Tropical cyclone formation and structure studies using a moist adjoint model

Theoretically, the evolution of a physical variable in a numerical model can be traced by performing backward integration of an adjoint version of the same model, and sensitivities (gradient fields) of the physical variable at the initial time to the other variables can be calculated. These so-called adjoint sensitivities have been applied to tropical cyclone (TC) studies for some time. However, since some of the popular mesoscale models have only dry version of their adjoint, they may be adequate for TC motion studies (e.g., Wu et al. 2007) but not for formation and structure studies in which convection and associated moisture processes play essential role. This study utilizes an adjoint of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) to identify essential parameters and/or systems that play determining role in certain TC evolution processes such as organization of cloud clusters in the early stage or changes in radius of gale-force winds. The COAMPS adjoint model system includes explicit moisture physics (Amerault 2005) so that sensitivity fields that resulted in diabatic processes can be simulated, and they can also be compared with dry simulations to isolate influences from moist processes.

References:

Amerault, C. M., 2005: Development of the COAMPS adjoint mesoscale modelling system for assimilating microwave radiances within hurricanes. Ph. D. Dissertation, College of Arts and Sciences, Florida State University, 84 pp.

Wu C.-C., J.-H. Chen, P.-H. Lin, and K.-H. Chou, 2007: Targeted observations of tropical cyclone movement based on the adjoint-derived sensitivity steering vector. J. Atmos. Sci., 64, 2611-2626.