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1.
北京秋季一次降雪前污染天气的激光雷达观测研究   总被引：1，自引：0，他引：1  
以2009年11月5~8日北京地区发生的一次特殊天气形势下的重污染天气过程为例,研究分析本次污染特点和大气边界层结构特征以及此天气过程的大气温度和相对湿度结构特点。激光雷达是探测大气边界层及气溶胶的一个高效工具,利用ALS300激光雷达系统测量信号,应用Fernald方法反演大气消光系数,根据反演的气溶胶消光系数的最大突变,即最大递减率的高度来确定大气边界层的高度。利用其观测的退偏比分析大气污染物特性。利用微波辐射计数据,确定大气温度和湿度时空特征。研究结果表明:在本次污染天气下,大气具有很强的逆温结构,逆温最大可达近1 K(100 m)-1,500 m以上的大气相对湿度很低,在这种天气特征下的大气边界层高度在400 m左右,非常稳定。污染结束降雪开始前,大气逆温结构消失,大气湿度大幅度增加,接近饱和。根据lidar(light detection and ranging)退偏比的分析,本次污染天气是一次典型的烟尘类颗粒物的污染,污染具有区域性特点。PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物)与AOT(Aerosol Optical Thickness)之间有明显的线性关系,相关系数达到0.72。该lidar系统能够反演出秋季降雪前本次污染天气背景下北京城区上空的大气污染特性和大气边界层高度。  相似文献   

2.
毕凯  王广河  毛节泰 《气象》2012,38(2):220-227
利用2009年上海浦东新区气象站高时间分辨率的能见度资料及其同步地面气象要素资料,在气块静力稳定的假设下研究了由于辐射冷却引起的霾或雾在演变的各阶段气溶胶吸湿性增长及其消光系数随相对湿度的变化,结果表明：气溶胶吸湿性增长率f（RH）随相对湿度的增长具有先慢后快平滑连续的特点;气溶胶吸湿性增长率在不同季节有所差异,在夏季和秋季较高,在冬季和春季时较低;平均而言,当相对湿度从40%增大到95%时,气溶胶吸湿性增长率可达6.6;对比国内外实验和观测结果,发现f（RH）随相对湿度的变化曲线与硫酸铵亲水增长相似;在这种雾消散时,随着气温的升高,测量给出的相对湿度值不会立即下降,而是在接近饱和的情况下维持一段时间,然后再迅速下降,其滞后大约为1～2小时。这很可能是测湿元件不能及时反映外界湿度变化所致。  相似文献   

3.
深圳市大气能见度与细粒子浓度统计模型   总被引：7，自引：3，他引：4       下载免费PDF全文
利用深圳市2007年全年逐时能见度、PM2.5质量浓度和相对湿度观测数据, 在分析大气消光机理及其影响因素的基础上确立了能见度与PM2.5之间的基本模型关系, 着重讨论分析了相对湿度对颗粒物消光影响的常见修正方式, 并通过线性和非线性回归分析筛选相对湿度影响修正因子fRH的表达形式和确定模型参数, 最终建立起适合于深圳本地情况的能见度与PM2.5之间的最优统计模型 (R2=0.43, n=8024)。进一步利用能见度与PM2.5的日平均值进行了多元回归分析, 模型拟合值与实测值之间的相关系数 (R2) 高达0.73(n=350), 而且预测偏差范围小, 较好地反映了深圳市大气能见度与PM2.5之间的定量相关关系。  相似文献   

4.
We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz 2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ (w, Pz 2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed. An erratum to this article can be found at  相似文献   

