This study evaluates the potential of using only aerosol optical depth measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP algorithm. The practical motivation for the present study is the large amount of optical-depth-only measurements that exist in the ground-based networks. The retrievals could complete an existing data set of aerosol properties that is key to understanding aerosol climate effects. Hide

Microwave radiometers have the capability of observing temperature and humidity profiles with a few minute time resolution. This study investigates the potential benefit of this instrument to improve weather forecasts thanks to a better initialization of the model. Our results show that a significant improvement can be expected in the model initialization in the first 3 km with potential impacts on weather forecasts. Hide

Raindrop fall velocities are important for rain rate estimation, soil erosion studies and in numerical modelling of rain formation in clouds. The assumption that the fall velocity is uniquely related to drop size is made inherently based on laboratory measurements under still air conditions from nearly 68 years ago. There have been very few measurements of drop fall speeds in natural rain under both still and turbulent wind conditions. We report on fall speed measurements in natural rain shafts. Hide

In this work we describe a method to directly quantify water adsorption and mass hygroscopic growth of atmospheric particles as a function of RH at different temperature, using a commercial vapor sorption analyzer. We have demonstrated that this commercial instrument provides a simple, sensitive, and robust method to determine water adsorption and hygroscopicity of atmospheric particles. Hide

This research assesses the influence of biomass burning during forest fires throughout summer 2010 on aerosol load over Ukraine, the European territory of Russia (ETR) and Eastern Europe. We apply and compare ground-based and satellite measurements to determine aerosol content, dynamics, and properties. With the application of modeling techniques (HYSPLIT), we show that the maximum AOD in August 2010 over Ukraine was caused by particle transport from the forest fires in the ETR. Hide

Tropical atmospheric variability is often described using proxy indices of the Quasi-Biennial Oscillation and the El Niño–Southern Oscillation. We introduce new proxies derived from GNSS radio occultation (RO) satellite measurements. Using the high vertical resolution of the RO temperature fields we obtain altitude-resolved indices which can improve the description of atmospheric variability patterns and can be used in climate studies where a detailed knowledge of these patterns is required. Hide

We study the collocation mismatch uncertainty related to validating coarse-resolution satellite-based aerosol data against point-like ground based measurements. We use the spatial variability in the satellite data to estimate the upper limit for the uncertainty and study the effect of sampling parameters in the validation. We find that accounting for the collocation mismatch uncertainty increases the fraction of consistent data in the validation. Hide

The concept of a rain event is used to obtain a parsimonious characterisation of rain events using a minimal subset of variables at macrophysical scale. A classification in five classes is obtained in a unsupervised way from this subset. Relationships between these classes of microphysical parameters of precipitation are highlighted. There are several implications especially for remote sensing in the context of weather radar applications and quantitative precipitation estimation. Hide

Latent heat fluxes (LHF) play a major role in the climate system. Over open ocean, they are increasingly observed by satellite instruments. To access their quality, this research focuses on thorough uncertainty analysis of all LHF-related variables of the HOAPS satellite climatology, in parts making use of novel analysis approaches. Results indicate climatological LHF uncertainies up to 50 W m⁻², whereby underlying specific humidities tend to be more uncertain than contributing wind speeds. Hide

Results of the temperature characterization of the global UV spectral measurements of eight different Brewer spectrophotometers operating in Greece, Finland, Germany and Spain are presented. Different temperature characterization methods are evaluated and an improved methodology for the correction of the measurements for the effects of temperature is presented. Hide

Vertical air motion retrievals from 3DVAR multiple distributed scanning Doppler radars are compared against collocated profiling radars and retrieved from an upward iteration integration iterative technique to characterize their veracity. The retrieved vertical air motions are generally within 1–2 m s⁻¹ of agreement with profiling radars and better solution than the upward integration technique, and therefore can be used as a means to improve parameterizations in numerical models moving forward. Hide

The model RS92 radiosonde manufactured by Vaisala Ltd. is now being replaced with a successor model, the RS41, and we need to clarify accuracy differences between them for a variety of research. For this purpose, 36 twin-radiosonde flights were performed over the oceans from the Arctic to the tropics. Basically the differences between the RS41 and RS92 were smaller than the nominal combined uncertainties of the RS41; however, we found non-negligible biases in relative humidity and pressure. Hide

