果进行比较。结果表明：两种方法具有较好的相关性,相关系数为0.94。两种方法产生差异的原因在于窗口标准偏差法不考虑夹卷层厚度而逐步曲线拟合法考虑夹卷层厚度。窗口标准偏差法可以降低高空背景光噪音对反演结果的影响。通过该方法反演出的边界层高度,在时间序列上具有连续性强的特点,反演结果更有利于研究大气边界层高度的时间变化趋势。     

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。     

基于激光雷达资料的小波变换法反演边界层高度的方法

利用小波变换法反演边界层高度时,不同小波母函数的选取可能得到不同的边界层高度。因此,对构造的白天及夜间激光雷达后向散射信号理想廓线进行Haar小波协方差变换,并对后向散射信号梯度廓线进行Morlet与Mexican Hat小波变换反演边界层高度。结果表明,宜采用Haar函数与Mexican Hat函数作为小波母函数,其中Haar函数准确性优于Mexican Hat函数,而Mexican Hat函数更易稳定。同时为了进一步检验3种小波变换法的反演结果对小波振幅的敏感性,通过改变小波母函数的小波振幅,发现无论是理想廓线还是叠加扰动的廓线,较大的小波振幅易得到比较稳定准确的白天边界层高度与夜间混合层高度。     

基于激光雷达和微波辐射计观测确定混合层高度方法的比较

利用苏州地区2010年1月4,7,16日和2月4日4天的激光雷达及微波辐射计观测资料,比较了不同遥感手段探测晴天大气混合层高度的差异,发现试验期间该地区的混合层高度在300~1500 m之间。利用梯度法、标准偏差法、小波法从激光雷达数据中提取混合层高度并进行了对比,结果表明三种方法都能较好地反演混合层高度并且一致性较好,三者差异主要存在于大气边界层的发展和消亡阶段;梯度法和小波法结果无明显差异,而标准偏差法结果稍高于其他方法。在此基础上,利用微波辐射计探测的大气温度,使用温度梯度法估算大气混合层高度,并与激光雷达探测结果进行了比较,结果表明,大多数情况下激光雷达探测结果高于微波辐射计观测结果;两种遥感手段有较好的相关性,相关系数为0.76。激光雷达同微波辐射计结果存在差异,尤其是在边界层的发展和消散阶段,这是由两种遥感手段探测原理不同造成的。     

气溶胶激光雷达和无线电探空观测边界层高度的对比分析

利用北京地区2017年11月至2018年1月连续3个月的激光雷达资料和无线电探空数据,按照清洁天、污染天和多云天3种天气条件,对大气边界层高度的计算方法和结果进行对比分析。结果表明,基于激光雷达消光系数的梯度法、标准差法和小波法都能够较好地提取边界层高度。清洁天标准差法计算的边界层高度高于梯度法和小波法,08:00（当地时间,下同）和20:00由无线电探空得到的清洁天边界层高度平均值分别为1176 m和1224 m。污染天标准差法的计算结果要低于梯度法和小波法,污染天无线电探空得到的边界层高度平均值约为956 m,和清洁天相比降低了两百多米,重污染时最低降低至562 m,逆温层高度和PM2.5浓度具有明显的反相关关系。有云时,梯度法和小波法确定的边界层高度和云高非常接近,标准差法计算的结果略低。总体而言,气溶胶激光雷达计算的边界层高度随着污染等级的提高没有明显的降低趋势,相反在重度污染情况下反而有所增加,这可能是由于污染物的不断堆积导致的。梯度法确定的边界层高度易受到污染物传输过程的影响,略高于逆温层高度。另外,激光雷达确定的边界层高度受到残留层影响时,也会高于逆温层。     

青藏高原东部及下游关键区大气边界层高度的观测分析

利用2007年12月10-24日在红原、温江和宜昌同步观测的3小时加密探空资料,分析了青藏高原东部及下游关键区大气边界层位温廓线日变化特征,以及对流边界层高度和稳定边界层高度的变化特征.分析结果表明,不同地形位温廓线具有相同的日变化特征,对流边界层在白天出现和发展,而稳定边界层在夜间出现和发展;对流边界层的发展史和发展高度与海拔高度有关,高海拔地区对流边界层的发展史较短但发展高度较高,而低海拔地区对流边界层的发展史较长但发展高度较低;稳定边界层的发展史和发展高度也与海拔高度有关,高海拔地区稳定边界层的发展史较长且发展高度较高,而低海拔地区稳定边界层的发展史较短且发展高度较低;对流边界层的最大发展高度多出现在地方时17时,而稳定边界层的最大发展高度多出现在地方时02时;红原、温江和宜昌的对流边界层高度分别可达4 930 m、1 000 m和710 m.而其稳定边界层高度分别可达1 100 m、920 m和650 m.     

