Representation of the Stratospheric Circulation in CRA-40 Reanalysis: The Arctic Polar Vortex and the Quasi-Biennial Oscillation

Abstract

The representation of the Arctic stratospheric circulation and the quasi-biennial oscillation (QBO) during the period 1981–2019 in a 40-yr Chinese global reanalysis dataset (CRA-40) is evaluated by comparing two widely used reanalysis datasets, ERA-5 and MERRA-2. CRA-40 demonstrates a comparable performance with ERA-5 and MERRA-2 in characterizing the winter and spring circulation in the lower and middle Arctic stratosphere. Specifically, differences in the climatological polar-mean temperature and polar night jet among the three reanalyses are within ±0.5 K and ±0.5 m s⁻¹, respectively. The onset dates of the stratospheric sudden warming and stratospheric final warming events at 10 hPa in CRA-40, together with the dynamics and circulation anomalies during the onset process of warming events, are nearly identical to the other two reanalyses with slight differences. By contrast, the CRA-40 dataset demonstrates a deteriorated performance in describing the QBO below 10 hPa compared to the other two reanalysis products, manifested by the larger easterly biases of the QBO index, the remarkably weaker amplitude of the QBO, and the weaker wavelet power of the QBO period. Such pronounced biases are mainly concentrated in the period 1981–98 and largely reduced by at least 39% in 1999–2019. Thus, particular caution is needed in studying the QBO based on CRA-40. All three reanalyses exhibit greater disagreement in the upper stratosphere compared to the lower and middle stratosphere for both the polar region and the tropics.

摘 要

本文系统评估了我国首套大气再分析资料CRA-40对1981–2019年北极平流层环流以及平流层准两年振荡的表征能力,并将结果与国际上广泛使用的ERA-5和MERRA-2两套再分析资料进行对比。结果表明,CRA-40对北极平流层中低层冬春环流的表征能力与ERA-5和MERRA-2相当。具体而言,三套再分析资料对于北极平流层气候平均温度和极夜急流的刻画误差分别在±0.5 K和±0.5 m s–1之内。同时,CRA-40中10 hPa层次上平流层爆发性增温事件、最后增温事件的爆发日期,以及两类增温事件爆发过程中的动力和环流异常与另外两套再分析资料几乎一致。相比之下,CRA-40在刻画10 hPa以下平流层准两年振荡(QBO)的能力明显弱于其他两套再分析资料,具体表现为:CRA-40中QBO的东风位相明显偏强,QBO振幅和周期的强度明显偏弱。这样的偏差主要集中在1981–1998年;在1999–2019年,该偏差迅速减小,比前一个时期至少减少了39%。因此,在使用CRA-40对QBO进行研究时我们需要特别注意。另外,在平流层上层,三套再分析资料之间的差异要明显大于平流层中低层。