RUC testing – Updated 8 June 2006

-       Stan Benjamin, NOAA/ESRL/GSD, Geoff Manikin, NCEP/EMC

-       Other contributors to code changes, testing – ESRL/GSD - John Brown, Steve Weygandt, Tanya Smirnova

 

Changes listed below for RUC analysis and model code are in real-time testing as Feb 2006 - current

-       NCEP/EMC parallel RUC13 cycle (Geoff Manikin has real-time parallel/oper graphics available at http://www.emc.ncep.noaa.gov/mmb/ruc2/para .)

o      NCEP para RUC13 has been running with the main analysis/model changes since November 2005

-       NOAA/ESRL/GSD development RUC13 cycle since fall 2005 and GSD backup RUC13 cycle since March 2006.

 

Overall effects of changes:

¤       Improved precipitation over oceans and coastal areas.

¤       Improved RH forecasts

¤       Improved upper-level winds – related to improved precipitation

¤       Improved surface fields in coastal areas

 

 

Analysis

  1. More restrictive observation quality control.
    1. Now uses obs-minus-background threshold checks (e.g., ~8 K for temps, 12-20 m/s for winds.   More detailed conditions also set – larger thresholds in stratosphere, smaller thresholds at surface, etc.).  RUC 1h forecasts are used for background.  
    2. Helps screen isolated problem obs with profiler, RASS temperature, aircraft, and surface observations, that are not consistently detectable by RUC buddy-check QC.

 

  1. Added check of mean temperature innovation (O-B) for aircraft reports, flagging all reports from a given aircraft with at least 2K bias and at least 20 reports in last 1-h period.  (Added 16 Feb 2006 to GSD devRUC13.) – IMPLEMENTED Wed 22 Feb 2006 in operational NCEP RUC13.

 

  1. Improved usage of coastal and ocean surface observations
    1. Revised check of observation-model elevation difference for observations over water grid points in model (e.g., KEYW, KACKÉ)
    2. Improves representation of winds and ceiling/visibility over coastal and ocean areas in RUC analysis.
    3. Nudging of soil temperature and moisture (introduced with 13km RUC in June 2005) is now strongly damped in coastal regions where the surface obs and model land/water type result in representativeness problems.  [This was evident in a 2m temp / soil temp problem in eastern North Carolina found by EMC in Feb 2006.] 
    4. Matching of nearby grid points (land or water) to coastal observations for calculating of innovations (observation-background difference) is improved.  This matching uses the grid point with the smallest 2m temp innovation, assuming that this indicates whether the coastal station is under a marine or land influence.   With this the overall mean-absolute difference for METARs is decreased from ~1.4K to ~1.0K, meaning that the coastal surface obs are now introducing less noise in coastal areas, especially for temperature.

 

  1. Fix to avoid bullseye in RUC analysis if lowest mandatory level with temp data has elevation less than station elevation (shouldnŐt happen, but it did for 12z on12 Nov 05 at Birmingham, AL).

 

  1. Fix errors in cloud analysis
    1. The current RUC cloud analysis inadvertently removes all rain and snow mixing ratios under the condition of current precipitation from the nearest METAR station.   This is exactly the opposite of what should happen.
    2. Use of GOES cloud-top data over water – The code for height assignment for marine stratus to identify the top of the marine PBL in the RUC background had a bug under a certain condition.  With the correction, the RUC initial cloud fields now depict marine stratus much better than in the current operational RUC.   This leads to improved coastal cloud forecasts, especially on the West Coast.

 

  1. Check for zero observations to avoid 3DVAR problem in this case with mass/wind imbalance.

 

Model

  1. Fix to error in Grell-Devenyi convective parameterization over water areas
    1. G-D convective parameterization uses an ensemble closure approach to estimate mean mass flux, but the denominator to calculate this mean mass flux was in error over water areas (where different closures are used).  This problem was inadvertently introduced with the RUC13 in June 2005.
    2. The convective precipitation behavior is more realistic (and generally stronger) with the fix over water areas (e.g., especially Gulf of Mexico, but also off West Coast over eastern Pacific, and even over Great Lakes).   Some differences are also noted over land areas.  Upper-level winds affected by latent heating from oceanic convection are also improved.

 

  1. Digital filter initialization (DFI) redesigned to provide more robust model behavior and improve initial cloud fields (diabatic DFI)
    1. The revised DFI in the RUC model now applies a backward integration first (rather than second).
    2. The forward DFI step is now with full physics, allowing more physical consistency with latent heat effects and improved initial cloud/hydrometeor fields affecting 0-2h forecasts of these variables.
    3. Diabatic DFI allows the RUC model to run without failure using the higher-resolution terrain elevation field for model failure cases (19 Nov, 22 Nov) with the RUC model using the original adiabatic DFI with the high-res terrain elevation.
    4. The new diabatic DFI also resets the RH and hydrometeor values back to the analyzed values after the completion of the DFI.   This was found to improve the accuracy of short-range RH forecasts.

 

  1. Higher-resolution topography (works reliably with diabatic DFI, last bullet)
    1. Better orographic effects on near-surface winds (including downslope winds, blocking) and precipitation.

 

Post-processing

  1. Modifications to ceiling (cloud base) diagnostic
    1. Change to eliminate ground fog (lowest 2 RUC native levels) from ceiling identification to distinguish fog from low ceiling as done with METAR observations.
    2. Correction to ceiling interpolation to 20-km (and 40-km) grid to avoid waffle-pattern.
  2. Correction to equivalent potential temperature calculation
  3. Correction to temperature calculation in downscaling of RUC13 data to 5km for RTMA first-guess.   Avoids problem in situation with very strong inversion near surface to provide reasonable temperatures along sides of slopes in mountainous areas.
  4. Correction to 2m RH calculation so that it is consistent with the 2m T and surface pressure (at the minimum topography level) such that recalculation of dewpoint (Td) via 2m RH gives the proper 2m Td (as is done in AWIPS).  This change will improve AWIPS calculations using 2m RH (Td, CAPE, etc.)