Changeset 2351 for branches/nemo_v3_3_beta/DOC/TexFiles/Chapters/Chap_SBC.tex

Timestamp:

2010-11-02T08:09:00+01:00 (13 years ago)

Author:

sga

Message:

NEMO branch nemo_v3_3_beta
modify interpolation on the fly scheme within fldread.F90.
Instead of attempting to decide on cyclicity of input non-model grid by inspecting a longitude variable,
fld_read now expects to find an attribute in the input weights file to tell it how many columns overlap
at the east-west edges of the grid.
iom and iom_nf90.F90 have new routines to expose netcdf attributes to the model.

File:

• branches/nemo_v3_3_beta/DOC/TexFiles/Chapters/Chap_SBC.tex (modified) (3 diffs)

branches/nemo_v3_3_beta/DOC/TexFiles/Chapters/Chap_SBC.tex

@@ -641 +641 @@
 if this is left as an empty string no action is taken.
 In the model, weights files are read in and stored in a structured type (WGT) in the fldread module, as and when they are first required.
-This initialisation procedure tries to determine whether the input data grid should be treated as cyclical or not.
+This initialisation procedure determines whether the input data grid should be treated as cyclical or not by inspecting a global attribute stored in the weights input file.
+This attribute must be called "ew_wrap" and be of integer type.
+If it is negative, the input non-model grid is assumed not to be cyclic.
+If zero or greater, then the value represents the number of columns that overlap.
+E.g. if the input grid has columns at longitudes 0, 1, 2, .... , 359, then ew_wrap should be set to 0;
+if longitudes are 0.5, 2.5, .... , 358.5, 360.5, 362.5, ew_wrap should be 2.
+If the model does not find attribute ew_wrap, then a value of -999 is assumed.
+In this case the fld_read routine defaults ew_wrap to value 0 and therefore the grid is assumed to be cyclic
+with no overlapping columns.
 (In fact this only matters when bicubic interpolation is required.)
-To do this the model looks in the input data file (i.e. the data to which the weights are to be applied) for a variable with name "nav\_lon" or "lon".
-If found, it checks the difference between the first and last values of longitude along a single row.
-If the absolute value of this difference is close to 360 degrees or less than twice the maximum spacing from 360 degrees, the grid is assumed to be cyclical, and the difference determines whether the first column is a repeat of the last one or not.
-If neither "nav\_lon" or "lon" can be found, the model resorts to looking at the first and last columns of data.
-If the sum of the absolute values of the differences between the columns is very small, then the grid is assumed to be cyclical with coincident first and last columns.
-If both of these tests fail, the grid is assumed not to be cyclical.
+Note that no testing is done to check the validity in the model, since there is no way of knowing the name used for the longitude variable,
+so it is up to the user to make sure his or her data is correctly represented.
 
 Next the routine reads in the weights.
@@ -655 +659 @@
 The size of the input data array is determined by examining the values in the "src" arrays to find the minimum and maximum i and j values required.
 Since bicubic interpolation requires the calculation of gradients at each point on the grid, the corresponding arrays are dimensioned with a halo of width one grid point all the way around.
-When the array of points from the data file is adjacent to an edge of the data grid, the halo is either a copy of the row/column next to it (non-cyclical case), or is a copy of one from the first two rows/columns on the opposite side of the grid (cyclical case with coincident end rows/columns, or cyclical case with non-coincident end rows/columns).
+When the array of points from the data file is adjacent to an edge of the data grid, the halo is either a copy of the row/column next to it (non-cyclical case), or is a copy of one from the first few columns on the opposite side of the grid (cyclical case).
 
 \subsection{Limitations}
@@ -662 +666 @@
 \begin{description}
 \item
-Input data grids must be logically rectangular.
+The case where input data grids are not logically rectangular has not been tested.
 \item
 This code is not guaranteed to produce positive definite answers from positive definite inputs.