Gemclim 3.3.3.1 nudging : Différence entre versions

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Spectral nudging is a way to force (nudge) the larger scales of an RCM towards the ones of its driving GCM resp. RCM.<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>  ===
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=== Spectral nudging parameters in GEM:<br>  ===
  
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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 get the possible values to set 'Grd_ni' and 'Grd_nj' in your gemclim_settings.nml. (You need to set the model environment first to have access to 'find'fft'.)<br>For example:
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&nbsp;&nbsp;&nbsp;[[spn GEM3.3.3|GEM3.3.3.1 (CRCM5)]]<br>
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&nbsp;&nbsp;&nbsp;[[spn GEM4.8.lts12|GEM4.8.lts12]]
  
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&nbsp;&nbsp;&nbsp; findfft -gnimax 500 -cfl Pil_maxcfl
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Set the key '-cfl' to value of 'Pil_maxcfl' from your gemclim_settings.nml.<br> Your 'Grd_ni' and 'Grd_nj' will then have to be set to one of the values findfft is listing.<br> If your grid is larger than 500 points, just set '-gnimax' to a number large enough.
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=== References:<br> ===
  
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== Activate spectral nudging in CRCM5  ==
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*'''Xu''' Z. and Z.-L. Yang (2015): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2015_Xu_Spectral_Nudging_Bias_Correction.pdf '''A new dynamical downscaling approach with GCM bias corrections and spectral nudging.'''] J. Geophys. Res. Atmos., 120, 3063–3084
  
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To activate spectral nudging in CRCM5 one has to set several parameters in the file 'gemclim_settings.nml' in the namelist 'gem_cfgs'.<br>
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*'''Berg''' P., R. Döscher, and T. Koenigk (2013): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2013_Berg_RCAO_nudging.pdf '''Impacts of using spectral nudging on regional climate model RCA4 simulations of the Arctic'''] Geosci. Model Dev., 6, 849–859, 2013
  
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=== Fields to nudge<br>  ===
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*'''Wang''' J., and V.R. Kotamarthi (2013): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2013_Wang_Kotamarthi_Nudging.pdf '''Assessment of Dynamical Downscaling in Near-Surface Fields with Different Spectral Nudging Approaches Using the Nested Regional Climate Model (NRCM)'''] JAMC Vol 52, 1576-1591
  
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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&nbsp;suggest to set:  
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*'''Bowden''' J.H., C.G. Nolte, and T.L. Otte (2012): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2013_Bowden_WRF_Spectral_nudging.pdf '''Simulating the impact of the large-scale circulation on the 2-m temperature and precipitation climatology.'''] Clim Dyn (2013) 40:1903–1920
  
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&nbsp; &nbsp; '''Lam_spn_nudging_S = 'UV'&nbsp;&nbsp;&nbsp;&nbsp; ,'''  
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*'''Šeparović''' L., R. de Elía, and R. Laprise (2012) [http://link.springer.com/article/10.1007%2Fs00382-011-1072-7 '''Impact of spectral nudging and domain size in studies of RCM response to parameter modification.'''] Clim Dyn 38(7-8): 1325-1343 <br>'''Exerpt:'''<br>"Nested limited-area Regional Climate Models (RCMs) are models that dynamically downscale global General Circulation Model (GCM) simulations or objective analyses to high-resolution computational grids, using a high-resolution representation of the surface forcing and model dynamics. RCMs require the information on some prognostic variables as their lateral boundary conditions (LBC). The choices of integration domains and nesting techniques are free parameters of RCMs. The optimal integration domain depends on the particular situation, although there are some general recommendations that can facilitate user’s judgment (e.g., Laprise et al. 2008). For example, Leduc and Laprise (2008) showed that the use of a too small domain could result in the simulations being deficient in fine-scale variance. It has been also noted that in large continental-scale domains RCM large-scale variables can considerably drift from the driving fields, which can then result in appearance of large spurious gradients in the vicinity of the outflow boundaries. Spectral nudging (SN; von Storch et al. 2000; Biner et al. 2000) has been employed to ensure that the model solution remains close to the large-scale components of the driving fields over the entire domain. However, the use of spectral nudging remains an open issue. …"
  
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=== Half responds wavelength<br>  ===
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*'''Mohino''' E., S. Janicot, H. Douville, L.Z.X. Li (2011): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2012_Mohino_Nudging.pdf '''Impact of the Indian part of the summer MJO on West Africa using nudged climate simulations.'''] Clim Dyn (2012) 38:2319–2334
  
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This is the wavelength at which equal weight is given to the driving data and the RCM solution. 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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*'''Alexandru''' A. (2009): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2009_Adelina_SN.pdf '''Sensitivity Study of Regional Climate Model Simulations to Large-Scale Nudging Parameters.'''] Mon Weather Rev 137: 1666-1686
  
