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

Abstract

The ground-based velocity track display (GBVTD) technique was developed to estimate the primary circulations of landfalling tropical cyclones (TCs) from single-Doppler radar data. However, GBVTD cannot process aliased Doppler velocities, which are often encountered in intense TCs. This study presents a new gradient velocity track display (GrVTD) algorithm that is essentially immune to the Doppler velocity aliasing. GrVTD applies the concept of gradient velocity-azimuth display (GVAD) to the GBVTD method. A GrVTD-simplex algorithm is also developed to accompany GrVTD as a self-sufficient algorithm suite.The results from idealized experiments demonstrate that the circulation center and winds retrieved from GrVTD with aliased velocity and GBVTD with dealiased velocity are in good agreement, but GrVTD is more sensitive to random observation errors. GrVTD was applied to Hurricane Charley (2004) where the majority of the Doppler velocities of the inner-core region were aliased. The GrVTD-retrieved circulation pattern and magnitude are nearly identical to those retrieved in GBVTD with manually dealiased velocities. Overall, the performance of GrVTD is comparable but is more sensitive to the data distribution than that of the original GBVTD using dealiased velocity. GrVTD can be used as a preprocessor for dealiasing velocity in TCs before the data are used in GBVTD or other algorithms.

An investigation on how inner‐core structures obtained through radar data assimilation affect track forecasting of typhoon Jangmi (2008) near Taiwan Island

“…[], except that the TC center is determined by using 850 hPa fields to reduce the influence of terrain. The Simplex method is employed to determine the TC center by maximizing the axisymmetric circulation [ Nelder and Mead , ; Lee and Marks , ; M. Wang et al ., ]. The separation procedure is applied to the prognostic variables on the model levels of the ARPS, including the wind components ( u , v , and w ), potential temperature ( θ ), pressure ( p ), and water vapor mixing ratio ( q v ).…”

Fitting Parametric Vortices to Aliased Doppler Velocities Scanned from Hurricanes

“…As mentioned in the introduction, the GrVTD algorithm (Wang et al 2012) retrieves hurricane primary circulation from aliased velocities, but it requires good data coverage around the hurricane. For the above hurricane case, the raw data have gaps larger than 1208 almost over the entire R range on the lowest tilt (see Fig.…”

“…For the above hurricane case, the raw data have gaps larger than 1208 almost over the entire R range on the lowest tilt (see Fig. 6a), so only the hurricane center location and axisymmetric tangential velocity V T (R) can be retrieved because of the limitations inherited from the GBVTD technique (see section 2a of Wang et al 2012). Note that V T (R) is retrieved by the GBVTD as a function of discretized R, so the number of unknowns is still much larger than that of merely (V M , R M ) considered by the vortex analysis in this paper.…”

“…Using this idea, the MVAD and GVAD analyses can improve dealiasing (Gong et al 2003;Gao and Droegemeier 2004) but not always without risking false dealiasing especially when data noises are amplified in the computed gradient field and become too high to reliably filter alias-caused spikes (according to the operational tests described in the introduction of Xu et al 2011). Recently, by adopting the above idea used in the GVAD, Wang et al (2012) modified the ground-based velocity track display (GBVTD) technique (Lee et al 1999) into a gradient velocity track display (GrVTD) algorithm for retrieving hurricane primary circulation from aliased velocities. This algorithm retains nearly all the merits but also inherits nearly all the limitations from the GBVTD technique other than the use of the above GVAD idea.…”

The Improvement to the Environmental Wind and Tropical Cyclone Circulation Retrievals with the Modified GBVTD (MGBVTD) Technique

“…Recently, successful applications of GBVTD to several landfalling TCs (Lee et al 2000;Lee and Bell 2007;Zhao et al 2008) have demonstrated its ability in monitoring and warning. A series of GBVTD extensions-including ground-based extended VTD (GB-EVTD; Roux et al 2004), extended GBVTD (EGBVTD; Liou et al 2006), generalized VTD (GVTD; Jou et al 2008), and gradient VTD (GrVTD; Wang et al 2012)-expanded the GBVTD analysis into multiple flight legs for airborne Doppler radar, multiple ground-based Doppler radars and direct use of aliased radial velocity data, and so on. However, the cross-beam component of the mean wind V M?…”