资源环境科技发展态势分析平台

Observational studies have shown that, on average, the quasi-biennial oscillation (QBO) exhibits a faster phase progression and shorter period during El Nino than during La Nina. Here, the possible mechanism of QBO modulation associated with ENSO is investigated using the MIROC-AGCM with T106 (similar to 1.125 degrees) horizontal resolution. The MIROC-AGCM simulates QBO-like oscillations without any nonorographic gravity wave parameterizations. A 100-yr integration was conducted during which annually repeating sea surface temperatures based on the composite observed El Nino conditions were imposed. A similar 100-yr La Nina integration was also conducted. The MIROC-AGCM simulates realistic differences between El Nino and La Nina, notably shorter QBO periods, a weaker Walker circulation, and more equatorial precipitation during El Nino than during La Nina. Near the equator, vertical wave fluxes of zonal momentum in the uppermost troposphere are larger and the stratospheric QBO forcing due to interaction of the mean flow with resolved gravity waves (particularly for zonal wavenumber >= 43) is much larger during El Nino. The tropical upwelling associated with the Brewer-Dobson circulation is also stronger in the El Nino simulation. The effects of the enhanced tropical upwelling during El Nino are evidently overcome by enhanced wave driving, resulting in the shorter QBO period. The integrations were repeated with another model version (MIROC-ECM with T42 horizontal resolution) that employs a parameterization of nonorographic gravity waves in order to simulate a QBO. In the MIROC-ECM the average QBO periods are nearly identical in the El Nino and La Nina simulations.