Convective damping of buoyancy anomalies and its effect on lapse rates in the tropical lower troposphere I. Folkins Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 3J5, Canada
Abstract. In regions of the tropics undergoing active deep convection, the
variation of lower tropospheric lapse rates (2.0 km to 5.2 km) with
height is inconsistent with both reversible moist adiabatic and
pseudoadiabatic assumptions. It is argued that this anomalous behavior
arises from the tendency for the divergence of a convective buoyancy
anomaly to be primarily offset by the collective divergence of other
updrafts and downdrafts within one Rossby radius of deformation.
Ordinarily, convective mass flux divergences are at least partially
offset by an induced radiative mass flux divergence in the background
atmosphere. If mass flux divergences from lower tropospheric convection
are balanced mainly by those of neighboring updrafts/downdrafts, it would
force the vertical clear sky radiative mass flux of the background
atmosphere to be weakly dependent on height. This is observed at several
radiosonde locations in the Western Tropical Pacific between 2.0 and the
5.2 km melting level. At tropical locations where SST's exceed
27°C over a region whose horizontal extent exceeds the local
Rossby radius, this condition on the vertical variation of the background
radiative mass flux partially constrains the range of physically allowed
mean temperature and moisture profiles in the lower troposphere.
Citation: Folkins, I.: Convective damping of buoyancy anomalies and its effect on lapse rates in the tropical lower troposphere, Atmos. Chem. Phys., 6, 1-12, doi:10.5194/acp-6-1-2006, 2006.