Annual emissions of trace gases requires knowledge of the emissions throughout the day and year. Unfortunately emissions into the surface boundary layer during calm nights are rarely measured. During such conditions surface layer concentrations of carbon dioxide (CO₂) and nitrous oxide (N₂O) often accumulate in the surface boundary layer and the time rate of change of this accumulation was used to estimate emissions. Results showed this approach to be reasonable. Hide

We evaluate the comparability of aerosol and cloud vertically resolved optical properties obtained with varying lidar profiling techniques and/or data processing methodologies. The discrepancies are assessed by evaluating climate-sensitive direct radiative effects, computed by radiative transfer code means. Results show important discrepancies up to 0.8 W m⁻² due to lidar data smoothing in cirrus clouds and a 0.05 W m⁻² difference between Raman and elastic lidar technique on a dust layer aloft. Hide

Atmospheric aerosols are small solid or liquid particles suspended in the atmosphere and they have a significant effect on the climate. Satellite data are used to get global estimates of atmospheric aerosols. In this work, a statistics-based Bayesian aerosol retrieval algorithm was developed to improve the accuracy and quantify the uncertainties related to the aerosol estimates. The algorithm is tested with NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. Hide

This study analyses how much information can be obtained about liquid clouds over oceans using measurements of reflected sunlight by the OCO-2 satellite. We find that using 75 of the 853 functioning oxygen A-band channels is sufficient to retrieve cloud optical depth, and the height and thickness of the cloud in terms of atmospheric pressure coordinates, to better than 3 hPa. Hide

This study cross-compares the 10-year record of GPS radio occultation (GPS-RO) specific humidity product against independent databases (e.g., AIRS satellite, NASA/MERRA, and ERA-Interim). Our objective is to investigate the suitability of the GPS-RO humidity as a climate variable, which the science community could use in climate research. GPS-RO offers high vertical resolution, low sensitivity to clouds, and long-term stability making GPS-RO humidity a valuable complementary data set. Hide

This paper presents different depolarization calibration procedures used to improve the quality of the depolarization data. The results illustrate a significant improvement of the depolarization lidar products for all the selected EARLINET lidar instruments. The calibrated volume and particle depolarization profiles at 532 nm show values that fall within a range that is accepted in the literature. The depolarization accuracy estimate at 532 nm is better than ±0.03 for all cases. Hide

The distribution of ice and liquid particles in clouds (i.e., their thermodynamic phase) has a large impact on Earth's climate. We report a global high spatial resolution survey of cloud phase based on a decade of data from the Hyperion orbital imaging spectrometer. Seasonal and latitudinal trends corroborate observations by the Atmospheric Infrared Sounder (AIRS). Most variance observed at climate model grid scales of 100 km is explained by spatial structure at finer spatial resolutions. Hide

In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing. From the statistics, average bias (and standard deviation) of the bending angle and refractivity profiles were found to be as small as about 0.05–0.2 % (and 0.7–1.6 %) over the upper troposphere and lower stratosphere, including for the GEO, IGSO, and MEO subsets. Zero differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. Hide

Data from the high-sensitivity CALIOP cloud lidar onboard the CALIPSO satellite have been used to evaluate cloud amounts estimated from satellite imagery and, specifically, from the climate data record CLARA-A2. The main purpose has been to study the limit of how thin clouds that can be detected efficiently (i.e., detected at the 50 % level) in CLARA-A2 data and how this limit varies globally. The study revealed very large geographical differences in the cloud detection efficiency. Hide

The Generalized Aerosol Retrieval from Radiometer and Lidar Combined data algorithm (GARRLiC) and the LIdar-Radiometer Inversion Code (LIRIC) provide the opportunity to study the aerosol vertical distribution by combining ground-based lidar and sun-photometric measurements. Here, we utilize the capabilities of both algorithms for the characterization of Saharan dust and marine particles, along with their mixtures, in the south-eastern Mediterranean. Hide

This study presents a new concept for estimating the pollutant emission rates of a site combining the tracer release method, local-scale atmospheric transport modelling and a statistical atmospheric inversion approach. The potential of this new concept is evaluated with a practical implementation based on a series of inversions of controlled methane and tracer point sources in different spatial configurations to assess the efficiency of the method in comparison with the classic tracer method. Hide