5.
This paper evaluates convective boundary layer (CBL) budget methods as a tool for estimating regionally averaged sensible and latent heat fluxes for the study region used in OASIS (Observations at Several Interacting Scales). This is an agricultural region of mixed cropping and grazing extending about 100 km west of the town of Wagga Wagga, NSW, Australia.The analysis proceeds in three stages: first, a simpleone-dimensional model of the well-mixed layer (the CBL slab model), forced with measurements of the surface heat and evaporation fluxes, is evaluated by comparing measured and modelled CBL temperature, humidity and depths. A comparison of several entrainment schemes shows that a simple model, where the entrainment kinetic energy is parameterised as a fraction (3) of the surface sensible heat flux, works well if is set to 0.5. Second, the slab model is coupled to a Penman–Monteith model of surface evaporation to predict regional scale evaporation and thence heat fluxes. Finally, the integral CBL budget approach, which is an inverse method using theone-dimensional slab model, is used to infer regional heat and evaporation fluxes from measured time series of CBL temperature and humidity.We find that the simple CBL slab model works reasonably well for predicting CBL depth and very well for CBL temperature, especially if approximate estimates of subsidence velocity and warming due to advection are included. Regional sensible heat fluxes estimated from the integral CBL method match those measured, although the method is very sensitive to measurement errors. Measurement-model differences were larger for short integration times, because the well-mixed assumptions are violated at particular times of the day. The corollary is that `whole-day' (0530–1530 h) estimates are in reasonable agreement with measured values. Integral methods could not be used to infer the regional evaporation flux directly because CBL humidity profiles were complex and often not well mixed until mid-afternoon. We recommend that regional evaporation fluxes be predicted either from a coupled Penman–Monteith – CBL slab model, or inferred as a residual term from estimates of the regionally averaged available energy and sensible heat flux. Furthermore, we show that inferring fluxes via integral methods will always be difficult when the scalar concentrations have either a large surface source and free atmosphere sink (in the case of water vapour and methane), or a large surface sink and upper level source (in the case of CO2).  相似文献   

6.
在下垫面相对比较复杂的四川区域,为了解风云二号F(FY-2F)卫星相对湿度产品的可靠性,利用2013~2017年加密观测期间研究区内11个加密观测站点探空探测资料与FY-2F卫星湿度产品进行对比分析,给出了FY-2F卫星相对湿度产品的分析结果,并从偏差统计、相关系数统计等方面对比分析了二者数据间的差异。结果显示:FY-2F卫星湿度产品整体数值小于探空湿度,和探空数据间的相关系数区间为-0.16~0.64;相对偏差区间为-1.65~-0.19;相关系数变化趋势均随气压层高度变化呈线性变化趋势;FY-2F卫星产品的可靠性随着高度升高而升高。   相似文献   

7.
Slope flow mechanisms are crucial for the transport of air pollutants in complex terrain. Previous observations in sloping terrain showed upslope flows filling the entire convective boundary layer (CBL) and reducing air pollution concentrations by venting air pollutants out of the CBL into the free atmosphere. During the Pacific 2001 Air Quality Field Study in the Lower Fraser Valley, British Columbia, Canada, we observed slope flows during weak synoptic winds, clear skies, and strong daytime solar heating. With a Doppler sodar we measured the three wind components at the foot of a slope having an average angle of 19° and a ridge height of 780 m. We operated a scanning lidar system and a tethersonde at a nearby site on the adjacent plain to measure backscatter of particulate matter, temperature, wind speed, wind direction, and specific humidity. Strong daytime upslope flows of up to 6 m s−1 through a depth of up to 500 m occurred in the lower CBL, but with often equally strong and deep return flows in the upper part of the CBL. The mass transport of upslope flow and return flow approximately balanced over a 4-h morning period, suggesting a closed slope-flow circulation within the CBL. These observations showed that air pollutants can remain trapped within a CBL rather than being vented from the CBL into the free atmosphere.  相似文献   

8.
The temporal evolution and spatial structure of the aerosol layer (AL) height as observed with an airborne downlooking lidar over the Swiss Alps were investigated with a three-dimensional mesoscale numerical model and a particle dispersion model. Convective boundary-layer (CBL) heights were derived from the mesoscale model output, and the behaviour of surface-released particles was investigated with the particle dispersion model. While a previous investigation, using data from the same field study, equated the observed AL height with the CBL height, the results of the current investigation indicate that there is a considerable difference between AL and CBL heights caused by mixing and transport processes between the CBL and the free atmosphere. CBL heights show a more terrain-following behaviour and are lower than AL heights. We argue that processes causing the difference between AL and CBL heights are common over mountainous terrain and that the AL height is a length scale that needs to be considered in air pollution studies in mountainous terrain.  相似文献   

9.
The thermodynamic structure of the Convective Boundary Layer (CBL) over the Deccan Plateau, India has been investigated using aerological data during the summer monsoon seasons of 1980 and 1981. Conserved-variable analysis and the saturation-point approach, which were used in this study, suggest that the top of the CBL varied between 700–600 mb during the monsoon. The air above the top of the CBL during a weak monsoon was estimated to have subsided for 4 days with a subsidence rate of 30 mb day-1.  相似文献   

