Interpretation of Tropical Cyclone Forecast Sensitivity from the Singular Vector Perspective
NATIONAL TAIWAN UNIV TAIPEI
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In this study, the leading singular vectors SVs, which are the fastest-growing perturbations in a linear sense to a given forecast, are used to examine and classify the dynamic relationship between tropical cyclones TCs and synoptic-scale environmental features that influence their evolution. Based on the 72 two-day forecasts of the 18 western North Pacific TCs in 2006, the SVs are constructed to optimize perturbation energy within a 20 deg x 20 deg latitude-longitude box centered on the 48-h forecast position of the TCs using the Navy Operational Global Atmospheric Prediction System NOGAPS forecast and adjoint systems. Composite techniques are employed to explore these relationships and highlight how the dominant synoptic-scale features that impact TC forecasts evolve on seasonal time scales. The NOGAPS initial SVs show several different patterns that highlight the relationship between the TC forecast sensitivity and the environment during the western North Pacific typhoon season in 2006. In addition to the relation of the SV maximum to the inward flow region of the TC, there are three patterns identified where the local SV maxima collocate with low-radial-wind-speed regions. These regions are likely caused by the confluence of the flow associated with the TC itself and the flow from other synoptic systems, such as the subtropical high and the midlatitude jet. This is the new finding beyond the previous NOGAPS SV results on TCs. The subseasonal variations of these patterns corresponding to the dynamic characteristics are discussed. The SV total energy vertical structures for the different composites are used to demonstrate the contributions from kinetic and potential energy components of different vertical levels at initial and final times.