With the launch of the novel Aeolus wind profiling mission, a wealth of direct wind and atmospheric backscatter profile observations has become available across the globe, revealing new information on atmospheric dynamics and optical properties to the benefit of a number of applications. These applications include, for example, improvements in numerical weather prediction (NWP), general circulation models (GCMs) and their included parameterized processes, such as land and ocean drag, convection, stratosphere–troposphere interaction and atmospheric waves, air quality and air pollution transport, etc. In this special issue, new data products and their validation as well as studies using the Aeolus data for application in meteorology, air quality, and climate studies are discussed. Topics vary from observation interpretation to GCM or NWP model diagnostics, parameterization, and data assimilation experiments. This is the first special issue on scientific analysis of Aeolus mission data, including inter-comparisons with different collocated wind profiling, aerosol and cloud in situ and remote-sensing measurements, and atmospheric models. Contributions concerning Aeolus data calibration, processing, and tools for data access and exploitation are also provided.

This special issue consists of papers that describe the modelling, observations, and analysis of data related to the ACROSS (Atmospheric Chemistry of the Suburban Forest) field measurement campaign that took place in summer 2022 in the Paris region. It could also include papers describing new instrumentation or new instrumental configurations used during the campaign. Any papers directly related to the ACROSS project are welcome for submittal to this special issue.

Review process: This inter-journal special issue co-lists papers of different journals. Thereby, each paper was submitted to 1 particular journal and underwent the regular interactive peer-review process of that journal. Depending on the journal, the peer review was handled by regular members of the editorial board and/or by guest editors designated by the journal's chief/executive editors.

The Clouds, Aerosol Monsoon Processes Philippines Experiment (CAMP2Ex) was a NASA-led study to understand the interdisciplinary relationships between aerosol lifecyle, convection and the radiation budget within the Southeast Asian boreal summer southwest monsoon system. Central to CAMP2Ex was a 25 August–5 October 2019 airborne campaign based at Clark, Philippines, including the NASA P3 and SPEC Inc. Lear 35 research aircraft outfitted with radars, microwave sounders, lidar, radiation, cloud microphysics, composition and state instrumentation, aligned with significant remote sensing data collections and informatics efforts. Operations were the pinnacle of a multi-year monitoring effort that included development of an aerosol and radiation monitoring site at the Manila Observatory, performed in partnership with the ONR-sponsored Propagation of Intraseasonal Tropical Oscillations (PISTON) R/V Sally Ride deployment and contributing to the International Years of the Maritime Continent (YMC) effort. Given its interdisciplinary nature, CAMP2Ex is generating papers on numerous classes of research. We request a Special Issue be granted to the CAMP2Ex team and its partners specifically as a venue for aerosol–cloud–radiation research.

The EarthCARE satellite (Earth Cloud, Aerosol and Radiation Explorer) is a joint ESA–JAXA mission due for launch in 2023, carrying a Doppler cloud profiling radar (CPR), a high spectral-resolution atmospheric lidar (ATLID), a multi-spectral imager (MSI) and a broadband radiometer (BBR). A large number of cloud, aerosol, precipitation and radiation data products will be produced, some derived from individual EarthCARE instruments and some from the synergy of multiple instruments. This collection of papers will document the theoretical basis for the EarthCARE Level 2 algorithms and evaluate their performance. An innovative aspect that links a number of the papers together is the use of realistic 3D test scenes, 6000 km in length, with cloud, precipitation and aerosol fields from a high-resolution cloud-resolving model and an aerosol transport model, from which observations by the four Earth CARE instruments have been simulated using state-of-the-art instrument simulators. This approach has enabled these algorithms to be evaluated and compared on a common dataset. The special issue is limited to invited papers describing official ESA or JAXA retrieval algorithms and their evaluation, plus several closely related papers.

