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 natural and anthropogenic climate drivers that impact Earth’s radiation balance, influencing climate states and forcing climate change are termed climate forcing agents. Globally representative forcing estimates are needed to drive Earth system models to simulate past and project future climate states. The Coupled Model Intercomparison Project (CMIP) Forcing Task Team aims to identify, develop, document, and deliver forcings for next-generation models participating in the seventh phase of CMIP (CMIP7). This next phase is likely to be a core contribution to the IPCC seventh assessment cycle (AR7). The special issue welcomes papers documenting forcing data development and evaluation, along with those describing CMIP7 forcing characteristics (in contrast to previous versions). We also invite papers that quantify and assess uncertainties in the spatial and temporal forcing distributions and the influence of forcing on the evolution of climate states across Earth system model configurations.

This ESSD special issue responds to an international need to improve the understanding and modelling of mountain snow and ice hydrological processes. Data sets contributed to the special issue should support and promote research on the effects of mountain snowpacks and glaciers on water supply as well as study of variations in energy and water exchange amongst different high-altitude regions. This initiative arises from a new GEWEX Hydroclimatology Panel cross-cut project – INARCH, the International Network for Alpine Research Catchment Hydrology (www.usask.ca/inarch ). The guest editors invite contributions of openly available detailed meteorological and hydrological observational archives from long-term research catchments at high temporal resolution (at least 5 years of continuous data with hourly sampling intervals for meteorological data, daily precipitation and streamflow, and regular snow and/or glacier mass balance surveys) in well-instrumented mountain regions around the world. Contributors and researchers will use this mountain hydrology data publication special issue for the benefit of global alpine hydrological research.

For this SI we welcome manuscripts on activities such as MIIPs – Model Intercomparison and Improvement Projects that target long-standing issues in the representation of small-scale processes in numerical weather prediction and climate models. The initiatives may have been taken during the 10-year Polar Prediction Project (PPP) that finished at the end of 2022 or during the Polar Coupled Analysis and Prediction for Services (PCAPS) both part of the WMO World Weather Research Program. These programs suggest an emphasis on processes that are especially important for the polar regions, but contributions that are relevant and important for model performance in other regions of the world are also welcome. Specific targets are the representation of stably stratified boundary layers, mixed-phase clouds and atmospheric coupling with snow and or ice-covered surfaces, sea-ice, ocean mixing etc.

The intention of this SI is to publish results from MIIPs that establish new and improved workflows to facilitate a more efficient path to improved process representation. This includes research-grade observations that are packaged in an easy-to-use format which combine high-frequency observations of the surface and the atmosphere above to be able to directly compare with the parameterizations used in models using time-step data. The Merged Data File (MDF) format that is defined for both observations and model output come with a series of tools that is transferable between models and observational data collections for both file production and analysis. The SI especially welcome contributions that build on, or further develop the MDF concept including new variables, types of data, sites or new analysis tools such as process-oriented diagnostics or insights in models using the targeted files.

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 natural and anthropogenic climate drivers that impact Earth’s radiation balance, influencing climate states and forcing climate change are termed climate forcing agents. Globally representative forcing estimates are needed to drive Earth system models to simulate past and project future climate states. The Coupled Model Intercomparison Project (CMIP) Forcing Task Team aims to identify, develop, document, and deliver forcings for next-generation models participating in the seventh phase of CMIP (CMIP7). This next phase is likely to be a core contribution to the IPCC seventh assessment cycle (AR7). The special issue welcomes papers documenting forcing data development and evaluation, along with those describing CMIP7 forcing characteristics (in contrast to previous versions). We also invite papers that quantify and assess uncertainties in the spatial and temporal forcing distributions and the influence of forcing on the evolution of climate states across Earth system model configurations.

For this SI we welcome manuscripts on activities such as MIIPs – Model Intercomparison and Improvement Projects that target long-standing issues in the representation of small-scale processes in numerical weather prediction and climate models. The initiatives may have been taken during the 10-year Polar Prediction Project (PPP) that finished at the end of 2022 or during the Polar Coupled Analysis and Prediction for Services (PCAPS) both part of the WMO World Weather Research Program. These programs suggest an emphasis on processes that are especially important for the polar regions, but contributions that are relevant and important for model performance in other regions of the world are also welcome. Specific targets are the representation of stably stratified boundary layers, mixed-phase clouds and atmospheric coupling with snow and or ice-covered surfaces, sea-ice, ocean mixing etc.

The intention of this SI is to publish results from MIIPs that establish new and improved workflows to facilitate a more efficient path to improved process representation. This includes research-grade observations that are packaged in an easy-to-use format which combine high-frequency observations of the surface and the atmosphere above to be able to directly compare with the parameterizations used in models using time-step data. The Merged Data File (MDF) format that is defined for both observations and model output come with a series of tools that is transferable between models and observational data collections for both file production and analysis. The SI especially welcome contributions that build on, or further develop the MDF concept including new variables, types of data, sites or new analysis tools such as process-oriented diagnostics or insights in models using the targeted files.

This ESSD special issue responds to an international need to improve the understanding and modelling of mountain snow and ice hydrological processes. Data sets contributed to the special issue should support and promote research on the effects of mountain snowpacks and glaciers on water supply as well as study of variations in energy and water exchange amongst different high-altitude regions. This initiative arises from a new GEWEX Hydroclimatology Panel cross-cut project – INARCH, the International Network for Alpine Research Catchment Hydrology (www.usask.ca/inarch ). The guest editors invite contributions of openly available detailed meteorological and hydrological observational archives from long-term research catchments at high temporal resolution (at least 5 years of continuous data with hourly sampling intervals for meteorological data, daily precipitation and streamflow, and regular snow and/or glacier mass balance surveys) in well-instrumented mountain regions around the world. Contributors and researchers will use this mountain hydrology data publication special issue for the benefit of global alpine hydrological research.