Structural characteristics of Typhoon Sinlaku (2008) during its extratropical transition: an observational study

During extratropical transition (ET) structural changes of a tropical cyclone (TC) are responsible for high impact weather. One of the primary goals of the THORPEX-Pacific Asian Regional Campaign (T-PARC) in 2008 was to obtain insights into the various physical processes governing these structural changes. The campaign allowed to investigate one of the major typhoons in the West Pacific in 2008 -Typhoon Sinlaku- from tropical cyclogenesis until ET.

As Sinlaku approached the midlatitude baroclinic zone a strong convective system developed to the east of the transitioning typhoon. Research flights with the NRL-P3 and the USAF-C130 aircrafts equipped with the Dual-Doppler-Radar ELDORA and dropsondes allowed to capture a unique dataset for the detailed structure of this convective event. The observational data are analysed with the recently developed Spline Analysis at Mesoscale Utilizing Radar and Aircraft Instrumentation (SAMURAI) software tool at 5 km horizontal resolution. The SAMURAI analysis enabled us to identify deep convection, a stratiform region, warm- and cold frontal structures, and a dry intrusion within the transitioning TC. Q-vector diagnostics suggest that forced ascent in a potential instable environment triggers the deep convection.

Strong potential vorticity production by latent heat release within the deep convection leads to a deformation of Sinlaku's wind field and presumably favors the cyclone's decay. Finally, the ECMWF operational analysis is validated against the SAMURAI analysis.

This study, based on the T-PARC observations, presents a unique documentation of the various physical processes involved in ET.