Interpretation of tropical cyclone forecast sensitivity and dynamics from a NOGAPS singular vector perspective

The leading Singular Vectors (SVs) provide the fastest growing perturbations to which the tropical cyclones (TCs) or other downstream synoptic systems are most sensitive. Based on the 72 given 2-days forecast trajectories of the 18 TCs in 2006, the SVs are constructed that optimize perturbation energy within a 20 by 20 degree latitude/longitude box centered on the 48 hour forecast position of the TCs by the Navy Operational Global Atmospheric Prediction System (NOGAPS). The NOGAPS initial SVs show several different patterns that highlight the relationship between the TC forecast sensitivity and the environments during the western Pacific typhoon season.

Detailed analysis of the SV sensitivities associated with the wind and height fields is discussed. In addition to the relation of the SV maximum to the inward flow region of the TC (Peng et al. 2006), there are three patterns identified where the SV maximum collocates with small-wind-speed regions that are caused by the confluence between the flow associated with the TC itself and the flow of other synoptic systems, such as the sub-tropical high or a mid-latitude jet. The seasonal distributions of the three patterns which correspond to the change of dynamics characteristic in different seasons will also be present.