WRF - Developmental Testbed Center

18. MASKED : Either land or water, indicating whether the field is invalid over land orwater, respectively. When a field is masked, or invalid, the static LANDMASK field willbe used to determine which model grid points the field should be interpolated to; invalidpoints will be assigned the value given by the FILL_MISSING keyword. Default value isnull (i.e., the field is valid for both land and water points).19. MISSING_VALUE : A real number giving the value in the input field that is assumedto represent missing data. No default value.20. VERTICAL_INTERP_OPTION : A character string specifying the verticalinterpolation method that should be used when vertically interpolating to missing points.Currently, this option is not implemented. No default value.21. FLAG_IN_OUTPUT : A character string giving the name of a global attribute whichwill be assigned a value of 1 and written to the metgrid output if the interpolated field isto be output (output=yes). Default value is null (i.e., no flag will be written for the field).Available Interpolation Options in Geogrid and MetgridThrough the GEOGRID.TBL and METGRID.TBL files, the user can control the methodby which source data – either static fields in the case of geogrid or meteorological fieldsin the case of metgrid – are interpolated. In fact, a list of interpolation methods may begiven, in which case, if it is not possible to employ the i-th method in the list, the (i+1)-stmethod will be employed, until either some method can be used or there are no methodsleft to try in the list. For example, to use a four-point bi-linear interpolation scheme for afield, we could specify interp_option=four_pt. However, if the field had areas ofmissing values, which could prevent the four_pt option from being used, we couldrequest that a simple four-point average be tried if the four_pt method couldn't be usedby specifying interp_option=four_pt+average_4pt instead. Below, each of theavailable interpolation options in the WPS are described conceptually; for the details ofeach method, the user is referred to the source code in the fileWPS/geogrid/src/interp_options.F.WRF-NMM V3: User’s Guide 3-46