In April 2017, the Senate of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) established the Priority Programme “Polarimetric Radar Observations meet Atmospheric Modelling (PROM)” (SPP 2115). The programme is designed to run for 6 years and is now in the third funding year. The overall motivation of the SPP PROM is a better understanding and representation of cloud and precipitation processes in numerical weather prediction and climate models. Since 2015 the whole atmosphere over Germany has been monitored by 17 state-of-the-art polarimetric Doppler weather radar observations suitable to challenge the representation of cloud and precipitation processes in atmospheric models. Data assimilation merges observations and models for state estimation as a prerequisite for prediction and can be regarded as a smart interpolation between observations while exploiting the physical consistency of atmospheric models as mathematical constraints. However, considerable knowledge gaps exist both in radar polarimetry and atmospheric models, which impede the full exploitation of the triangle radar-polarimetry–atmospheric-models–data-assimilation. Objectives of SPP PROM and thus the envisioned publications within the special issue are (1) the exploitation of radar polarimetry for quantitative process detection in precipitating clouds and for model evaluation, (2) the improvement of cloud and precipitation schemes in atmospheric models based on process fingerprints detectable in polarimetric observations, (3) monitoring of the energy budget evolution due to phase changes in the cloudy, precipitating atmosphere for a better understanding of its dynamics, (4) the generation of precipitation system analyses by the assimilation of polarimetric radar observations into atmospheric models for weather forecasting, and (5) radar-based detection of the initiation of convection for the improvement of thunderstorm prediction.

Geostationary Environment Monitoring Spectrometer (GEMS) is the first instrument to observe air quality from a geostationary Earth orbit (GEO) successfully launched on 19 February 2020 and in initial operation after in-orbit tests (IOTs). GEMS provides hourly air quality information on both aerosols and gases at unprecedented spatial resolution of 7 km × 8 km. GEMS is a scanning UV–visible spectrometer measuring the hyperspectral spectrum in the ultraviolet and visible, which allows for the observation of key atmospheric constituents including O₃, NO₂, CO, SO₂, CH₂O, CHOCHO, aerosols, clouds, and UV indices. The mission opened a new era of air quality monitoring from space and will be joined by NASA’s TEMPO and ESA’s Sentinel-4 to form the GEO Air Quality Constellation in ~3 years to cover the most polluted region in the Northern Hemisphere. In this ACP–AMT special issue, the first results will be presented including instruments, IOT results, initial products, algorithm, calibration, validation from the recent GMAP field campaign, applications in modelling, etc.

The version 8 spectral data of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), released in January 2019, are supposed to be the final set. Besides the ORM reprocessed version 8 level-2 MIPAS data distributed by ESA, a research processor has been run at IMK and IAA to generate temperature and trace gas concentrations. The IMK–IAA data product includes a larger list of atmospheric constituents and covers a wider altitude range in the case of the special observation modes than the operational data. The processing is based on independent algorithms. This special issue collects articles which 1) document the retrieval strategies used to derive these distributions along with uncertainty estimates, 2) report validation studies, and 3) use the data to answer current questions in atmospheric research.

The Tibetan Plateau is referred to as the third pole of the world and is representative of background region of the Earth’s atmosphere. Atmospheric photochemistry, in conjunction with the unique circulation pattern of Asian Monsoon outflow and prevailing westerly wind, leads to, as of yet, unidentified implications for climate change, the oxidative capacity of the atmosphere, local air quality, and health effects on local residents and visitors.

For a better scientific understanding of the background atmospheric chemistry and its impacts on climate change, air quality, and human health, multiple international campaigns, referred to as the @Tibet field campaigns, have been conducted since 2019 under the umbrella of the second Tibetan Plateau Scientific Expedition and Research Program (STEP). As supported by the major research plan of the National Natural Science Foundation of China (NSFC) entitled fundamental researches on the formation and response mechanism of air pollution complex, the research conducted in the Tibetan Plateau and eastern China was underpinned by a number of instrument developments required to meet the specific demands of exploring air pollution and fundamental atmospheric photochemistry. This AMT–ACP joint special issue is therefore designed to intensively discuss data from @Tibet field campaigns and instrument development progress.

The purpose of this special issue is the compilation of modelling and observational studies in connection with five international field deployments (AEROCLO-sA, CLARIFY, LASIC, ORACLES, and NaFoLiCA) that focus on the interactions of natural and anthropogenic aerosols with radiation, clouds, and regional climate in the South Atlantic Ocean and the southern African region. These deployments, based in Namibia, Ascension Island, and São Tomé, took place between 2016 and 2018 and support a significant number of investigations extending beyond just the individual science teams. The airborne and ground-based observations, as well as the related satellite measurements and climate modelling studies, address all aspects of aerosol–cloud–climate interactions, including the link of aerosol properties to meteorological fields and dynamical processes that influence aerosol emission and transport. The projects also target the advancement of remote sensing of aerosols for complex scenes over land, sea, and clouds. The special issue will be open to all submissions, with complementary goals to the five mentioned deployments, so as to encourage the exchange of ideas from inside and outside the science teams of all projects.

