Mechanisms determining the organization of deep tropical convection on aqua-planet GCM with Arakawa-Schubert type convection schemes

Key Words: 

Mechanisms of tropical deep convective organization (ITCZ), Double ITCZ problem, convective parameterization (Tiedkte/Nordeng), aqua-planet

Abstract:

In Global Climate Models a double ITCZ in the eastern pacific is observed substantially more often than in observations. This is known as the double ITCZ problem. The ITCZ is a essential part of tropical climate. Deep convection, which is directly connected to the ITCZ, is a mayor heat source in the tropical atmosphere and therefore a main driving force for the atmospheric circulation. Hence, if we want a realistic representation of the tropics in the models we need to fix the double ITCZ problem. 

Deep convection is a quite complex phenomenon, so we need to simplify as much as possible in order to analyze the organization of deep convection. In order to do so we use a aqua-planet version of ECHAM6, with prescribed zonally and time independent sea surface temperature profiles.

With ECHAM6 we have two convection schemes available, namely the one of Tiedkte (1989) and an improved version of the Tiedtke scheme by Nordeng (1994). With the Qobs SST-curve (Neal & Hoskins 2000) we see a single ITCZ with the Nordeng scheme and a double ITCZ with the Tiedkte scheme. Thus, if we understand why the two schemes have different preference in forming double ITCZ, we might also understand how to change the convection scheme towards a more realistic representation of the ITCZ.

So far as I know the mechanisms and feedback loops which determine the ITCZ pattern in the models is unknown yet. Thus, it is very difficult to find out what we need to change in the parameterization of convection to improve the representation of the ITCZ. To identify this feedback loops and understand how the two convection schemes couple different on it, is the basic idea of my research.