Models Overestimate Strength of Deep Tropical Convection


Atmospheric convection in the tropical regions is one of the main mechanisms of transporting solar energy from the equator to the polar regions (convection) of our planet. To project how climate change will affect global precipitation, it is important that models accurately simulate the upwelling and divergence of moisture in tropical clouds. DOE scientists at Pacific Northwest National Laboratory showed that global climate models are not accurately depicting the true depth and strength of tropical clouds that have a strong hold on the general circulation of atmospheric heat and the global water balance. The team surveyed tropical divergence in three global climate models, three global reanalyses (models corrected with observational data), and four sets of atmospheric measurements from field campaigns. Their survey uncovered significant uncertainties in current climate simulations and, in future projections, of the intensity and vertical structure of the low-level convergence of moisture to and upper-level divergence of heat away from the tropics. In the tropics and subtropics, deep divergent circulation is the largest contributor to net precipitation. Further, all global circulation models studied portray this process as deeper and stronger than what is observed in field measurements. Their analysis points to the need for model improvements to project water cycle changes in the 21st century.


Hagos, S. and L. R. Leung. 2012. “On the Relationship Between Uncertainties in Tropical Divergence and the Hydrological Cycle in Global Models,” Journal of Climate 25(1), 381-291. DOI: 10.1175/JCLI-D-11-00058.1.