Reconciling Model Differences to Obtain Robust Features of Convective Influence Calculations for the Tropical Tropopause Layer

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Wednesday, 7 January 2015
John W. Bergman, Bay Area Environmental Research Inst., Petaluma, CA; and L. Pfister and E. Jensen

Many constituents that influence the chemistry and radiative balance of the upper troposphere and stratosphere are introduced to the atmosphere at the Earth's surface and transported to the tropical tropopause layer (TTL) via deep convection. As such, the strong influence of unresolved variations of wind and diabatic heating rates associated with convection are a large source of uncertainty for transport calculations used to understand the chemical concentrations in the TTL. This uncertainty is exemplified by obvious differences in the geographic distribution of boundary layer sources from 2 different trajectory calculations: a diabatic calculation that performs backward (in time) trajectories from the tropical tropopause to the location of convective detrainment as determined from satellite observations of clouds and rainfall and a kinematic calculations that performs back trajectories from those same locations to the boundary layer from resolved winds. We perform experiments that reconcile the different boundary layer sources from these calculations. Results from these experiments clearly imply that the differences are not due to differences in the space-time distributions of convection as determined by satellite observations and by reanalysis data. Instead the differences are due to the different convective transport assumptions inherent in the two calculations. We then use this information to develop transport calculations that parameterized unresolved wind variations based on airborne observations to understand which aspects of the unresolved wind statistics are most important for modeling chemical transport from the boundary layer to the TTL