10.
Based on the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) Version 4.10 products released on 8 November 2016, the Level 2 (L2) aerosol product over the Tibetan Plateau (TP) is evaluated and the aerosol radiative effect is also estimated in this study. As there are still some missing aerosol data points in the daytime CALIPSO Version 4.10 L2 product, this study re-calculated the aerosol extinction coefficient to explore the aerosol radiative effect over the TP based on the CALIPSO Level 1 (L1) and CloudSat 2B-CLDCLASS-LIDAR products. The energy budget estimation obtained by using the AODs (aerosol optical depths) from calculated aerosol extinction coefficient as an input to a radiative transfer model shows better agreement with the Earth’s Radiant Energy System (CERES) and CloudSat 2B-FLXHR-LIDAR observations than that with the input of AODs from aerosol extinction coefficient from CALIPSO Version 4.10 L2 product. The radiative effect and heating rate of aerosols over the TP are further simulated by using the calculated aerosol extinction coefficient. The dust aerosols may heat the atmosphere by retaining the energy in the layer. The instantaneous heating rate can be as high as 5.5 K day–1 depending on the density of the dust layers. Overall, the dust aerosols significantly affect the radiative energy budget and thermodynamic structure of the air over the TP, mainly by altering the shortwave radiation budget. The significant influence of dust aerosols over the TP on the radiation budget may have important implications for investigating the atmospheric circulation and future regional and global climate.  相似文献   

11.
Spectral analysis was performed on aircraft observations of a convective boundary layer (CBL) that developed over a thermally inhomogeneous, well-marked mesoscale land surface. The observations, part of the GAME-Siberia experiment, were recorded between April and June 2000 over the Lena River near Yakutsk City. A special integral parameter termed the ‘reduced depth of the CBL’ was used to scale the height of the mixed layer with variable depth. Analysis of wavelet cospectra and spectra facilitated the separation of fluxes and other variables into small-scale turbulent fluctuations (with scales less than the reduced depth of the CBL, approximately 2 km) and mesoscale fluctuations (up to 20 km). This separation approach allows for independent exploration of the scales. Analyses showed that vertical distributions obeyed different laws for small-scale fluxes and mesoscale fluxes (of sensible heat, water vapour, momentum and carbon dioxide) and for other variables (wind speed and air temperature fluctuations, coherence and degree of anisotropy). Vertical profiles of small-scale turbulent fluxes showed a strong decay that differed from generally accepted similarity models for the CBL. Vertical profiles of mesoscale fluxes and other variables clearly showed sharp inflections at the same relative (with respect to the reduced depth of the CBL) height of approximately 0.55 in the CBL. Conventional similarity models for sensible heat fluxes describe both small-scale turbulent and mesoscale flows. The present results suggest that mesoscale motions that reach up to the relative level of 0.55 could be initiated by thermal surface heterogeneity. Entrainment between the upper part of the CBL and the free atmosphere may cause mesoscale motions in that region of the CBL.  相似文献   

12.
张哲  师宇  王咏薇  刘磊  胡非 《气象科学》2019,39(3):359-367
大气边界层高度对于天气、气候和大气污染研究是一个至关重要的参量。对流边界层(Convective Boundary Layer,CBL)顶部的夹卷过程造成温度和湿度垂直梯度增强,导致这一层的折射率结构常数C■变高。C■的这种垂直分布特征经常被用来定位出CBL高度Z_i。本文利用2010年7—8月天津大港的风廓线雷达数据推断出CBL高度Z_i,对于多重C■峰值或不明确的C■峰值,本文改进了对Z_i的测定,分别讨论了C■最大后向散射法与C■和垂直速度方差(σ■)相结合的新方法的适用性。研究显示:(1)C■廓线具有单峰时,最大后向散射强度法能正确估计CBL高度,这种情况往往对应的是晴天。CBL上存在的残留层或云层引起的温湿起伏变化导致C■廓线具有双峰甚至多峰时,最大后向散射强度法可能会错误估计CBL高度;(2)C■和σ■结合的方法不仅与晴天时C■最大后向散射法有较好的一致性,而且可以将CBL造成的C■峰值从云层造成的C■峰值中区分出来,从而正确估计CBL高度;(3)一般而言,对流边界层中存在有明显的、破碎或者分散不明显的云时,C■和σ■结合的方法都能较好地识别出CBL对应的C■峰值。但由于边界层中的情况极为复杂,C■和σ■结合法也会因不同的原因而错误估计CBL高度。  相似文献   

