Assimilation of GBVTD‐retrieved winds from single‐Doppler radar for short‐term forecasting of super typhoon Saomai (0608) at landfall

Abstract

Display technique (GBVTD) has been developed in recent years to retrieve horizontal circulations of tropical cyclones. The technique is able to retrieve axisymmetric tangential and radial winds, asymmetric tangential winds for wave numbers 1-3, and along-beam mean winds in tropical cyclones. It has been successfully applied to tropical cyclone monitoring and warning. This study explores, for the first time, the assimilation of GBVTD-retrieved winds into a tropical cyclone prediction model, and examines its impact relative to that of directly assimilated radial velocity data. super typhoon Saomai (2006), the most intense landfalling typhoon ever recorded in China, is chosen as the test case, and data from the coastal operational radar at Wenzhou, China, are used. The ARPS 3DVAR system is used to assimilate either the radial velocity data directly or the GBVTD-retrieved winds, at 30 min intervals for 2 hours.The assimilation of the GBVTD-retrieved winds results in much improved structure and intensity analyses of Saomai compared to those in the Japan Meteorological Agency mesoscale reanalysis and compared to the analysis assimilating radial velocity (V r ) data directly. The ability of the GBVTD method in providing wind information covering the full circle of the inner-core circulation is the primary reason for its superior performance over direct assimilation of V r data; for the latter, the azimuthal data coverage is often incomplete. With the improved initial conditions, the subsequent forecasts of typhoon intensity, track and precipitation are also improved. The improvements to both track and intensity predictions persist over a 12-hour forecast period, which is mostly after landfall. Subjective and quantitative evaluations of the precipitation and circulation patterns show consistent results. A further sensitivity experiment shows that the axisymmetric wind component in the GBVTD retrieval has the dominant impact on the prediction.

Assimilation of radial velocity and reflectivity data from coastal WSR‐88D radars using an ensemble Kalman filter for the analysis and forecast of landfalling hurricaneIke(2008)

“…Without resorting to vortex bogusing, radar observations have been used to define vortex initial conditions, leading to improved forecasts in both track and intensity when using high-resolution models (e.g. Xiao et al, 2007;Zhao and Jin, 2008;Pu et al, 2009;Xiao et al, 2009b;Zhang et al, 2009;Zhao and Xue, 2009;Zhao et al, 2012aZhao et al, , 2012b.…”

The Gradient Velocity Track Display (GrVTD) Technique for Retrieving Tropical Cyclone Primary Circulation from Aliased Velocities Measured by Single-Doppler Radar

“…Finally, the GrVTD algorithm enables the real-time retrieval of primary circulations in landfalling TCs. As demonstrated in Zhao et al (2012), assimilating GBVTD-retrieved primary circulations can improve the structure and intensity analyses and forecasts of TCs compared to directly assimilating radial velocity. With the benefit of being aliasing proof, GrVTD retrievals can be used in a similar way.…”

“…A series of VTD extensions (referred to as the ''VTD family of techniques'')-including extended VTD (EVTD; Roux and Marks 1996), the ground-based VTD (GBVTD; Lee et al 1999, hereafter LJCD), ground-based extended VTD (GB-EVTD; Roux et al 2004), extended GBVTD (EGBVTD; Liou et al 2006), and generalized VTD (GVTD; Jou et al 2008)-expanded the VTD analysis into multiple flight legs for airborne Doppler radar and multiple ground-based Doppler radars (e.g., Roux and Marks 1996;Lee et al 2000;Harasti et al 2004;Liou et al 2006; Lee and Bell 2007;Zhao et al 2008). Recently, the GBVTD technique has been incorporated into the Vortex Objective Radar Tracking and Circulation (VORTRAC) software for real-time analysis of TCs at the National Hurricane Center (NHC) of the United States.…”

A numerical study of orographic forcing on TC Dina (2002) in South West Indian Ocean

“…Assimilating coastal Doppler radar data in numerical weather prediction models shows very encouraging improvements in TC forecasting during landfall (Zhao et al, 2012). Here the RDVC (Radar and Dropwindsonde Vortex Conditioning) technique is used to initialise Méso-NH (Nuissier et al, 2005).…”