Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation (TBO) over East Asian monsoon region at the interannual timescales, which has the important influences on East China climate. Based on a set of reconstructed indices which describes the western Pacific subtropical high (WPSH) objectively, this paper focuses on the TBO component of WPSH, one of the key members of the East Asian Monsoon system, and its relationships with the tropical SST and atmospheric circulation anomalies. It is found that (1) As an important interannual component of WPSH, the time series of TBO has the obvious transition in the late 1970s, and the variability of the WPSH's TBO component is more significant after the late 1970s. (2) The time-lag correlations between the WPSH's TBO and the tropical sea surface temperature (SST) anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data. The response of the western boundary index to ENSO is earlier than the intensity index, and the time-lag correlations of them are up to maximum when lagging ENSO by 3-5 months and 5-6 months, respectively. (3) In the course of the WPSH's TBO cycle, the occurrence of the El Nio-like anomaly in the tropical centraleastern Pacific in winter is always coupled with the weak East Asian winter monsoon, with the most significant enhancing phase of the WPSH' TBO. In contrast, the La Nia-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon, with the most weakening phase of the WPSH's TBO. (4) The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle. The WPSH's TBO is more significant in the period of the developing El Nio-like anomaly in central-eastern Pacific than in the period of the developing La Nia-like anomaly. Therefore, during the period of developing El Nio-like anomaly, more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.