Development and Initial Evaluation of A Generalized Asymmetric Tropical Cyclone Vortex Model in ADCIRC Jie Gao, Rick Luettich University of North Carolina at Chapel Hill Jason Fleming Seahorse Coastal Consulting ADCIRC Users Group Meeting, USACE Vicksburg, MS, April 29, 2013
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Jie Gao, Rick Luettich University of North Carolina at Chapel Hill Jason Fleming
Development and Initial Evaluation of A Generalized Asymmetric Tropical Cyclone Vortex Model in ADCIRC. Jie Gao, Rick Luettich University of North Carolina at Chapel Hill Jason Fleming Seahorse Coastal Consulting ADCIRC Users Group Meeting, USACE Vicksburg, MS, April 29, 2013. - PowerPoint PPT Presentation
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Development and Initial Evaluation of A Generalized Asymmetric Tropical Cyclone Vortex Model in ADCIRC
Jie Gao, Rick LuettichUniversity of North Carolina at Chapel Hill
Jason FlemingSeahorse Coastal Consulting
ADCIRC Users Group Meeting, USACE Vicksburg, MS, April 29, 2013
Introduction
NW NE
SW SE
Storm forward motion
Schematic cross section of a hurricane wind field
Goal: use tropical cyclone storm parameters provided in NHC ATCF Best Track or Forecast Advisories to generate dynamically consistent pressure and wind fields for storm surge predictions.
Storm Parameterslon, lat of center of eye VmaxR64 , R50 , R34 in 4 storm quadrantsPc - ATCF BT only
โข Use either R64 , R50 , or R34 distance to strongest wind isotach (64kt, 50kt, 34kt) to solve for a different Rmax in each storm quadrant (NE, NW, SW, SE)
Asymmetric Holland Wind Model (ADCIRC: NWS=19)
Hurricane Bob of 1991 was extremely asymmetrical, having uneven distribution of the wind radii at Aug 19 1991 1226Z.
The asymmetrical characteristic of a hurricane can be addressed in AHW with spatially varying Rmax.
โข Use either R64 , R50 , or R34 distance to strongest wind isotach (64kt, 50kt, 34kt) to solve for a different Rmax in each storm quadrant (NE, NW, SW, SE)
โข Interpolate Rmax around storm Rmax (ฮธ)
Asymmetric Holland Wind Model (ADCIRC: NWS=19)
Hurricane Bob of 1991 was extremely asymmetrical, having uneven distribution of the wind radii at Aug 19 1991 1226Z.
The asymmetrical characteristic of a hurricane can be addressed in AHW with spatially varying Rmax.
๐ ๐๐๐ฅ (๐ )
โข Holland Equations (4), (5), (6)
โข Use either R64 , R50 , or R34 distance to strongest wind isotach (64kt, 50kt, 34kt) to solve for a different Rmax in each storm quadrant (NE, NW, SW, SE)
โข Interpolate Rmax around storm Rmax (ฮธ)
Asymmetric Holland Wind Model (ADCIRC: NWS=19)
Hurricane Bob of 1991 was extremely asymmetrical, having uneven distribution of the wind radii at Aug 19 1991 1226Z.
The asymmetrical characteristic of a hurricane can be addressed in AHW with spatially varying Rmax.
โข Re-calculate B and ฯ using the latest Rmax in each quadrant
B , ฯ
โข Use brute-force marching to solve for Rmax in each quadrant
Rmax
โข Guess initial values without considering coriolis force
B0 , ฯ0
converge ?
โข Spatially interpolate Rmax, B, and ฯ at each ADCIRC node.
Spatial Interpolation
โข Procedures
Implementation of GAM
โข Calculate dynamic wind and pressure fields
Vg(r, ฮธ), P(r, ฮธ)
โข Storm center locations, Vmax, Pn, Pc, multiple Isotachs and their radii, etc
Inputs
ASWIP ADCIRC
Fort.22
Output
Weighted Composite Wind Field
NE
Isot 34
Isot 50
Isot 64
Composite
SE SW NW
Weighted Composite Wind Field
NE
Isot 34
Isot 50
Isot 64
Composite
SE SW NW
Weighted Composite Wind Field
NE
Isot 34
Isot 50
Isot 64
Composite
SE SW NW
AHM (NWS = 19) only uses the highest isotach in each quadrant to generate its wind/pressure field.
GAM uses a linear weighting of parameter sets computed from all available isotachs in each quadrant.
Weighted Composite Wind Field in GAM
R64 R50 R34
Weighted Composite Wind Field
NE
Isot 34
Isot 50
Isot 64
Composite
SE SW NW
Comparison of Spatial Wind Fields (Strong Wind)
GAMAHM NWS=19
Comparison of Spatial Wind Fields (Weak Wind)
GAMAHM NWS=19
โข A new โGeneralized Asymmetric vortex Model" is implemented in ASWIP / ADCIRC, that solves the full gradient wind equation, and utilizes all available isotachs to generate composite wind fields.
โข The new formulation allows the model to (i) faithfully represent weaker and larger storms and (ii) to exactly fit multiple wind isotachs that are typically specified in each storm quadrant in either forecast or best track input.
โข Because GAM is still a parametric model, it lacks complexity when compared to re-analysis H*Wind. Does best available job of representing available ATCF BT / forecast parameters.
Conclusions
NWS = 19 GAM H*Wind
Thank you!
NWS = 19 NWS = 20 H*Wind
Comparison of Spatial Wind Fields (Strong Wind) Cont.
AHM NWS=19 GAM
Comparison of Spatial Wind Fields (Weak Wind) Cont.AHM