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Binary Scaling of 2.5-km CONUS Gridded LAMP GRIB2 Files

The Localized Aviation Model Output Statistics Program (LAMP) is producing Gridded LAMP (GLMP) analyses and forecasts over the CONUS at 2.5-km grid resolution via NCEP's parallel production system. GLMP generates forecasts for the elements of temperature, dewpoint temperature, continuous ceiling height, and continuous visibility for projections 1-25 hours. Since each GRIB2 file contains several grids (one per projection hour) at a 2.5-km resolution, these GRIB2 files can be large. In order to reduce the GRIB2 file sizes, MDL will use binary scaling when packing 2.5-km NDGD data into GRIB2. Previously, MDL used decimal scaling which did not affect the precision of the forecast guidance. Decimal scaling simply multiplies the data by powers of 10 (i.e. any real value forecast will be packed as integer). The following equation describes the scaling used in GRIB2 packing:

NINT Formula

where X = packed value; Y = actual value; D = decimal scale factor; B = binary scale factor. The C function, NINT, allows the value to be rounded to the nearest integer, instead of truncating. As shown from the equation above, binary scaling is performing division arithmetic on the data which will introduce a loss of precision.

MDL will begin to use binary scaling with the 1200 UTC cycle on June 21, 2011 when packing data in GRIB2 format for the GLMP elements listed in the table below. This change is announced in TIN 11-18. Click on the element name to see animated GIF images comparing non binary scaling vs. binary scaling.

Element

Original Precision

Decimal Scale Factor

Binary Scale Factor

Maximum Possible Loss of Precision After Scaling

Temperature Analysis

0.1 K

1

2

0.4 K

Temperaure Error Analysis

0.1 K

1

2

0.4 K

Dewpoint Temperature Analysis

0.1 K

1

2

0.4 K

Dewpoint Temperature Error Analysis

0.1 K

1

2

0.4 K

Ceiling Height Analysis

1 M

0

3

4 M

Visibility Analysis

1 M

0

7

64 M

Temperature Forecast

0.1 K

1

2

0.4 K

Dewpoint Temperature Forecast

0.1 K

1

2

0.4 K

Ceiling Height Forecast

1 M

0

3

4 M

Visibility Forecast

1 M

0

7

64 M

Using the scaling factors listed above, we were able to decrease file sizes between 21% - 26% of their original size for the temperature analysis and forecasts, temperature error analysis, dewpoint temperature analysis and forecasts, dewpoint temperature error analysis, and ceiling height analysis and forecasts.  The file sizes for the visibility analysis and forecasts were reduced by approximately 61% and 50%, respectively.


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Page Last Modified: May 31 2011 12:50:33. UTC