Vol.16 No.4 JOURNAL OF TROPICAL METEOROLOGY December 2010 Article ID: 1006-8775(2010) 04-0390-12 A SENSITIVITY SIMULATION ABOUT CLOUD MICROPHYSICAL PROCESSES OF TYPHOON CHANCHU 1 1 1 2 LIN Wen-shi (林文实) , WU Jian-bin (吴剑斌) , LI Jiang-nan (李江南) , LIANG Xu-dong (梁旭东) , FANG 1 1 Xing-qin (方杏芹) , XU Sui-shan (徐穗珊) (1. School of Environmental Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275 China; 2. Shanghai Typhoon Institute, China Meteorological Administration, Shanghai 200030 China) Abstract: With the Reisner-2 bulk microphysical parameterization of the fifth-generation Pennsylvania State University–U.S. National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5), this paper investigates the microphysical sensitivities of Typhoon Chanchu. Four different microphysical sensitivity experiments were designed with an objective to evaluate their respective impacts in modulating intensity forecasts and microphysics budgets of the typhoon. The set of sensitivity experiments were conducted that comprised (a) a control experiment (CTL), (b) NEVPRW from which evaporation of rain water was suppressed, (c) NGP from which graupel was taken, and (d) NMLT from which melting of snow and graupel was removed. We studied the impacts of different cloud microphysical processes on the track, intensity and precipitation of the typhoon, as well as the kinematics, thermodynamics and vertical structural characteristics of hydrometeors in the inner core of the typhoon. Additionally, the budgets of the cloud microphysical processes in the fine domain were calculated to quantify the importance of each microphysical process for every sensitivity experiment. The primary results are as follows: (1) It is found that varying cloud microphysics parameters produce little sensitivity in typhoon track experiments. (2) The experiment of NGP produces the weakest storm, while the experiment of NMLT produces the strongest storm, and the experiment of NEVPRW also produces stronger storms than CTL. (3) Varying parameters of cloud microphysics have obvious impacts on the precipitation, kinematics, and thermodynamics of the typhoon and the vertical structural characteristics of hydrometeors in the typhoon’s inner core. (4) Most budgets of cloud microphysics in NMLT are larger than in CTL, while they are 20%–60% smaller in NEVPRW than in CTL. Key words: Typhoon Chanchu; cloud microphysics; simulation CLC number: P444 Document code: A doi: 10.3969/j.issn.1006-8775.2010.04.011 1 INTRODUCTION 10, 11] was developed approximately 20 years ago when coarser resolution models were in use, and it is not In recent years, it has become more and more known whether these observations are still popular to use explicit cloud microphysics in [3] [1-3] representative of tropical cyclones. Recently, Wang modeling tropical cyclones . In high-resolution conducted a series of sensitivity experiments with models, bulk microphysical parameterization (BMP) idealized initial conditions to study the effects of schemes play a particularly important role in the varying cloud microphysical processes on tropical model-produced quantitative precipitation forecast cyclones, and found that although neither the (QPF)[4]. Braun and Tao[2] modified the Goddard [5] intensification rate nor intensity of the typhoon is microphysical scheme in their simulations of sensitive to the parameterizations of cloud Hurricane Bob to have more accurate representation microphysics, the cloud structures and the peak and of conditions observed in tropical cyclones. [6] area coverage of precipitation in the simulated tropical McFarquhar and Black pointed out that the majority cyclone are quite sensitive to the details of the cloud of current microphysical schemes are based on microphysics parameterization in the model. microphysical observations obtained in midlatitudes[7, 8] [9, Sensitivity studies of numerically simulated tropical . The basis for most bulk parameterization schemes cyclone convection to ice-phase microphysical Received date: 2010-01-11; revised date: 2010-08-30 Foundation item: National Science Foundation of China (40775066); Shanghai Typhoon Research Foundation (2008ST07) Biography: LIN Wen-shi, associate professor, Ph.D., mainly undertaking the research with numerical simulation. E-mail for corresponding author: [email protected] No.4 LIN Wen-shi (林文实), WU Jian-bin (吴剑斌) et al. 391 parameters showed that the model was sensitive to microphysical budget, which is different from the changes in the graupel fall speed parameters[12]. Zhu previous works. and Zhang[13] (hereafter referred to as ZZ) found that The remainder of this paper is organized as varying cloud microphysics processes produce little follows. Section 2 describes the setup of sensitivity sensitivity in hurricane track, except for very weak experiments. Section 3 describes the simulation and shallow storms, but they produce pronounced results and impacts of microphysics on the track, departures in hurricane intensity and inner-core intensity, precipitation, propagation speed, kinematics structures. McFarquhar et al.