Occultation techniques for observing the Earth’s atmosphere and climate comprise solar, lunar, stellar, navigation, and satellite-crosslink occultation methods, exploiting the electromagnetic spectrum from optical to radio signals via refraction, absorption, scattering, and reflection. Retrieved atmospheric variables range from bending angle, refractivity, pressure, geopotential height, temperature, and water vapor to greenhouse gases and particulate species such as aerosols and cloud liquid water. Information on ionosphere and space weather is also provided.

Occultation methods share the unique properties of self-calibration; high accuracy and vertical resolution; global coverage; and, if using radio signals, all-weather capability. Global navigation satellite system (GNSS) radio occultation has become particularly successful over the recent decades and provides accurate refraction-based measurements using data from all GNSS systems.

Occultation data are of high utility in numerical weather prediction, atmospheric physics, and climate science. Their application has further broadened in recent years, and new satellite missions and observation methods are on the way.

The OPAC-IROWG 2022 workshop brought together members from the different sub-communities and users of occultation data. The present Atmospheric Measurement Techniques special issue is dedicated to the results of this conference and recent achievements.

An overlapping need exists between the climate research and the radiation protection communities to improve the metrology for atmospheric radon concentration and radon flux measurements. The EMPIR project 19ENV01 traceRadon works toward these goals for the benefit of both large scientific communities by providing the necessary infrastructure for measuring these aforementioned variables. In addition, it will generate data at four selected European sites for validation of radon flux models and inventories and will create the first standard protocol for applying the radon tracer method (RTM). The proposed special issue aims to collect the direct and indirect outcomes of the traceRadon project. It will include papers presenting results of the laboratory and field campaigns carried out within the project. In addition, papers directly related to the project goals will be welcome too.

The proposed special issue has the goal of collecting original publications addressing profiles of the atmospheric boundary layer from a variety of perspectives. Aligned with the objectives of the EU COST action PROBE (http://probe-cost.eu), topics include both observational aspects (latest technological sensor developments, quality control and retrieval methods, calibration, implementation of harmonised monitoring networks, measurement campaigns, instrument synergy, combination with satellite data) and the exploitation of the profile observations (process understanding, model development and assessment, data assimilation) for a wide range of applications (including meteorology and climate, air quality, renewable energy, radio propagation).

ACTRIS statements of the purpose of the special issue on stay-at-home policies in response to the COVID-19 pandemic have resulted in an unprecedented decrease in pollutant emissions and in a well-publicized improvement of air quality in many cities in Asia, Europe and America. While the impact of lockdown on air quality was unambiguously detected in the urban areas through both in situ and space remote-sensing observations and its spatial and temporal extents, the specific role of meteorology and the cascade responses from indirect and non-linear effects are far from being fully evaluated. Throughout the very specific year 2020, ACTRIS and its partner institutions engaged in a pan-European effort to document the impact of governmental policies on atmospheric composition. ACTRIS maintained its operations at fully nominal standards, even increasing its sampling capacity in some cases. The ACTRIS data collection containing measurements of aerosol, cloud and trace gas properties across Europe measured during the year 2020 has been compiled and made available by the ACTRIS Data Centre units. Data from the year 2021 will soon follow. A community of scientists started evaluating the impact of the repeated lockdowns over the European regions. Because concentration and properties of short-lived atmospheric species are highly variable in space and time, evaluating the impact of reduced emissions is not straightforward. The special issue “Quantifying the impacts of stay-at-home policies on atmospheric composition and properties of aerosol and clouds over the European regions using ACTRIS related observations” will gather a series of scientific papers dealing with the measurable effects of lockdown measures over Europe. The special issue will particularly be dealing with • quantifying the spatial and temporal extent of stay-at-home policies on the European atmosphere, at both local and regional scales, • evaluating the impact of lockdown measures on the formation of secondary pollutants, • documenting the impact of reduced emissions (including air-traffic emissions) on cloud properties and occurrence, and • estimating the “missing” emissions using observation–model approaches. The outcome from the special issue aims to provide an in-depth analysis of the perturbation induced by the repeated lockdowns on the complex atmospheric system. The special issue is open for all submissions within its scope.

