Dynamics of Typhoon Intensity - Sensitivity to PBL Processes and the Superintensity Behavior

• Main Authors: Treng-Shi Huang, 黃椿喜
• Other Authors: Chieh-Chun Wu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/19638733609451594881

博士 === 國立臺灣大學 === 大氣科學研究所 === 97 === In this paper we examine the simulated tropical cyclone (TC) structure in a full-physics but highly idealized three dimensional model to examine the accuracy of Potential Intensity (E-PI) developed by Emanuel in a three dimensional context. In the first part of the thesis work, we focus on the sensitivities of the simulated TC intensity to the planetary boundary layer (PBL) schemes. Both the equivalent Ck and CD calculated from a more sophisticated PBL scheme, such as the Blackadar and Burk-Thompson PBL schemes, are employed in a modified bulk aerodynamic PBL scheme. The simulated TC intensity and structure strongly resemble those produced by the Blackdar and Burk-Thompson PBL schemes. Based on these works it is suggested that a simple PBL scheme, such as bulk-aerodynamic PBL scheme, with equivalent Ck and CD curves can produce consistent TC intensity with those based on more complicated schemes. This result provides useful physical insights into the vital role of the Ck and CD in determining the TC potential intensity regardless of the detailed representation of the boundary layer parameterization. In the second part of the thesis work, the superintesity behavior as described by Persion and Montgomery (2003) is demonstrated in the simulation with Typhoon intensity exceeding E-PI It is hypothesized that superintensity occurs only with the presence of enhanced low-level eye entropy as indicated by the high equivalent potential temperature in the eye. The high-entropy air is entrained into the eyewall primarily by a breakdown of an azimuthal vortex sheet at the inner edge of the eyewall. It is found that superintensity of a factor of two is shown in both experiments with bulk aerodynamic and with Blackadar PBL schemes. A portion of the low-level inflow moves inward in the PBL under the eyewall and enters the eye, acquiring enhanced entropy through interaction with the ocean beneath the eye. Strong mixing between the low level eye and eyewall below the inversion layer in the eye is identified, fueling the eyewall air with extra entropy from the eye. Meanwhile, the process of inner-core intensification is not in gradient wind balance different from the process of outer region intensification. Supergradient wind is present only in the the region of small radius with large inflow speed, especially in the PBL where the Coriolis force torque exceeds the friction torque. It is shown that the dynamical process based on the gradient wind balance is not valid in the inner-core region.