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Maps

For the entire domain of the regional models and for several views of the global model maps of the significant wave heights (Hs) peak wave periods (Tp), and wind speeds (U10) are available. The peak wave period is estimated as the period corresponding to the highest peak in the one dimensional frequency spectrum of the wave field. Some of the maps also depict wind barbs and peak wave directions. The peak direction is defined as the mean direction in the frequency bin corresponding to Tp. The run date and cycle are shown at the top of each map. The originating model (global, regional) is identified at the top left corner of the plot, the valid time at the top right corner. 00z equals midnight GMT, 12z equals noon GMT, etc. The maps are presented as gif files. The output locations are marked with yellow squares with red borders wherever the map resolution allows for identification of individual points. Dark green identifies land, grey identifies ice.

The significant wave height is a commonly used statistical measure for the wave height, and closely corresponds to what a trained observer would consider to be the mean wave height. Note that the highest wave height of an individual wave will be significantly larger. The peak period is not commonly presented. The wave field generally consists of a set of individual wave fields. The peak period identifies either the locally generated "wind sea" (in cases with strong local winds) or the dominant wave system ("swell") that is generated elsewhere. Note that the peak period field shows discontinuities. These discontinuities can loosely be interpreted as swell fronts, although in reality many swell systems overlap at most locations and times (see spectra below).


Spectra and Source Terms

Spectra and source term are presented for selected output locations in the form of polar plots. The radial lines in the polar plots depict the directional resolution of the model. The concentric circles are plotted at 0.05 Hz intervals, where the innermost circle corresponds to 0.05 Hz and the outermost circle corresponds to 0.25 Hz. Wave energy plotted in the lower left quadrant travels in SW directions etc. The blue arrow in the center of the plots depicts wind speed and direction. Colors represent wave energy density for spectra and rates of change of energy density for source terms and are plotted at a logarithmic scale where the contours separating the colors increase by a factor of 2. For spectra, the color sequence is identical to that of the maps. For source terms a similar scaling is used where white indicates little or no change, blue indicates a decrease of spectral energy density and red an increase. Per page, all six spectra use the same contour levels, with the maximum contour level scaled to the maximum energy density in the six plots. The four source term plots per page are scaled similarly. The spectra and source term plots are presented as gif files. Numerical information corresponding to these figures can be found in the bulletins.


GRIB Files

Fields of mean wave parameters are available in the WMO GRIB format (e.g., NCEP 1998 or MMAB tools page). The table below gives the so-called kpds number, a GRIB identifier and a description of all fields packed in GRIB. The GRIB files contain data at 3 hour intervals, starting at the 0 hour forecast (i.e., no hindcast data available).

kpds number GRIB identifier Description
31 WDIR Wind direction (degr., oceanographical convention).
32 WIND Wind speed (m/s).
33 UGRD Wind U component (m/s).
34 VGRD Wind V component (m/s).
100 HTSGW Significant wave height (m).
101 WVDIR Mean wave direction (degrees, oceanographical convention).
103 WVPER Mean wave period (s)
107 DIRPW Peak wave direction (degrees, oceanographical convention).
108 PERPW Peak wave period (s)
109 DIRSW Wind sea direction (degrees, oceanographical convention). Undefined if wind too weak to generate wave in spectral model domain.
110 PERSW Corresponding wind sea period (s).

For a more detailed description of the definition of the parameters see section 2.4 of the manual of WAVEWATCH III®.

All GRIB files can be retrieved from the directory ftp://polar.ncep.noaa.gov/pub/waves/. The GRIB directory format is YYYYMMDD.tHHz where YYYYMMDD is the date, tHHz is the run cycle identifier (t00z through t18z, respectively). The number of dates and cycles for which data are available may vary based upon available resources.

Alternatively, ftp://polar.ncep.noaa.gov/pub/waves/latest_run/ gives access to the most recent model results.

The file names for the GRIB files are model_ID.grib_ID.grb, where model_ID is a model identifier (nww3, akw, wna, nah or enp for global, Alaskan Waters Western North Atlantic, North Atlantic Hurricane and Easrern North Pacific model, respectively), and where grib_ID represents a GRIB identifier as in the table above. The file model_ID.all.grb contains all GRIB fields.


Spectral data

Spectral data is available in compressed (gzip) ASCII files, which contain environmental data and the full two-dimensional spectra. These files are direct output files of the WAVEWATCH III® post-processor. A description can be found in the manual on page 72 for ITYPE = 1 and subtype 3. The actual location of the output in the model can be retrieved from these files or from the table or text version of the NWW3 data interface. The spectra are frequency-direction spectra where the direction is the Cartesian direction in which the waves travel. Note that within WAVEWATCH III®, the band width for spectral integration is set to 0.5*(XFR-1./XFR)*FREQ, where XFR = 1.1 is the logarithmic increment factor in the spectral grid.

All spectral data files can be retrieved from the directory ftp://polar.ncep.noaa.gov/pub/waves/. The directory format is YYYYMMDD.tHHz where YYYYMMDD is the date, tHHz is the run cycle identifier (t00z through t18z, respectively). The number of dates and cycles for which data are available may vary based upon available resources.

Alternatively, ftp://polar.ncep.noaa.gov/pub/waves/latest_run/ gives access to the most recent model results.

The file names for the data files are model_ID.location_ID.spec.gz, where model_ID is a model identifier (nww3, akw, wna, nah or enp for global, Alaskan Waters Western North Atlantic, North Atlantic Hurricane and Easrern North Pacific model, respectively) and where location_ID represents the name of the output location. Browse the ftp directory for valid location identifiers. All files are compressed using gzip and can be uncompressed using gunzip.


Spectral bulletins

Spectral text bulletins are presented for all output points of the global and regional NWW3 implementations. The bulletins are presented in plain ASCII. The line length of the main table is 130, and the bulletin typically consists of about 100 lines. The header of the table identifies the output location, the generating model and the run date and cycle of the data presented. At the bottom of the table, a legend is printed. The table consists of 8 columns. The first column gives the time of the model results as day and hour (the corresponding month and year can be deduced from the head information). The second column presents the overall significant wave height (Hs), the number of individual wave fields identified with a wave height greater than 0.05 m (n), and the number of such fields with a wave height over 0.15 m that could not be tracked in the remainder of the table (x). Individual wave fields in the spectrum are identified using a partitioning scheme similar to that of Gerling (1992). In the remaining six columns individual wave fields are tracked with their wave height (Hs), peak wave period (Tp) and mean wave direction (dir, direction in which waves travel relative to North). Generally, each separate wave field is tracked in its own column. Such tracking, however, is not guaranteed to work all the time. A `*' in a column identifies that the wave field is at least partially under the influence of the local wind, and therefore most likely part of the local wind sea.

All bulletins can be retrieved from the directory ftp://polar.ncep.noaa.gov/pub/waves/. The directory format is YYYYMMDD.tHHz where YYYYMMDD is the date, tHHz is the run cycle identifier (t00z through t18z, respectively). The number of dates and cycles for which data are available may vary based upon available resources.

Alternatively, ftp://polar.ncep.noaa.gov/pub/waves/latest_run/ gives access to the most recent model results.

The file names for the bulletin files are model_ID.location_ID.bull, where model_ID is a model identifier (nww3, akw, wna, nah or enp for global, Alaskan Waters Western North Atlantic, North Atlantic Hurricane and Eastern North Pacific model, respectively), and where location_ID represents the name of the output location. Browse the ftp directory for valid location identifiers.


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Page last modified: Thursday, 15-Nov-2012 18:56:51 UTC