Understanding the processes which control the distribution and radiative properties of clouds is essential for the successful modeling of Earth's climate. The feedbacks associated with tropical convective and boundary layer clouds are particularly important in this regard as they are believed to play a key role in determining the response of the climate system to an increase in greenhouse gases. The premise of this proposal is that the basic physical processes controlling the distribution and lifecycle of tropical cloud systems must be known before their feedback on climate can be reliably predicted in GCMs.
To address this, we propose an innovative method of combining CloudSat/CALIPSO measurements with Lagrangian cloud trajectories from geostationary satellites and mid-tropospheric vertical velocity from operational analyses to examine the lifecycle of tropical cloud systems, their dependence upon dynamical regimes, and their impacts on the radiative and hydrologic budgets. The resulting data sets will then be used to assess the representation of these processes in the Global Climate Models (GCMs). By integrating Lagrangian cloud trajectories and dynamical compositing techniques with 3-dimensional cloud fields from CloudSat and CALIPSO we intend to test and ultimately improve the representation of tropical clouds in these models and, in so doing, reduce uncertainty in their simulation of cloud feedback.
The primary tasks to be accomplished are:
- Compute the forward / backward trajectories and related Lagrangian diagnostics for tropical convective cloud systems observed by the CloudSat and CALIPSO instruments.
- Use Lagrangian-based composites to: (a) characterize the radiative, macrophysical, and microphysical evolution of tropical cloud systems and (b) assess the dependence of the detrained cirrus cloud properties upon the convective sources which generate them.
- Diagnose the local environmental dependences of tropical boundary layer cloud systems observed by CloudSat / CALIPSO using the method of Bony et al. (2004).
- Evaluate the ability of GCMs to simulate the lifecycle and environmental dependences of tropical cloud systems, and their hydrologic and radiative impacts.
