Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
01 December 2016

The Meridional Mode in an Idealized Aquaplanet Model: Dependence on the Mean State


The meridional mode provides a source of predictability for the tropical climate variability and change on seasonal and longer time scales by transporting extratropical climate signals into the tropics. Previous research shows that the tropical imprint of the meridional mode is constrained by geography.


In this study, zonal asymmetry is investigated using CAM4 configured as an aquaplanet with a slab ocean model. By controlling the zonal asymmetry of the mean climate state, we examine the response of the meridional mode. In a zonally symmetric case, the meridional mode operates throughout the subtropics but only becomes evident after removing a dominant global-scale eastward-propagating mode. In a zonally asymmetric case, the meridional mode operates only in regions where trade winds converge onto the equator. In both simulations, the tropical imprint of the meridional mode is modulated by the seasonal migration of the tropical rain belt.


These results suggest that the meridional mode does not require particular geography: it is intrinsic to the coupled system, but its characteristics do depend on the climate state. An implication is that internal climate variability must be assessed in the context of the mean climate state.

Brian Medeiros
National Center for Atmospheric Research (NCAR)