SCOR (Scientific Committee on Oceanic Research) Working Group 167 (Reducing Uncertainty in Soluble aerosol Trace Element Deposition, RUSTED), appointed in October 2022, brings together experts from the atmospheric chemistry, ocean biogeochemistry, and modelling communities. Aiming to reduce uncertainties in soluble aerosol trace element deposition, RUSTED will quantitatively assess different aerosol leaching schemes; formulate standard operating procedures (SOPs) for frequently used aerosol leaching schemes; and develop a user-friendly, open-access database of aerosol trace element data which includes advice on the use of the data in Earth system models.

In this special issue, we propose to curate cutting-edge studies which advance our knowledge of the deposition of soluble aerosol trace elements and their impacts on marine ecosystems. We also encourage the submission of manuscripts which address challenges and/or report recent advances in the field of aerosol trace element deposition from researchers outside the working group.

Review process: This inter-journal special issue co-lists papers of different journals. Thereby, each paper was submitted to 1 particular journal and underwent the regular interactive peer-review process of that journal. Depending on the journal, the peer review was handled by regular members of the editorial board and/or by guest editors designated by the journal’s chief/executive editors.

SKYNET is an international research network dedicated to aerosol—cloud—radiation interaction studies.
It consists of about 60 sites located all over the world. The main instrument at each site is the sun—sky radiometer, but to strengthen the ability of SKYNET, simultaneous measurements with other instruments such as pyranometers, pirgeometers, microwave radiometers, absorption meters, cloud cameras, lidars, MAX-DOAS, and instrumentation for in situ characterisation are also conducted for some selected sites.
This special issue will face issues related to the following topics: aerosol and cloud properties from radiometers; developments on instrumentation; aerosol radiative forcing and climate effects; intercomparison among radiometer networks; validation of aerosol and cloud properties from satellite and models; applications for air pollution studies; and applications for solar energy.

The Tropospheric Ozone Assessment Report (TOAR-II) is an official activity of the International Global Atmospheric Chemistry Project (IGAC) (https://igacproject.org/activities/TOAR/TOAR-II). The goal of TOAR-II is to build on the success of TOAR-I (2014–2019) and produce an updated assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause. This effort will include an analysis of the impacts of ozone on human health, crop and ecosystem productivity, and climate. Original tropospheric ozone research conducted by the TOAR-II community may be submitted to one of six Copernicus journals (ACP/AMT/BG/GMD/ESSD/ASCMO), and the accepted papers will be linked through the TOAR-II Community Special Issue.

The prediction of the winter weather over complex terrain is quite challenging due to the highly variable nature of winds, visibility, and snowfall. As a World Meteorological Organization (WMO) World Weather Research Program (WWRP) Research Demonstration Project (RDP) and Forecast Demonstration Project (FDP), ICE-POP 2018 (International Collaborative Experiments for PyeongChang 2018 Olympic and Paralympic winter games) was held in the PyeongChang region from November 2017 to April 2018 with contributions from 29 agencies from 12 countries. The region was quite unique for observing winter weathers that are influenced by cold air and warm ocean interaction, sudden uplifting by steep terrains near the coast, and modulation by complex terrains. The main scientific goal was to understand the precipitation processes in this unique region during the cold season and to evaluate/improve forecasting from numerical models based on intensive observations. Dense observational networks of upper air observation (eight soundings, two wind profilers, shipborne sounding, and dropsonde), remote sensing (three X-Pol radars, one Ku/Ka-Pol radar and three S-Pol, one S-band, two C-band, and three Doppler lidars), microphysical observation (2DVD, MASC, PIP, Parsivel, MRR, POSS, Pluvio), and surface stations (64 stations) were implemented, in particular, to observe the evolution of precipitation along and across atmospheric flows. The field experiment and real-time forecast demonstration ended and the second phase of the experiment has started for better understanding of the microphysical processes, their better representation in the numerical modeling, and further improvement of winter weather prediction through various international collaborations.

The main purposes of the special issue are

1) to document the scientific findings on the winter weather during the forecast demonstration project

2) to share scientific knowledge on processes of winter weathers that have been investigated with unprecedented dense observational networks,

3) to share current status and improved knowledge of forecasting of winter weathers, and

4) to document new retrieval and quality control methods of the operational and advanced instruments.

The special issue will include all manuscripts related to observational data, products, NWP modeling, researches on observational instrumentation, process/mechanism study, reanalysis, integration of observation and numerical modeling, and prediction of the winter weathers.

