Comparison of initial and lateral boundary condition sensitivity for a limited-area model

The sensitivities of two forecast aspects with respect to perturbations of initial and lateral boundary conditions are determined using an adjoint of a limited-area model. Sensitivities are presented as gradient fields. Some characteristics of the sensitivity fields have simple dynamical explanations, such as their strong dependence on winds, and do not require an adjoint model to reveal them. Other characteristics would be difficult to ascertain without an adjoint model, although they, too, in retrospect, have simple dynamical explanations. Still others, although equally important and undoubtedly dependent on the dynamics, would be practically impossible to determine without an adjoint. The quantity and quality of information provided by the adjoint solutions render the adjoint model a tool that is indispensable for sensitivity analysis.