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3dVAR implementation planned for oper RUC on 20 May

Posted By: Stan Benjamin
Date: 19-May-03 2027Z

Hello. A change in the analysis of the operational RUC is planned for Tuesday 20 May 2003 (date subject to possible change). The change is to a 3-d variational (3DVAR) analysis, replacing the previous optimal interpolation (OI) analysis. While the code change is significant, the difference in RUC analyses and forecasts is not so big. Generally, the RUC 3DVAR analysis fits obs more closely but avoids some small-scale noise produced by the OI analysis. Forecast skill from RUC forecasts using 3DVAR is very nearly the same as that from the OI analysis, slightly better for upper-level winds.

A Technical Procedures Bulletin with more detail on the change, verification statistics, and examples of comparisons of analysis and forecast is available online at http://ruc.fsl.noaa.gov/ppt_pres/RUC-3dvar-tpb-May03.htm.

Please write if you have questions.

Stan Benjamin

The following is a "notice of intent to change" the RUC analysis to a 3DVAR version, distributed last Friday:

Brief Description of Changes:

An upgrade to the NCEP Rapid Update Cycle analysis from an optimal interpolation (OI) technique to a 3-d variational (3DVAR) technique. As described in the Notice of Intent to Change in Feb 2002, the RUC 3DVAR implementation was deferred from the original 20-km RUC implementation
in April 2002.

The RUC 3DVAR analysis uses the same hybrid isentropic-sigma coordinate as used in the RUC OI analysis (and RUC forecast model). Overall, the RUC 3DVAR provides
- Slight improvement or about equal skill overall in 3-h and 12-h forecasts compared to those from the previous RUC OI analysis as verified against rawinsondes.
- Closer fit to observations than the RUC OI analysis.
- A smoother analysis increment (correction to 1-h forecast field) and quieter short-range forecasts.
- Capability for assimilation of indirect observations such as radial winds, satellite radiances, and wind speed.

Also, a few minor changes to the RUC post-processing are also being implemented with this change package, including addition of 0-1 km helicity and some small fixes.

A Technical Procedures Bulletin describing these changes in detail can be found at http://ruc.fsl.noaa.gov/ppt_pres/RUC-3dvar-tpb-May03.htm.
(figures seem to show up better with Internet Explorer browser than with Netscape).

Reasons for Changes:

3DVAR analysis

To improve forecast accuracy, fit to observations, to provide quieter short-range forecasts and the capability for assimilating indirect observations such as radar radial winds, satellite radiances, and wind speeds.

More detail is provided in the online TPB at:

Schedule for change:

Final testing : Ongoing since November 2002
Expected implementation : Tuesday 20 May 2003

Description of testing:

Initial testing was done at NOAA/FSL for retrospective periods in May 2000 and February 2001. Testing at NCEP was performed for a parallel real-time cold season period from November 2002 through January 2003. A retrospective warm season period test was conducted for a 28-day period during August 2002 into early September 2002.

Again, this testing is described in more detail with graphics of examples and overall statistics in the RUC 3DVAR TPB at

Points of Contact:

Stan Benjamin Stan.Benjamin@noaa.gov 303-497-6387
Steve Weygandt Stephen.Weygandt@noaa.gov 303-497-5529
Geoff Manikin Geoffrey.Manikin@noaa.gov 301-763-8000 ext 7263

Messages In This Thread

3dVAR implementation planned for oper RUC on 20 May -- Stan Benjamin -- 19-May-03 2027Z
Re: 3dVAR implementation planned for oper RUC on 20 May -- Geoff Manikin -- 19-May-03 2027Z

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