Interdecadal Change in the Relationship between the Winter Siberian High and Summer Tropical Cyclone Genesis Frequency over the Western North Pacific

Interdecadal change in the relationship between the winter Siberian high (SH) and tropical cyclone genesis frequency (TCGF) is investigated using observational and reanalysis data. Focus is on the Western North Pacific (WNP) where environmental background associated with TCGF is closely related to the winter SH. It is demonstrated that the relationship presents clear interdecadal change during 1980–2020. A significant negative correlation dominates in the last two decades of the 20th century (P1), but it clearly weakens from the early 2000s onward (P2). Observational evidence shows that such interdecadal change is related dominantly to variations in the air–sea responses associated with the winter SH over the North Pacific. During P1, when the SH is anomalously strengthened, an Aleutian Low (AL) response occurs over the downstream North Pacific, which gradually develops into a meridional dipole distribution pattern consistent with the negative North Pacific Oscillation (NPO) mode during the following spring. The northeasterly wind anomaly over the subtropical North Pacific maintains and further delivers into the tropical Pacific. It favors easterly wind anomaly enhancement over the tropical Pacific around summer and grows into an anticyclonic circulation response in the WNP, which restrains the genesis of TCs. During P2, the eastward shift of the SH anomaly favors a weak AL over the Northeast Pacific followed by a northeastward-shifted anticyclone over the subtropical central-eastern Pacific, which confines the relatively weak northeasterly wind anomalies far away from the tropical Pacific. This was concurrent with a weakening relationship between the SH and WNP TCGF, indicating weaker downstream impacts of the winter SH.

利用观测和再分析数据，研究了冬季西伯利亚高压（SH）与热带气旋生成频率（TCGF）之间关系的年代际变化。重点关注西北太平洋（WNP），该区域与热带气旋生成频率相关的环境背景与冬季西伯利亚高压密切相关。研究表明，在1980 - 2020年期间，这种关系呈现出明显的年代际变化。在20世纪的最后20年（P1阶段），显著的负相关占主导地位，但从21世纪初开始（P2阶段），这种相关性明显减弱。观测证据表明，这种年代际变化主要与北太平洋冬季西伯利亚高压相关的海 - 气响应变化有关。在P1阶段，当西伯利亚高压异常增强时，在下游的北太平洋会出现阿留申低压（AL）响应，在随后的春季逐渐发展成与负北太平洋涛动（NPO）模态一致的经向偶极子分布模式。北太平洋副热带地区的东北风异常得以维持，并进一步传递到热带太平洋。这有利于在夏季前后热带太平洋上东风异常增强，并在西北太平洋发展成反气旋环流响应，从而抑制了热带气旋的生成。在P2阶段，西伯利亚高压异常的东移有利于在东北太平洋形成弱阿留申低压，随后在副热带中东部太平洋出现向东北偏移的反气旋，这使得相对较弱的东北风异常被限制在远离热带太平洋的区域。这与西伯利亚高压和西北太平洋热带气旋生成频率之间的关系减弱同时发生，表明冬季西伯利亚高压的下游影响变弱。