A comparison of two paradigms: The relative global roles of moist convective versus nonconvective transport

[1] Global-scale transport processes are examined in the troposphere using the Model of Ozone and Related Trace Species, version 2 (MOZART-2). Here MOZART-2 is driven by input meteorological fields from the National Center for Environmental Prediction/ National Center for Atmospheric Chemistry (NCEP/NCAR) reanalysis data set during 2001 - 2002 filtered at approximately 2.8 degrees latitude by 2.8 degrees longitude. Idealized tracers are used to identify deep moist convectively processed airmasses in MOZART-2, where the convection is parameterized using the Zhang and McFarlane scheme. The simulations show that the troposphere can be divided into a convectively processed regime where deep moist convective transport is predominantly responsible for the transport of trace species from the boundary layer and a nonconvectively processed regime. The boundary between the convectively processed and nonconvectively processed regimes lies between approximately 300 and 310 K. The interplay between moist convective and nonconvective transport explains many aspects of the global tropospheric distribution of trace species, including seasonal, latitudinal and longitudinal changes in species distribution. Evidence is presented that transport in the warm conveyor belts of synoptic systems is the process primarily responsible for lofting trace species into the middle and upper troposphere in the nonconvectively processed regime. The Northern Hemisphere (N. H.) midlatitude troposphere undergoes a substantial seasonal cycle in convective influence with much greater convective impact during summer, primarily from convection north of 30 degrees N. There is a barrier to poleward transport in the upper troposphere across 30 degrees, even during the Northern Hemisphere summer. In specific applications the seasonal change in the transport regimes from Asia to North America is examined during the Intercontinental and Chemical Transformation 2002 (ITCT 2K2) campaign and the chemical consequences of convection are explored. An isentropic viewpoint is emphasized in this study. We use this viewpoint to explain the fact that poleward tracer gradients can be explained by transport considerations alone.