13.
Model Simulations of the Boundary-Layer Evolution over an Arid Andes Valley   总被引：1，自引：1，他引：0  
The boundary layer of the Elqui valley in the arid north of Chile exhibits several interesting phenomena, such as a very shallow convective boundary layer (CBL) during the day. In the morning, warming is observed in and above the CBL, while the humidity decreases in the CBL. At midday, in and above the CBL of the valley, the temperature stagnates. In the afternoon in the CBL the temperature decreases and humidity increases, although the latent heat flux is very low. Because the characteristic features of the valley atmosphere are hard to interpret from observations alone, model simulations were applied. The simulations indicate that all components of the budget equations, i.e. the turbulent flux divergences, advection via the sea breeze, the upvalley and upslope wind systems, as well as subsidence, contribute to the evolution of the valley atmosphere.  相似文献   

14.
Spatiotemporal changes in air temperature and humidity associated with the restoration of an inner-city stream in Seoul, Korea, are investigated based on long-term monitoring data. The Cheonggye stream, covered under a concrete structure for 46 years, was restored in 2005 and runs 5.8 km eastward through a central region of Seoul. Long-term monitoring of the air temperature and relative humidity was made along the stream throughout the restoration and across the stream after the restoration. The area along the stream had a higher air temperature than the entire metropolitan area. The temperature anomaly between the monitoring area and the surrounding metropolitan area was 0.13oC lower on average at the center of the stream after the restoration. The stream's effect on the air temperature was also evident in the temperature distribution along a street traversing the stream. The relative and specific humidities were increased due to the restoration. The restored stream modified the nearby urban climate in the opposite direction compared to urbanization. The results could be used as a model case in mitigating urban climate by a stream in future urban planning practices.  相似文献   

15.
Abstract

The optical parameters of Arctic haze, such as the scattering and the absorption coefficients and the asymmetry factor, have been estimated using a theoretical haze model. The Aden and Kerker solution for spherical nuclei coated with a spherical shell was employed to account for the observed sulphuric acid coating on Arctic aerosols. Six original aerosol materials are considered; four are natural and two are anthropogenic in origin (sulphuric acid and soot). The relative humidity is varied between 0 and 99% and the effects of anthropogenic substances are examined. Carbonaceous material can increase the absorption coefficient by up to a factor 5 in the visible range, while sulphuric acid significantly increases the growth of particles and affects all of the optical parameters. The haze model is found to be consistent with available measurements of aerosol characteristics and optical parameters. The haze model is then used to convert a vertical profile of the extinction coefficient to a profile of particle concentration.  相似文献   

16.
A Novel Four-Wavelength Transmissometer for Distinguishing Haze and Fog   总被引：1，自引：1，他引：0  
Haze and fog exhibit different microphysical and optical properties according to Mie scattering theory. Haze particles are smaller than fog droplets. Light of a shorter wavelength is reduced more than that of a longer wavelength during haze events. In fog, the differences between the extinction coefficients at different wavelengths are not as apparent. On the basis of the different light extinction characteristics of haze and fog, a novel four-wavelength transmissometer based on charge-coupled device （CCD） imaging was designed to distinguish haze from fog with central wavelengths at 415, 516, 650, and 850 nm. The four-wavelength transmissometer was tested in an insitu experiment during the winter of 2009. Fog was determined when the differences of the extinction coefficients at the four wavelengths were not notable, whereas haze was determined when the light at shorter wavelengths was significantly more reduced than that at longer wavelengths. A threshold which describes the relative size of the extinction coefficients at the four wavelengths was defined to distinguish between fog and haze. The four-wavelength transmissometer provided results consistent with the commercial fog monitor during several measurements made in fog and haze events, especially under conditions of low visibility and high relative humidity.  相似文献   

17.
利用空气质量历史监测数据、地面气象要素及激光雷达探测资料,综合分析了2019年1月10—15日长春市一次霾污染过程,探讨了污染过程中污染物和气象要素的变化特征与影响机制。结果表明：此次霾污染过程中12—13日污染最重,PM2.5和PM10质量浓度均超过150 μg·m-3,气溶胶消光最强,超过70%的PM2.5/PM10比值大于0.7,指出了细粒子对重污染事件的贡献;重污染期间近地面风速偏小、相对湿度增加、变压较小,同时低空风出现明显的风向转变,弱下沉运动与逆温以及较低的边界层共同削弱了大气的水平和垂直扩散能力,有利于污染物累积,导致霾污染。500 hPa天气形势表明长春市位于槽前脊后,850 hPa高度场为弱西风,相对湿度大;海平面气压场存在低压气旋及弱西南气流,该气流有利于将污染物输送至长春市,造成霾污染加剧;1月14—15日高空槽加深东移,850 hPa西北气流增强,近地面气压梯度力变大,污染物得到扩散,霾污染逐渐结束。  相似文献   

