Abstract
Understanding of the tropical atmosphere is elaborated around two
elementary ideas, one being that density is homogenized on isobars,
which is referred to as the weak temperature gradient (WTG), the other
being that the vertical structure follows a moist-adiabatic lapse rate.
This study uses simulations from global storm-resolving models to
investigate the accuracy of these ideas. Our results show that
horizontally the density temperature appears to be homogeneous, but only
in the mid- and lower troposphere (between 400 hPa and 800 hPa). To
achieve a homogeneous density temperature, the horizontal absolute
temperature structure adjusts to balance the horizontal moisture
difference. Thus, water vapor plays an important role in the horizontal
temperature distribution. Density temperature patterns in the mid- and
lower troposphere vary by about 0.3 K on the scale of individual ocean
basins, but differ by 1K among basins. We use equivalent potential
temperature to explore the vertical structure of the tropical atmosphere
and we compare the results assuming pseudo-adiabat and the
reversible-adiabat (isentropic) with the effect of condensate loading.
Our results suggest that the tropical atmosphere in saturated convective
regions tends to adopt a thermal structure that is isentropic below the
zero-degree isotherm and pseudo-adiabatic above. However, the tropical
mean temperature is substantially colder, and is set by the bulk of
convection which is affected by entrainment in the lower troposphere.