Surface Fluctuations Associated with Tropical Cyclone Rainbands

With radar measurements and temporally high-resolution surface observations, this study investigates surface fluctuations associated with tropical cyclone rainbands (TCRs) observed in the vicinity of Taiwan during 2000-2008. A total of 263 TCRs identified from 37 typhoon events during the study period were analyzed to show the mean and common nature of perturbations of various meteorological variables associated with the passage of TCRs. The analyses indicate that the mean patterns of surface thermodynamic fluctuations across the rainband include a persistent decrease in temperature, dew-point temperature, and equivalent potential temperature. A wave-like variation of pressure perturbations associated with the rainband was evident, with a minimum coincident with the outer edge and a maximum located inside the inner edge. The kinematics of the rainband was found to be characterized by an obvious decrease in cross-band wind component, relatively minor variations in along-band wind component, and the wind veering. Quantitative analyses indicate that the majority of the TCRs exhibited variations in surface temperature, pressure, wind speed, and wind direction less than 2 degree C, 1.5 mb, 5 m s^-1, and 20^o, respectively. However, a clear trend of the magnitude of TCR thermodynamic fluctuations increasing with the radial distance from the tropical cyclone center was observed. The detailed composite and magnitude analyses of surface fluctuations show that the outer TCRs had a higher potential than the inner TCRs to reduce the near-surface values of equivalent potential temperature. Distinctly different features of surface pressure fluctuations between the outer and inner TCRs were also documented. Nevertheless, there was no dramatic difference in the pattern of kinematic fluctuations between the outer and inner TCRs, and their mean fluctuation magnitudes were also found to be statistically identical. These observational findings do not suggest an entirely clear distinction of surface characteristics for these two types of rainbands.