Presentation on theme: "Keith Brewster Radar Assimilation Workshop National Weather Center 18-Oct-2011."— Presentation transcript:
Keith Brewster Radar Assimilation Workshop National Weather Center 18-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)
Accessory Script: Scan2a (Perl) Creates pseudo-volume lists using meta-data in NetCDF files for use in NCRAD2ARPS Plotting Routines radarpltncar & radarpltpost Polar Coordinate data pltradcol Radar Column data ARPSplot 2D (by tilt) and 3D remapped data
Radar Column Data 2D and 3D gridded single-variable files Grid-tilt: remapped to Cartesian on tilt surface. Diagnostic data on tilts
a b x y
a b x z
Local least-squares interpolation/smoothing Quadratic 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
Despeckle (remove isolated point targets) Calculate 3 terms in small regions around each gate a) dBZ between 0.5° and 1 st tilt above 1.1° dBZ < -12 dBZ assoc with AP b) dBZ < -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
Read Tilt Anomalous Radial Removal Despeckle & Median Filter (opt) Assemble Volume Ground Clutter Removal Despeckle Continue to Remapping For All Elev < 1.0 All Tilts
Despeckli ng Template If fewer than 2 valid neighbors of 8 in template mark missing.
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.
Raw Obs Anomalo us Radial Removed Clutter Removal
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.
Velocity QC & Dealiasing Steps Find mean wind profile in area within 90 km of radar. From model background or sounding Process by tilt: Spectrum Width Filter Remove mean wind from each radial velocity Start on a radial perpendicular to the mean wind For each radial Check for horizontal continuity Unfold where v t =v m +nV n improves continuity Flag any outliers that cant be resolved After entire tilt processed Recheck flagged gates vs. least-squares quadratic fit of neighboring gates
Read Tilt Spectrum Width Filter Assemble Volume Ground Clutter Removal Despeckle Continue to Unfolding For All Elev < 1.0 Despeckle & Median Filter (opt) All Tilts
Compare to mean wind Gate-to-Gate Shear Check Quadratic Check at Gates Marked Uncertain Calculate Mean Wind Profile Model Data or Sounding …Continued Create perturbation Vr Field Mean Wind Profile Continue to Remapping
Find Radial Perpendicular to Mean WInd Reverse Pass Begin Forward Pass Mean Wind Profile Continue to Remapping Step Direction Shear Comparison Template Repeat
Shear Check Raw Obs Mean Wind
Raw Obs Mean Wind Shear Check 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?