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.

The purpose of this special issue is to bring together papers summarizing the results of the Radio Occultation Modeling Experiment (ROMEX) in a special issue of Atmospheric Measurement Techniques (AMT). ROMEX is an international collaboration the purpose of which is to test the impact of varying numbers of vertical profiles of radio occultation (RO) observations in numerical weather prediction (NWP) models. An average of 35 000 RO profiles per day for September–November 2022 from 13 different missions are being used in experiments at major international weather prediction centres along with other atmospheric case studies demonstrating their effectiveness in observing atmospheric phenomena.

The primary focus of the special issue is the evaluation and intercomparison of the quality, characteristics, and impact on NWP models of an unprecedented number of RO observations from multiple missions across the public and private sectors in the US, Europe, and China. ROMEX represents a coordinated measurement campaign with contributions from data providers, processing centres, space agencies, and operational forecasting centres.

Central to this special issue are studies involving ROMEX-related datasets, with topics including but not limited to observation data quality and characteristics, advances in data processing methodologies, data evaluation and validation efforts, and impact studies on numerical weather prediction and other applications. Collectively, these topics – particularly the impact assessments – offer critical insights into the strengths and limitations of radio occultation as an atmospheric measurement technique.

The special issue is open to all studies evaluating or using ROMEX observations in NWP and other areas of atmospheric research. Papers for the special issue may be submitted between 1 May 2025 and 31 December 2026.