SCOR (Scientific Committee on Oceanic Research) Working Group 167 (Reducing Uncertainty in Soluble aerosol Trace Element Deposition, RUSTED), appointed in October 2022, brings together experts from the atmospheric chemistry, ocean biogeochemistry, and modelling communities. Aiming to reduce uncertainties in soluble aerosol trace element deposition, RUSTED will quantitatively assess different aerosol leaching schemes; formulate standard operating procedures (SOPs) for frequently used aerosol leaching schemes; and develop a user-friendly, open-access database of aerosol trace element data which includes advice on the use of the data in Earth system models.

In this special issue, we propose to curate cutting-edge studies which advance our knowledge of the deposition of soluble aerosol trace elements and their impacts on marine ecosystems. We also encourage the submission of manuscripts which address challenges and/or report recent advances in the field of aerosol trace element deposition from researchers outside the working group.

Review process: This inter-journal special issue co-lists papers of different journals. Thereby, each paper was submitted to 1 particular journal and underwent the regular interactive peer-review process of that journal. Depending on the journal, the peer review was handled by regular members of the editorial board and/or by guest editors designated by the journal’s chief/executive editors.

This special issue consists of papers that describe the modelling, observations, and analysis of data related to the ACROSS (Atmospheric Chemistry of the Suburban Forest) field measurement campaign that took place in summer 2022 in the Paris region. It could also include papers describing new instrumentation or new instrumental configurations used during the campaign. Any papers directly related to the ACROSS project are welcome for submittal to this special issue.

Review process: This inter-journal special issue co-lists papers of different journals. Thereby, each paper was submitted to 1 particular journal and underwent the regular interactive peer-review process of that journal. Depending on the journal, the peer review was handled by regular members of the editorial board and/or by guest editors designated by the journal's chief/executive editors.

Occultation techniques for observing the Earth’s atmosphere and climate comprise solar, lunar, stellar, navigation, and satellite-crosslink occultation methods, exploiting the electromagnetic spectrum from optical to radio signals via refraction, absorption, scattering, and reflection. Retrieved atmospheric variables range from bending angle, refractivity, pressure, geopotential height, temperature, and water vapor to greenhouse gases and particulate species such as aerosols and cloud liquid water. Information on ionosphere and space weather is also provided.

Occultation methods share the unique properties of self-calibration; high accuracy and vertical resolution; global coverage; and, if using radio signals, all-weather capability. Global navigation satellite system (GNSS) radio occultation has become particularly successful over the recent decades and provides accurate refraction-based measurements using data from all GNSS systems.

Occultation data are of high utility in numerical weather prediction, atmospheric physics, and climate science. Their application has further broadened in recent years, and new satellite missions and observation methods are on the way.

The OPAC-IROWG 2022 workshop brought together members from the different sub-communities and users of occultation data. The present Atmospheric Measurement Techniques special issue is dedicated to the results of this conference and recent achievements.

An overlapping need exists between the climate research and the radiation protection communities to improve the metrology for atmospheric radon concentration and radon flux measurements. The EMPIR project 19ENV01 traceRadon works toward these goals for the benefit of both large scientific communities by providing the necessary infrastructure for measuring these aforementioned variables. In addition, it will generate data at four selected European sites for validation of radon flux models and inventories and will create the first standard protocol for applying the radon tracer method (RTM). The proposed special issue aims to collect the direct and indirect outcomes of the traceRadon project. It will include papers presenting results of the laboratory and field campaigns carried out within the project. In addition, papers directly related to the project goals will be welcome too.

The Tropospheric Ozone Assessment Report (TOAR-II) is an official activity of the International Global Atmospheric Chemistry Project (IGAC) (https://igacproject.org/activities/TOAR/TOAR-II). The goal of TOAR-II is to build on the success of TOAR-I (2014–2019) and produce an updated assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause. This effort will include an analysis of the impacts of ozone on human health, crop and ecosystem productivity, and climate. Original tropospheric ozone research conducted by the TOAR-II community may be submitted to one of six Copernicus journals (ACP/AMT/BG/GMD/ESSD/ASCMO), and the accepted papers will be linked through the TOAR-II Community Special Issue.