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'''&nbsp; &nbsp; Lam_spn_half_respon = 1000.&nbsp; ,'''<br>
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*'''Omrani''' H., P. Drobinski, and T. Dubos (2009): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2011_Drobinski_QJRMS_spectral_nudging.pdf '''Spectral nudging in regional climate modeling: how strong should we nudge?'''] Q.J.R. Meteorol. Soc. 00: 1–6 (2009)
  
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=== Controlling the profile<br>  ===
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*'''Radu''' R., M. Déqué, and S. Somot (2008): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2008_Radu_ALADIN_Nudging.pdf '''Spectral nudging in a spectral regional climate model'''] Tellus (2008), 60A, 898–910
  
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There are 3 parameters to control the nudging profile:
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*'''Riette''' S., and D. Caya (2002): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2002_Riette_Caya.pdf '''Sensitivity of short simulations to the various parameters in the new CRCM spectral nudging. Research Activities in Atmospheric and Oceanic Modelling'''] WMO/TD-1105, Rep. 32, H. Ritchie, Ed., WMO, 7.39–7.40
  
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&nbsp;&nbsp;&nbsp; Lam_spn_up_const_lev&nbsp;&nbsp;&nbsp;&nbsp;: above this level (in hybrid values) the profile is set to 1 (default 0.).<br> &nbsp;&nbsp;&nbsp; Lam_spn_start_lev &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;: below this level (in hybrid values) the profile is set to 0 (default 1.).<br>&nbsp;&nbsp;&nbsp; Lam_spn_trans_shape_S&nbsp;: Between these two levels the profile goes from 0 to 1. Either linearly (''''LINEAR'''') or with a cos2 (''''COS2'''') function. <br>
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*'''Riette''' S. (2000): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2000_Riette_Pilotage_Spectral.pdf '''Technique de Pilotage Spectral du Modele Regional Canadien de Climat''']
  
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For example set:  
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*'''Biner''' S., D. Caya, R. Laprise, L. Spacek (2000) Nesting of RCMs by imposing large scales. Research activities in Atmospheric and Oceanic Modelling, WMO/TD 987, Report 30: 7.3-7.4
  
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'''&nbsp;&nbsp;&nbsp; Lam_spn_up_const_lev &nbsp; = 0.&nbsp;&nbsp;&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; , <br> &nbsp;&nbsp;&nbsp; Lam_spn_start_lev&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; = 0.5 &nbsp; &nbsp;&nbsp; &nbsp;&nbsp; ,<br> &nbsp;&nbsp;&nbsp; Lam_spn_trans_shape_S = 'LINEAR' ,<br>'''
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*'''von Storch''' H., H. Langenberg, and F. Feser (2000): [http://pascal.sca.uqam.ca/~winger/Documents/Spectral_Nudging/2000_vonStorch_Spectral_Nudging.pdf '''A spectral nudging technique for dynamical downscaling purposes.'''] Mon Weather Rev 128: 3664–3673
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Version actuelle datée du 12 de février 2019 à 19:18

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.

Spectral nudging parameters in GEM:

   GEM3.3.3.1 (CRCM5)
   GEM4.8.lts12


References:

  • Šeparović L., R. de Elía, and R. Laprise (2012) Impact of spectral nudging and domain size in studies of RCM response to parameter modification. Clim Dyn 38(7-8): 1325-1343
    Exerpt:
    "Nested limited-area Regional Climate Models (RCMs) are models that dynamically downscale global General Circulation Model (GCM) simulations or objective analyses to high-resolution computational grids, using a high-resolution representation of the surface forcing and model dynamics. RCMs require the information on some prognostic variables as their lateral boundary conditions (LBC). The choices of integration domains and nesting techniques are free parameters of RCMs. The optimal integration domain depends on the particular situation, although there are some general recommendations that can facilitate user’s judgment (e.g., Laprise et al. 2008). For example, Leduc and Laprise (2008) showed that the use of a too small domain could result in the simulations being deficient in fine-scale variance. It has been also noted that in large continental-scale domains RCM large-scale variables can considerably drift from the driving fields, which can then result in appearance of large spurious gradients in the vicinity of the outflow boundaries. Spectral nudging (SN; von Storch et al. 2000; Biner et al. 2000) has been employed to ensure that the model solution remains close to the large-scale components of the driving fields over the entire domain. However, the use of spectral nudging remains an open issue. …"
  • Biner S., D. Caya, R. Laprise, L. Spacek (2000) Nesting of RCMs by imposing large scales. Research activities in Atmospheric and Oceanic Modelling, WMO/TD 987, Report 30: 7.3-7.4


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