More or Less: How Do Inhomogeneous Sea‐Salt Aerosols Affect the Precipitation of Landfalling Tropical Cyclones?

• Published in: Geophysical research letters Vol. 49; no. 3
• Main Authors: Zhu, Limin, Shu, Shoujuan, Wang, Zheng, Bi, Lei
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.02.2022
• Subjects: Aerosols; Air; Atmospheric models; Atmospheric precipitations; Atmospheric stability; Coastal zone; Cooling; Cooling effects; Cyclones; Dry air; Hurricanes; Inhomogeneity; Low humidity; Mathematical models; Numerical models; Optical properties; Precipitation; Precipitation forecasting; Radiation; Rain; Raindrop velocity; Rainfall; Rainfall simulators; Relative humidity; Salts; sea‐salt aerosol; Simulated rainfall; Simulation; Stability; Tropical climate; tropical cyclone; Tropical cyclone rainfall; Tropical cyclones; Troposphere; Typhoons; Velocity; Vertical velocities; Weather forecasting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097023

The evolution of landfalling Typhoon Fitow in the western North Pacific in 2013 is simulated with an emphasis on the direct radiative effect of sea‐salt aerosols (SSAs) on the precipitation of Fitow. The inhomogeneous SSAs, formed under the environment with low relative humidity (50%–70%), exhibit different optical properties (particular the decreased asymmetry factor) compared with the commonly used homogeneous sea‐salt droplets. We find that incorporating the inhomogeneity of SSAs in the Weather Research and Forecasting (WRF) model decreases the simulated rainfall of Fitow in coastal regions where the continental dry air intrudes. Fundamentally, the cooling effect induced by the particle inhomogeneity and its hysteresis increase atmospheric stability and weaken vertical velocity, which reduce the accumulated rainfall of Fitow. These findings of radiation‐related effects of SSAs provide a new clue for improving the physical processes responsible for precipitation of tropical cyclones in numerical models. Plain Language Summary For the landfalling tropical cyclones (TCs) over the western North Pacific, the intrusion of dry air into the TCs is extensive and significant since the dry air may come from both a high‐pressure system and the dry mid‐to‐high‐latitude continent. Under the dry environment, the sea‐salt aerosols (SSAs) appear to be coated inhomogeneous spheres according to previous findings. However, the physical process associated with the inhomogeneity of the SSAs has never been considered in both research and operational forecast of TCs, which may partly account for the discrepancy between simulation (or forecast) and observation of TCs. This study explores the direct radiative effects of inhomogeneous SSAs on the precipitation of a landfalling TC in 2013 first, and reveals that the cooling effect associated with the inhomogeneity of SSAs increases the stability of the low‐level troposphere and weakens the vertical velocity, which finally suppresses the total rainfall of the TC in the coastal regions, suggesting that the inhomogeneity of SSAs should be carefully considered in numerical models for improving the precipitation forecast of landfalling TCs. Key Points Direct radiative effects of inhomogeneous sea‐salt aerosols (SSAs) on the precipitation of a landfalling tropical cyclone (TC) are explored Incorporating the inhomogeneity of SSAs enhances atmospheric stability, weakens vertical velocity and reduces the rainfall of the TC The results provide a new clue to improve the physical processes responsible for precipitation associated with TCs in numerical models