Open AccessCumulus transport of chemical tracers: 1. Cloud‐resolving model simulations
Author(s) -
Lu Rong,
Lin Chichung,
Turco Richard,
Arakawa Akio
Publication year - 2000
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2000jd900009
Subject(s) - mesoscale meteorology , convection , troposphere , entrainment (biomusicology) , outflow , atmospheric sciences , tracer , free convective layer , atmosphere (unit) , subsidence , atmospheric convection , environmental science , geology , meteorology , climatology , physics , paleontology , structural basin , rhythm , acoustics , nuclear physics
Convective transport in the tropics and middle latitudes is a critical mechanism leading to the vertical and, eventually, the horizontal redistribution of chemical tracers throughout the lower atmosphere. Accordingly, a better understanding and accurate representation of convective transport are essential in simulating tracer distributions and long‐range dispersion in chemical transport models. We employ the UCLA cloud‐resolving model (CRM) to simulate a 5‐day period during the GATE phase III experiment, during which several mesoscale convective systems were observed. The dynamical structures and thermodynamic balances of the simulated versions of these events compare favorably with observations. The distributions of six tagged tracers originating at different levels in the atmosphere are calculated and analyzed. This represents the first in‐depth analysis of regional dispersion over a multi‐day period utilizing multiple tracers in a high‐resolution model. It is found that the dominant process affecting tracer transport by individual clouds involves convective updrafts and related downdrafts. Entrainment, anvil cloud outflow, and detrainment at various levels all have important effects in different regions of the troposphere. In addition to the convective‐scale transport, mesoscale subsidence induced by deep convection is capable of moving chemical tracers downward as much as several hundred hPa during a single deep convective event, which can substantially modify tracer distributions in the middle and lower troposphere. On the basis of our analysis we conclude that deep convection profoundly affects the distribution of tropospheric chemical tracers in at least three fundamental ways: (1) by quickly and directly transporting tracers from the boundary layer to the upper troposphere, (2) by accelerating downward transport of chemical tracers from the upper troposphere to the surface, both locally in downdrafts and over broader areas via subsidence, and (3) by inducing the exchange of air between the upper troposphere and the lower stratosphere.