Several terrain-induced processes in the atmospheric boundary layer over mountains affect the transport and exchange of heat, momentum, moisture, aerosols, and trace constituents between the surface and the atmosphere and within the atmosphere.

TEAMx (Multi-scale transport and exchange processes in the atmosphere over mountains – programme and experiment) is an international research program that aims at improving our understanding of these processes and their representation in numerical weather and climate prediction models. Measurements were collected in a north–south transect through the Alps using a range of different instruments as part of the 1-year-long TEAMx Observational Campaign between September 2024 and September 2025. To sample the mountain boundary layer at multiple spatial and temporal scales, observations from various platforms were combined: surface weather and eddy-covariance stations, surface-based remote sensing instruments, radiosoundings, drone-based measurements, and aircraft flights. The observational data were complemented by numerical modeling for process understanding and model development.

This special issue collects observational, modeling, and theoretical studies originating from the TEAMx research programme. In particular, we call for contributions that use data collected during the TEAMx Observational Campaign (TOC), use data collected during other TEAMx-related measurement campaigns (e.g., pre-campaign PC22, HEFEX), and result from funded projects endorsed by TEAMx. Idealized modeling studies and theoretical work dealing with meteorological processes in the mountain boundary layer and their parameterization are also welcome.

This special issue invites original research and technical papers focused on novel spectral imaging and lightning imager data from the Meteosat Third Generation (MTG) imager satellite, operational since late 2024. The flexible combined imager (FCI) and the lightning imager (LI) instruments provide unprecedented spatial, temporal, and spectral resolution for atmospheric monitoring, as well as new lightning-monitoring capability over Europe, Africa, and the Middle East.

We welcome submissions that address the following:

• calibration and validation – technical assessments of FCI and LI instrument performance;

• environmental monitoring – innovative applications, new products, and significance of MTG FCI and LI data in improving weather monitoring, nowcasting, forecasting, and atmospheric research; and

• comparative studies – research emphasizing advancements in measurement techniques, data, and products over Meteosat Second Generation (MSG) capabilities.

The international Network for the Detection of Atmospheric Composition Change (NDACC) began official network operations in January 1991. Today it is composed of more than 110 globally distributed, ground-based, remote-sensing stations with more than 160 currently active instruments. The overriding goal of NDACC is to collect and maintain high-quality data for achieving the following scientific objectives:

• establishing long-term databases for the characterization of the state and behaviour of the atmosphere
• establishing links and feedbacks between changes in atmospheric composition, climate, and air quality
• validating atmospheric measurements from other platforms
• providing critical datasets to fill gaps in satellite observations
• collaboratively supporting field campaigns and other observing networks
• providing validation and development support for atmospheric models
• contributing to assessments of the state of the atmosphere (WMO, IPCC, etc.)

To achieve its objectives, NDACC collaborates with 10 cooperating networks, satellite teams, and model developers.

This special Issue marks the 35th anniversary of NDACC (https://ndacc.org). Its purpose is to present past scientific achievements and to inform readers about the updated strategy of the network in light of the evolution of the scientific questions regarding the state and behaviour of the atmosphere by taking advantage of the current landscape of observations. We also welcome papers that focus on related studies with important implications for our understanding of the state and behaviour of the atmosphere.

The introductory paper to the special issue will provide an overview of NDACC's revised strategy for the next decade.

The purpose of this special issue is the compilation of modelling and observational studies on the role of atmospheric aerosols in the life cycle and composition of fog and low clouds in southern Africa as well as their mutual links with climate and biogeochemistry.

The special issue is motivated by new results from the AeroFog project, focusing on the hyperarid coastal deserts of Namibia, on the western coast of southern Africa. AeroFog is based on two intensive, ground-based field deployments, which took place in May and September 2024 along the coast and in the desert, and the long-term monitoring and analysis of remote-sensing products. Observations, satellite measurements, and modelling address the aerosol radiative, chemical, and microphysical interactions relevant to fog as well as the meteorological fields and dynamical processes that influence aerosol emission, transport, and deposition. Building on the diverse expertise of scientists in both the Northern and the Southern hemispheres, AeroFog aims to develop a holistic understanding of the mechanisms by which nutrients and pollutants are found in fog and the effect of fog on the biogeochemistry of regional ecosystems. The special issue comprises papers with complementary goals so as to encourage the exchange of ideas among previous, current, and planned large-scale projects and activities in the region.