QBO, SAO, and tropical waves in the Berlin TSM GCM: Sensitivity to radiation, vertical resolution, and convection

Abstract

The sensitivity of tropical waves in a general circulation model (GCM) to radiation, vertical resolution, and deep convection is investigated. The implications of this for the simulation of the quasi‐biennial oscillation (QBO) and the stratopause seminannual oscillation (SAO) are examined. Varying the vertical resolution produced the greatest impact. Increasing the resolution leads to a more realistic Kelvin wave dissipation, and the westerly phase of a QBO starts to develop but is ended early by the advection of unrealistically strong easterly winds from the southern summer hemisphere. The dissipation of Kelvin waves at lower altitudes leads to a weakening of the westerly phase of the SAO. Only small, not statisically significant differences have been found between the integrations using the Kuo and the Betts‐Miller convection schemes. There is slightly more westerly momentum in the integration with the Kuo parameterization. The mass flux convection scheme of Tiedtke is unsuitable for use in the Berlin Troposphere‐Stratosphere‐Mesosphere GCM. It simulates unrealistic latent heat distributions and favors instabilities which generate artifical Kelvin waves. The radiation scheme has little impact on the dissipation of the tropical waves, but replacing the Newtonian cooling approach allows more physically consistent integrations.