Observational study on thermodynamic and kinematic structures of Typhoon Vicente (2012) at landfall.

Severe Typhoon Vicente was the strongest tropical cyclone (TC) that has attacked Hong Kong (HK) since 1999. This paper presents a comprehensive observational study on this windstorm during its landfall, based on in-situ measurements from weather radars, radiosonde balloons, wind profilers and other ground-based devices at various meteorological stations in HK. Both its thermodynamic and kinematic structures are investigated to explore the TC characteristics at landfall. The results of this study reflected that the vortex extended to the tropopause around 16 km. Vertical profiles of pressure deficit below TC outflow layer depicted a linear distribution pattern with respect to isobar-expressed altitude, with a slope increasing almost linearly with increasing surface pressure deficit. The inner and outer rainband regions were respectively dominated by stratiform and convective precipitations, and the inner region was vertically separated into two discriminatory layers by the melting layer located at 5.4 km. The sea-air contrast temperature varied noticeably during the landfall process, with an increase of 1–1.5 °C in the TC inner region where sea-air flux exchange strengthened distinctly compared to that at outer areas. Vertical wind profiles from balloons showed that horizontal wind speed and wind direction experienced a sharp change around the tropopause, above which flow motions were dominated by the anti-cyclone of Tibetan high. The inflow layer depth was found on the order of 2 km, compared to 1–2 km for the atmospheric mixing layer depth. The gradient height, recognized via the maximum horizontal wind, was in the range of 0.5–2.5 km which decreased with decreasing radii prior to landfall. Examination of the results from wind profilers over marine, urban and rugged terrain showed that the wind structures in the TC boundary layer (TCBL) depended upon storm-relative position and underlying terrain features. Vertical profiles of marine winds in the inner rainband region demonstrated a jet feature, with mean speed being logarithmical with height in the lowest 1 km. TCBL winds above rugged areas were influenced severely by topographic effects. The low-level wind maximum, or the gradient speed, changed insignificantly above different sites. [ABSTRACT FROM AUTHOR]