激光雷达反演边界层高度方法评估及在北京的应用

边界层高度是影响大气边界层发展和空气污染程度的重要因子,是环境和气候研究的重要参数。本文利用激光雷达对北京地区2011年5月至2012年4月的边界层高度进行探测分析,采用小波协方差方法反演边界层高度,评估了该方法的适用性。得到基于小波协方差方法自动判断边界层高度的最优参数组合,激光雷达与飞机探测结果对比一致性较好;与探空结果相关系数0.88,激光雷达反演的边界层高度略偏高。当激光雷达的垂直分辨率为30 m时,更加适合北京地区的步长和阈值分别为210 m和0.05;当激光雷达的垂直分辨率为15 m时,步长和阈值分别为135 m和0.05。分析期间,不同季节边界层高度日变化有明显的不同,夏季14:00（北京时）左右达到最高,较高的边界层高度可维持3~4 h,平均可达1.30 km;冬季较高边界层高度只能维持2 h左右,平均为1.08 km。有云与无云天气边界层日变化特征以及边界层高度存在显著的差异,云的存在减少了到达地面的直接辐射,抑制了湍流的发展,进一步抑制了边界层的发展;本文也将激光雷达反演边界层高度结果应用于观测时期边界层高度与地面污染的关系研究中,统计得到边界层高度与PM2.5浓度的相关系数为－0.340。     

云底高度的地基毫米波云雷达观测及其对比

对2014年11月20日—12月31日中国气象局大气探测综合试验基地Ka波段毫米波云雷达、Vaisala CL51激光云高仪、L波段高空探测系统观测的云底高度进行对比分析。结果表明:在低能见度条件下,毫米波云雷达对云的探测能力明显优于激光云高仪,随着能见度的增加,两设备云探测能力差距在减小;毫米波云雷达与激光云高仪同时观测到有云时,二者观测的云底高度相关系数为0.92;毫米波云雷达与探空观测云底、云顶高度的相关系数分别为0.93和0.78;云雷达观测的云底高度均略低于激光云高仪和探空,云雷达观测的云顶高度略高于探空。     

Ka波段固态发射机体制云雷达和激光云高仪探测青藏高原夏季云底能力和效果对比分析

激光云高仪和云雷达是探测云底的两种设备,但其探测能力和探测结果有一定的差异,对比分析两种设备的测云效果有助于正确认识它们的探测优势,推进我国云雷达在云探测中的应用。本文提出了基于云雷达数据的云底和云顶高度分析方法,利用2014年夏季第三次青藏高原大气科学试验云雷达、激光雷达和激光云高仪数据,统计了三种设备探测青藏高原低云、中云和高云的云底高度偏差、探测率,分析了激光云高仪探测云底偏高的原因,根据探测结果提出了固态发射机体制雷达探测青藏高原低云的优化观测模式,模拟分析了探测效果。结果表明:（1）云雷达对高云的探测能力要明显优于激光云高仪,但其对低云的探测能力有待改进,激光云高仪探测云底下部的边界层内的云雷达回波信号可能是非云降水回波;低层云的遮挡作用明显降低了激光云高仪对多层云的观测能力;与激光云高仪相比,云雷达仍然会漏掉一些高云和中云。（2）激光云高仪探测的中云和高云的云底很多在云雷达回波内部,云雷达和激光云高仪观测的云底的时空对应关系比较差。（3）增大激光发射功率和优化固态发射机体制云雷达观测模式可提高云的观测能力,微波和激光雷达数据融合可全面了解不同类型云的宏观特征。这一工作为云雷达和激光雷达数据的应用,评估激光云高仪和云雷达探测青藏高原云的能力,讨论设计优化的云观测方案,为推进我国云观测技术的发展提供了重要参考依据。     

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。     

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-2for downward shortwave radiation(DSR) and a mean increase of 19.2 W m-2for downward longwave radiation(DLR), as well as a mean decrease of 9.6W m-2for 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 PM2.5column 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 PM2.5reaches 200 mg m-2, the decrease in the PBLH at 1600 LST(local standard time) is about 450 m.     

