Atmos.Meas.Tech. discussions

Validation of acetonitrile (CH3CN) measurements in the stratosphere and lower mesosphere from the SMILES instrument on the International Space Station
Tamaki Fujinawa, Tomohiro O. Sato, Takayoshi Yamada, Seidai Nara, Yuki Uchiyama, Kodai Takahashi, Naohiro Yoshida, and Yasuko Kasai
Atmos. Meas. Tech., 13, 2119–2129, https://doi.org/10.5194/amt-13-2119-2020, 2020
We performed an error analysis of SMILES observations for acetonitrile and a validation using the MLS observations by extracting the coincident points between SMILES and MLS data. The major error sources for the SMILES observations were quantitatively estimated. At upper pressure levels the difference between the two datasets increased because of an uncertainty in MLS observations. The results showed that SMILES has an advantage in measuring acetonitrile in the upper stratosphere and mesosphere.

Retrieval of daytime mesospheric ozone using OSIRIS observation of O2(a1∆g) emission
Anqi Li, Chris Roth, Kristell Pérot, Ole Martin Christensen, Adam M. Bourassa, Doug Degenstein, and Donal Murtagh
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-56,2020
Preprint under review for AMT (discussion: open, 0 comments)

Improving knowledge of the ozone global distributions in the mesosphere-lower thermosphere (MLT) is a crucial step in understanding the behaviour of the middle atmosphere. However, the ozone concentration under sunlit conditions in the MLT is often so low that its measurement requires instruments with very high sensitivity. Fortunately, the bright oxygen airglow can serve as a proxy to retrieve the daytime ozone density indirectly, due to the strong connection to ozone photolysis in the Hartley band. The OSIRIS IR imager (hereafter IRI), one of the instruments on the Odin satellite, routinely measures the oxygen infrared atmospheric band (IRA band) at 1.27 μm. In this paper, we will describe the detailed steps of retrieving the calibrated IRA band limb radiance, the volume emission rate of O2(a1∆g) and, finally, the ozone number density. This retrieval technique is applied to a one-year-sample IRI dataset. The resulting product is a completely new ozone dataset with very high along-track resolution. The performance of the retrieval technique is demonstrated by a comparison of the coincident ozone measurements from the same spacecraft, as well as zonal mean and monthly average comparisons between OS, SMR, MIPAS and ACE-FTS. The consistency of this IRI ozone dataset implies that such a retrieval technique can be further applied to all the measurements made throughout the 19 years-long mission, leading to a long-term, high resolution dataset in the middle atmosphere.

Effects of clouds on the UV Absorbing Aerosol Index from TROPOMI
Maurits L. Kooreman, Piet Stammes, Victor Trees, Maarten Sneep, L. Gijsbert Tilstra, Martin de Graaf, Deborah C. Stein Zweers, Ping Wang, Olaf N. E. Tuinder, and J. Pepijn Veefkind
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-112,2020
Preprint under review for AMT (discussion: open, 0 comments)
We investigated the influence of clouds on the AAI, which is an indicator of the presence of small particles suspended in the atmosphere. Clouds produce artefacts in the AAI calculation on the individual measurement (7 km) scale, which was not seen with previous instruments, as well as large (1000+ km) scales. To reduce these artefacts, we used three different AAI calculation techniques with varying complexity. We find that the AAI artefacts are reduced when using more complex techniques.

Retrieval of Lower-Order Moments of the Drop Size Distribution using CSU-CHILL X-band Polarimetric Radar: A Case Study
Viswanathan Bringi, Kumar Vijay Mishra, Merhala Thurai, Patrick C. Kennedy, and Timothy H. Raupach
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-160,2020
Preprint under review for AMT (discussion: open, 0 comments)
The raindrop size distribution and its moments are fundamental in many areas such as radar measurement of rainfall using polarimetry and numerical modelling of the microphysical processes of rain formation and evolution. We develop a technique which uses advanced radar measurements and complete drop size distributions using two collocated instruments to retrieve the lower order moments such as total drop concentration and rain water content. We demonstrate proof-of-concept using a case study.

