On the Sensitivity of the Diurnal Cycle in the Amazon to Convective Intensity

Thursday, 18 December 2014
Kyle Frederick Itterly, Science Systems and Applications, Inc. Hampton, Hampton, VA, United States and Patrick C Taylor, NASA Langley Research Center, Hampton, VA, United States
Recent work on the evaluation of the TOA flux diurnal cycle shows a consistent misrepresentation of the convective diurnal cycle over the Amazon by both climate models and reanalysis models. Models initiate convection too early in the afternoon and dry out too early in the evening compared to observations. The models generally underestimate the diurnal amplitude of convective cloudiness and are shown to have the largest diurnal cycle errors on days with observed convection. Misrepresenting the diurnal cycle of convection can result in climatological model errors upwards of 20% and much higher errors at short time-scales. The 11-year record of 3-hourly data used in this analysis includes: TOA/surface fluxes, precipitable water and cloud fraction from CERES Ed3a, precipitation flux from TRMM 3B42 and atmospheric state data from MERRA and ERA-Interim. This study identifies under which atmospheric conditions the model errors are largest, provides critical insight on reducing these errors over the Amazon and helps gain a better understanding of the physical mechanisms responsible for the triggering of convection in the Amazon in both the observations and models.