Long-Term Measurements of Light Hydrocarbons (C2–C5) at Schauinsland (Black Forest)

Long-term measurements of light hydrocarbons(C₂–C₅ HCs) were performed in the courseof the EUROTRAC sub-project TOR (Tropospheric Ozone Research) in thesouthern part of the Black Forest in southwest Germany. The measurementscover a time period of five years (January 1989–January 1994) and theair samples were analyzed onsite by an automated GC-system. Pronouncedannual cycles with maxima in late winter and minima in late summer wereobserved in the case of the slowly reacting hydrocarbons ethane, propane andacetylene, reflecting the fact that the seasonal variation of these speciesis photochemically driven. For the shorter lived compounds the seasonalvariations are considerably weaker, connected with a stronger scatter of theindividual measurements, which is caused by different distances to theirmain sources for different wind vectors as well as by varying sourcestrengths. From a detailed characterization of the hydrocarbon patterns theinfluence of two different sources could be distinguished. An extrapolationto photochemical age of zero and completion of our data with those from aspeciated VOC inventory yields an estimated [VOC]/NO_x sourceratio for Schauinsland of 5 [ppbC/ppb]. Comparable[VOC]/NO_x ratios are observed in automobile exhaust gasesunder low speed conditions, which points to the important role of trafficunder conditions, when freshly polluted air masses from a near-by city areadvected to the site. From an investigation of the photochemical age of theadvected air masses it becomes clear that there must exist biogenic sourcesof light olefins in the vicinity of the observatory during the vegetationperiod. For propene and the butenes we are able to estimate a lower limit oftheir contributions in terms of reactivity to the total reactivity( [HC](i) k_OH(i),i=C₂-C₅) of the measured hydrocarbons. Forlowest pollution levels in summer (acetylene <300 ppt, about 40%of the summer values) this source is found to be responsible for15–20% of the total C₂–C₅reactivity observed at Schauinsland. On the average, this source accountsfor 5–10% of the total C₂–C₅reactivity.     

Humidity Measurements in Cold and Humid Environments

Recent studies have shed new light on humidity conditions in the polar atmospheric boundary layer, and cast doubt on the reliability of humidity measurements above the frost point humidity. These issues are addressed herein by considering the processes that affect humidity and its measurement in cold climate conditions and by analyzing observations from two sites, at which the relative humidity is frequently above 100% at sub-freezing temperatures, as shown by repeatedly observed in-cloud icing events. Humidity measurements were made at these two sites by the commonly used Vaisala HMP35 probe and HMP233 capacitance probes respectively and simultaneously by the same manufacturer’s HMP243 probe that determines the frost point by a heated capacitance sensor. The results confirm that the relative humidity is frequently well above the frost point, both due to radiative cooling and to the advection of moist air, and that the conventional humidity measurements are unable to detect these events. Furthermore, after such events, the iced sensors show too high a humidity. The false values occur due to ice growth on the probe and cannot be corrected by any algorithm. Our results indicate that these problems, inherent to conventional humidity measurements in cold and humid environments, are avoided by the use of HMP243, which has a heated humidity probe.     

Correcting Distortions in Measurements of Atmospheric Pressure Fluctuations

Although recognized as important, measurements of turbulent atmospheric pressure are considered difficult and are conducted infrequently. Here we discuss the essential elements in the design of an instrument for measuring turbulent fluctuations of atmospheric pressure. Our analysis of the instrument’s dynamics is focused on the signal distortions resulting from a pneumatic filter, a necessary element in the instrument’s design. Such distortions substantially affect the observed spectral scaling of the pressure field as well as other quantities of physical interest, such as pressure-velocity 〈p, v〉 and pressure-wave 〈p, η〉 covariances. We propose a computationally efficient discrete-time signal processing method for complete compensation of pneumatic filter distortions and review the criteria for selecting the instrument parameters (sampling frequency and time constant), so that digital filter distortions, precision degradation, clipping, and over-damping, are simultaneously avoided. This correction method must be an inherent part of the instrument’s design.     