The proposed special issue has the goal of collecting original publications addressing profiles of the atmospheric boundary layer from a variety of perspectives. Aligned with the objectives of the EU COST action PROBE (http://probe-cost.eu), topics include both observational aspects (latest technological sensor developments, quality control and retrieval methods, calibration, implementation of harmonised monitoring networks, measurement campaigns, instrument synergy, combination with satellite data) and the exploitation of the profile observations (process understanding, model development and assessment, data assimilation) for a wide range of applications (including meteorology and climate, air quality, renewable energy, radio propagation).

The Tibetan Plateau is referred to as the third pole of the world and is representative of background region of the Earth’s atmosphere. Atmospheric photochemistry, in conjunction with the unique circulation pattern of Asian Monsoon outflow and prevailing westerly wind, leads to, as of yet, unidentified implications for climate change, the oxidative capacity of the atmosphere, local air quality, and health effects on local residents and visitors.

For a better scientific understanding of the background atmospheric chemistry and its impacts on climate change, air quality, and human health, multiple international campaigns, referred to as the @Tibet field campaigns, have been conducted since 2019 under the umbrella of the second Tibetan Plateau Scientific Expedition and Research Program (STEP). As supported by the major research plan of the National Natural Science Foundation of China (NSFC) entitled fundamental researches on the formation and response mechanism of air pollution complex, the research conducted in the Tibetan Plateau and eastern China was underpinned by a number of instrument developments required to meet the specific demands of exploring air pollution and fundamental atmospheric photochemistry. This AMT–ACP joint special issue is therefore designed to intensively discuss data from @Tibet field campaigns and instrument development progress.

Geostationary Environment Monitoring Spectrometer (GEMS) is the first instrument to observe air quality from a geostationary Earth orbit (GEO) successfully launched on 19 February 2020 and in initial operation after in-orbit tests (IOTs). GEMS provides hourly air quality information on both aerosols and gases at unprecedented spatial resolution of 7 km × 8 km. GEMS is a scanning UV–visible spectrometer measuring the hyperspectral spectrum in the ultraviolet and visible, which allows for the observation of key atmospheric constituents including O₃, NO₂, CO, SO₂, CH₂O, CHOCHO, aerosols, clouds, and UV indices. The mission opened a new era of air quality monitoring from space and will be joined by NASA’s TEMPO and ESA’s Sentinel-4 to form the GEO Air Quality Constellation in ~3 years to cover the most polluted region in the Northern Hemisphere. In this ACP–AMT special issue, the first results will be presented including instruments, IOT results, initial products, algorithm, calibration, validation from the recent GMAP field campaign, applications in modelling, etc.

ACTRIS statements of the purpose of the special issue on stay-at-home policies in response to the COVID-19 pandemic have resulted in an unprecedented decrease in pollutant emissions and in a well-publicized improvement of air quality in many cities in Asia, Europe and America. While the impact of lockdown on air quality was unambiguously detected in the urban areas through both in situ and space remote-sensing observations and its spatial and temporal extents, the specific role of meteorology and the cascade responses from indirect and non-linear effects are far from being fully evaluated. Throughout the very specific year 2020, ACTRIS and its partner institutions engaged in a pan-European effort to document the impact of governmental policies on atmospheric composition. ACTRIS maintained its operations at fully nominal standards, even increasing its sampling capacity in some cases. The ACTRIS data collection containing measurements of aerosol, cloud and trace gas properties across Europe measured during the year 2020 has been compiled and made available by the ACTRIS Data Centre units. Data from the year 2021 will soon follow. A community of scientists started evaluating the impact of the repeated lockdowns over the European regions. Because concentration and properties of short-lived atmospheric species are highly variable in space and time, evaluating the impact of reduced emissions is not straightforward. The special issue “Quantifying the impacts of stay-at-home policies on atmospheric composition and properties of aerosol and clouds over the European regions using ACTRIS related observations” will gather a series of scientific papers dealing with the measurable effects of lockdown measures over Europe. The special issue will particularly be dealing with • quantifying the spatial and temporal extent of stay-at-home policies on the European atmosphere, at both local and regional scales, • evaluating the impact of lockdown measures on the formation of secondary pollutants, • documenting the impact of reduced emissions (including air-traffic emissions) on cloud properties and occurrence, and • estimating the “missing” emissions using observation–model approaches. The outcome from the special issue aims to provide an in-depth analysis of the perturbation induced by the repeated lockdowns on the complex atmospheric system. The special issue is open for all submissions within its scope.

