Gemclim 3.3.3.1 nudging : Différence entre versions
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= Spectral nudging<br> = | = Spectral nudging<br> = | ||
| − | <br> | + | Spectral nudging is a way to force (nudge) the larger scales of an RCM towards the ones of its driving GCM resp. RCM.<br> |
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=== Grid size restrictions<br> === | === Grid size restrictions<br> === | ||
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Put the value of 'Pil_maxcfl' from your gemclim_settings.nml!<br> Your 'Grd_ni' and 'Grd_nj' will then have to be one of the values findfft spits out.<br> If your grid is larger than 500 points, just set '-gnimax' to a number large enough for you. | Put the value of 'Pil_maxcfl' from your gemclim_settings.nml!<br> Your 'Grd_ni' and 'Grd_nj' will then have to be one of the values findfft spits out.<br> If your grid is larger than 500 points, just set '-gnimax' to a number large enough for you. | ||
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| − | To activate spectral nudging in CRCM5 one has to / can set several parameters in the file 'gemclim_settings.nml' into the namelist 'gem_cfgs'. | + | |
| + | == Activate spectral nudging in CRCM5 == | ||
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| + | To activate spectral nudging in CRCM5 one has to / can set several parameters in the file 'gemclim_settings.nml' into the namelist 'gem_cfgs'. | ||
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=== Fields to nudge<br> === | === Fields to nudge<br> === | ||
| − | In CRCM5 one has the option of nudging u-wind, v-wind, and/or temperature.<br>Tests have shown that it is sufficient to nudge u-wind and v-wind and that nudging the temperature as well does not change much the results. Therefore I suggest to set: | + | In CRCM5 one has the option of nudging u-wind, v-wind, and/or temperature.<br>Tests have shown that it is sufficient to nudge u-wind and v-wind and that nudging the temperature as well does not change much the results. Therefore I suggest to set: |
'''Lam_spn_nudging_S = 'UV' ,'''<br> | '''Lam_spn_nudging_S = 'UV' ,'''<br> | ||
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| − | ''' Lam_spn_half_respon = 1000. ,''' | + | === Half responds wavelength<br> === |
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| + | This is the wavelength at which equal weight is given to the driving data and RCM. For longer wavelength more weight is given to the driving data, for shorter wavelength more weight is given to the RCM. Therefore this is one way to control the strength of the nudging. Typical wavelengths are between 1000km and 2000km. For example set:<br> | ||
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| + | ''' Lam_spn_half_respon = 1000. ,''' | ||
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=== Controlling the profile<br> === | === Controlling the profile<br> === | ||
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There are 3 parameters to control the nudging profile: | There are 3 parameters to control the nudging profile: | ||
| − | Lam_spn_up_const_lev : above this level (in hybrid values) the profile is set to 1 (default 0.).<br> Lam_spn_start_lev : below this level (in hybrid values) the profile is set to 0 (default 1.).<br> Lam_spn_trans_shape_S : Between these two levels the profile goes from 0 to 1. Either linearly (''''LINEAR'''') or with a cos2 (''''COS2'''') function. <br> | + | Lam_spn_up_const_lev : above this level (in hybrid values) the profile is set to 1 (default 0.).<br> Lam_spn_start_lev : below this level (in hybrid values) the profile is set to 0 (default 1.).<br> Lam_spn_trans_shape_S : Between these two levels the profile goes from 0 to 1. Either linearly (''''LINEAR'''') or with a cos2 (''''COS2'''') function. <br> |
For example set: | For example set: | ||
''' Lam_spn_up_const_lev = 0. , <br> Lam_spn_start_lev = 0.5 ,<br> Lam_spn_trans_shape_S = 'LINEAR' ,<br>''' | ''' Lam_spn_up_const_lev = 0. , <br> Lam_spn_start_lev = 0.5 ,<br> Lam_spn_trans_shape_S = 'LINEAR' ,<br>''' | ||
Version depuis le 19 de septembre 2014 à 14:32
Matières
Spectral nudging
Spectral nudging is a way to force (nudge) the larger scales of an RCM towards the ones of its driving GCM resp. RCM.
Grid size restrictions
To be able to use spectral nudging in CRCM5, the core grid needs to match the FFT criteria in x- and y-direction. You can use 'findfft' to find get the possible values for 'Grd_ni' and 'Grd_nj' in your gemclim_settings.nml.
For example:
findfft -gnimax 500 -cfl Pil_maxcfl
Put the value of 'Pil_maxcfl' from your gemclim_settings.nml!
Your 'Grd_ni' and 'Grd_nj' will then have to be one of the values findfft spits out.
If your grid is larger than 500 points, just set '-gnimax' to a number large enough for you.
Activate spectral nudging in CRCM5
To activate spectral nudging in CRCM5 one has to / can set several parameters in the file 'gemclim_settings.nml' into the namelist 'gem_cfgs'.
Fields to nudge
In CRCM5 one has the option of nudging u-wind, v-wind, and/or temperature.
Tests have shown that it is sufficient to nudge u-wind and v-wind and that nudging the temperature as well does not change much the results. Therefore I suggest to set:
Lam_spn_nudging_S = 'UV' ,
Half responds wavelength
This is the wavelength at which equal weight is given to the driving data and RCM. For longer wavelength more weight is given to the driving data, for shorter wavelength more weight is given to the RCM. Therefore this is one way to control the strength of the nudging. Typical wavelengths are between 1000km and 2000km. For example set:
Lam_spn_half_respon = 1000. ,
Controlling the profile
There are 3 parameters to control the nudging profile:
Lam_spn_up_const_lev : above this level (in hybrid values) the profile is set to 1 (default 0.).
Lam_spn_start_lev : below this level (in hybrid values) the profile is set to 0 (default 1.).
Lam_spn_trans_shape_S : Between these two levels the profile goes from 0 to 1. Either linearly ('LINEAR') or with a cos2 ('COS2') function.
For example set:
Lam_spn_up_const_lev = 0. ,
Lam_spn_start_lev = 0.5 ,
Lam_spn_trans_shape_S = 'LINEAR' ,
