How to interpret WRF variables - Revision history

Jmandel: /* Storage order */ rm one more ref to fortran

2025-11-22T18:07:03Z

Storage order: rm one more ref to fortran

← Older revision		Revision as of 18:07, 22 November 2025
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	The value of the time at the step '''t''' is stored in character array '''Times(:,t)'''.		The value of the time at the step '''t''' is stored in character array '''Times(:,t)'''.

	Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. This is how the variables appear when read e.g. in Python. ~~However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.~~		Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. This is how the variables appear when read e.g. in Python or C/C++. To read the surface values of such 3D arrays at time step '''t''' and indices '''(x,y)''', use in Python or C/C++ the indexing '''(t, 0, y, x)''' .

	To read the surface values of such 3D arrays at time step '''t''' and indices '''(x,y)''', use in Python or C/C++ the indexing '''(t, 0, y, x)''' .

	WRF 3D arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.		WRF 3D arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.

Jmandel: /* Storage order */ rm fortran ordering in files

2025-11-22T18:05:46Z

Storage order: rm fortran ordering in files

← Older revision		Revision as of 18:05, 22 November 2025
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	The value of the time at the step '''t''' is stored in character array '''Times(:,t)'''.		The value of the time at the step '''t''' is stored in character array '''Times(:,t)'''.

	Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. ~~The~~ is how the variables appear when read e.g. in Python. However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.		Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. This is how the variables appear when read e.g. in Python. However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.

	To read the surface values of such 3D arrays at ~~the~~ indices '''(x,y)''', use the indexing '''(t, 0, y, x)''' ~~in Python, and '''(x, y, 1, t)''' in FORTRAN~~.		To read the surface values of such 3D arrays at time step '''t''' and indices '''(x,y)''', use in Python or C/C++ the indexing '''(t, 0, y, x)''' .

	~~Arrays~~ in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.		WRF 3D arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.

	==Wind==		==Wind==

Jmandel: /* Storage order */

2025-11-22T06:01:39Z

Storage order

← Older revision		Revision as of 06:01, 22 November 2025
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	Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. The is how the variables appear when read e.g. in Python. However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.		Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. The is how the variables appear when read e.g. in Python. However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.

	To read the surface values of a 3D ~~array~~, use the indexing '''(t, z, 0, x)''' in Python, and '''(x, y, 1, t)''' in FORTRAN.		To read the surface values of such 3D arrays at the indices '''(x,y)''', use the indexing '''(t, 0, y, x)''' in Python, and '''(x, y, 1, t)''' in FORTRAN.

	Arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.		Arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.

Jmandel: /* Arrays and Storage Order */ -> Storage order

2025-11-22T03:43:55Z

Arrays and Storage Order: -> Storage order

← Older revision		Revision as of 03:43, 22 November 2025
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	The orientation of the axes in the real world, such as "east-west", in the order of increasing index, such as '''i''', are defined in the registry. For postprocessing, they can be found at runtime as attributes in the NetCDF files.		The orientation of the axes in the real world, such as "east-west", in the order of increasing index, such as '''i''', are defined in the registry. For postprocessing, they can be found at runtime as attributes in the NetCDF files.

	==~~Arrays and~~ Storage ~~Order~~==		==Storage order==

	Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.		Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.

Jmandel: indexing

2025-11-22T03:42:12Z

indexing

← Older revision		Revision as of 03:42, 22 November 2025
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	Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.		Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.

	~~Files are (by default) in [[NetCDF]] format. The values associated with the cell '''(i,j,k)''' at time step '''n''' are stored in the files as the array entry '''u(i,j,k,n)''', e.t.c.~~ The value of the time at the step '''n''' is stored in character array '''Times(:,n)'''.		The value of the time at the step '''t''' is stored in character array '''Times(:,t)'''.

	Arrays in WRF NETCDF files, like the WRFOUT files, are ~~stored~~ with the indexing as '''(t, z, y, x)''', arrays in memory are indexed as '''(i,k,j)''' by [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. ~~Of course, there~~ is no ~~4th~~ index for the time step in arrays in memory, ~~and in some~~ arrays there is no vertical '''k''' dimension.		Arrays in WRF NETCDF files, like the WRFOUT files, are written with the indexing as '''(t, z, y, x)''', where '''t''' is the time index, which varies the slowest. The is how the variables appear when read e.g. in Python. However, when read in FORTRAN, the same arrays appear in the FORTRAN column major odering '''(x, y, z, t)'''.

			To read the surface values of a 3D array, use the indexing '''(t, z, 0, x)''' in Python, and '''(x, y, 1, t)''' in FORTRAN.

			Arrays in memory are indexed as '''(i,k,j)''' (in FORTRAN) following [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. There is no time index for the time step in arrays in memory, because WRF works with only one time step at a time. In 2D arrays, there is no vertical '''k''' dimension.

	==Wind==		==Wind==

Jmandel: /* Arrays */ storage order

2025-11-22T03:27:36Z

Arrays: storage order

← Older revision		Revision as of 03:27, 22 November 2025
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	The orientation of the axes in the real world, such as "east-west", in the order of increasing index, such as '''i''', are defined in the registry. For postprocessing, they can be found at runtime as attributes in the NetCDF files.		The orientation of the axes in the real world, such as "east-west", in the order of increasing index, such as '''i''', are defined in the registry. For postprocessing, they can be found at runtime as attributes in the NetCDF files.

