非线性阻塞指数的定义与应用  

Definition and application of nonlinear blocking index

作　　者：汪梦凌 孔海妹 李银娥 WANG Mengling;KONG Haimei;LI Yin'e(Hubei Meteorological Observatory,Wuhan 430074,China)

机构地区：[1]湖北省气象台,湖北武汉430074

出　　处：《大气科学学报》2025年第2期312-327,共16页Transactions of Atmospheric Sciences

基　　金：湖北省自然科学基金青年项目(2023AFB541);湖北省气象局青年基金项目(2023Q01);湖北省气象局科技发展基金项目(2021Z02)。

摘　　要：利用反气旋式局地有限振幅波作用量(anti-cyclonic local finite-amplitude wave activity,ALWA)定义了冬季北大西洋和乌拉尔山区域的瞬时阻塞指数I_(BA)。I_(BA)是基于准地转位势涡度(quasi-geostrophic potential vorticity,QGPV)的非线性物理量,反映了任意QGPV对于无扰动参考态的极向偏移程度以及任意振幅波动与温带急流在时空上的反相关关系,故其不仅涵盖了传统2类阻塞指数的特点,即同时描述西风翻转和振幅异常,而且弥补了传统指数对急流时空变异性描述的不足,防止了对切断低压、弱槽以及副热带、副极的虚假系统的错误识别。最重要的是,I_(BA)具有动力学意义,可以直接通过其收支方程对阻塞系统的变化进行定量诊断。本文给出了冬季北大西洋和乌拉尔山区域的I_(BA)阈值。通过计算基于I_(BA)的阻塞事件的各参数趋势,发现乌拉尔山阻塞的发生频率和阻塞总天数自1990年之后存在显著的增加。在年际尺度上,北大西洋阻塞的变率与NAO(North Atlantic Oscillation)呈显著的负相关关系,NAO负位相时期阻塞频率更高、强度更强、生命史更长;而乌拉尔山阻塞的变率则与EA/WR(East Atlantic/West Russia)以及ENSO(El Ni1o-Southern Oscillation)循环存在显著的负相关关系,其频率在EA/WR负位相和La Ni1a位相时期更高,生命史在EA/WR负位相时期更长,且均对应着强烈发展的槽脊和明显的东亚冷空气活动。Atmospheric blocking is a significant large-scale anticyclonic circulation system in midlatitude,characterized by prolonged duration beyond synoptic timescales and strong nonlinearity.Blocking events often occur at the exit of jet stream,exerting substantial meteorological impacts such as cold surges,heat waves,and flooding,and pollutants stagnation,both locally and downstream.Understanding blocking dynamics is thus of critical scientific and practical importance.Since the 1950s,extensive observational and statistical studies have been conducted to characterized blocking patterns,leading to the development of multiple detection indices.These indices generally fall into two main types:one capturing the meridional gradient reversal of the zonal wind anomalies at latitude of the eddy-driven jet,and the other quantifying the anomalous amplitude of the large scale circulation.However,discrepancies in blocking frequency,location,and intensity due to index-specific sensitivities pose challenges for both observational and simulation studies.In this study,we introduce the instantaneous blocking index(I_(BA))formulated within the anti-cyclonic local finite-amplitude wave activity(ALWA)framework.As a nonlinear diagnostic based on quasi-geostrophic potential vorticity(QGPV),I_(BA)effectively quantify the polar displacement of QGPV relative to the eddy-free reference state,while maintain as inverse correlation with the spatial-temporal variability of the eddy-driven jet.Consequently,I_(BA)integrates the key attributes of conventional blocking indices,capturing both westerly flow reversals and wave amplitude anomaly.Furthermore,it addresses limitations of existing indices by accurately characterizing jet variability,and prevents misidentification of unrelated large-scale systems,such as cut-off low,weak trough,and subtropical or subpolar highs.Most importantly,I_(BA)possesses intrinsic dynamical significance which can be used to quantify the blocking variability directly through the LWA budget.Statistical analysis of I_(BA)for

关 键 词：大气阻塞 阻塞动力学 局地有限振幅波作用量 长期变率 涡旋驱动流 

分 类 号：P433[天文地球—大气科学及气象学]