User Guide 005
Oceanweather Wind File The Oceanweather format uses separate ASCII files to specify the wind speeds, atmospheric pressure and grid coordinates. The CMS-Flow cards used to specify the Oceanweather files are described below.
table 2-36
example 2-21
The last two arguments of the header are the starting and end times in yyyymmddhh. The wind data are preceded by a header line with the grid information. iLat and iLong are latitude North and longitude West. DX and DY are the grid spacing in units of degrees. SWLat and SWLon are the coordinates of the south-west grid point. DT is the actual time in yyyymmddhhMM. First the wind velocities in the x-direction are read then the velocities in the y-direction. The wind speeds are written in m/s.
example 2-22
Oceanweather Pressure File The file format for the Oceanweather pressure file (*.pre) is best described with an example.
example 2-23
The last two arguments of the header are the starting and end times in yyyymmddhh. The atmospheric pressure data (in units of mbar) is preceded by a header line with the grid information. iLat and iLong are latitude North and longitude West. DX and DY are the grid spacing in units of degrees. SWLat and SWLon are the coordinates of the south-west grid point. DT is the actual time in yyyymmddhhMM. Oceanweather Coordinate File
The file format for the Oceanweather coordinate file (*.xy) should contain the coordinates of the Oceanweather grid in the same coordinate system as the CMS-Flow grid. The order of the points should be from the south-west corner along each row. An example of an Oceanweather Coordinate File is shown below. ________________________________________
Notes: • The first column is the horizontal coordinate, and the second is the vertical coordinate. • The coordinates must be in the same coordinate as the CMS.
Tip: • The easiest way to generate the Oceanweather Coordinate File is to make an ASCII file containing the coordinates in geographical coordi-nates, bring it into SMS, reproject on the CMS coordinate system and export the coordinates into a file to be used as the Oceanweather Coordinates File. A small Fortran program provided which converts the Oceanweather grid information to an *.xy file on the CIRP website: http://cirp.usace.army.mil/CIRPwiki/images/8/82/WINDLOC.rar
Meteorological Stations Meteorological stations can be used to force the model. The locations of the stations are specified in the same coordinate system as the CMS-Flow (world coordinates). There are several options and parameters that can be set for each meteorological (met) station. The table below describes the CMS-Flow cards related to the met stations.
figure 2-37
table 2-37
example 2-24
The wind components from meteorological stations is interpolated spatially using inverse-distance interpolation. A description of the interpolation procedure is provided in Appendix H. One advantage of the inverse-distance interpolation is the interpolation weights are independent of the interpolation function, and therefore only need to be calculated once and can be saved for computational efficiency.
Wind Reference Frames Winds are specified in an Eulerian reference frame with respect to the solid earth. When the wind in the same direction of the currents the wind shear stress is lowered (Figure 2 38). When the wind and currents are in opposing directions, the wind shear stress is increased. For example, in the case of a current velocity of 1 m/s, with an opposing wind speed of 5 m/s, the Eulerian reference frame will give a surface stress proportional to (5 m/s)2 = 25 m2/s2, while the Lagrangian reference frame will produce a surface proportional to (5-(-1) m/s)2 = 36 m2/s2, which is an increase of 44%.
figure 2-38
The wind reference frame is specified with the advanced card described in the table below.
table 2-38
examle 2-25
Notes: • By default, the wind reference frame is set to Eulerian. It is recom-mended field applications to change the wind reference frame to Lagrangian. • The Lagrangian reference frame is especially important for cases with high wind velocities such as storms.
Wind Drag Coefficient The wind drag coefficient is calculated with the Hsu (1988) formula. The drag coefficient may be modified to scale the wind surface stress. The table below described the cards related to the wind drag coefficient. For further details on the wind drag coefficient see section Wind Surface Stress in the technical report.
table 2-39
example 2-26
example 2-27
Anemometer Height By default, the CMS assumes that the input wind velocities are specified at a 10-m height, if the height is different, the user may enter a different value as the Anemometer height. In SMS 11.0, the anemometer height is specified in the Wind/Wave tab of the CMS-Flow Model Control window. The wind velocities are internally converted to a 10-m reference height using the 1/7 rule (see Section Wind Surface Stress).
table 2-40
example 2-28