	==Arrays==		==Arrays and Storage Order==

	Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.		Arrays are stored in files and in memory. All arrays are described in the Registry, which is a collection of text files in '''WRFV3/Registry'''. The variable names in memory and in files are sometimes different.
Line 23:		Line 23:
	Files are (by default) in [[NetCDF]] format. The values associated with the cell '''(i,j,k)''' at time step '''n''' are stored in the files as the array entry '''u(i,j,k,n)''', e.t.c. The value of the time at the step '''n''' is stored in character array '''Times(:,n)'''.		Files are (by default) in [[NetCDF]] format. The values associated with the cell '''(i,j,k)''' at time step '''n''' are stored in the files as the array entry '''u(i,j,k,n)''', e.t.c. The value of the time at the step '''n''' is stored in character array '''Times(:,n)'''.

	~~While arrays~~ in files are ~~indexed~~ as '''(i,j,k,n)''', arrays in memory are indexed as '''(i,k,j)''' by [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. Of course, there is no 4th index for the time step in arrays in memory, and in some arrays there is no vertical '''k''' dimension.		Arrays in WRF NETCDF files, like the WRFOUT files, are stored with the indexing as '''(t, z, y, x)''', arrays in memory are indexed as '''(i,k,j)''' by [http://www.mmm.ucar.edu/wrf/WG2/WRF_conventions.html WRF coding conventions]. Of course, there is no 4th index for the time step in arrays in memory, and in some arrays there is no vertical '''k''' dimension.

	==Wind==		==Wind==

Jmandel: /* Location */

2012-12-23T16:29:31Z

Location

← Older revision		Revision as of 16:29, 23 December 2012
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	:'''ELEVATION_THETA(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81		:'''ELEVATION_THETA(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81

	This variable is also part of WRF state as '''z''' and its output to wrfout or wrfrst files can be enabled in the registry.		This variable is also part of WRF state as '''Z''' and its output to wrfout or wrfrst files can be enabled in the [https://github.com/jbeezley/wrf-fire/blob/master/wrfv2_fire/Registry/Registry.EM_COMMON#L306 registry].

	==Temperature==		==Temperature==

Jmandel: /* Location */

2012-12-14T20:02:53Z

Location

← Older revision		Revision as of 20:02, 14 December 2012
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	PH and PHB live at the W-points, thus the geopotential height at the lowest level is the same as terrain height		PH and PHB live at the W-points, thus the geopotential height at the lowest level is the same as terrain height
	: '''~~HGT_W~~(i,j) = PHB(i,j,1)/9.81		: '''ELEVATION_W(i,j) = PHB(i,j,1)/9.81
	up to rounding error. This variable is also part of WRF state as '''z_at_w''' and its output to wrfout or wrfrst files can be enabled in the registry.		up to rounding error. This variable is also part of WRF state as '''z_at_w''' and its output to wrfout or wrfrst files can be enabled in the registry.

	To find the elevation of the cell theta-points (the cell midplane, where the pressure and other variables than wind live), you need to interpolate between the elevation of the top and the bottom:		To find the elevation of the cell theta-points (the cell midplane, where the pressure and other variables than wind live), you need to interpolate between the elevation of the top and the bottom:
	:'''~~HGT_THETA~~(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81		:'''ELEVATION_THETA(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81

	This variable is also part of WRF state as '''z''' and its output to wrfout or wrfrst files can be enabled in the registry.		This variable is also part of WRF state as '''z''' and its output to wrfout or wrfrst files can be enabled in the registry.

Jmandel: /* See also */

2012-12-14T19:24:15Z

Jmandel: /* Location */

2012-12-14T19:21:01Z

Location

← Older revision		Revision as of 19:21, 14 December 2012
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	PH and PHB live at the W-points, thus the geopotential height at the lowest level is the same as terrain height		PH and PHB live at the W-points, thus the geopotential height at the lowest level is the same as terrain height
	: '''~~HGT~~(i,j) = PHB(i,j,1)/9.81		: '''HGT_W(i,j) = PHB(i,j,1)/9.81
	up to rounding error.		up to rounding error. This variable is also part of WRF state as '''z_at_w''' and its output to wrfout or wrfrst files can be enabled in the registry.

	To find the elevation of the cell theta-points (the cell midplane, where the pressure and other variables than wind live), you need to interpolate between the elevation of the top and the bottom:		To find the elevation of the cell theta-points (the cell midplane, where the pressure and other variables than wind live), you need to interpolate between the elevation of the top and the bottom:
	:'''Z(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81		:'''HGT_THETA(i,j,k) =0.5*(PHB(i,j,k) + PH(i,j,k) + PHB(i,j,k+1) + PH(i,j,k+1))/9.81

	~~Variable~~ '''Z''' ~~is also available in WRF directly as state~~ and its output to wrfout or wrfrst files can be enabled in the registry.		This variable is also part of WRF state as '''z''' and its output to wrfout or wrfrst files can be enabled in the registry.

	==Temperature==		==Temperature==

← Older revision		Revision as of 19:24, 14 December 2012
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	==See also==		==See also==
			* [[SFIRE variables]]
	* [[WRF-Fire documentation]]		* [[WRF-Fire documentation]]
	* [http://www.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap5.htm#fields WRF output fields from the WRF-ARW user's guide]		* [http://www.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap5.htm#fields WRF output fields from the WRF-ARW user's guide]