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heimbach |
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\section{EXF: The external forcing package |
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\label{sec:pkg:exf}} |
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\begin{rawhtml} |
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<!-- CMIREDIR:sectionexf: --> |
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\end{rawhtml} |
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\subsection{Introduction |
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\label{sec:pkg:exf:intro}} |
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The external forcing package, in conjunction with the |
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calendar package (cal), enables the handling of real-time |
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(or ``model-time'') forcing |
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fields of differing temporal forcing patterns. |
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It comprises climatological restoring and relaxation. |
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Bulk formulae are implemented to convert atmospheric fields |
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to surface fluxes. |
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An interpolation routine provides on-the-fly interpolation of |
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forcing fields an arbitrary grid onto the model grid. |
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CPP options enable or disable different aspects of the package |
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(Section \ref{sec:pkg:exf:config}). |
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Runtime options, flags, filenames and field-related dates/times are |
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set in \texttt{data.exf} and \texttt{data.exf\_clim} |
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(Section \ref{sec:pkg:exf:runtime}). |
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A description of key subroutines is given in Section |
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\ref{sec:pkg:exf:subroutines}. |
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Input fields, units and sign conventions are summarized in |
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Section \ref{sec:pkg:exf:fields_units}, and available diagnostics |
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output is listed in Section \ref{sec:pkg:exf:fields_diagnostics}. |
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%---------------------------------------------------------------------- |
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\subsection{EXF configuration \& compiling |
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\label{sec:pkg:exf:config}} |
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As with all MITgcm packages, EXF can be turned on or off at compile time |
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using the \texttt{packages.conf} file or the \texttt{genmake2} |
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\texttt{-enable=exf} or \texttt{-disable=exf} switches. |
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Parts of the exf code can be enabled or disabled at compile time |
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via CPP preprocessor flags. These options are set in either |
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\texttt{EXF\_OPTIONS.h} or in \texttt{ECCO\_CPPOPTIONS.h}. |
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Table \ref{tab:pkg:exf:cpp} summarizes these options. |
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\begin{table}[b!] |
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\label{tab:pkg:exf:cpp} |
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{\footnotesize |
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\begin{tabular}{|l|l|} |
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\hline |
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\textbf{CPP option} & \textbf{Description} \\ |
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\hline |
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\texttt{EXF\_VERBOSE} & |
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verbose mode (recommended only for testing) \\ |
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\texttt{ALLOW\_ATM\_TEMP} & |
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compute heat/freshwater fluxes from atmos. state input \\ |
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\texttt{ALLOW\_ATM\_WIND} & |
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compute wind stress from wind speed input\\ |
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\texttt{ALLOW\_BULKFORMULAE} & |
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is used if either ALLOW\_ATM\_TEMP or ALLOW\_ATM\_WIND is enabled \\ |
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\texttt{EXF\_READ\_EVAP} & read evaporation instead of computing it \\ |
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\texttt{ALLOW\_RUNOFF} & read time-constant river/glacier run-off field \\ |
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\texttt{ALLOW\_DOWNWARD\_RADIATION} & compute net from downward or downward from net radiation \\ |
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\texttt{USE\_EXF\_INTERPOLATION} & enable on-the-fly bilinear or bicubic interpolation of input fields \\ |
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\hline |
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\texttt{ALLOW\_CLIMTEMP\_RELAXATION} & |
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relaxation to 3-D potential temperature field \\ |
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\texttt{ALLOW\_CLIMSALT\_RELAXATION} & |
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relaxation to 3-D salinity field \\ |
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\texttt{ALLOW\_CLIMSST\_RELAXATION} & |
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relaxation to 2-D SST relaxation \\ |
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\texttt{ALLOW\_CLIMSSS\_RELAXATION} & |
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relaxation to 2-D SSS relaxation \\ |
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\hline |
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\texttt{SHORTWAVE\_HEATING} & in \texttt{CPP\_OPTIONS.h}: enable shortwave radiation \\ |
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\texttt{ATMOSPHERIC\_LOADING} & in \texttt{CPP\_OPTIONS.h}: enable surface pressure forcing \\ |
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\hline |
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\end{tabular} |
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} |
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\caption{~} |
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\end{table} |
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%---------------------------------------------------------------------- |
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\subsection{EXF runtime parameters |
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\label{sec:pkg:exf:runtime}} |
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%---------------------------------------------------------------------- |
