1 | \newpage |
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2 | \appendix |
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3 | \chapter{The grid types for the transformations} |
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4 | \label{subsec_gridtypes} |
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5 | |
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6 | As described in section \ref{sec_transformations}, the different |
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7 | transformations in OASIS3 support different types of grids. The |
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8 | characteristics of these grids are detailed here. |
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9 | |
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10 | \begin{enumerate} |
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11 | |
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12 | \item Grids supported for the {\tt INTERP} |
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13 | interpolations (see section \ref{subsec_interp}) |
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14 | |
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15 | \begin{itemize} |
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16 | |
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17 | \item {\tt `A' grid}: this is a regular Lat-Lon grid covering either |
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18 | the whole globe or an hemisphere, going from South to North and |
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19 | from West to East. There is no grid point at the |
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20 | pole and at the equator, and the first latitude has an offset of |
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21 | 0.5 grid interval. The first longitude is 0$^o$ (the Greenwhich |
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22 | meridian) and is not repeated at the end of the grid ({\tt |
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23 | \$CPER} = P and {\tt \$NPER}= 0). The latitudinal grid length |
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24 | is 180/NJ for a global grid, 90/NJ otherwise. The longitudinal |
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25 | grid length is 360/NI. |
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26 | |
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27 | \item {\tt `B' grid}: this is a regular Lat-Lon grid covering either |
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28 | an hemisphere or the whole globe, going from South to North and |
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29 | from West to East. There is a grid point at the |
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30 | pole and at the equator (if the grid is hemispheric or global |
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31 | with NJ odd). The first longitude is 0$^o$ (the Greenwhich |
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32 | meridian), and is repeated at the end of the grid ({\tt \$CPER} |
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33 | = P and {\tt \$NPER}= 1). The latitudinal grid length is |
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34 | 180/(NJ-1) for a global grid, 90/(NJ-1) otherwise. The |
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35 | longitudinal grid length is 360/(NI-1). |
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36 | |
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37 | |
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38 | \item {\tt `G' grid}: this is a irregular Lat-Lon Gaussian grid |
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39 | covering either an hemisphere or the whole globe, going from South to |
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40 | North and from West to East. This grid is used in spectral models. It |
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41 | is very much alike the A grid, except that the latitudes are not |
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42 | equidistant. There is no grid point at the pole and at the |
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43 | equator. The first longitude is 0$^o$ (the Greenwhich meridian) and is |
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44 | not repeated at the end of the grid ({\tt \$CPER} = P and {\tt |
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45 | \$NPER}= 0). The longitudinal grid length is 360/NI. |
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46 | |
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47 | |
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48 | \item {\tt `L' grid}: this type covers regular Lat-Lon grids in |
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49 | general, going from South to |
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50 | North and from West to East.. The grid can be described by the latitude and the |
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51 | longitude of the southwest corner of the grid, and by the |
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52 | latitudinal and longitudinal grid mesh sizes in degrees. |
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53 | |
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54 | \item {\tt `Z' grid}: this is a Lat-Lon grid with non-constant |
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55 | latitudinal and longitudinal grid mesh sizes, going from South to |
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56 | North and from West to East. The deformation of |
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57 | the mesh can be described with the help of 1-dimensional |
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58 | positional records in each direction. This grid is periodical |
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59 | ({\tt \$CPER} = P) with {\tt \$NPER} overlapping grid points. |
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60 | |
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61 | \item {\tt `Y' grid}: this grid is like `Z' grid except that it is |
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62 | regional ({\tt \$CPER} = R and {\tt \$NPER} = 0). |
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63 | |
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64 | \end{itemize} |
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65 | |
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66 | \item Grids supported for the {\tt SCRIPR} interpolations |
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67 | |
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68 | \begin{itemize} |
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69 | |
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70 | \item {\tt `LR' grid}: The longitudes and the latitudes of |
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71 | 2D Logically-Rectangular (LR) grid points can be described by two arrays |
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72 | {\tt longitude(i,j)} and {\tt latitude(i,j)}, where i and j |
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73 | are respectively the first and second index dimensions. Streched |
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74 | or/and rotated grids are LR grids. Note that A, B, G, L, Y, or Z |
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75 | grids are all particular cases of LR grids. |
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76 | |
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77 | \item {\tt `U' grid}: Unstructured (U) grids do have any particular |
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78 | structure. The longitudes and the latitudes of 2D Unstructured |
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79 | grid points must be described by two arrays {\tt |
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80 | longitude(nbr\_pts,1)} and {\tt latitude(nbr\_pts,1)}, where nbr\_pts |
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81 | is the total grid size. |
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82 | |
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83 | \item {\tt `D' grid} The Reduced (D) grid is composed of a certain |
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84 | number of latitude circles, each one being divided into a varying |
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85 | number of longitudinal segments. In OASIS3, the grid data (longitudes, |
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86 | latitudes, etc.) must be described by arrays dimensioned {\tt |
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87 | (nbr\_pts,1)}, where {\tt nbr\_pts} is the total number of grid |
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88 | points. There is no overlap of the grid, and no grid point at the |
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89 | equator nor at the poles. There are grid points on the Greenwich |
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90 | meridian. |
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91 | |
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92 | \end{itemize} |
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93 | |
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94 | \end{enumerate} |
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95 | |
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96 | |
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97 | |
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