The Impact of Microphysics Schemes on Typhoon Simulation

• Main Authors: Tsan-Chu Hsieh, 謝璨筑
• Other Authors: 陳正平
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/53677037759337034759

碩士 === 國立臺灣大學 === 大氣科學研究所 === 103 === Through the use of double-moment bulk scheme with aerosol activation process, this study was expected to realize the impact of microphysics schemes on typhoon simulation. For simulating typhoon USAGI and TRAMI (2013), this study selected WDM6, Morrison and CLR schemes and set different background aerosols number concentrations. The results showed that background aerosols number concentrations and microphysics schemes (MPs) themselves would influence the tracks, intensities and microphysical structures of typhoon USAGI and TRAMI. The differences of the simulated synoptic-scale systems with those MPs were small. However, those MPs used in this study applied different methods to the formation and phase transform processes of hydrometeors, which might influence the latent heat distribution of typhoon. Therefore, that result would affect typhoon’s track, moving speed and intensity. Besides, comparing the simulation results of two typhoons with different intensities, the simulation results of typhoon TRAMI with weaker intensity exist larger differences from those MPs. In terms of typhoon’s track, the results of TRAMI exist larger differences from different MPs causing small scale differences. The asymmetric distribution of latent heat release may further influence the moving directions and speeds of the simulated typhoon. For instance, a stronger latent heat release at the south side leads to a southward movement of the simulated typhoon. In terms of different MPs, the intensities results of using WDM6 scheme to simulate typhoon USAGI and TRAMI exist the strongest intensity. This result was related to the rapid cloud drops autoconversion process and more rain from more graupel melting process which might cause more latent heat concentrating at the center of typhoon. Besides, from simulations using CLR scheme we demonstrated significant aerosol impact on typhoon. For instance, urban type aerosol tends to produce more but smaller cloud drops, which lead to stronger mixed-phase processes and thus a stronger latent heat release. This effect is more obvious at TC’s outer rainbands, such that the enhancement of the outer rainband disrupted the moisture transport into the TC center. In consequence, urban type aerosol makes the typhoon weaker than that with marine type aerosol. Finally, this study further discussed how cloud-radiative interaction processes may possibly influence the tracks and intensities of the simulated typhoon. In the USAGI case, shortwave radiation in the atmosphere did not show significant differences between the northern and southern parts of the typhoon center. However, CLR_marine showed larger differences in atmospheric longwave radiation between the northern and southern parts of the typhoon center. This resulted in cooling to the north of typhoon center but warming to the south, and this favored typhoon’s moving southward. In the TRAMI case, shortwave radiation in the atmosphere showed significant differences between northern and southern parts of the typhoon center. Among different microphysical schemes, the CLR scheme simulated more downward shortwave radiation to the north of the typhoon center, which favored northward movement of typhoon. However, that scheme also simulated more upward longwave radiation to the north of the typhoon center, which was unfavorable for northward movement of typhoon. The combined effect of latent heat and radiation effects using the CLR scheme simulated a net northward track in TRAMI case. However, this study did not include a full coupling of the radiation scheme with the ocean, so no definite conclusion can be made regarding the cloud-radiative effects on the track and intensity of typhoon.