NOGAPS is the principal model system in FLENUMOCEANCENs operational data runs which begin at 00Z and 12Z. It starts approximately 4 hours into a data run. NOGAPS replaced the Primitive Equation (PE) model as FLENUMOCEANCENs primary forecast model in 1982. NOGAPS was last updated in 1986.

NOGAPS upper-air subset is run every 6 hours, even though radiosonde and rawinsonde observations are taken synoptically at 0000Z and 1200Z only. By running the program every 6 hours, off-time observations can be included in the run. This permits the inclusion of satellite data and aircraft reports, as well as off-time buoy and ship reports. This means that during any single analysis, there can be as much as a 6-hour difference in observations. The program carries the off-time data forward to analysis time. This process is referred to as data assimilation.

The 0600Z and 1800Z upper-air analyses are used as a basis for the 1200Z and 0000Z data runs. They are NOT transmitted to the Fleet.

In addition to the NOGAPS-generated spherical upper-air analyses, FLENUMOCEAN-CEN also produces global band upper-air analyses and southern hemispheric polar stereographic upper-air analyses.

Winds and temperatures are analyzed on a global band grid every 12 hours. The grid is a Mercator projection true at 22 1/2 degrees latitude and extends from 40S to 60N. The first-guess field south of 22N is based on persistence, reverted to climatology. This is primarily due to the sparseness of data over large portions of this region. North of 22N, NOGAPS upper-air analysis fields are used.

Numerous types of data are used in the analysis. Convent ional radiosonde and aircraft reports are used in both the wind and temperature analyses. The wind analysis also includes Pibal reports and satellite derived winds. Vertical temperature profiles obtained from satellite radiometers are used in the temperature analysis. The temperature profiles greatly increase the data base in the Southern Hemisphere.

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