Brief description of change(s): This change will replace the use of the 1 degree by 1 degree Reynolds optimum interpolation (OI) analysis of sea-surface temperature (SST) in the Meso Eta Model runs with a new SST analysis. EMC's Ocean Modeling Branch has designated this the Real Time Global SST (RTG_SST) which is performed on a 50 km grid and had been referred to in earlier messages as the 2DVAR. The following changes are also being made at this time but they do not effect the model evolution in any way. We are a) refining our restart capability which will be used for the 84 hour extension in February, b) adding output to the lateral boundary condition files that are generated each hour of the forecast for the nested Meso runs "threats" and allow the sea-level pressure reduction in the nest to match that in the parent, and c) correcting the procedure for diagnosing the 10 m winds.
Reason for Change(s): EMC has been working towards this SST change since October, but it has been elevated to crisis status following the meetings of a Tiger Team recently assembled to examine the poor Meso Eta guidance for the DC and Baltimore areas for the winter storm of 30 December. Following discussions between NESDIS and EMC on 12 January, it was decided that the new high-resolution daily RTG_SST analysis with inhomogeneous (variable) background-error covariance function provided the best possible solution. This new SST analysis is expected to be a major improvement over the current operational SST analysis products (NCEP's Reynolds analysis and NESDIS' MCSST) and a slight improvement over the one studied during the Tiger Team evaluation which used a homogeneous (fixed) covariance length of 222 km. The new analysis includes in-situ observations and high-resolution (4 km) satellite SST retrievals, generating a daily analysis with variable-scale (100 to 450 km) covariance functions. These data are also used in the Reynolds OI, however it uses 7-days of data, with 1 degree super-obing resulting in a very smooth analysis. The NESDIS analysis product is at 50 km but uses the satellite retrievals only. The RTG_SST analysis uses only the most recent 24 hours of data, is performed on a higher-resolution (50 km) grid than the Reynolds and produces a sharper depiction of the warm core of the Gulf Stream and associated gradients. It also is the only analysis to properly depict the colder shelf water - a feature that was noted by the Tiger Team to be critical in getting an accurate model prediction for the recent east coast winter storm. The Meso Eta Model is capable of providing the proper mesoscale response to ocean forcing but only if it has the proper mesoscale structures depicted in the SST. EMC's parallel run (Etax) at the time was running with the fixed correlation length version of the RTG_SST and now uses the variable length version.
The change to the 10 m wind diagnosis is in response to an inadvertent change that was implemented when operations were being established on the IBM SP following the fire in the Cray C-90. We had been testing ways to correct a low bias in 10 m wind speeds in the mountainous west and a code change that resulted in stronger winds everywhere was mistakenly implemented on the IBM. This change had the desired effect over elevated terrain of increasing the diagnosed 10 m wind speeds but the change had not been localized to elevated terrain and had a negative effect over areas of lower elevation. This can be seen by comparing the statistics for the same month before and after November 1999 at our web page of near surface verifications: http://www.emc.ncep.noaa.gov/mmb/research/nearsfc/nearsfc.verf.html . A localized variant of the correction to 10 m winds has been in the 22 km parallel since November. Verifications have been added to the above web page. Again, the computation of the 10 m wind is purely diagnostic so this change does not effect the model prediction.