Observations of Inner-Core Structure during the Eyewall Replacement Cycle of Typhoon Sinlaku (2008)

Accurate tropical cyclone (TC) intensity analyses are critical to enhancing readiness and mitigating risk for coastal populations. In land-falling systems, surface wind field structure is a vital component of this analysis, as the radial locations of critical wind speeds guide disaster preparation and provide proper vortex initialization in numerical models. Objective identification of features such as the radii of maximum and of 34-, 50-, and 64-kt winds, as well as the general evolution of the radial distribution of winds throughout a TC lifecycle, remains particularly challenging in basins without a routine aircraft reconnaissance program. In the western North Pacific, operational meteorologists rely primarily on satellite-based techniques to evaluate TC intensity and structure, including Dvorak-type diagnostic assessments that make use of infrared brightness temperatures observed by geostationary satellites. These geostationary-based techniques generally do not provide objective estimation of critical wind radii, nor do they offer much insight into the structure of the surface wind field. Thus, techniques that use geostationary satellite observations to diagnose surface wind field structure would be useful.

In this study, reconnaissance aircraft and satellite observations of the concurrent evolution of the surface wind field and cloud-top brightness temperatures are examined before and during an eyewall replacement cycle in Typhoon Sinlaku (2008). Preliminary results reveal strongly negative correlations between brightness temperature and surface wind speed as well as between eyewall slope and TC intensity, linking the thermodynamic and dynamic aspects of the secondary and primary circulations, respectively. Lagged correlations show that strongest surface winds are located radially inward of coldest cloud tops, providing further insight into the nature of the relationship between brightness temperature and TC intensity. These relationships will be extended in space and time, with particular emphasis given to their evolution during the eyewall replacement cycle of Typhoon Sinlaku.