Global Distribution and Propagation of the Tropospheric Biennial Oscillation

The tropospheric biennial oscillation (TBO) is a typical interannual variation in global climate systems, especially whose signal is strong in the Asian monsoon (AM) and the North Atlantic Oscillation (NAO). This work reveals the seasonal transition of TBO anomalies with a global perspective. The comparison between the TBO and the El Nino/Southern Oscillation (ENSO) anomalies emphasizes the spatiotemporal characteristics of the TBO. Using the TBO anomalies of stream function at 850 hPa, the spatial distribution of contribution rate is examined, which is defined as the ratio of standard deviation (SD) of the TBO anomaly to the total SD of all interannual variations. The large contribution rates appear over the Indian Ocean, the marinetime continent, the South Pacific Convergence Zone (SPCZ), the Atlantic Ocean, and along the Antarctic coast, although the large contribution rate of ENSO anomaly concentrates along the equatorial Pacific. The large TBO anomalies are distributed widely, including the entire AM region, and locations of the action centers are different from those of the ENSO anomalies. To reveal the spatiotemporal structures of the TBO in more detail the composite analysis is performed for both of the TBO and ENSO anomalies based on the temporal phase. The TBO has more global variability with anomalous circulations from the AM region to the SPCZ with the marinetime continent as the center, and concurrently, opposite circulation anomalies are dominant from the Indian Ocean to the South Atlantic. The tripole pattern of lower tropospheric anomalies in the Atlantic Ocean seems to be essential of the TBO of NAO. Sea surface temperature anomalies and anomalous Walker circulations are coherent and determine the seasonal development of the TBO anomalies. The global comparison between the TBO and the ENSO anomalies reveals that the TBO is spatiotemporally different from the ENSO.