多要素表征的东亚季风区准双周振荡特征

为评估不同要素对东亚季风区准双周振荡的表征能力，对大气向外长波辐射（OLR）、500 hPa位势涡度、850 hPa相对涡度、850 hPa风场和750 hPa比湿等要素的准双周振荡特征进行对比，发现各要素均能很好反映东亚季风区明显的准双周振荡时空特征。OLR及500 hPa位势涡度、850 hPa相对涡度、850 hPa纬向风表征的准双周振荡呈明显的西北向传播特征，500 hPa位势涡度、850 hPa相对涡度、850 hPa纬向风北传更强，北传速度更快。850 hPa经向风的准双周振荡呈明显西移特征，北传弱，北传速度最慢。而750 hPa比湿准双周振荡呈东南向传播。不同要素准双周振荡的强度略有差异，其中750 hPa比湿与其他要素的差异大。总体而言，750 hPa比湿不能较好地表现出东亚季风区准双周振荡活动特征，而其余要素能很好地表征东亚季风区大气准双周振荡，其中500 hPa位势涡度和850 hPa相对涡度准双周振荡特征一致性高。

Characteristics of QBWO over the East Asian Monsoon Region Presented by Different Elements

Different variables present discrepancy in characteristics of the quasi-biweekly oscillation (QBWO), which is a dominant sub-seasonal signal in the East Asian monsoon regime. However, there is limited investigation about similarities and differences in features of QBWO presented by varying variables. In order to fill this gap, adopting the empirical orthogonal function (EOF) and composite analysis, such variables as outgoing longwave radiation (OLR), 500 hPa potential vorticity (PV), 850 hPa relative vorticity, 850 hPa zonal wind, 850 hPa meridional wind and 750 hPa specific humidity are compared, regarding of the spatial-temporal distribution, intensity and propagation of QBWO over the East Asian monsoon region. It is found that all these variables show significant QBWO across the region with similar spatial and temporal variation. And the strongest QBWO is observed over the South China Sea (SCS) with all variables. QBWO in OLR propagates north-westward over the East Asian monsoon regime. Centres of active (suppressed) QBWO convection correspond to positive (negative) PV anomalies at 500 hPa level and cyclonic (anticyclonic) vortex at 850 hPa level. These circulations form a northwest-southeast tilted wave train. Two leading modes of QBWO in 500 hPa PV, 850 hPa relative vorticity and 850 hPa zonal wind have greater meridional magnitude than those of OLR. QBWO in three variables also propagate north-westward, but spread faster to north. Oppositely, two leading modes of QBWO in 850 hPa meridional wind are characterized by the zonal dipole pattern and the westward propagation is evident. Actually, its speed of northward propagation is the slowest of all. Different from all others, QBWO in 750 hPa specific humidity propagates south-eastward, and variances explained by QBWO of 750 hPa specific humidity is the smallest. As for the intensity of QBWO, except for 750 hPa specific humidity, other variables have consistent inter-annual variation. Totally, affected by such complex physical processes as transformation of precipitation state, release of heat and so on, characteristics of QBWO is hardly captured by 750 hPa specific humidity. However, OLR, 500 hPa PV, 850 hPa relative vorticity, 850 hPa zonal wind and 850 hPa meridional wind can well characterize QBWO over the East Asian monsoon region. Of all variables compared in this analysis, 500 hPa PV and 850 hPa relative vorticity are highly consistent in describing QBWO over the East Asian monsoon region. Specific causes that lead to different characteristics of QBWO over the East Asian monsoon regime presented by different variables need further discussion, which can provide a new reference for selecting monitoring indices for QBWO over the East Asian monsoon region.