This paper analyzed the collocated GPS radio occultation profiles near the convective systems identified from ISCCP over two orographic regions of the Alps and Andes. Gravity wave (GW) analysis over both selected regions was also carried out. The gravity wave signature from the two case studies were investigated using mesoscale WRF simulations, ERA-Interim reanalysis data, and measured RO temperature profiles. The absence of fronts or jets during both case studies reveals similar relevant GWs. Hide

We have adopted a new technique for measuring glass-forming properties of atmospherically relevant organic aerosols at submicron sizes and relatively low mass concentrations. Aerosol particles are deposited in the form of a thin film with interdigitated electrodes using electrostatic precipitation. Broadband dielectric spectroscopy is used to measure the kinetically controlled glass transition temperatures of glycerol and citric acid aerosols with three atmospheric relevant cooling rates. Hide

This research was conducted to determine the impact of multiple a priori ozone (O₃) profile products on Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite retrievals. It was determined that non-climatological model predictions, in particular those from a chemical transport model, when applied as the a priori profile improved the accuracy of TEMPO tropospheric O₃ retrievals in comparison to the TB-Clim product that is currently suggested for use in the TEMPO retrieval algorithm. Hide

We describe the operating principle, design and performance of the Nucleation Mode Aerosol Size Spectrometer (NMASS), an instrument composed of 5 condensation particle counters measuring size selected particle concentrations between 3 and 60 nm. An inversion to recover size distributions from the data is evaluated. Calibrations of a 2-NMASS system for measuring size distributions on the NASA Atmospheric Tomography Mission, and examples of its in-flight performance are presented. Hide

This paper compares aerosol extinction records from two limb scattering instruments, OSIRIS and SCIAMACHY, to that from the occultation instrument SAGE II. Differences are investigated through modelling and retrieval studies and important sources of systematic errors are quantified. It is found that the largest biases come from uncertainties in the aerosol size distribution and the aerosol particle concentration at altitudes above 30 km. Hide

This paper presents a new cloud detection and classification framework, CC4CL. It applies a sophisticated optimal estimation method to derive cloud variables from satellite data of various polar-orbiting platforms and sensors (AVHRR, MODIS, AATSR). CC4CL provides explicit uncertainty quantification and long-term consistency for decadal timeseries at various spatial resolutions. We analysed 5 case studies to show that cloud height estimates are very realistic unless optically thin clouds overlap. Hide

Satellites are vital for measuring cloud properties necessary for climate prediction studies. We present a method to retrieve cloud properties from satellite based radiometric measurements. The methodology employed is known as optimal estimation and belongs in the class of statistical inversion methods based on Bayes' theorem. We show, through theoretical retrieval simulations, that the solution is stable and accurate to within 10–20% depending on cloud thickness. Hide

We present new primary calibration scales for five halogenated greenhouse gases. The preparation method, newly applied to halocarbons, is dynamic and gravimetric and allows the generation of reference gas mixtures at near-ambient levels (pmol mol⁻¹). Each prepared molar fraction is traceable to the realisation of SI units (International System of Units) and is assigned an uncertainty estimate following international guidelines. Hide

A new data set of vertical column densities of the water vapour isotopologues H₂O and HDO retrieved from short-wave infrared measurements (2339 nm to 2383 nm) by the SCIAMACHY satellite instrument for the whole of the mission period from 2003 to 2012 is presented. The data are validated against ground-based Fourier transform infrared measurements. High-altitude stations observe different air columns; thus in this case collocated scenes with clouds around station height are needed for agreement. Hide

The Brewer spectrophotometer has been used for decades as reference instrument to retrieve total ozone column (TOC) and for validation of satellite based measurements. This spectrophotometer has a thermal sensitivity already known, which is usually characterized using two different retrieval procedures. In this work, we report on a comparative study of the temperature coefficients retrieval procedures, obtaining differences less that 0.08 % in TOC when using any of the procedures. Hide

This work reports airborne wind lidar observations performed in a recent field campaign. The deployed lidar system serves as a demonstrator for the satellite instrument ALADIN on board Aeolus, which is scheduled for launch in 2018 and will become the first wind lidar in space. After presenting the measurement principle, operation procedures and wind retrieval algorithm, the obtained wind results are validated and discussed, providing valuable information in preparation for the satellite mission. Hide

This paper presents an innovative retrieval method that translates the CALIOP land surface laser pulse returns into the surface bidirectional reflectance. The surface bidirectional reflectances retrieved from CALIOP measurements contribute complementary data for existing MODIS standard data products and could be used to detect and monitor seasonal surface reflectance changes in high latitude regions where passive MODIS measurements are limited. Hide

Chemical ionization mass spectrometry has emerged as a versatile tool for the study of reactive gases. Robust calibration is required to assess the sensitivity of these instruments and their dependence on external factors such as specific humidity. Here, we report the sensitivity of benzene cluster cation chemical ionization for an array of terpene compounds. This work permits a more universal understanding of the sensitivity of this technique to a host of isobaric compounds. Hide

An approach to estimate the height of aerosol plumes over land from satellite measurements of the oxygen A band is proposed. The method, termed dynamic scaling, forces the retrieval to use spectral points that contain more height information. The method is tested in a synthetic environment as well as with GOME-2A and GOME-2B measurements of wildfire plumes over Europe, with very encouraging results. This method can be easily applied to other aerosol height algorithms using least squares. Hide

