CAJ | 학술논문

太平洋年代际振荡（PDO）和北太平洋涡旋振荡（NPGO）是北太平洋（20°～60°N，120°E～120°W）海温（SST）的EOF前两个模态，本文通过比较1990年前后北太平洋冬季SST EOF前两个模态，揭示了PDO和NPGO在1990年前后特征，并从关键区海温变化、北太平洋涛动（NPO）、赤道太平洋中部变暖（CPW）和北极涛动（AO）的影响，揭示了北太平洋主模态在1990年之后调整的成因。我们发现，1990年之前，北太平洋SST场的EOF前两个模态与PDO和NPGO的空间结构类似，但是在1990年之后，SST的EOF第一模态的最大荷载中心向日界线移动，40°N以北的太平洋被正的SST异常控制，表现出与NPGO模态的负位相相似的空间分布特征，而 EOF 第二模态由偶极子演变成了三极子结构。北太平洋中部（28°～36°N，152°～178°W）和北太平洋北部（44°～49°N，151°～177°W）海温距平在1990年之后呈显著的负相关变化，是导致在1990年之后冬季NPGO成为主模态的内部原因，而NPO在1990年之后的显著增强则是重要的外部原因。分析显示，NPO在1980年开始表现出增强趋势，通过风生流机制，NPO可以增强北太平洋45°N附近的气压梯度和西风异常幅度，从而导致了1990年之后NPGO海温模态的加强。虽然CPW和AO对NPO的南支（夏威夷）和北支（阿拉斯加）的海平面气压异常中心加强有贡献，但是上述两个因子与 NPGO 之间的关系在1990年之前并不明显。因此，CPW 和AO与NPGO之间并不存在稳定的物理联系。
태평양년대제진탕（PDO）화북태평양와선진탕（NPGO）시북태평양（20°～60°N，120°E～120°W）해온（SST）적EOF전량개모태，본문통과비교1990년전후북태평양동계SST EOF전량개모태，게시료PDO화NPGO재1990년전후특정，병종관건구해온변화、북태평양도동（NPO）、적도태평양중부변난（CPW）화북겁도동（AO）적영향，게시료북태평양주모태재1990년지후조정적성인。아문발현，1990년지전，북태평양SST장적EOF전량개모태여PDO화NPGO적공간결구유사，단시재1990년지후，SST적EOF제일모태적최대하재중심향일계선이동，40°N이북적태평양피정적SST이상공제，표현출여NPGO모태적부위상상사적공간분포특정，이 EOF 제이모태유우겁자연변성료삼겁자결구。북태평양중부（28°～36°N，152°～178°W）화북태평양북부（44°～49°N，151°～177°W）해온거평재1990년지후정현저적부상관변화，시도치재1990년지후동계NPGO성위주모태적내부원인，이NPO재1990년지후적현저증강칙시중요적외부원인。분석현시，NPO재1980년개시표현출증강추세，통과풍생류궤제，NPO가이증강북태평양45°N부근적기압제도화서풍이상폭도，종이도치료1990년지후NPGO해온모태적가강。수연CPW화AO대NPO적남지（하위이）화북지（아랍사가）적해평면기압이상중심가강유공헌，단시상술량개인자여 NPGO 지간적관계재1990년지전병불명현。인차，CPW 화AO여NPGO지간병불존재은정적물리련계。
The Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) are generally referred to as the first two EOF modes of Sea Surface Temperature (SST) in the North Pacific (20°–60°N, 120°E–120°W). In the present study, the authors compared the first two EOF modes of winter SST anomalies in North Pacific for the period before and after 1990. Based on the impacts of key regional SST changes, the North Pacific Oscillation (NPO), Central Pacific Warming (CPW), as well as Artic Oscillation (AO), the authors discuss the possible causes of the first mode of the NPGO after 1990. Our results suggest that before 1990, the first two EOF modes of SST exhibit the PDO and NPGO pattern, respectively. However, after 1990 the center of the maximal load of the first EOF tilts to the dateline, and gives rises to positive SST anomalies north of 40°N, resulting in a negative phase of NPGO; meanwhile, the previous NPGO changes from a dipole pattern to the triple mode. Analyses suggest that the negative correlation between the changes of SST in the northern (44°–49°N, 151°–177°W) and central (28°–36°N, 152°–178°W) North Pacific could have resulted in the internal shift of the dominant SST modes after 1990. Evidence shows that the NPO played an important external forcing in enhancing the NPGO after 1990. Based on wind-driven oceanic current theory, the increased amplitude of NPO in Sea Level Pressure (SLP) may intensify the polar gradient of the SLP along 45°N, enhancing the zonal sea surface winds, and causing the NPGO mode to prevail after 1990. The increase in CPW and AO may have enhanced the NPO by intensifying the southern and northern branch of the NPO in Hawaii and Alaska after 1990, but there is no evidence to show that both these factors were closely related to the NPO before 1990.