18.
Using the new high-frequency measurement equipment of the research aircraft DO 128, which is described in detail, turbulent vertical fluxes of ozone and nitric oxide have been calculated from data sampled during the ESCOMPTE program in the south of France. Based on airborne turbulence measurements, radiosonde data and surface energy balance measurements, the convective boundary layer (CBL) is examined under two different aspects. The analysis covers boundary-layer convection with respect to (i) the control of CBL depth by surface heating and synoptic scale influences, and (ii) the structure of convective plumes and their vertical transport of ozone and nitric oxides. The orographic structure of the terrain causes significant differences between planetary boundary layer (PBL) heights, which are found to exceed those of terrain height variations on average. A comparison of boundary-layer flux profiles as well as mean quantities over flat and complex terrain and also under different pollution situations and weather conditions shows relationships between vertical gradients and corresponding turbulent fluxes. Generally, NOx transports are directed upward independent of the terrain, since primary emission sources are located near the ground. For ozone, negative fluxes are common in the lower CBL in accordance with the deposition of O3 at the surface.The detailed structure of thermals, which largely carry out vertical transports in the boundary layer, are examined with a conditional sampling technique. Updrafts mostly contain warm, moist and NOx loaded air, while the ozone transport by thermals alternates with the background ozone gradient. Evidence for handover processes of trace gases to the free atmosphere can be found in the case of existing gradients across the boundary-layer top. An analysis of the size of eddies suggests the possibility of some influence of the heterogeneous terrain in mountainous area on the length scales of eddies.  相似文献   

19.
Spectra of CO2 and water vapour fluctuations from measurements made in the marine atmospheric surface layer have been analyzed. A normalization of spectra based on Monin–Obukhov similarity theory, originally developed for wind speed and temperature, has been successfully extended also to CO2 and humidity spectra. The normalized CO2 spectra were observed to have somewhat larger contributions from low frequencies compared to humidity spectra during unstable stratification. However, overall, the CO2 and humidity spectra showed good agreement as did the cospectra of vertical velocity with water vapour and CO2 respectively. During stable stratification the spectra and cospectra displayed a well-defined spectral gap separating the mesoscale and small-scale turbulent fluctuations. Two-dimensional turbulence was suggested as a possible source for the mesoscale fluctuations, which in combination with wave activity in the vertical wind is likely to explain the increase in the cospectral energy for the corresponding frequency range. Prior to the analysis the turbulence time series of the density measurements were converted to time series of mixing ratios relative to dry air. Some differences were observed when the spectra based on the original density measurements were compared to the spectra based on the mixing ratio time series. It is thus recommended to always convert the density time series to mixing ratio before performing spectral analysis.  相似文献   

20.
利用西昌国家基本气象站2007年1月1日～12月31日人工和自动气象站24小时基准观测期间的相对湿度资料,以日、月不同时间尺度及不同天气现象情况下的差异规律作统计分析,并建立订正方程和方差分析,结果表明：人工与自动站逐日24时次相对湿度相关系数在0.826～0.998之间;日平均对比差值变化范围2.27%～8.79%,年平均对比差值为5.25%;干季和雨季差值分别为4.90%与5.32%;时次平均对比差值峰谷明显,最小差值出现在19：00,为4.36%,最大差值出现在12：00,为6.34%;不同天气状况对相对湿度有不同的对比差值,2007年99个晴天对比差值范围是4.91%～7.66%,平均为5.66%;30个阴天对比差值范围4.29%～6.52%,平均为5.32%;118个雨天对比差值范围是4.22%～5.16%,平均为4.88%;分别建立2007年逐月相对湿度、晴天,阴天,雨天逐月相对湿度订正方程,并进行方差分析,建立的48个订正方程均通过0.05信度检验,订正效果较好。造成人工与自动站相对湿度差异的原因有：仪器测量原理差异、观测时间差异、人工操作误差、观测样本差异、时次差异、天气状况等。  相似文献   

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