Effects of sea salt aerosols on precipitation and upper troposphere/lower stratosphere water vapour in tropical cyclone systems

Abstract

The effects of sea salt aerosols (SSA) on cloud microphysical processes, precipitation, and upper troposphere/lower stratosphere water vapour in tropical cyclones were studied with the Weather Research and Forecasting with Chemistry model. Two numerical experiments were conducted: a control experiment (CTL) and an experiment with sea salt emission intensity one-tenth of that in the CTL experiment (CLEAN). Results show increased SSA concentrations, increased production rates of auto-conversion of cloud water to form rain, and increased accretion of cloud water by rain in the CTL experiment, leading to an increase in the precipitation amount. The peak value of precipitation is ~17 mm/h in the CTL experiment and ~13 mm/h in the CLEAN experiment, a difference of ~30%. The CTL experiment has more intense vertical movement in the eyewall and thus more water vapour is transported to the upper atmosphere, which promotes cloud ice deposition. This process consumes more water vapour, which makes the CTL experiment drier in the upper troposphere/lower stratosphere layer (altitude above 17 km). At 18–20 km altitude, the domain-averaged water vapour mixing ratio of the CTL experiment is ~0.02 ppmv lower than that of the CLEAN experiment. SSA have the effect of strengthening tropical cyclones and increasing precipitation.