GFDL - Geophysical Fluid Dynamics Laboratory

Tropical Dynamics

The effects of climate variability and climate change on tropical precipitation is clearly of great importance for tropical societies and ecosystems. Yet our understanding of how the distribution of precipitation is controlled in the tropics remains very imperfect.  This uncertainty results in part from the fact that the tropical atmosphere is very difficult to simulate from first principles because of the important role played by motions with horizontal scales of a few kilometers and smaller.  These scales are not resolved in today’s global atmospheric models, requiring the use of imperfect sub-grid closure schemes.  In addition, we have only limited understanding of the dynamical interplay between the planetary scale flows in the tropics and precipitation patterns, and of the relative importance of difference aspects of our sub-grid closures on our model simulations.  We have a variety of lines of research aimed at improving our understanding of the dynamics of the tropical atmosphere:

The CM2.0/CM2.1 climate models developed by GFDL for input into the 4th IPCC assessment simulate dramatic changes in African precipitation in the 21st century.  We continue to investigate whether or not these projections are plausible.

Starting with the dry dynamical core of a global atmospheric model, we add simple moist physics and study the interplay between large-scale flows and tropical convection

  • Extratropical control of tropical precipitation

Using global atmospheric models in which the lower boundary is simplified by eliminating land surfaces and covering the  surface with a thin stagnant layer of water (a “slab” ocean) we create models in which the factors controlling the intertropical convergence zone can be studied carefully, focusing in particular on the way in which perturbations to the atmosphere outside of the tropics influences the precipitation within the tropics

Making use of a drastic simplification of the model geometry, replacing the rotating sphere by a horizontally homogeneous non-rotating (or uniformly rotating) plane, we study how assumptions about the sub-grid closure for moist convection control the organization of precipitation and cloud cover, as a starting point for considering more realistic horizontally-inhomogeneous atmospheres.