Isolating aerosol particle effects on precipitation in data is tricky because aerosol-precipitation interactions work both ways. This is because most aerosol particles are removed from the atmosphere by precipitation. Moreover, winds associated with precipitation are a major source of natural aerosol particles, both over deserts (dust) and over the ocean (sea salt), and the optical signature of the aerosol particles (aerosol optical depth) increases as the aerosol swells with accumulated water when relative humidity is high during rainy conditions.

Recently a team including researchers from at the Scripps Institution of Oceanography at the University of California – San Diego and scientists at the DOE’s Pacific Northwest National Laboratory applied a partial correlation analysis to two long climate simulations. One of the simulations had prescribed sea salt emissions and one had sea salt emissions that fluctuate depending on surface wind speed. Precipitation is lighter during polluted conditions in both simulations, partly because increasing amounts of aerosols suppress precipitation, and partly because fewer aerosol particles are scavenged (removed) from the atmosphere when there is less precipitation. But the team found that the rain-aerosol linkage is much stronger when sea salt emissions are prescribed. This stronger link suggests that the increase of wind speed associated with storms comes with a number of effects: it increases sea salt emissions and diminishes the reduction in aerosol particles due to precipitation removing them from the cloud.

Researchers in this study found that wind speed makes a large contribution to the rain-aerosol relationship by changing sea salt emissions.