Increased aerosols can reverse Twomey effect in water clouds through radiative pathway.

Area of Science:

• Atmospheric Science
• Cloud Physics
• Aerosol Science

Background:

• Aerosols influence cloud properties and the hydrological cycle.
• The Twomey effect describes how aerosols decrease cloud droplet size with fixed liquid water path.

Purpose of the Study:

• To investigate how aerosols affect cloud droplet size beyond the microphysical effect.
• To explore the dual role of aerosols in cloud droplet size modulation.

Main Methods:

• Utilized high-quality surface aerosol observation data.
• Statistically decoupled meteorological factors to isolate aerosol influences.
• Analyzed relationships between aerosol loading, liquid water path, and cloud droplet size.

Main Results:

• Highly loaded aerosols can counteract the microphysical effect via radiative effects.
• Cloud droplet size can increase or decrease with aerosol loading, depending on liquid water path.
• Radiative effects promote droplet coalescence in thicker clouds, increasing droplet size with aerosol loading.
• In thinner clouds, the microphysical effect dominates, decreasing droplet size with aerosol loading.

Conclusions:

• Both negative and positive relationships between cloud droplet size and aerosol loading exist in polluted regions.
• Aerosol radiative effects significantly modulate cloud microphysics, challenging the universal applicability of the Twomey effect.
• Cloud thickness is a critical factor in determining the net effect of aerosols on cloud droplet size.