Land-Atmosphere Coupling in the CORDEX Central America Region

Studies using global climate models have found evidence of strong land-atmosphere coupling in parts of Central America. This research extends those findings by using the regional climate model RegCM4 to perform GLACE-type experiments over the CORDEX Central America (CCA) domain at higher spatial resolution than used in global models. These experiments first perform a long-term simulation while saving predicted soil moisture every time step, then redoing the simulation using the same initial and boundary conditions but with soil moisture taken from the averaged output of the first simulation instead of being predicted by the model. Comparing results from the two simulations gives a measure of the strength of land-atmosphere coupling.

Results over the CCA domain using ERA-interim boundary conditions for 1989-2009 show that land-atmosphere coupling has substantial influences on interannual variability of precipitation in the region, with coupling "hot spots" that differ from global model results. Diagnosed land-atmosphere coupling also appears important for regional circulation features such as the North American monsoon. Consistent with prior results it is also found that diagnosed coupling strength is model dependent, in the sense that locations and magnitudes of coupling hot spots differ when different convective parameterizations are used. Methodological aspects of using RegCM4 for GLACE-type experiments also are discussed. These include strategies for performing GLACE-type experiments more efficiently, along with advantages and disadvantages of using regional models compared to global models for such experiments.