Probabilistic analysis of ambiguities in radar echo direction of arrival from meteors
Daniel Kastinen and Johan Kero
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-157,2020
Preprint under review for AMT (discussion: open, 0 comments)
The behavior of position determination with interferometric radar systems and possible ambiguities therein depend on the spatial configuration of the radar receiving antennas and their individual characteristics. We have simulated the position determination performance of five different radar systems. These simulation showed that ambiguities are dynamic and need to be examined on a case by case basis. However, the simulations can be used to analyse and understand previously ambiguous data.

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods
Cornelia Strube, Manfred Ern, Peter Preusse, and Martin Riese
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-29,2020
Preprint under review for AMT (discussion: open, 1 comment)
We present how inertial instabilities affect gravity wave background removals on different temperature data sets. Vertical filtering has to remove a part of the gravity wave spectrum to eliminate inertial instability remnants, while horizontal filtering leaves typical gravity wave scales untouched. In addition, we show that it is possible to separate inertial instabilities from gravity wave perturbations for infrared limb-sounding satellite profiles using a cutoff zonal wavenumber of 6.

Combining low-cost, surface-based aerosol monitors with size-resolved satellite data for air quality applications
Priyanka deSouza, Ralph A. Kahn, James A. Limbacher, Eloise A. Marais, Fábio Duarte, and Carlo Ratti
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-136,2020
Preprint under review for AMT (discussion: open, 0 comments)
This paper presents a novel method to calibrate satellite data using low-cost optical particle counters (OPCs) to develop higher quality particulate matter (PM) estimates. This method could enable cities that do not have access to expensive reference air quality monitors, many of which are in the global South, to develop locally calibrated PM estimates from satellite data. Such information can be crucial for the development of effective air quality management plans.

An improved TROPOMI tropospheric HCHO retrieval over China
Wenjing Su, Cheng Liu, Ka Lok Chan, Qihou Hu, Haoran Liu, Xiangguang Ji, Yizhi Zhu, Ting Liu, Chengxin Zhang, Yujia Chen, and Jianguo Liu
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-109,2020
Preprint under review for AMT (discussion: open, 0 comments)
The manuscript presents an improved retrieval of TROPOMI tropospheric HCHO column over China. The new retrieval optimized both slant column retrieval and air mass factor calculation for TROPOMI observations of HCHO over China. The improved TROPOMI HCHO is subsequently validated by MAX-DOAS observations. Compared to the operational product, the improved HCHO agrees better to the MAX-DOAS data and thus better suit for the analysis of regional and city scale pollution in China.

Shallow cumuli cover and its uncertainties from ground-based lidar–radar data and sky images
Erin A. Riley, Jessica M. Kleiss, Laura D. Riihimaki, Charles N. Long, Larry K. Berg, and Evgueni Kassianov
Atmos. Meas. Tech., 13, 2099–2117, https://doi.org/10.5194/amt-13-2099-2020, 2020
Discrepancies in hourly shallow cumuli cover estimates can be substantial. Instrument detection differences contribute to long-term bias in shallow cumuli cover estimates, whereas narrow field-of-view configurations impact measurement uncertainty as averaging time decreases. A new tool is introduced to visually assess both impacts on sub-hourly cloud cover estimates. Accurate shallow cumuli cover estimation is needed for model–observation comparisons and studying cloud-surface interactions.

Intercomparison of wind observations from the European Space Agency's Aeolus satellite mission and the ALADIN Airborne Demonstrator
Oliver Lux, Christian Lemmerz, Fabian Weiler, Uwe Marksteiner, Benjamin Witschas, Stephan Rahm, Alexander Geiß, and Oliver Reitebuch
Atmos. Meas. Tech., 13, 2075–2097, https://doi.org/10.5194/amt-13-2075-2020, 2020
This work reports on the first airborne validation campaign of ESA’s Earth Explorer mission Aeolus, conducted in central Europe during the commissioning phase in November 2018. After presenting the methodology used to compare the data sets from the satellite, the airborne wind lidar and the ECWMF model, the wind results from the underflights performed are analyzed and discussed, providing a first assessment of the accuracy and precision of the preliminary Aeolus wind data.

