Description of the RTG_SST_HR analysis
NOTE for frequent visitors: Go to Changes to the RTG_SST_HR analysis for
information on changes in the operational 1/12 deg. Real-Time Global SST analysis.
A daily, high-resolution, real-time, global, sea surface temperature (RTG_SST) analysis has been
developed at the National Centers for Environmental Prediction/Marine Modeling and Analysis Branch (NCEP / MMAB).
The analysis was implemented in the NCEP parallel production suite 16 August 2005. It became fully operational on September 27, 2005.
The daily sea surface temperature product is produced on a twelfth-degree (latitude, longitude) grid,
with a two-dimensional variational interpolation analysis of the most recent 24-hours buoy and ship data,
satellite-retrieved SST data, and SST's derived from satellite-observed sea-ice coverage. The
algorithm employs the following data-handling and analysis techniques:
Satellite retrieved SST values are averaged within 1/12 o grid boxes
with day and night 'superobs' created separately for each satellite;
Evaluations of the analysis products have shown it to produce realistically tight gradients in the
Gulf Stream regions of the Atlantic and the Kuroshio region of the Pacific, and to be in close
agreement with SST reports from moored buoys in both oceans. Also, it has been shown to
properly depict the wintertime colder shelf water -- a feature critical in getting an accurate
model prediction for coastal winter storms.
Bias calculation and removal, for satellite retrieved SST, is the technique
employed in the 7-day Reynolds-Smith climatological analysis;
Currently, the satellite SST retrievals are generated by a physically-based algorithm from the Joint Center for Satellite Data Assimilation. Retrievals are from NOAA-19 and METOP-A AVHRR data;
SST reports from individual ships and buoys are separately averaged within
The first-guess is the prior (un-smoothed) analysis with one-day's climate
Late-arriving data which did not make it into the previous SST analysis
are accepted if they are less than 36 hours old;
Surface temperature is calculated for water where the ice cover exceeds
50%, using salinity climatology in Millero's formula for the freezing point
of salt water:
t(S) = -0.0575 S + 0.0017 S3/2 - 0.0002 S2,
with S in psu.
An inhomogeneous correlation-scale-parameter l, for the
correlation function: exp(-d2/l2) ,
is calculated from a climatological temperature gradient, as
l = min ( 450 , max( 2.25 / |grad T| , 100 )),
with d and l in kilometers. "grad T" is in oC / km