The QBO Influence on Tropical Convection : Cloud-Resolving Modeling Study

The QBO influence on tropical deep convection is investigated with cloud resolving modeling for isolated convection in a limited domain and convection coupled with a large-scale walker circulation within a equatorial channel. In the isolated convection cases, the QBO-like near tropopause temperature anomaly modifies the amount of high cirrus clouds, however there is little precipitation response to the temperature forcing. In the idealized Walker circulation cases, there is more precipitation in the area with the strongest precipitation during the QBO westerly phase. The difference between the two sets of cases indicates that the coupling between convection and large-scale circulations is important to the QBO modulation on the tropical deep convection.

Results of the idealized Walker circulation experiments reveal a potential mechanism for the QBO effects on the tropical circulation and the associated convection. During the QBO easterly phase for example, with a cold temperature anomaly near the tropopause, the tropopause height is lifted upward. The vertical extension of the raising branch of the Walker circulation increases in height, and the peak of the vertical velocity profile moves upward, leading to an increase of the gross moist stability and the decrease of precipitation in the area with the strongest precipitation.