Use of NetCDF-Formatted Wind Fields from OWI in ADCIRC

This new OWI file format was developed by Alex Crosby and his team at Oceanweather Inc. Most of the ADCIRC code to handle these new input files was implemented by Casey Dietrich.

ADCIRC has now been updated to allow the usage of NetCDF-formatted atmospheric fields from Oceanweather Inc. (OWI). In this new format, the surface pressure and wind fields have flexibility to represent different storms with different fields, to track storms with moving fields, and to vary resolution of the fields in both space and time. These updates have been added to the latest development version of ADCIRC, and they will be available in the next release version. These new fields are read by ADCIRC using the NWS=13 parameter and a new input file.

The following animation shows the use of this new file format in an ADCIRC simulation for the wind fields due to Hurricane Charley (1999). Note that Charley is one of several storms during this period, and each storm is represented by a moving field overlaid on a coarser background field.

In the rest of this page, we describe the new input file format, how it is used in ADCIRC, and then provide a set of example files.


NetCDF-Formatted Wind Fields

This new atmospheric input is formatted in NetCDF, which allows for greater flexibility. ADCIRC users may be familiar with using OWI input in ASCII format (NWS=12), which allows for two fields (typically called basin- and region-scale), and which can lead to large file sizes (often a few GB for a week’s worth of atmospheric input). In contrast, the NetCDF format is compressed for smaller file sizes, and it allows for fields (called groups in the NetCDF file) with varying coverages.

The new NetCDF files must be constructed in a particular way. The format is described on the ADCIRC Wiki. To avoid duplication, the specific requirements are not reproduced here.

The new NetCDF-formatted input files will allow for greater flexibility in defining the atmospheric forcing. Storms can be specified as groups with moving, stretching grids and greater resolution in space and time. Storm center locations can be specified with exact coordinates for use in wind drag parameterizations. The new input files will be self-contained and likely smaller than the older file format.

The following animation shows another view of the example above for Hurricane Charley (2004). In this animation, the contours show the number of the group used for surface pressures and wind speeds. In most of the domain, the atmospheric forcing is from the first group, but closer to the storms, the atmospheric forcing comes from a higher-numbered group. Note that there are three storms: Bonnie, Charley, and Earl. The new file format allows for all three storms to be represented during this time period.


How to Use the New File Format with ADCIRC

ADCIRC can read and apply the atmospheric forcing from this new NetCDF-formatted input file. There are only a few minor changes to the ADCIRC workflow. These are also described on the ADCIRC Wiki.

With these minor changes, ADCIRC will know to look for atmospheric forcing in the new input file, to connect the surface pressure and wind fields to the correct times during the simulation, to multiply the input wind velocities by a value specified by the user, and to apply the sector-based wind drag scheme to only the group specified by the user.

The following animation shows another view of the example above for Hurricane Charley (2004). In this animation, the contours show the wind drag coefficients. ADCIRC has been instructed to apply the sector-based drag scheme only to group 3 (Charley), and thus the other two groups (Bonnie and Earl) use the default drag scheme from Garratt. Note how the largest drag coefficients are applied when Charley is strongest, as it moves near Cuba.


Example Input Files for Charley (2004) Simulation with ADCIRC

Alex Crosby and his team at Oceanweather Inc. have constructed an example input file for Hurricane Charley (2004), as shown in the preceding animations. It is emphasized that these surface pressure and wind fields have not been validated in any rigorous manner, and thus their accuracy cannot be guaranteed. They are provided only as an example of the file format and its use by ADCIRC.

The entire set of example input files is:

That ZIP file contains an example NetCDF-formatted input file (as the, as well as other input files for a 7-day simulation on the very-coarse EC95d mesh. The mesh and its attributes are described in the fort.14 and fort.13 files, respectively. In the fort.15 file, the sector-based wind drag scheme is activated, and it will be applied only to the third group (Charley) in the wind file.

Please let us know if you have any questions about this new input file format. Good luck with your modeling!