The EarthCARE satellite (Earth Cloud, Aerosol and Radiation Explorer) is a joint ESA–JAXA mission due for launch in 2023, carrying a Doppler cloud profiling radar (CPR), a high spectral-resolution atmospheric lidar (ATLID), a multi-spectral imager (MSI) and a broadband radiometer (BBR). A large number of cloud, aerosol, precipitation and radiation data products will be produced, some derived from individual EarthCARE instruments and some from the synergy of multiple instruments. This collection of papers will document the theoretical basis for the EarthCARE Level 2 algorithms and evaluate their performance. An innovative aspect that links a number of the papers together is the use of realistic 3D test scenes, 6000 km in length, with cloud, precipitation and aerosol fields from a high-resolution cloud-resolving model and an aerosol transport model, from which observations by the four Earth CARE instruments have been simulated using state-of-the-art instrument simulators. This approach has enabled these algorithms to be evaluated and compared on a common dataset. The special issue is limited to invited papers describing official ESA or JAXA retrieval algorithms and their evaluation, plus several closely related papers.

In April 2017, the Senate of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) established the Priority Programme “Polarimetric Radar Observations meet Atmospheric Modelling (PROM)” (SPP 2115). The programme is designed to run for 6 years and is now in the third funding year. The overall motivation of the SPP PROM is a better understanding and representation of cloud and precipitation processes in numerical weather prediction and climate models. Since 2015 the whole atmosphere over Germany has been monitored by 17 state-of-the-art polarimetric Doppler weather radar observations suitable to challenge the representation of cloud and precipitation processes in atmospheric models. Data assimilation merges observations and models for state estimation as a prerequisite for prediction and can be regarded as a smart interpolation between observations while exploiting the physical consistency of atmospheric models as mathematical constraints. However, considerable knowledge gaps exist both in radar polarimetry and atmospheric models, which impede the full exploitation of the triangle radar-polarimetry–atmospheric-models–data-assimilation. Objectives of SPP PROM and thus the envisioned publications within the special issue are (1) the exploitation of radar polarimetry for quantitative process detection in precipitating clouds and for model evaluation, (2) the improvement of cloud and precipitation schemes in atmospheric models based on process fingerprints detectable in polarimetric observations, (3) monitoring of the energy budget evolution due to phase changes in the cloudy, precipitating atmosphere for a better understanding of its dynamics, (4) the generation of precipitation system analyses by the assimilation of polarimetric radar observations into atmospheric models for weather forecasting, and (5) radar-based detection of the initiation of convection for the improvement of thunderstorm prediction.

The Clouds, Aerosol Monsoon Processes Philippines Experiment (CAMP2Ex) was a NASA-led study to understand the interdisciplinary relationships between aerosol lifecyle, convection and the radiation budget within the Southeast Asian boreal summer southwest monsoon system. Central to CAMP2Ex was a 25 August–5 October 2019 airborne campaign based at Clark, Philippines, including the NASA P3 and SPEC Inc. Lear 35 research aircraft outfitted with radars, microwave sounders, lidar, radiation, cloud microphysics, composition and state instrumentation, aligned with significant remote sensing data collections and informatics efforts. Operations were the pinnacle of a multi-year monitoring effort that included development of an aerosol and radiation monitoring site at the Manila Observatory, performed in partnership with the ONR-sponsored Propagation of Intraseasonal Tropical Oscillations (PISTON) R/V Sally Ride deployment and contributing to the International Years of the Maritime Continent (YMC) effort. Given its interdisciplinary nature, CAMP2Ex is generating papers on numerous classes of research. We request a Special Issue be granted to the CAMP2Ex team and its partners specifically as a venue for aerosol–cloud–radiation research.

The prediction of the winter weather over complex terrain is quite challenging due to the highly variable nature of winds, visibility, and snowfall. As a World Meteorological Organization (WMO) World Weather Research Program (WWRP) Research Demonstration Project (RDP) and Forecast Demonstration Project (FDP), ICE-POP 2018 (International Collaborative Experiments for PyeongChang 2018 Olympic and Paralympic winter games) was held in the PyeongChang region from November 2017 to April 2018 with contributions from 29 agencies from 12 countries. The region was quite unique for observing winter weathers that are influenced by cold air and warm ocean interaction, sudden uplifting by steep terrains near the coast, and modulation by complex terrains. The main scientific goal was to understand the precipitation processes in this unique region during the cold season and to evaluate/improve forecasting from numerical models based on intensive observations. Dense observational networks of upper air observation (eight soundings, two wind profilers, shipborne sounding, and dropsonde), remote sensing (three X-Pol radars, one Ku/Ka-Pol radar and three S-Pol, one S-band, two C-band, and three Doppler lidars), microphysical observation (2DVD, MASC, PIP, Parsivel, MRR, POSS, Pluvio), and surface stations (64 stations) were implemented, in particular, to observe the evolution of precipitation along and across atmospheric flows. The field experiment and real-time forecast demonstration ended and the second phase of the experiment has started for better understanding of the microphysical processes, their better representation in the numerical modeling, and further improvement of winter weather prediction through various international collaborations.

