以對流建構準兩年震盪簡化模型

本研究的目標是想瞭解對流與準兩年震盪在雲解析模式中的交互作用，特別針對準兩年震盪下，緯向風如何影響對流，以及對流引發的重力波如何影響准兩年震盪的發展。為了聚焦在對流與準兩年震盪的關係，Yoden等人(Yoden et al., 2014)利用了理想的雲解析模式當作模擬真實世界準兩年震盪動力的最小模式。我們參考了他們部分的實驗設計，利用三維的渦度方程雲解析模式進行模擬(Jung Arakawa, 2008)，為了讓對流的發展更為真實，我們也擴大了空間範圍(1024公里對比640公里)並提高空間上的解析度(2公里對比5公里)。在我們的模擬中，前期的兩個震盪為西風極強的不對稱震盪，後期的兩個震盪發展則較為對稱。在研究不對稱震盪中東西風相位對流的差異時，我們發現在強上升對流雲數量上不太相同的兩種對流型態，其中一種是發生在強風切、高水氣環境下，逆風向前進的組織對流；另一種是在相位交替、風切弱與平均水氣低的環境中，發展成較為聚集的對流。聚集對流會產生比組織對流還要多的強上升對流雲並導致更快速的相位轉換，因此在兩種環境差異的影響下，產生了我們的模擬中看見的不對稱震盪現象。

關鍵字

準兩年震盪；雲解析模式；組織對流；聚集對流；對流引發重力波；垂直風切

並列摘要

This study investigates the interaction between convection and quasi-biennial oscillation (QBO) in an idealized cloud-resolving model. We focused on how zonal wind under QBO modulates the convection and how convectively generated gravity waves influence the evolution of QBO. To extract the critical interaction between QBO and convection, Yoden et al. (2014) used idealized cloud-resolving simulations as a minimal model for the dynamics of real-world QBO. Following their experiment setup, we use the three-dimensional vector-vorticity equation cloud-resolving model (VVM) (Jung Arakawa, 2008) with extended horizontal domain size (1024 km vs. 640 km) and high horizontal resolution (2 km vs. 5 km) to evaluate the impact of convective variabilities to the QBO-like oscillation in the model. Our results show asymmetric oscillations with extremely strong westerly phases in the first two cycles and symmetric oscillations in the last two cycles. When exploring the difference in convection structures in asymmetric oscillations, we found two kinds of convective structures with different numbers of convective core clouds based on their convective structures. One is the organized convection which evolves upstream under strong vertical wind shear and high column water vapor in the domain. The other is the aggregated convection in the domain with weak vertical wind shear, and low averaged column water vapor, especially in the phase transition periods. The aggregated convection creates more convective core clouds than the organized convection leading to a faster transition of the QBO phases. Therefore, the difference between the two kinds of environments results in the asymmetric oscillation in our simulation.

並列關鍵字

quasi-biennial oscillation ； cloud-resolving model ； organized convection ； aggregated convection ； convectively generated gravity waves ； vertical wind shear

參考文獻

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