Simulations Of Anthropogenic Emissions Effects On Typhoon Fitow (201323) Using WRF-Chem Model

To investigate the impacts of anthropogenic aerosols on Typhoon Fitow,the twenty-third typhoon in 2013, three simulations with zero, normal and increased anthropogenic emissions are conducted by using WRF-Chem V3.5, in which the meterology and chemistry modules are fully coupled online. The results of the Control test are verified of reliable by comparing simulated typhoon tracks, intensity and precipitation with observations.Comparison of the results shows that anthropogenic aerosols hardly influence the track of Fitow. The increased anthropogenic aerosols lead to weakened intensity,reduced total accumulated precipitation in typhoon main body, and decreased precipitation rate in typhoon main body during the approaching land phase of Fitow.As to the distribution of precipitation in typhoon main body, it decreases in eyewall but increases in periphery area.The aerosols concentration increases in the active area of Fitow thanks to the raised anthropogenic emission intensity, and the preipgery is the area where the concentration increases evidently in typhoon main body. Increased aerosols can provide more cloud condensation nuclei, which leads to increased cloud droplet number concentration and cloud water at the periphery. Therefore, more cloud water can rise above the freezing level producing more supercooled water, which provides an advantage for the forming of ice particles and rain water. These processes not only release extra amount of latent heat, but also enhance the convection and precipitation at the periphery of typhoon.What’s more, the invigorated convection at periphery causes an increase of warm and moist air lifted there, and a decrease of inflow reaching typhoon inner core,and hence results in weakened eyewall, hydrometeors and precipitation near eyewall,and the strength of typhoon is weakened. Thanks to the weaker convection at periphery, comparing to the convection at eyewall, precipitation at eyewall still dominates the precipitation of typhoon main body. So, total accumulated precipitation and precipitation rate in typhoon main body are both decreased.The weakened typhoon shows weakened warm core, and loosely organized horizontal structure. Typhoon eyewall does not encircle the eye completely, of which the cyclonic rotation is also weakened.