Use of Radar Data For Tc Initialization and Predictions

Abstract

Hurricane track forecasts improve steadily over the last several decades primarily due to the increasing use of satellite observations in operational centers to improve large-scale environmental ow over ocean. However, intensity forecasts show very little improvement over the last decade because small-scale inner-core circulation can not be properly resolved by satellite observations. To improve intensity forecasts, it is important to use high-resolution Doppler radar data to properly initialize inner-core circulation for highresolution numerical models. A technique is developed for initialization of a hurricane vortex using horizontal velocities through a deep layer of the atmosphere obtained from Doppler radar. The technique uses two new innovations. The rst is the use of the mesoscale vorticity method ( Lee et al. 2003) to diagnose the vertical velocity and divergent wind based on the vorticity equation including the tilting terms. The second is the use of mesoscale Bounded Derivative Initialization ( Lee and MacDonald, 2000) to obtain two dynamic constraints, one each for gravity and sound waves. With the fast waves controlled, a nonhydrostatic model can be initialized to allow a smooth and balanced start. In this study, the mesoscale vorticity method is used to derive hurricane Danny's divergent wind/vertical velocity from the high temporal and spatial vorticity variations retrieved from the ground-based velocity track display (GBVTD) (Lee et al. 1999) technique based on single Doppler radar data. A fourdimensional data assimilation system (FDDA) (Stauer and Seaman, 1990) based on Newtonian relaxation/nudging is used to generate the dynamically consistent datasets for unobserved elds such as heating and cloud elds.