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\subsection{EXF fields and units |
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\label{sec:pkg:exf:fields_units}} |
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The following list is taken from the header file \texttt{exf\_fields.h}. |
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{\footnotesize |
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\begin{verbatim} |
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c ustress :: Zonal surface wind stress in N/m^2 |
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c > 0 for increase in uVel, which is west to |
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c east for cartesian and spherical polar grids |
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c Typical range: -0.5 < ustress < 0.5 |
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c Southwest C-grid U point |
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c Input field |
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c |
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c vstress :: Meridional surface wind stress in N/m^2 |
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c > 0 for increase in vVel, which is south to |
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c north for cartesian and spherical polar grids |
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c Typical range: -0.5 < vstress < 0.5 |
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c Southwest C-grid V point |
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c Input field |
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c |
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c hflux :: Net upward surface heat flux in W/m^2 |
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c excluding shortwave (on input) |
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c hflux = latent + sensible + lwflux |
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c > 0 for decrease in theta (ocean cooling) |
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c Typical range: -250 < hflux < 600 |
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c Southwest C-grid tracer point |
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c Input field |
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c |
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c sflux :: Net upward freshwater flux in m/s |
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c sflux = evap - precip - runoff |
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c > 0 for increase in salt (ocean salinity) |
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c Typical range: -1e-7 < sflux < 1e-7 |
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c Southwest C-grid tracer point |
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c Input field |
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c |
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c swflux :: Net upward shortwave radiation in W/m^2 |
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c swflux = - ( swdown - ice and snow absorption - reflected ) |
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c > 0 for decrease in theta (ocean cooling) |
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c Typical range: -350 < swflux < 0 |
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c Southwest C-grid tracer point |
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c Input field |
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c |
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c uwind :: Surface (10-m) zonal wind velocity in m/s |
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c > 0 for increase in uVel, which is west to |
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c east for cartesian and spherical polar grids |
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c Typical range: -10 < uwind < 10 |
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c Southwest C-grid U point |
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c Input or input/output field |
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c |
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c vwind :: Surface (10-m) meridional wind velocity in m/s |
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c > 0 for increase in vVel, which is south to |
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c north for cartesian and spherical polar grids |
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c Typical range: -10 < vwind < 10 |
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c Southwest C-grid V point |
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c Input or input/output field |
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c |
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c atemp :: Surface (2-m) air temperature in deg K |
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c Typical range: 200 < atemp < 300 |
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c Southwest C-grid tracer point |
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c Input or input/output field |
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c |
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c aqh :: Surface (2m) specific humidity in kg/kg |
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c Typical range: 0 < aqh < 0.02 |
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c Southwest C-grid tracer point |
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c Input or input/output field |
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c |
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c lwflux :: Net upward longwave radiation in W/m^2 |
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c lwflux = - ( lwdown - ice and snow absorption - emitted ) |
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c > 0 for decrease in theta (ocean cooling) |
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c Typical range: -20 < lwflux < 170 |
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c Southwest C-grid tracer point |
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c Input field |
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c |
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c evap :: Evaporation in m/s |
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c > 0 for increase in salt (ocean salinity) |
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c Typical range: 0 < evap < 2.5e-7 |
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c Southwest C-grid tracer point |
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c Input, input/output, or output field |
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c |
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c precip :: Precipitation in m/s |
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c > 0 for decrease in salt (ocean salinity) |
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c Typical range: 0 < precip < 5e-7 |
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c Southwest C-grid tracer point |
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c Input or input/output field |
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c |
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c runoff :: River and glacier runoff in m/s |
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c > 0 for decrease in salt (ocean salinity) |
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c Typical range: 0 < runoff < ???? |
