keith brewster radar assimilation workshop national weather center 18-oct-2011
TRANSCRIPT
CAPS Radar QC and Remapping
Keith BrewsterRadar Assimilation Workshop
National Weather Center18-Oct-2011
Remapping Drivers 88D2ARPS
◦ NEXRAD WSR-88D Level-II◦ China 98D WSR-98D Level-II◦ TDWR◦ Output to Solo DORADE
NIDS2ARPS◦ NEXRAD Level-III
NCRAD2ARPS◦ CASA NetCDF◦ WDSS-II Tilt NetCDF (KOUN, Taiwan data)◦ OU-PRIME NetCDF◦ FORAY NetCDF (field project data)
Radar I/O & Remapping Capabilities
Radar Sampling Problem-Horizontal
a
b
x
y
Radar Sampling Problem -Vertical
a
bx
z
Local least-squares interpolation/smoothingQuadratic in horizontal Linear in vertical
Smooths dense data Superobbing consistent with model grid Interpolates accurately in
data-sparse regions Can be applied in 2D on ray surface. Ray paths: 4/3-earth ray path or estimate of bulk
refractive index gradient with height Full range of map projections & vertical grid stretching
supported
CAPS Radar Remapping
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Remapping to Dx = 2 km
Remapped Radar Field x-z Cross-section
Despeckle (remove isolated point targets) Calculate 3 terms in small regions
around each gatea) DdBZ between 0.5° and 1st tilt above 1.1°
DdBZ < -12 dBZ assoc with APb) DdBZ < -20 dBZ assoc with ground targets such as
wind turbines c) Texture.. Spin Change. A lot of changes in sign of
gate-to-gate reflectivity gradients associated with AP. d) Mean Radial Velocity
Small magnitude of mean radial velocity associated with AP
Weak check: Fails 2 or more of 3 checks Strong check: Fails 1 or more checks
AP/Clutter Detection
Sunrise/Sunset Radials
Sunrise/Sunset Radials
Point source interference, such as sun, produces characteristic signature.
• High percentage of radial is non-missing.• Reflectivity factor increasing linearly with range.• Small variance from linearity.
KDDC Sunset & Clutter
RawObs
AnomalousRadialRemoved
Clutter Removal
Sea Clutter
Three Pronged Approach◦ Background Comparison
Most useful for removing shear with height due to mean wind profile
Background from model or VAD◦ Two-dimensional continuity
Applied in multiple directions◦ Final Quadratic fit for uncertain points.
CAPS Real-time Velocity QC & Dealiasing
Gate-to-Gate Shear Check
Find Radial Perpendicular to
Mean WInd
Reverse Pass
Begin
Forward Pass
Mean Wind
Profile
Continue to Remapping
Step Direction
Shear Comparison
Template
Repeat
Multiple Folded Data
ShearCheck
Raw Obs
Mean Wind
KTLX 10 May 2010 6.5° Scan
Raw Obs
Mean Wind
ShearCheck
Quad Fit
Increasing Flexibility New NAMELIST control file added Correction factors for mobile radars Moving tunable parameters to NAMELIST
Dual-Pol for WSR-88D Some experience with CASA Additional algorithms for clutter and non-precip
echo identification & removal
Radial-by-radial ray tracing.
Can we use vortex recognition/fitting techniques to improve QC and analysis near strong vortices?
Ongoing Work