We have developed a new method which employs single particle depolarization to determine ice nucleating particle (INP) concentrations and to differentiate between ice crystals, water droplets, and aerosols. The method is used to interpret measurements collected using the Texas A&M Continuous Flow Diffusion Chamber (TAMU CFDC) coupled to a Cloud and Aerosol Spectrometer with Polarization (CASPOL). This new method extends the range of operating conditions for the CFDC to higher supersaturations. Hide

This study presents a comparison between active (CALIOP) and passive (POLDER) remote sensing methods, developed for retrieving aerosol above-cloud optical and microphysical properties. Main results show a good agreement when the aerosol microphysics is dominated by fine-mode particles or coarse-mode dust or when the aerosol layer is well separated from the cloud below. The paper is also focused on understanding the differences between the retrievals and the limitations of each method. Hide

Measurements of ice cloud particle populations are needed to improve climate and weather prediction. This paper makes a comparison between ice cloud particle populations measured using two different airborne cloud particle probes. It is concluded that measurements of particle populations from older probes are similar to those from newer probes, except in total numbers of particles counted. Therefore, more airborne studies of ice clouds need to be made using newer cloud particle probes. Hide

Based on measurements with a ceilometer and from an air quality network, the relationship between the mixing layer height (MLH) and near surface concentrations of pollutants was investigated for summer 2014 in Berlin. It was found that the heterogeneity of the concentrations exceeds the differences due to different MLH retrievals. In particular for PM₁₀ it seems to be unrealistic to find correlations between MLH and concentrations representative for an entire metropolitan area in flat terrain. Hide

Halo displays are produced by scattering of sunlight by smooth, hexagonal ice crystals. Consequently, the presence of a halo should contain information on particle shape. This study presents HaloCam, a novel sun-tracking camera system, and an automated detection algorithm to collect and evaluate long-term halo observations. Two-year HaloCam observations revealed that about 25 % of the detected cirrus clouds occurred together with a 22° halo indicating the presence of smooth, hexagonal crystals. Hide

The accurate detection of reactive nitrogen species (NO_y) is key to understanding tropospheric ozone production. Typically, NO_y is detected by thermal conversion to NO₂, followed by NO₂ detection. Here, we assess the conversion efficiency of several NO_y species to NO₂ in a thermal dissociation cavity ring-down spectrometer and discuss how this conversion efficiency is affected by certain experimental conditions, such as oven residence time, and interferences from non-NO_y species. Hide

The Turbulence and Intermittency Long-Duration Atmospheric Experiment (TILDAE) was developed to characterize small-scale fluctuations in the troposphere and stratosphere. The mission's key instrument, a customized sonic anemometer, made high-speed calibrated measurements of the 3-D wind velocity and air temperature. TILDAE was incorporated as an "add-on" experiment to the payload of a NASA long-duration balloon mission that launched in January 2016 from McMurdo Station, Antarctica. Hide

GPS radio occultation (GPS-RO) is a method of probing the atmosphere using GPS signals. Such measurements can be assimilated into operational numerical weather prediction (NWP) systems and can reduce stratospheric temperature biases. This indicates that they could have an important role in climate monitoring and climate reanalyses. However, the measurements must be corrected to account for the effects of the ionosphere and this paper proposes an enhanced correction that removes residual biases. Hide

Ground-level ozone has negative human health impacts. In the summer of 2015, 13 low-cost sensor monitors were deployed to several neighborhoods around Riverside, California. There were significant spatial differences between monitors. This is important because it means that ozone in certain places may be higher than what EPA monitors report for an area, which is pertinent for residents of those communities. This research helps inform the limitations and advantages of low-cost sensor networks. Hide

A new technique to separate cloud and non-hydrometeor returns from a cloud radar high-resolution reflectivity measurements is proposed. The TEST algorithm potentially identifies cloud height with the theoretical echo sensitivity curves and observed echo statistics for the cloud height tracing. TEST is more robust in identifying and filtering out the biota contributions by constraining further with spectral width and LDR measurements. This algorithm improves the monsoon cloud characterization. Hide

This paper describes the absolute validation of the novel, calibration-free SEALDH-II hygrometer at a traceable humidity generator. During 23 days of permanent operation, 15 H₂O mole fractions levels (5–1200 ppmv) at 6 gas pressures (65–950 hPa) were validated. With this validation, SEALDH-II is the first metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale. Hide