Implementation of an IBBCEAS technique in an atmospheric simulation chamber for in situ NO3 monitoring: characterization and validation for kinetic studies
Axel Fouqueau, Manuela Cirtog, Mathieu Cazaunau, Edouard Pangui, Pascal Zapf, Guillaume Siour, Xavier Landsheere, Guillaume Méjean, Daniele Romanini, and Bénédicte Picquet-Varrault
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-103,2020
Preprint under review for AMT (discussion: open, 0 comments)
An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for in situ monitoring of NO3 radicals in the CSA simulation chamber (at LISA). The optical cavity allows a high sensitivity for NO3 detection up to 6 ppt for an integration time of 10 seconds. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (with rate constants up to 10-10 cm3 molecule-1 s-1).

Microwave single scattering properties of non-spheroidal rain drops
Robin Ekelund, Patrick Eriksson, and Michael Kahnert
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-85,2020
Preprint under review for AMT (discussion: open, 0 comments)
Rain drops become flattened due to aerodynamic drag, as they increase in mass and fall-speed. The shape of such rain drops was calculated, and the electromagnetic interaction between microwave radiation and the rain drops was calculated. The calculations are made publicly available to the scientific community, in order to promote accurate representations of rain drops in measurements. Tests show that the drop shape can indeed have a noticeable effect on microwave observations of heavy rainfall.

Uncertainty Quantification for Atmospheric Motion Vectors with Machine Learning
Joaquim V. Teixeira, Hai Nguyen, Derek J. Posselt, Hui Su, and Longtao Wu
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-95,2020
Preprint under review for AMT (discussion: open, 0 comments)
Wind-tracking algorithms produce atmospheric motion vectors (AMVs) by tracking satellite observations. Accurately characterizing the uncertainties in AMVs is essential in assimilating them into data assimilation models. We develop a machine learning based approach for error characterization which involves gaussian mixture model clustering and random forest using a simulation dataset of water vapor, AMVs, and true winds. We show that our method improves on existing AMV error characterizations.

Mind-the-gap Part II: Improving quantitative estimates of cloud and rain water path in oceanic warm rain using spaceborne radars
Alessandro Battaglia, Pavlos Kollias, Ranvir Dhillon, Katia Lamer, Marat Khairoutdinov, and Daniel Watters
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-80,2020
Preprint under review for AMT (discussion: open, 0 comments)
Warm rain accounts for slightly more than 30 % of the total rain amount and 70 % of the total rain area in the tropical belt and usually appears in kilometre-size cells. Space-borne radars adopting millimetre wavelengths are excellent tools for detecting such precipitation type and in separating between the cloud and rain components. Our work highlights the benefits of operating multi-frequency radars and discuss the impact of antenna footprints in quantitative estimates of liquid water paths.

Using Two-Stream Theory to Capture Fluctuations of Satellite-Perceived TOA SW Radiances Reflected from Clouds over Ocean
Florian Tornow, Carlos Domenech, Howard W. Barker, René Preusker, and Jürgen Fischer
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-149,2020
Preprint under review for AMT (discussion: open, 0 comments)
Clouds reflect sunlight unevenly which makes it difficult to quantify the portion reflected back to space via satellite observation. To improve quantification, we propose a new statistical model that incorporates more satellite-inferred cloud and atmospheric properties than state-of-the-art models. We use concepts from radiative transfer theory that we statistically optimize to fit observations. The new model often explains past satellite observations better and predicts reflection plausibly.

