Abstract
摘要:本兩年計畫之重點有兩大項目:(I)中尺度數值模式熱力學的改善與颱風熱效率理論,以及(II)延伸過去研究成果,持續探討中尺度激烈天氣系統的動力。熱力學項目為新研究構想,首次提出;由於參與計畫的博士學生參加國科會千里馬計畫,因此本計畫會和Colorado State University的W.H. Schubert教授以及UCLA Fovell教授合作。
在中尺度數值模式熱力學改善部分,我們將利用Ooyama (1990) 以及 Ooyama (2001) 所提出之目前最精確的熱力學模式架構, 推導包含降水物理過程的濕可用位能。並且將Ooyama(1990)之完整原始熱力模式架構應用在WRF(the Weather Research and Forecasting model)中,使模式之熱力過程更加準確(雲物理也可以更精確),並能透過高解析度的模擬,直接模擬小尺度的積雲對流過程,更進一步瞭解颱風雙眼牆之形成過程,以及眼牆附近小尺度的物理過程,如:雲對流、沈降作用、逸入(entrainment)等過程對於颱風渦度產生以及颱風強度的影響,進而增進颱風強度預報之能力。我們也計畫將所推導出的濕可用位能應用在分析颱風的研究, 延續 Hack and Schubert (1986), 探討透過濕可用位能對於颱風的加熱效率.此部分的工作會與Colorado State University的W.H. Schubert教授合作。我們工作將以Kuo and Cheng (1999) 為基礎,探討time-splitting 和熱力學的結合。
中尺度激烈天氣系統的動力研究方面,在未來兩年內將持續過去的研究,針對以下三個方向:(1)局部高層輻散場激發中尺度劇烈對流之探討:我們觀察到深對流的前緣常伴隨著局部區域的輻散場,因此想要探討此局部輻散場與深對流發展的關係,這部分模式工作也將和UCLA Fovell教授合作。(2)強旋轉流場下的濕對流發展與颱風強度變化的關係:颱風渦旋所伴隨的強旋轉會產生帶狀化的拉伸效應,而產生單一分散的對流胞,我們想要探討颱風渦旋對於對流系統發展的影響。(3)二維亂流以及能量頻散和不穩定度間的關係:持續探討雙眼牆形成動力,非絕熱加熱會激發出慣性重力波,慣性重力波能量頻散將會移除不穩定系統中的能量,從而減緩正壓不穩度的釋放,我們計畫將進一步探討重力波和渦旋不穩定度間的關係,我們也將探討羅士比波非線性的能量頻散。以上三個方向所涉及的論文都是國際上很新的研究工作,引用的論文有的方發表,有的則尚在審查或印刷當中,目的是希望能深入了解豪雨發生的原因,了解豪雨過程和颱風渦旋的交互作用,建立豪雨系統生命期包括形成、發展、維持、以及消散過程之物理特徵,作為數值模式參數化所需參數設定的基礎,以期能有效改善現有定量降雨預報能力。
Abstract: We propose to work in the following area of interests: implementation of a new thermodynamics framework in the mesoscale model such as WRF, and the severe weather dynamics research.
The thermodynamic scheme proposed by Ooyama (1990, 2001) is the state-of-the-art thermodynamic form. Moist entropy is used as a conservative prognostic parameter in the model scheme. The prognostic parameters contain momentum, mass density of dry air, moist specific entropy, total airborne water mixing ratio, and the mixing ratio of precipitation. Associated with the prognostic equations is a set of diagnostic equations to determine other thermodynamic parameters such as pressure and temperature. The model performance results are referred to Ooyama (2001) and Hausman et al. (2006). We will collaborate with Prof. Wayne Schubert of Colorado State University to implement this thermodynamic scheme into the prevailing mesoscale model – WRF. We also intend to derive the moist available energy based on this thermodynamics and derive a more general heating efficiency (following the Hack and Schubert 1986) for the typhoon dynamics. Our starting point will be Kuo and Cheng (1999); the thermodynamics with time-splitting technique.
The severe weather dynamics research may cover the following three areas (1) The impact of local upper level divergence on the development of the new convections. This local divergence in the upper level may stem from the undiluted air mass from the boundary layer. We will use a cloud model to simulate the dynamics. This portion of work will collaborated with Prof. Fovell of UCLA. (2) We propose to study the mesoscale convective systems in the vortex environment under strong and weak strain and rotational effects. The development of the systems are important for development and intensification of tropical cyclones. The upscale transfer of energy from the convective systems in the cyclone environment may also be crucial to the genesis and intensification of TCs. (3) We will investigate the typhoon vortex dynamics in the framework of the two-dimensional turbulence. In particular, we will study the formation of the concentric eyewalls; the energy dispersion by Rossby waves and by the inertial gravity waves. We will study the vortex dynamics with instability in the presence of the strong energy dispersion.
Keyword(s)
濕可用位能
加熱效率
帶狀化動力
渦旋能量頻散
moist available potential energy
heating efficiency
filamentation dynamics
vortex energy dispersion