[14] indicated that the and thermodynamics, vertical structural characteristics, application of bulk ice microphysics in cloud models and the microphysical processes of simulated might be case specific, and microphysical sensitivity Typhoon Chanchu. The significance of the results is studies for other cloud systems may not apply to summarized in section 4. hurricanes. They conducted simulations of Hurricane Erin (2001) with MM5 to examine roles of 2 SYNOPTIC OVERVIEW OF TYPHOON microphysical, thermodynamic, and boundary-layer CHANCHU processes in hydrometeor distributions and in the structure and evolution of Erin and showed that the Typhoon Chanchu formed in the western Pacific simulated intensity of Erin is insensitive to the choice on 8 May, 2006 about 420 km west-southwest of Yap of microphysical parameterization schemes and Islands and acquired the name Chanchu at 1200 coefficients used to describe graupel fall velocities. (Coordinated Univeral Time, UTC hereafter) on 9 [15] Pattnaik and Krishnamurti (hereafter referred to as May. At 0600 UTC 10 May, it continued to intensify PK) studied the impacts of cloud microphysical into a tropical storm as it tracked predominantly processes on the track, intensity, precipitation, west-northwestward along the southern periphery of a propagation speed, kinematics and thermodynamics of subtropical ridge. It was upgraded to a typhoon at the typhoon, and vertical structural characteristics of 1800 UTC 10 May. Chanchu made its first landfall in the hurricane inner core. Their major findings are that the Philippines on 11 May with sustained winds of the inter-conversion processes such as melting and around 33 m s-1. It then moved towards the northwest evaporation among hydrometeors and associated after coming ashore, passing to the southeast of feedback mechanisms significantly modulate the Manila. Tracking mainly towards the west-northwest, intensity of the hurricane. Therefore, an evaluation of it traversed the central Philippines and re-strengthened the impact of cloud microphysics parameterization on despite the hindering effects of land. The storm tropical cyclone structure and intensity in a emerged into the South China Sea early on 13 May three-dimensional tropical cyclone model is required. where it slowly began to reorganize. Drifting Although these previous works have also westwards, Chanchu underwent rapid intensification demonstrated that varying cloud microphysics over the South China Sea on 14 May. It abruptly processes have impacts on the track, intensity, veered north at 0000 UTC 15 May. It remained a structure, surface precipitation, and the hydrometeor powerful system for the next two days while moving [3, 13, 14, 15] profiles of the tropical cyclone , the on a north to north-northeasterly trajectory through variations of the cloud microphysical processes affect the South China Sea towards the Chinese coast, away first the production and depletion of a specific from Hong Kong. The typhoon made landfall again hydrometeor category, the size distribution and fall near Shantou, Guangdong province, late on 17 May speed of the hydrometeors, and then the release of with the maximum surface wind (MSW) estimated at latent heat, and ultimately the thermodynamics and 38 m s-1. Chanchu continued its northward movement dynamics fields and the strength of the storm. along the coastal areas of neighboring Fujian province Therefore, it is necessary to calculate the conversion during daytime on 18 May, bringing gale-force winds rate of a specific microphysical process in simulating and rainstorms to the regions and triggering flooding, tropical cyclones in order to assess the sensitivity of mountain torrents and landslides. It had weakened to a these simulations to variations in some of the tropical storm at 0000 UTC, 18 May. That evening, it underlying assumptions in the cloud microphysics entered the East China Sea and became an scheme. In this paper the authors not only investigate extratropical cyclone. impacts of different cloud microphysics parameters on the track, intensity, structure, surface precipitation, 3 SETUP OF SENSITIVITY EXPERIMENTS and the hydrometeor profiles of the tropical cyclone, but also calculate the conversion rates of a specific The model to be used for the simulation is the microphysical process and compare among them in fifth-generation U.S. National Centers for different cloud microphysics parameters. The main Atmospheric