Most cumulus parametrizations today make use of a simple conceptual
model of convection, called the mass-flux approach. This approach
depicts convection as an ensemble of updrafts and downdrafts occurring
within a model grid-box. The aim of this study is to determine
convective mass-fluxes and their constituents on the scale of a 100 km
GCM grid-box from a C-band polarimetric radar and thereafter investigate
the relative role of area fraction and vertical velocity in determining
the shape and magnitude of bulk mass-flux profiles. We make use of
observational estimates of these quantities spanning 13 wet seasons in
the tropical region of Darwin. Following a bulk approach, the results
show that the distribution of mass-flux is positively skewed and its
mean profile peaks at 4 km. This is the result of constant area
fractions and increasing vertical velocities below that level. Above 4
km, in-cloud vertical velocity plays a marginal role compared to the
convective area fraction in controlling mass-flux profiles.