LMDZ zoom parameters - Historique des versions

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The "Z" in LMDZ stands for "Zoom".
This is because it is possible to define, instead of a regular longitude-latitude grid, a grid with varying mesh sizes along longitudes and latitudes.

== Zoom parameters ==
In practice one defines a "zoomed region" of interest where the resolution will be highest (and homogeneous), whereas outside this region the resolution will be low (and also homogeneous, apart from a transition region between the two). This is achieved by specifying the following parameters (usually in gcm.def):
* The zoom center coordinates (in degrees), ''clon'' and ''clat''
* The zoom factor along longitude(x)/latitude(y) directions, ''grossismx'' and ''grossismy''. These ratio represent the ratio between meshes in the zoomed region versus meshes far outside of it.
* The fraction of the zoomed region (i.e. relative to the whole planet which is 360° in longitude and 180° in latitude) along longitude (x) and latitude (y), ''dzoomx'' and ''dzoomy''. In practice the extension in longitude and latitude of the zoomed region will thus be of dzoomx*360° in longitude and dzoomy*180° in latitude
* The steepness of the mesh transition between the inner zoom and outer meshes, ''taux'' and ''tauy''. Typically one should avoid a too sharp transition; tau ~3 is a typically reasonable value; with strong nudging harsher transitions , e.g. tau~8 can also work).

== Choosing an adequate time step for a zoomed simulation ==
The rule of thumb, starting from a "day_step" value that works for a give regular (non-zoomed grid):
day_step(zoom) ~ day_step(regular)*max(grossismx,grossismy)

It is also advised to check what others users have successfully used, see e.g. [[LMDZ_zoom_collection]]

24/11/2021

[[Catégorie:Zoom]]

@@ Ligne 7 : / Ligne 7 : @@
 * The zoom factor along longitude(x)/latitude(y) directions, ''grossismx'' and ''grossismy''. These ratio represent the ratio between meshes in the zoomed region versus meshes far outside of it.
 * The fraction of the zoomed region (i.e. relative to the whole planet which is 360° in longitude and 180° in latitude) along longitude (x) and latitude (y), ''dzoomx'' and ''dzoomy''. In practice the extension in longitude and latitude of the zoomed region will thus be of dzoomx*360° in longitude and dzoomy*180° in latitude
-* The steepness of the mesh transition between the inner zoom and outer meshes, ''taux'' and ''tauy''. Typically one should avoid a too sharp transition; tau ~3 is a typically maximum value if running without nudging; with strong nudging harsher transitions, e.g. tau~8 or even 10 can also work).
+* The steepness of the mesh transition between the inner zoom and outer meshes, ''taux'' and ''tauy''. Typically one should avoid a too sharp transition; tau ~3 is a typically maximum value if running without nudging; with strong nudging harsher transitions, e.g. tau~8 or even 10 can also work.
-* It is advised to target, by adjusting number of points along longitude and latitude, to have something close to a "square" mesh (i.e. same extension, in degrees, along longitudes and latitudes)in the inner zoomed area.
+* It is advised to target, by adjusting number of points along longitude and latitude, to have something close to a "square" mesh (i.e. same extension, in degrees, along longitudes and latitudes) in the inner zoomed area.
 == Choosing an adequate time step for a zoomed simulation ==

@@ Ligne 11 : / Ligne 11 : @@
 == Choosing an adequate time step for a zoomed simulation ==
-The rule of thumb, starting from a "day_step" value that works for a give regular (non-zoomed grid):
+The rule of thumb, starting from a "day_step" value that works for a given regular (non-zoomed) grid:
   day_step(zoom) ~ day_step(regular)*max(grossismx,grossismy)