Applying Ensemble Sensitivity Analysis to Understand the Tropical Cyclogenesis of Typhoon Nuri (2008)

An Ensemble Kalman Filter (EnKF) is cycled on observations consisting of conventional and field observations from the TPARC/TCS08 campaign on Typhoon Nuri (2008). Conventional observations consist of rawindsonde, surface, cloud track winds, ACARS and GPS radio occultation data while the field observations are taken from the dropsondes released from aircraft during the field phase. The ensemble data therby generated is used to pose and test dynamical hypothesis related to the tropical cyclogenesis of typhoon Nuri. Specifically, the top-down v/s bottom-up hypothesis theories for genesis are tested for the case of typhoon Nuri. A variety of forecast metrics are defined to determine the sensitivity of initial conditions to the genesis of typhoon Nuri, e.g. low-level and mid-level vorticity. Initial-value experiments are devised based on the sensitivity results to "control" the evolution of the typhoon over a 24 hour forecast cycle, e.g. moisture-denial experiments in which all degrees of freedom except moisture fields are perturbed in the initial conditions to determine the effect of "altered" moisture state on the storm development. A concluding discussion on the impact of dropsonde observations taken during the field phase will be presented.