Determination of the Atmospheric Boundary Layer Height from Radiosonde and Lidar Backscatter

The height of the atmospheric boundary layer is derived with the help of two different measuring systems and methods. From radiosoundings the boundary layer height is determined by the parcel method and by temperature and humidity gradients. From lidar backscatter measurements a combination of the averaging variance method and the high-resolution gradient method is used to determine boundary layer heights. In this paper lidar-derived boundary layer heights on a 10 min basis are presented. Datasets from four experiments – two over land and two over the sea – are used to compare boundary layer heights from both methods. Only the daytime boundary layer is investigated because the height of the nighttime stable boundary layer is below the range of the lidar. In many situations the boundary layer heights from both systems coincide within ±200 m. This corresponds to the standard deviation of lidar-derived 10-min values within a 1-h interval and is due to the time and space variability of the boundary layer height. Deviations appear for certain situations and depend on which radiosonde method is applied. The parcel method fails over land surfaces in the afternoon when the boundary layer stabilizes and over the ocean when the boundary layer is slightly stable. An automatic radiosonde gradient method sometimes fails when multiple layers are present, e.g. a residual layer above the growing convective boundary layer. The lidar method has the advantage of continuous tracing and thus avoids confusion with elevated layers. On the other hand, it mostly fails in situations with boundary layer clouds     

VARIATION CHARACTERISTICS OF THE PLANETARY BOUNDARY LAYER HEIGHT AND ITS RELATIONSHIP WITH PM2.5 CONCENTRATION OVER CHINA

The planetary boundary layer height (PBLH) was calculated using the radiosonde sounding data, including 120 L-band operational sites and 8 GPS sites in China. The diurnal and seasonal variations of PBLH were analyzed using radiosonde sounding (OBS-PBLH) and ERA data (ERA-PBLH). Based on comparison and error analyses, we discussed the main error sources in these data. The frequency distributions of PBLH variations under different regimes (the convective boundary layer, the neutral residual layer, and the stable boundary layer) can be well fitted by a Gamma distribution and the shape parameter k and scale parameter s values were obtained for different regions of China. The variation characteristics of PBLH were found in summer under these three regimes for different regions. The relationships between PBLH and PM2.5 concentration generally follow a power law under very low or no precipitation conditions in the region of Beijing, Tianjin and Hebei in summer. The results usually deviated from this power distribution only under strong precipitation or high relative humidity conditions because of the effects of hygroscopic growth of aerosols or wet deposition. The OBS-PBLH provided a reasonable spatial distribution relative to ERA-PBLH. This indicates that OBS-PBLH has the potential for identifying the variation of PM2.5 concentration.     

基于无线电掩星数据,探空资料以及再分析资料估算大气边界层高度的比较

用11年的全球无线电掩星数据(COSMIC),无线电探空数据(IGRA)以及欧洲中心再分析资料(ERA-Interim)对全球大气边界层高度(PBLH)进行估算比较.结果表明:(1)在1200 UTC和0000 UTC,由ERA-Interim和IGRA数据估算得到的全球PBLH空间分布较为一致,相关性较好,在白天正午时候太阳辐射能力较强,对流活动频繁,估算得到的大气边界层高度较高.(2)由COSMIC掩星数据估算得到的边界层高度比探空数据和再分析数据估算结果整体偏大.(3)COSMIC掩星数据,IGRA探空数据以及ERA-Interim再分析资料估算结果都表明边界层高度在低纬度地区偏大,高纬度地区偏小.(4)分析不同数据估算边界层高度纬向季节性差异表明,IGRA探空数据和COSMIC数据间差异为-1700m至-500m,IGRA与ERA-Interim之间的差异为-500m至250m.此外,对于大多数纬度而言,三个数据集之间的差异在冬季较大,在夏季较小.     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA*

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urban area in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered structure of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heights and morning boundary layer development are combined with surface eddy correlation measurements of kinematic heat and moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is presented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed during the transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urbanarea in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered struc-ture of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heightsand morning boundary layer development are combined with surface eddy correlation measurements of kinematic heatand moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is pres-ented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed duringthe transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

Retrieval of Boundary Layer Height and Its Influence on PM 2.5 Concentration Based on Lidar Observation over Guangzhou

