模擬北太平洋年代際振盪與其遙相關

Abstract

北太平洋區域大氣與海洋的年代際低頻振盪影響天氣與氣候以及東亞與西北太平洋的海岸生態系統。然而北太平洋氣候除了北太平洋複雜的氣候變異性，年代際振盪的物理機制與其遙相關的連結至今也尚不明確，本研究希望藉由分析模式模擬的結果提供北太平洋氣候更清楚的結構。 研究中以被廣泛應用於分析變數特徵的經驗正交函數與波譜分析為主，分析不同時間尺度裡不同高度的變數在時間與空間上的特徵，並取解釋最多變異度的前兩個模態，以解釋三個不同的分析場：500百帕高度場、海表面氣壓與海表面溫度。北太平洋在500百帕高度場的第一個模態為 Pacific/North American Pattern (PNA)，而海表面氣壓的第一個模態則是由北邊的阿留申低壓與熱帶地區的南方振盪構成，在海表面溫度上的第一個模態的分布則是太平洋年代際振盪(Pacific Decadal Oscillation, PDO)與聖嬰現象。近年來，第二個模態也因為與生態系的密切關聯而持續受到關注，第二個模態有較低的振盪頻率，主要分布在年代際尺度，在太平洋上的表現在500百帕高度場、海平面氣壓與海表面溫度場分別是分布於西太平洋的 Western Pacific Pattern (WP)，北太平洋振盪(North Pacific Oscillation, NPO)以及北太平洋環流振盪(North Pacific Gyre Oscillation, NPGO)。透過最新的耦合模式 TaiWan Earth System Model (TWESM)，我們得以在模式中重建這些低頻振盪在空間上的分布以及遙相關，並與觀測資料和 IPCC-AR4 的模式進行比對，並依據此結果分析與西太平洋東亞地區的緣海日本海與黑潮親潮延伸流域之相關性。

Low-frequency fluctuations of the ocean and atmosphere over the North Pacific on interannual to decadal time scales significantly impact on the weather, climate and even the marine ecosystems in the East Asia and Western North Pacific. However, modeling the North Pacific climate variability remains a challenging task. It is well-known that the variability in the north Pacific is complicated, and the mechanisms behind the climate variability and its teleconnection with other basins still remain unclear. In this research, our goals are identifying and understanding these patterns and variations in the model so as to provide a completed picture of the North Pacific Climate. Empirical Orthogonal Function (EOF) has been commonly used to identify the leading modes at different horizontal levels, which change phase at annual, interannual to quasi-decadal scale. From top to the surface, the leading EOF mode of 500 hPa geopotential height is well-known as Pacific/North-American Pattern (PNA). For the Sea Level Pressure (SLP) pattern, the first EOF mode is known as Aleutian Low (AL) in the Pacific Ocean, and North Atlantic Oscillation (NAO) in the North Atlantic region. At the Sea Surface Temperature (SST) and Sea Surface Height (SSH), the corresponding pattern in the Pacific Ocean is well-known for Pacific Decadal Oscillation (PDO) in the mid-latitude and the El Nino Southern Oscillation (ENSO) in the tropics. Recently, the second modes of climate patterns raise more and more researches and they are referred as an important role on modulating the climate variability because they were highly correlated with the change of the ecosystems. The second EOF modes include low frequency oscillations in decadal scales. In the Pacific Ocean, the second mode at 500hPa, SLP and SSH(or SST) are Western Pacific (WP), North Pacific Oscillation (NPO) and North Pacific Gyre Oscillation (NPGO) respectively. We will evaluate those climate variables and teleconnection patterns in the North Pacific by using latest coupled model, TaiWan Earth System Model (TWESM). By comparing the model results with IPCC-AR4 models and observations data, we obtained a reasonable simulation. According to the simulation, we attempted to investigate the marginal maritime area in western Pacific to see if the variabilities would impact. The TWESM is able to reproduce the evolution of the leading modes in the marginal seas and with background variabilities while the hidden mechanisms still need more studies. Eventually, we anticipate to bridging the low-frequency climate variation to the global climate pattern.