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c Southwest C-grid tracer point |
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c Input or input/output field |
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c !!! WATCH OUT: Default exf_inscal_runoff !!! |
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c !!! in exf_readparms.F is not 1.0 !!! |
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c |
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c swdown :: Downward shortwave radiation in W/m^2 |
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c > 0 for increase in theta (ocean warming) |
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c Typical range: 0 < swdown < 450 |
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c Southwest C-grid tracer point |
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c Input/output field |
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c |
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c lwdown :: Downward longwave radiation in W/m^2 |
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c > 0 for increase in theta (ocean warming) |
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c Typical range: 50 < lwdown < 450 |
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c Southwest C-grid tracer point |
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c Input/output field |
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c |
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c apressure :: Atmospheric pressure field in N/m^2 |
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c > 0 for ???? |
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c Typical range: ???? < apressure < ???? |
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c Southwest C-grid tracer point |
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c Input field |
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C |
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C |
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c NOTES: |
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c ====== |
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c |
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c Input and output units and sign conventions can be customized |
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c using variables exf_inscal_* and exf_outscal_*, which are set |
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c by exf_readparms.F |
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c |
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c Output fields fu, fv, Qnet, Qsw, and EmPmR are |
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c defined in FFIELDS.h |
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c |
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c #ifndef SHORTWAVE_HEATING, hflux includes shortwave, |
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c that is, hflux = latent + sensible + lwflux +swflux |
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c |
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c If (EXFwindOnBgrid .EQ. .TRUE.), uwind and vwind are |
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c defined on northeast B-grid U and V points, respectively. |
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c |
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c Arrays *0 and *1 below are used for temporal interpolation. |
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\end{verbatim} |
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} |
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%---------------------------------------------------------------------- |
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\subsection{Key subroutines |
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\label{sec:pkg:exf:subroutines}} |
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%---------------------------------------------------------------------- |
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\subsection{EXF diagnostics |
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\label{sec:pkg:exf:diagnostics}} |
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Diagnostics output is available via the diagnostics package |
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(see Section \ref{sec:pkg:diagnostics}). |
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Available output fields are summarized in |
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Table \ref{tab:pkg:exf:diagnostics}. |
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\begin{table} |
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\label{tab:pkg:exf:diagnostics} |
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\caption{~} |
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{\footnotesize |
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\begin{verbatim} |
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------------------------------------------------------ |
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<-Name->|Levs|grid|<-- Units -->|<- Tile (max=80c) |
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------------------------------------------------------ |
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EXFlwdn | 1 | SM |W/m^2 |Downward longwave radiation, >0 increases theta |
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EXFswdn | 1 | SM |W/m^2 |Downward shortwave radiation, >0 increases theta |
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EXFqnet | 1 | SM |W/m^2 |Net upward heat flux (turb+rad), >0 decreases theta |
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EXFtaux | 1 | SU |N/m^2 |zonal surface wind stress, >0 increases uVel |
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EXFtauy | 1 | SV |N/m^2 |meridional surface wind stress, >0 increases vVel |
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EXFuwind| 1 | SM |m/s |zonal 10-m wind speed, >0 increases uVel |
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EXFvwind| 1 | SM |m/s |meridional 10-m wind speed, >0 increases uVel |
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EXFatemp| 1 | SM |degK |surface (2-m) air temperature |
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EXFaqh | 1 | SM |kg/kg |surface (2-m) specific humidity |
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EXFevap | 1 | SM |m/s |evaporation, > 0 increases salinity |
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EXFpreci| 1 | SM |m/s |evaporation, > 0 decreases salinity |
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EXFempmr| 1 | SM |m/s |net upward freshwater flux, > 0 increases salinity |
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EXFpress| 1 | SM |N/m^2 |atmospheric pressure field |
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\end{verbatim} |
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} |
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\end{table} |
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%---------------------------------------------------------------------- |
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\subsection{Reference experiments} |
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%---------------------------------------------------------------------- |
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\subsection{References} |
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