Concentric eyewall formation in Typhoon Sinlaku (2008) – Part I: Assimilation of T-PARC data based on the Ensemble Kalman Filter (EnKF)

Typhoon Sinlaku (2008) is a case in point under T-PARC (THORPEX – Pacific Asian Regional Campaign) with the most abundant flight observations taken and with great potential to address major scientific issues in T-PARC ranging from structure change, targeted observations to extra-tropical transition. A new method for TC initialization based on EnKF data assimilation and the WRF model is adopted. By continuously assimilating (with update cycle every 30 minutes) all available conventional soundings, 157 dropwindsondes and SFMR (Stepped Frequency Microwave Radiometer) data from 9 T-PARC flight missions during Sinlaku from September 9 to 13, this study constructed a unique high-spatial/temporal-resolution and model/observation-consistent dataset for Sinlaku during the 5-day window. Simulations of Sinlaku starting at different initial time are further investigated to assess the impact of the data. It is striking that some of the simulations are able to capture the secondary eyewall cycle, while the others started earlier with fewer data assimilated are not. This provides a unique opportunity to study the dynamical processes of the concentric eyewall formation in Sinlaku. In part I of this work, results from the data assimilation and simulations will be presented, while the detailed dynamical analyses are conducted in part II.