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

Baolin Jiang,Junwen Chen,Dongdong Wang,Wenshi Lin,Xiaodian Shen

doi:10.1038/s41598-019-51757-x

Baolin Jiang, Junwen Chen + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-51757-x

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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.

Highlights

This study aims to improve the understanding of the influence of sea salt aerosols (SSA) on precipitation and the upper troposphere/lower stratosphere (UT/LS) water vapour content in a tropical cyclone (TC) system by focusing on the following questions: how do cloud microphysical processes respond to SSA? How does the precipitation change? How does the UT/LS water vapour change under the effect of SSA?
We studied the effect of SSA on cloud microphysical processes and the precipitation of the TC Hato using the WRF-Chem model, with the focus on the influence of SSA on precipitation and the water vapour of the UT/LS layer
Two simulation experiments denoted as control experiment (CTL) and CLEAN are so defined according to their sea salt emission intensity

Summary

Model Description and Experimental Design

We used the Weather Research and Forecasting with Chemistry (WRF-Chem) model version 3.5.1, which is a fully-compressible and non-hydrostatic Euler model, employing dry hydrostatic terrain-following pressure for the vertical coordinate, an Arakawa C-grid staggering[49] for the horizontal grid, and a Runge–Kutta time integration scheme[50]. The accretion of cloud water by rain and the auto-conversion rate of cloud water of the CTL experiment exceeds that of the CLEAN experiment because the conditions are more favourable to the increase in cloud water number concentration and mixing ratio in the CTL experiment As these two processes consume cloud water and produce rainwater, their enhancement increases the precipitation of the eyewall area and mixing ratio of rainwater in the CTL experiment (Fig. 9). In the troposphere below 17 km, the cloud ice deposition growth rate of the TC in the CTL experiment exceeds that of the CLEAN experiment, so the former consumes more water vapour within the tropopause, which dries the lower stratosphere. The enhancement of cloud ice deposition growth, which consumes more water vapour in the upper troposphere in the CTL experiment compared with the CLEAN experiment, enhances air drying

Summary and Discussion

Findings

Additional information