In Situ Trace Gas and Particle Measurements in the Summer Lower Stratosphere during STREAM II: Implications for O3 Production

In situ aircraft measurements of O₃, CO,HNO₃, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO₃ concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 m decreased acrossthe tropopause, from >1000 cm^-3 in the uppertroposphere to <500 cm^-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO₃) determinethe availability of NO_x (=NO + NO₂) andtherefore largely control the total net O₃production in the lower kilometers of thestratosphere. Model simulations, applying additionalNO_x perturbations from aircraft, show that theO₃ production efficiency of NO_x is smallerthan previously assumed, under conditions withrelatively high HNO₃ mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O₃ productionefficiency from CO oxidation, as a result of therelatively high ambient HNO₃ and NO_xconcentrations, implying that upward transport of COrich air enhances O₃ production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere.     

Vertical profiles of acetylene in the troposphere and stratosphere

Stratospheric measurements of acetylene up to altitudes of 30 km are presented. The air samples were collected during three different balloon flights, two of them at 44°N, one at 32°N using balloon borne, liquid neon-cooled, cryosamplers. Their acetylene concentration was measured in the laboratory by flame ionisation gaschromatography. The different profiles at 32°N and 44°N are discussed with respect to possible vertical exchange processes and compared with published model calculations.     

差分反射率ZDR和反射率Ze测雨精度的对比分析

本文根据大量不同类型降雨的雨滴谱资料，分析了两种雷达测雨与滴尺度分布的关系，模拟计算了双线偏振雷达可测到的(R/ZH)-ZDR和常规天气雷达可测到的Z-R经验关系和它们在测量降雨率精度的对比分析。表明差分反射率ZDR对改进雷达测雨的精度有着明显的优势。     

A Simple Method of Estimating Scalar Fluxes Over Forests

A simple aerodynamic-variance method is proposed to fill gaps in continuous CO₂ flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions (friction velocity greater than 0.1 ms^–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO₂ concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible heat flux and CO₂ flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat and CO₂ flux estimates that are well correlated with the measured values.     

祁连山冷锋过程中积层混合云微物理特征飞机观测研究

利用高性能空中国王飞机搭载的DMT(Droplet Measurement Technologies)探测系统,分析2020年6月15—16日祁连山地区两次冷锋过程前后积层混合云的宏微观特征。结果表明:冷锋前CIP(Cloud Imaging Probe)粒子平均浓度在10¹~10²L^-1,PIP(Precipitation Imaging Probe)粒子浓度在10² L^-1;CIP粒子数浓度随高度逐渐上升,降水粒子在7 300 m时浓度达到峰值后下降;平均粒子谱拓宽速率为3.5 mm·km^-1,随着高度的下降而降低。冷锋前存在对流泡区域,对流泡内粒子浓度均高出对流泡外,粒子谱拓宽速率高出层云一倍。冷锋后大CIP粒子粒子浓度为10² L^-1,降水粒子浓度为10⁰~10² L^-1,粒子谱拓宽速率为1.5 mm·km^-1,较冷锋前粒子谱拓宽速率小1.7倍。锋前后粒子均呈现多峰型;锋前积层混合云云中对流泡内外谱型一致,云顶处对流泡内外峰值粒径不同。锋前云粒子形状为聚合状、枝状、柱状和不规则状,以聚合状为主;云内冰晶以凇附和聚合增长为主;对流泡内外在粒子形态上没有明显差异。锋后粒子形状以不规则粒子为主,云粒子增长形式以聚合增长为主,并伴有上层云向下层播撒大云粒子的现象。     

植被冠层日光诱导叶绿素荧光塔基自动观测方法及系统介绍

植物光合作用所提供的物质和能量是人类赖以生存的关键因素,而日光诱导叶绿素荧光SIF(Sun-Induced chlorophyll Fluorescence)是植物光合作用的副产品,与光合作用关系密切,深入研究SIF将对于更加深入理解光合作用机制有着重要的意义.目前,近地面植被冠层SIF遥感观测发展迅速,但不同SIF观...