Tropical Cyclone Initialization with Dynamical Retrieval from a modified UWPBL Model

【摘要】：A new scheme, termed Vortex Initialization with the Assimilation of Retrieved Variables (VIRV), is presented to improve the initialization of regional numerical model for Tropical Cyclone (TC) prediction. In this scheme, the horizontal winds in planetary boundary layer (PBL) and sea level pressure (SLP), retrieved from Quick Scatterometer (QuikSCAT) data with a modified University of Washington Planetary Boundary Layer (UWPBL) model, are assimilated with a cycled three-dimensional variational (3DVAR) technique to produce the initialized analysis. The procedures of retrieval are implemented under the joint dynamical constraints of the gradient wind, secondary circulation and thermal stratification. Moreover, in order to improve the analysis of TC intensity, the roughness parameterization in the UWPBL model was modified for the case of strong surface wind. The sensitivities of structure, intensity and track of TC to the VIRV are then examined through two numerical experiments for TC Bilis (2006) and TC Fung-wong (2008). The maximum wind speed (MWS) and minimum sea level pressure (MSLP) retrieved from the QuikSCAT data show more agreement with the observations, relative to those derived from the National Center for Environmental Prediction (NCEP). The analysis of TC intensity in the VIRV is increased by modifying the low-level (upper-level) convergence (divergence), vertical shear of horizontal wind, transportation of moisture. Significant improvement on 48-hours TC simulation is identified in the MWS, with 22.8% error reduction. In particular, the modification of roughness parameterization (MRP) enhanced the simulation of MWS by 6.9%. Finally, the VIRV also reduces the simulation error in the track of TC by affecting the steering flow throughout the troposphere.