Snow, frost formation and ice cubes in our drinks are part of our daily life. But what about our technical innovations like aviation, electrical power transmission and wind-energy production, can they cope with icing? Icing Wind Tunnels are an ideal laboratory environment to answer that question. In this paper, we show how the icing wind tunnel in Braunschweig (Germany) was built and how we can use it for engineering and climate research. Hide

For volatile organic compound (VOC) observations, zero gases free of VOC traces are essential for the characterisation of the measurement devices and procedures, for instrument operation as well as for calibrations. Three gas purifiers were tested for their removal efficiency of VOCs following a standardised procedure. Results show that not all purification methods removed VOCs from the zero gas and that a gas purifier needs to be tested before its intended application in the field. Hide

Satellite-measured radiance from an Earth scene comprises light scattered and absorbed by gases, clouds and aerosols in the atmosphere and by the Earth surface. To retrieve aerosol information, the signal from clouds, gases and the surface must be separated from the aerosol signal. This paper highlights the gas absorption correction method used by the MODIS dark-target aerosol retrieval algorithm and demonstrates that aerosol retrieval accuracy depends on accurate gas absorption correction. Hide

In this paper, we propose a new observation strategy, called sweep mode, for a real three-dimensional tomographic reconstruction of gravity waves in the mesosphere and lower thermosphere by modifying the observation geometry of conventional limb-sounding measurements. It enhances the horizontal resolution that typical limb sounders can achieve while at the same time retaining the good vertical resolution they have. Hide

In this paper a new algorithm for cloud top height retrieval from imager instruments like MODIS is presented. It uses artificial neural networks and reduces the mean absolute error by 32 % compared to two other operational cloud height algorithms. This means that improved cloud height retrieval for nowcasting, as input to models and in cloud climatologies is possible. Hide

Using high-resolution surface irradiance data with original temporal resolutions between 0.01 s and 1 s from six different locations in the Northern Hemisphere, we characterize the changes in representation of temporal variability resulting from time averaging. Our results indicate that a temporal averaging time scale of around 1 s marks a transition in representing single-point irradiance variability, such that longer averages result in substantial underestimates of variability. Hide

In this study, we perform global validation of MODIS high-resolution (3 km) AOD over global land by comparing against AERONET measurements. The MODIS–AERONET collocated data sets consist of 161 410 high-confidence AOD pairs from 2000 to 2015 for Terra MODIS and 2003 to 2015 for Aqua MODIS. We find that 62.5 and 68.4 % of AODs retrieved from Terra MODIS and Aqua MODIS, respectively, fall within previously published expected error. Hide

Estimating snowfall intensity from satellite and ground-based radar missions requires accurate retrieval models. Reflectivity–snowfall relations are obtained at cm and mm wavelengths using data recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland. Lightly, moderately and heavily rimed snow cases are identified. Numerical simulations are performed to relate snowflake microphysical (video disdrometer) and multifrequency backscattering properties (radars). Hide

Water vapor is the most important tropospheric greenhouse gas and is also highly variable in space and time. We study the vertical structure and variability of tropospheric humidity using various observing techniques (GPS radio occultation, radiosondes, Atmospheric Infrared Sounder) and models. Time–height cross sections reveal seasonal biases for different pressure layers. We find that radio occultation humidity has high accuracy and can contribute valuable information in data assimilation. Hide

Diesel fuel, lubricating oil and diesel exhaust emissions all contain a very complex mixture of chemical compounds with diverse molecular structures. The GC × GC-ToF-MS analytical method is a very powerful way of separating and identifying those compounds. This paper describes the allocation of compounds into groups with similar molecular structures and chemical properties, which facilitates the intercomparison of very complex mixtures such as are found in diesel fuel, oil and emissions. Hide

Vertical profiles of the aerosol physical and optical properties, with a focus on seasonal means and on transport events, were investigated by the synergistic method using lidar and sky radiometer. The retrieved vertical profiles were input to the one-dimensional atmospheric model, and the impacts of the transported aerosols on the evolution of the atmospheric boundary layer (ABL) were studied. The vertical profile of the aerosol direct heating has important effects on the ABL evolution. Hide

We investigate the feasibility of quantifying the difference in biases of two instrument types (i.e. radiosondes) by flying the old and new instruments on alternating days, so-called interlacing, to statistically derive the systematic biases between the instruments. While it is in principle possible to estimate the difference between two instrument biases from interlaced measurements, the number of required interlaced flights is very large for reasonable autocorrelation coefficient values. Hide

Few techniques can measure the contribution of refractory black carbon (rBC) to ice-nucleating particle (INP) concentrations. One technique uses the single particle soot photometer (SP2) as a pre-filter to an online INP counter to selectively remove rBC particles from an aerosol stream. In this work, we expand upon this technique by determining the effect of the SP2 laser on INP proxies mixed with rBC. We also bounded the SP2 conditions under which rBC is fully vaporized in the SP2 exhaust. Hide

To accurately infer air pollutant concentrations from satellite observations, we must first know the reflectivity of the Earth’s surface. Using a model, we show that satellite observations are better able to observe NO₂ near the surface if snow is present. However, knowing when snow is present is difficult due to its variability. We test seven existing snow cover data sets to assess their ability to inform future satellite observations and find that the IMS data set is best suited for this task. Hide

The performance of two kinds of optical instruments for aerosol mass measurements was explained by a Mie scattering theory. At the same time, the response of optical instruments for ambient aerosol with different size, chemical composition, and refractive index were also studied. These would help evaluate the applicability and limitations of these optical scattering instruments. Hide