penetration occurs in ~10% of tropical convective
events (B. Carlson 1996, personal communication).
Pollutants transported vertically in core updrafts
may exit clouds wherever there is detrainment, including
from cloud anvils in the upper troposphere.
One of the first observations of this phenomenon
was made during PRESTORM flights over Oklahoma
in 1985 (Dickerson et al. 1987). In the vicinity
of convective anvils, concentrations of
carbon monoxide (CO) at 9–11 km were similar to
CO concentrations in the rural boundary layer
(Fig. 1). Calculations suggest that over the central
United States in summertime, approximately half
the CO entering the boundary layer is transported
upward by deep convection (Thompson et al.
1994). A benefit is that convection acts as a chimney,
preventing concentrations of CO and other
pollutants at the surface from reaching unhealthy
levels. However, once aloft, CO is advected long
distances, where it contributes to ozone production.
Photochemical calculations using the Goddard Tro