9:30 AM - 9:45 AM
[AAS07-03] ENSO modulation of the QBO: Results from MIROC models with and without nonstationary gravity wave parameterization
Keywords:middle atmosphere, Quasi-Biennial Oscillation, El Nino Southern Oscillation
The MIROC-AGCM experiments display ~2 months shorter QBO periods in El Nino versus La Nina conditions. Differences of the Walker circulation and equatorial precipitation between El Nino and La Nina are realistically simulated. The simulated precipitation differences are largest over the equator, consistent with observations. Near the equator the vertical wave fluxes of zonal momentum in the upper troposphere and lower stratosphere are larger in the El Nino simulation. The tropical upwelling associated with the Brewer-Dobson circulation is also stronger in the El Nino simulation. The effects of the enhanced Brewer-Dobson circulation during El Nino must somehow be overcome by enhanced wave driving in order to shorten the QBO period. On the other hand, in the MIROC-ESM ENSO experiments, the average QBO periods are nearly identical in the El Nino and La Nina simulations. Because parameterized gravity wave sources are fixed in the MIROC-ESM only resolved waves with horizontal wavenumber up to 42 could be modulated by ENSO.