Emission Monitoring Mobile Experiment (EMME): an overview and first results of the St. Petersburg megacity campaign-2019
Maria V. Makarova, Carlos Alberti, Dmitry V. Ionov, Frank Hase, Stefani C. Foka, Thomas Blumenstock, Thorsten Warneke, Yana A. Virolainen, Vladimir S. Kostsov, Matthias Frey, Anatoly V. Poberovskii, Yuri M. Timofeyev, Nina N. Paramonova, Kristina A. Volkova, Nikita A. Zaitsev, Egor Y. Biryukov, Sergey I. Osipov, Boris K. Makarov, Alexander V. Polyakov, Viktor M. Ivakhov, Hamud Kh. Imhasin, and Eugene F. Mikhailov
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-87,2020
Preprint under review for AMT (discussion: open, 0 comments)
Fundamental understanding of the major processes driving climate change is the key problem which is to be solved not only on a global but also on regional scales. The Emission Monitoring Mobile Experiment (EMME) carried out in 2019 with two portable spectrometers Bruker EM27/SUN as core instruments provided new information on the emissions of greenhouse (CO2, CH4) and reactive (CO, NOx) gases from St. Petersburg (Russia) which is the largest northern megacity with the population of 5 million.

Aerosol optical properties as observed from an ultralight aircraft over the Strait of Gibraltar
Patrick Chazette
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-131,2020
Preprint under review for AMT (discussion: open, 0 comments)
By coupling airborne lidar and ground-based lidar measurements, this paper highlights the aerosol transport over the Strait of Gibraltar. It shows that the lidar-derived aerosol optical properties can be different from what is commonly accepted. It presents unprecedented vertical profiles over this region and relates them to the origin of air masses. The results are based on ground, airborne and spaceborne observations, as well as multiple retro trajectories analysis.

Eddy covariance flux measurements of gaseous elemental mercury over a grassland
Stefan Osterwalder, Werner Eugster, Iris Feigenwinter, and Martin Jiskra
Atmos. Meas. Tech., 13, 2057–2074, https://doi.org/10.5194/amt-13-2057-2020, 2020
Direct mercury (Hg) flux studies are crucial to improve our understanding of terrestrial Hg cycling and human Hg exposure. We tested a new system to measure Hg fluxes using the eddy covariance technique. Our Eddy Mercury system revealed a net Hg re-emission flux from a grassland. We concluded that the prevailing dry conditions resulted in low uptake of CO2 and Hg. Eddy Mercury has the potential to address some of the largest uncertainties in global Hg cycling through long-term flux measurements.

High-humidity tandem differential mobility analyzer for accurate determination of aerosol hygroscopic growth, microstructure, and activity coefficients over a wide range of relative humidity
Eugene F. Mikhailov and Sergey S. Vlasenko
Atmos. Meas. Tech., 13, 2035–2056, https://doi.org/10.5194/amt-13-2035-2020, 2020
Here we present the high-humidity tandem differential hygroscopicity analyzer (HHTDMA) and a new method to measure the hygroscopic growth of aerosol particles with in situ restructuring to minimize the influence of particle shape. Our results demonstrate that the HHTDMA system described in this work allows us to determine the thermodynamic characteristics of aqueous solutions with an accuracy close to that obtained by bulk methods.

The influence of the signal-to-noise ratio upon radio occultation inversion quality
Michael Gorbunov
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-114,2020
Preprint under review for AMT (discussion: open, 0 comments)

In this paper, we investigate the influence of the signal-to-noise ratio (SNR) upon the radio occultation (RO) retrieval quality. We perform two series of numerical simulations: (1) with artificial RO data and, (2) with real COSMIC observations. We superimpose the simulated white noise with varying magnitudes upon both types of the observation data and evaluate the response in the statistics. The statistics use the reference fields of the analyses of European Centre for Medium-Range Weather Forecasts (ECMWF). Our simulations indicate that the effect of additive white noise has a threshold character: the influence of the noise is very low up to some threshold, but when the threshold is exceeded, the influence increases dramatically. Another conclusion is that, given RO observations of fair quality, the enhancement of the SNR cannot be expected to provide significant improvement in retrieval quality.