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.

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.

Through their interaction with solar and thermal infrared radiation, clouds and aerosols have been implicated as two of the greatest sources of uncertainty in climate projections. The EarthCARE (Earth Cloud, Aerosol and Radiation Explorer) satellite is a joint ESA–JAXA mission designed to provide key new information to tackle this crucial challenge. Launched on 28 May 2024, it carries a Doppler cloud profiling radar (CPR), a high-spectral-resolution atmospheric lidar (ATLID), a multi-spectral imager (MSI), and a three-view broadband radiometer (BBR). CPR is the first radar in space that can measure how fast cloud and precipitation particles are falling in the atmosphere or rising in the cores of thunderstorms, while the ability of ATLID to separately measure the backscatter of particles and air molecules enables it to retrieve the all-important profile of the cloud and aerosol extinction coefficient without having to make any assumption regarding the scattering properties of the particles. A large number of cloud, aerosol, precipitation, and radiation data products are being produced, some derived from individual EarthCARE instruments and others from the synergy of multiple instruments.

This inter-journal special issue (SI) is dedicated to presenting early scientific results using data from the satellite. It is open to the submission of papers that use EarthCARE data and fall into the remit of one of the three journals participating in the SI: Atmospheric Measurement Techniques, Atmospheric Chemistry and Physics, and Geoscientific Model Development. Topics can include, but are not limited to, the following: calibration and validation of EarthCARE data, development of new retrieval algorithms and improvement of existing algorithms, generation of new open-access datasets, improvement of the understanding of atmospheric properties and processes, evaluation of atmospheric models, assimilation of EarthCARE data into weather forecast and air quality models, and combination of EarthCARE with other datasets to estimate climate trends.