Typhoon-trough interaction from the perspective of the adjoint-derived sensitivity steering vector (ADSSV)

Targeted observation is one of the most important research and forecasting issues for improving tropical cyclone (TC) predictability. A new parameter, Adjoint-Derived Sensitivity Steering Vector (ADSSV), has been proposed and adopted as one of the targeted observing strategies in DOTSTAR (Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region). The ADSSV identifies the sensitive areas at the observing time to the steering flow at the verifying time through the adjoint calculation.

In this study, the ADSSV calculated from the fifth-generation Pennsylvania State University—National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) nonlinear forecast model and its adjoint modeling system is used to interpret the dynamics and interactions between Typhoon Shanshan (2006) and the mid-latitude trough. The ADSSV results imply that the motion of Typhoon Shanshan is mainly associated with the edge of the subtropical high and the 500-hPa mid-latitude trough over northern central China. Furthermore, the vertical structure of the ADSSV is shown to gain more physical insights into the typhoon-trough interaction. It is demonstrated that the ADSSV can well capture the signal of the large-scale trough feature affecting the motion of TCs.