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Research |
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My research is devoted to the study of the
interactions between planetary scale tropical waves and cumulus convection.
These interactions are small scale features which, despite the latest
improvements in computational resources, are still not well captured by
Today's general circulation models (GCM's). They occur at scales proportional
to the size of the individual clouds of about 1 km while the GCM's use a grid
size of about 50 km to weather and short term climate and 200 km for long
term climate predictions. Although, it is well established that tropical
cumulus convection constitutes one of the major energy sources for the
atmospheric circulation, by means of the latent heat release and the mass
transport associated with convective clouds, the feedback of the large scale
dynamics and thermodynamics and its role in destabilizing/stabilizing the
atmosphere and initiating/shutting off moist-convection is poorly understood.
GCM's use parametrization schemes to represent
the bulk effects of the cloud supercluster envelopes on the atmospheric
circulation rather than searching to keep track of each individual cloud.
Closure theories are then used to assess the instability of the atmosphere
and somehow trigger moist convective motions which feed back into the large
scale circulation. Perhaps the most popular closure theories found in the
literature which are used for convective superclusters are the wave CISK
(convective instability of the second kind) and the WISHE (wind induced
surface heat exchange, also called evaporation-wind feedback) instability
mechanisms. One of the major discrepancies between these two theories is that
CISK uses a fixed reservoir of convectively available potential energy (CAPE)
while WISHE is based on the quasi-equilibrium assumption where the boundary
layer is nearly constantly in equilibrium so that the sink of heat and mass,
within the boundary layer, due to convective upward motions is almost always
balanced by downward motions and surface evaporative fluxes and often uses
rapid or instantaneous CAPE adjustment schemes. Simplified model
convective parametrizations with a crude vertical resolution are often used
for theoretical and numerical studies of the interactions between the large
scale atmospheric circulation and deep penetrative convection. One of the
objectives of theses studies is to establish and assess these closure
theories by comparing the numerical results to observational records. An other open question
of fundamental importance arising in this field is related to the fact that
unlike dry (or laboratory) convection, in the atmosphere there is a stable
layer separating the well mixed boundary layer (which is connected to the sea
surface) and the eventually unstable tropospheric interior inhibiting moist
convection to occur spontaneously so that it is difficult to predict where
and when deep penetrative convection is likely to happen. In my research I
use numerical and stochastic models to address these issues. |