A numerical simulation of the effect of the number concentration of cloud droplets on Typhoon Chanchu |
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| Authors: | WenShi Lin Suishan Xu C-H Sui |
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| Institution: | 1. School of Environmental Science and Engineering, Sun Yat-sen University, 510275, Guangzhou, People??s Republic of China
2. Institute of Hydrological and Oceanic Sciences, National Central University, Jhongli, 32001, Taiwan
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| Abstract: | In recent years, an increase in the number of anthropogenic aerosol particles has raised the global mean content of aerosol particles in the atmosphere from that of preindustrial times. The indirect effects of aerosols on weather and climate cannot be ignored. In this paper, the fifth generation Pennsylvania State University (PSU)?CNational Center of Atmospheric Research (NCAR) Nonhydrostatic Mesoscale Model (MM5) is used to simulate Typhoon Chanchu (international designation: 0601), which affected the northwest Pacific. Simulations are conducted in three two-way nested domains with Mercator map projection. The horizontal grid resolutions of the three domains are 27, 9, and 3?km. A period of 60?h is simulated. Surface and rawinsonde conventional observation data and ocean wind data are additionally incorporated into the initialization data. A control (CTL) experiment is run to produce a reasonable forecast. We change the parameter of the cloud condensation nuclei (CCN) concentration (CNP) in the Reisner-2 scheme of the CTL experiment (the default value is 100?cm?3) to conduct two sensitivity experiments. They are the very clean marine (VCM) CNP experiment (CNP?=?25?cm?3) and the severe contamination (SC) CNP experiment (CNP?=?1,000?cm?3). We investigate the effects of the CNP on Typhoon Chanchu by comparing and analyzing the simulation results of the three experiments in terms of the track, intensity, precipitation, vertical structure, and microphysical processes. The main results show that Typhoon Chanchu slightly weakens as the CNP increases. Increasing the CCN to 1,000?cm?3 results in less graupel, rainwater, and cloud ice but more cloud water. However, the mixing ratio of snow does not distinctly change as the CNP changes. Increasing the CCN leads a rapid decrease in the autoconversion of cloud water to rainwater. There is no autoconversion of cloud water to rainwater in a seriously polluted continental air mass. As the CNP increases, there is more condensation, evaporation, accretion of cloud water by rainwater, and precipitation fallout. Finally, a seriously polluted continental air mass can result in distinctly lower precipitation efficiency. |
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