Cloud Physics

Cloud physics examines the formation, evolution and interactions of suspended water in the atmosphere, spanning scales from microscopic droplets and ice crystals to kilometre-scale cloud systems. Central processes include the activation of aerosol particles as cloud condensation nuclei (CCN) or ice-nucleating particles (INP), vapour diffusion and deposition, droplet collision-coalescence and ice-phase growth mechanisms. These microphysical steps determine key properties—the number, size distribution and phase composition of hydrometeors—that in turn govern cloud optical depth, lifetime and precipitation efficiency. Clouds modulate Earth’s radiation budget through their reflection and absorption of solar and terrestrial radiation, and by influencing latent-heat release within the atmospheric column. Variations in natural aerosols (dust, sea salt, biological fragments) and anthropogenic emissions (sulphates, soot) alter CCN and INP concentrations, driving regional and global shifts in cloud albedo and rainfall patterns. Feedbacks emerge as cloud-driven changes in radiative forcing and surface temperatures affect atmospheric circulation, moisture transport and aerosol sources. Progress in remote-sensing, laboratory characterisation and numerical modelling has deepened understanding of aerosol-cloud-radiation interactions, yet significant uncertainties remain in quantifying cloud responses to changing aerosol loads and climate forcings.

Research from Nature Portfolio

Regionally sourced bioaerosols have been shown to dominate high-temperature ice nucleation in the Arctic summer, with over 90 % of active INP at –15 °C attributed to proteinaceous particles from terrestrial Arctic sources. This finding refines characterisation of biological ice nuclei and highlights their role in mixed-phase cloud glaciation and high-latitude climate feedbacks. Kilometre-scale aerosol gradients have been found to generate a thermally driven “aerosol breeze” circulation, leading to preferential cloud and precipitation development over cleaner air masses and suppression over more polluted regions. High-resolution process modelling and meso-scale observations reveal that accounting for these horizontal aerosol contrasts increases overall cloudiness compared to uniform aerosol distributions. Convection-permitting simulations further demonstrate that aerosol-induced suppression of shallow-convective rain enhances deep-convective latent heating and strengthens overturning circulation, thereby amplifying the effective radiative forcing from aerosol–cloud interactions once large-scale circulation adjustments are included.

Research from all publishers

A fast and accurate neural-network model has been developed to predict aerosol optical properties of internally mixed log-normal modes, reproducing traditional Mie-theory outputs with errors below 10 % and over a thousandfold increase in computational speed. This advance enables on-the-fly integration of evolving aerosol microphysics into global climate models, reducing radiative-forcing uncertainties. Ground-based in situ measurements on the southern Tibetan Plateau reveal unusually low aerosol hygroscopicity (κ < 0.1), much lower than the continental default of 0.3, leading to overestimation of cloud-droplet number and indirect forcing in high-altitude simulations. A region-specific parameterisation for κ corrects these biases and improves high-mountain-Asia cloud forecasts. In North China, six years of particulate-pollution control have halved PM2.5 levels, shifted composition toward more hydrophilic inorganics and reduced new-particle formation. Despite lower aerosol number concentrations, average hygroscopicity and CCN activation ratios have increased, underlining how emission policies subtly govern cloud-forming particle characteristics.

Cloud Physics publication trend

The graph below shows the total number of articles in cloud physics across all publications each year (not limited to Nature Index journals).

Technical terms

Cloud condensation nuclei (CCN): Aerosol particles on which water vapour condenses under supersaturated conditions to form cloud droplets.

Ice-nucleating particles (INP): Aerosols that trigger ice-crystal formation in supercooled clouds, affecting glaciation temperature and mixed-phase dynamics.

Hygroscopicity parameter (κ): Dimensionless measure of an aerosol’s water-uptake capacity, linking chemical composition to droplet activation.

Aerosol breeze: A meso-scale circulation driven by horizontal aerosol gradients, modulating cloud initiation and precipitation patterns.

Effective radiative forcing: Net change in top-of-atmosphere energy balance due to aerosol–cloud interactions, including rapid adjustments of cloud and circulation.

References

1. Regionally sourced bioaerosols drive high-temperature ice nucleating particles in the Arctic. Nature Communications (2023).
2. Aerosol breezes drive cloud and precipitation increases. Nature Communications (2023).
3. Radiative forcing from aerosol–cloud interactions enhanced by large-scale circulation adjustments. Nature Geoscience (2023).
4. MieAI: a neural network for calculating optical properties of internally mixed aerosol in atmospheric models. npj Climate and Atmospheric Science (2024).
5. In-situ observations reveal weak hygroscopicity in the Southern Tibetan Plateau: implications for aerosol activation and indirect effects. npj Climate and Atmospheric Science (2024).
6. The impact of particulate pollution control on aerosol hygroscopicity and CCN activity in North China. Environmental Research Letters (2023).