In order to improve our current knowledge on the budgets of the two most important anthropogenic greenhouse gases, CO₂ and CH₄, a co-ordinated measurement campaign in the central European region was successfully carried out in May-June 2018 with the German research aircraft HALO and two smaller Cessna aircraft as its main experimental platforms. The goal of CoMet is to combine a suite of state-of-the-art airborne active (lidar) and passive remote sensors (spectrometer) with in situ instruments to provide regional-scale data about greenhouse gases (GHGs) which are urgently required for their accurate modelling.

During the intensive observation period, HALO research flights were performed along extended latitudinal transects to capture GHG gradients, over known regions of strong emissions, and over the ground-based remote-sensing sites of the Total Carbon Column Observing Network (TCCON). While HALO provides a larger-scale picture, the two Cessna aircraft concentrated on a region of prime interest: the Upper Silesian Coal Basin in Poland, which, due to hard coal mining activities, is one of the hot spots of anthropogenic methane emissions in Europe. Here, a variety of ground-based instruments additionally supported the CoMet mission: FTIR spectrometers, wind lidars, mobile vans, and small drones provided valuable information to quantify CH₄ emissions from coal mining activities. A model infrastructure (regional inverse modelling, chemistry-climate modelling with regional refinement) has been employed in forecast mode to optimize flight strategies and is now used to hindcast the campaign period to evaluate GHG fluxes and transport. The CoMet mission is also part of validation activities for existing passive remote sounding GHG satellites (GOSAT, Sentinel-5P, and OCO-2) and preparation of the first active CH₄ satellite mission MERLIN. For that reason, the CHARM-F lidar developed at DLR as an airborne MERLIN demonstrator was one of the key instruments. In addition, CoMet is intended to investigate methodologies for the synergistic combination for GHG measurements using lidar and passive remote sensing.

StratoClim is a collaborative research project funded by the European Commission 7th Framework programme. The main objective of the project is to improve the understanding of key processes in the upper troposphere and stratosphere (UTS) for more reliable projections of climate change and stratospheric ozone. StratoClim focuses on the understanding of the microphysical, chemical, and dynamical processes that determine the composition of the UTS, such as the formation, loss, and redistribution of aerosol, ozone, and water vapour; how these processes are affected by climate change; and how they feed back on global climate.

The issue will include papers coming from all sectors included in the project: in situ and sonde measurement deployment, satellite data products and analysis, mesoscale and transport modelling, and CCM experiments and analysis. We expect a special emphasis on the results from the high-altitude research aircraft campaign in the Asian monsoon area carried out in 2017 deploying an innovative and comprehensive payload. Due to the expected contribution of instrumental manuscripts, the issue will also include AMT submissions.

This inter-journal special issue of AMT, ACP, and GMD serves as a thematic collection for manuscripts arising from the work of Horizon 2020 integrated infrastructure project Eurochamp-2020; cf. https://www.eurochamp.org/ . As Eurochamp-2020 has project parts dealing with new instrumentation, with atmospheric chemistry and physics studies as well as with modelling, contributions are expected for all three journals as part of the inter-journal special issue.

The Sentinel-5 Precursor mission is a single-payload satellite in a low-Earth orbit successfully launched on 13 October 2017. The mission provides daily global information at an unprecedented spatial resolution (~3.5x7km²) on trace gases and aerosols, important for air quality, climate forcing, and the ozone layer. The single payload of the mission is the TROPOspheric Monitoring Instrument (TROPOMI), which is a nadir-viewing push-broom spectrometer measuring in the ultraviolet, visible, near infrared, and shortwave infrared. The selected wavelength range allows for the observation of key atmospheric constituents, including O₃, NO₂, CO, SO₂, CH₄, CH₂O, aerosols, and clouds. The mission flies in loose formation with Suomi NPP to obtain detailed information on clouds and for further scientific exploitation of combined data products. In this combined ACP/AMT special issue the first results will be presented, including validation of operational products.

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.