The main purposes of the special issue are

1) to document the scientific findings on the winter weather during the forecast demonstration project

2) to share scientific knowledge on processes of winter weathers that have been investigated with unprecedented dense observational networks,

3) to share current status and improved knowledge of forecasting of winter weathers, and

4) to document new retrieval and quality control methods of the operational and advanced instruments.

The special issue will include all manuscripts related to observational data, products, NWP modeling, researches on observational instrumentation, process/mechanism study, reanalysis, integration of observation and numerical modeling, and prediction of the winter weathers.

The version 8 spectral data of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), released in January 2019, are supposed to be the final set. Besides the ORM reprocessed version 8 level-2 MIPAS data distributed by ESA, a research processor has been run at IMK and IAA to generate temperature and trace gas concentrations. The IMK–IAA data product includes a larger list of atmospheric constituents and covers a wider altitude range in the case of the special observation modes than the operational data. The processing is based on independent algorithms. This special issue collects articles which 1) document the retrieval strategies used to derive these distributions along with uncertainty estimates, 2) report validation studies, and 3) use the data to answer current questions in atmospheric research.

With the launch of the novel Aeolus wind profiling mission, a wealth of direct wind and atmospheric backscatter profile observations has become available across the globe, revealing new information on atmospheric dynamics and optical properties to the benefit of a number of applications. These applications include, for example, improvements in numerical weather prediction (NWP), general circulation models (GCMs) and their included parameterized processes, such as land and ocean drag, convection, stratosphere–troposphere interaction and atmospheric waves, air quality and air pollution transport, etc. In this special issue, new data products and their validation as well as studies using the Aeolus data for application in meteorology, air quality, and climate studies are discussed. Topics vary from observation interpretation to GCM or NWP model diagnostics, parameterization, and data assimilation experiments. This is the first special issue on scientific analysis of Aeolus mission data, including inter-comparisons with different collocated wind profiling, aerosol and cloud in situ and remote-sensing measurements, and atmospheric models. Contributions concerning Aeolus data calibration, processing, and tools for data access and exploitation are also provided.

The purpose of this special issue is the compilation of modelling and observational studies in connection with five international field deployments (AEROCLO-sA, CLARIFY, LASIC, ORACLES, and NaFoLiCA) that focus on the interactions of natural and anthropogenic aerosols with radiation, clouds, and regional climate in the South Atlantic Ocean and the southern African region. These deployments, based in Namibia, Ascension Island, and São Tomé, took place between 2016 and 2018 and support a significant number of investigations extending beyond just the individual science teams. The airborne and ground-based observations, as well as the related satellite measurements and climate modelling studies, address all aspects of aerosol–cloud–climate interactions, including the link of aerosol properties to meteorological fields and dynamical processes that influence aerosol emission and transport. The projects also target the advancement of remote sensing of aerosols for complex scenes over land, sea, and clouds. The special issue will be open to all submissions, with complementary goals to the five mentioned deployments, so as to encourage the exchange of ideas from inside and outside the science teams of all projects.

SKYNET is an international research network dedicated to aerosol—cloud—radiation interaction studies.
It consists of about 60 sites located all over the world. The main instrument at each site is the sun—sky radiometer, but to strengthen the ability of SKYNET, simultaneous measurements with other instruments such as pyranometers, pirgeometers, microwave radiometers, absorption meters, cloud cameras, lidars, MAX-DOAS, and instrumentation for in situ characterisation are also conducted for some selected sites.
This special issue will face issues related to the following topics: aerosol and cloud properties from radiometers; developments on instrumentation; aerosol radiative forcing and climate effects; intercomparison among radiometer networks; validation of aerosol and cloud properties from satellite and models; applications for air pollution studies; and applications for solar energy.