Wavelet analysis was applied to lidar observations to retrieve the planetary boundary layer height(PBLH)over Guangzhou from September 2013 to November 2014 over Guangzhou. Impact of the boundary effect and the wavelet scale factor on the accuracy of the retrieved PBLH has been explored thoroughly. In addition, the PBLH diurnal variations and the relationship between PM_(2.5) concentration and PBLH during polluted and clean episodes were studied. Results indicate that the most steady retrieved PBLH can be obtained when scale factor is chosen between 300-390 m. The retrieved maximum and minimum PBLH in the annual mean diurnal cycle were ～1100 m and ～650 m, respectively. The PBLH was significantly lower in the dry season than in the wet season, with the average highest PBLH in the dry season and the wet season being ～1050 m and ～1200 m respectively. Compared to the wet season, the development of PBLH in the dry season was delayed by at least one hour due to the seasonal cycle of solar radiation. Episode analysis indicated that the PBLH was ～50% higher during clean episodes than during haze episodes. The average highest PBLH in the haze episodes and clean episodes were ～800 m and ～1300 m,respectively. A significant negative correlation between PBLH and PM_(2.5) concentration(r =-0.55**) is discovered.According to China"Ambient Air Quality Standard", the PBLH values in good and slightly polluted conditions were 1/6-1/3 lower than that in excellent conditions, while the corresponding PM_(2.5) concentration were ～2-2.5 times higher.     

A Comparison Between Modelled and Measured Mixing-Layer Height Over Munich

An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurements, to those simulated by different atmospheric boundary-layer parameterization schemes. The comparison is performed at two sites (one suburban and one rural) close to Munich, Germany for two spring and two winter days. It is found that, under convective conditions, the mixing height determined, by both Sodar and ceilometer, corresponds to the middle or the top of the entrainment zone, respectively, as calculated from the eddy-viscosity profiles. Under stable conditions, the measured mixing height is related to the height where eddy viscosities attain their minimum values (Sodar) or to the height of residual mechanical turbulence (ceilometer). During a foehn case with weak turbulence, the measured mixing height from both Sodar and ceilometer is better inferred by considering the eddy-viscosity profiles during daytime and the height of the low-level jet during nighttime.     

A Study of the Atmospheric Boundary Layer Structure During a Clear Day in the Arid Region of Northwest China

The local climate and atmospheric circulation pattern exert a clear influence on the atmospheric boundary layer （ABL） formation and development in Northwest China. In this paper, we use field observational data to analyze the distribution and characteristics of the ABL in the extremely arid desert in Dunhuang, Northwest China. These data show that the daytime convective boundary layer and night time stable boundary layer in this area extend to higher altitudes than in other areas. In the night time, the stable boundary layer exceeds 900 m in altitude and can sometimes peak at 1750 m, above which the residual layer may reach up to about 4000 m. The daytime convective boundary layer develops rapidly after entering the residual layer, and exceeds 4000 m in thickness. The results show that the deep convective boundary layer in the daytime is a pre-requisite for maintaining the deep residual mixed layer in the night time. Meanwhile, the deep residual mixed layer in the night time provides favorable thermal conditions for the development of the convective boundary layer in the daytime. The prolonged periods of clear weather that often occurs in this area allow the cumulative effect of the atmospheric residual layer to develop fully, which creates thermal conditions beneficial for the growth of the daytime convective boundary layer. At the same time, the land surface process and atmospheric motion within the surface layer in this area also provide helpful support for forming the particular structure of the thermal ABL. High surface temperature is clearly the powerful external thermal forcing for the deep convective boundary layer. Strong sensible heat flux in the surface layer provides the required energy. Highly convective atmosphere and strong turbulence provide the necessary dynamic conditions, and the accumulative effect of the residual layer provides a favorable thermal environment.     

基于微波辐射计和气溶胶激光雷达的边界层高度研究及应用

分别基于微波辐射计温湿度廓线资料的气块法、位温法和比湿法,地面气象资料的罗氏法及气溶胶激光雷达数据的梯度法,计算得出广州地区大气边界层高度,对比分析5种边界层高度结果及其与气象条件、空气质量之间的关系,结合典型大气污染过程分析边界层高度对PM_2.5、O₃浓度的影响。结果显示:（1）利用位温法、气块法、罗氏法、比湿法和梯度法计算得出广州地区平均边界层高度分别为2 207 m、1 239 m、901 m、717 m和660 m,位温法显著高估了广州地区的边界层高度;（2）利用气块法得出的混合层高度日变化能够较好地表征白天大气边界层演变特征,利用气块法和比湿法得出的白天混合层高度与近地面O₃浓度有显著的正相关关系,相关系数在0.5以上,在O₃污染防治中,应同时考虑边界层内垂直输送的影响;（3）利用梯度法得出的边界层高度在污染天气时与PM_2.5浓度的相关性较好,能较好地表现出大气污染情况,在PM_2.5污染天气过程分析中具有较好的应用价值。