Recent developments in postprocessing

Laura Rontu and Carl Fortelius, FMI

Derivation of new variables and interpolation of data for different purposes is possible using HIRLAM model level data written into GRIB files. Probably the most universal and economic way is to do this postprocessing afterwards, outside the model runs. It should also be possible, e.g. when running HIRLAM experiments, to do postprocessing during the forecast run itself. Traditionally this is done when interpolating model output to pressure levels. A most important thing is, that postprocessing code remains an integral part of the HIRLAM system.

Derived variables involving derivatives or non-linear terms, such as isentropic potential vorticity or vorticity advection, may be quite sensitive to the approximations made during calculations. Requested complex parameters should in general be computed on the model grid and then interpolated to the needed output format. Interpolated variables should not be used for further calculations. It is our interest that data, which is said to originate from HIRLAM, is derived from the model level data in accordance with the finite difference approximations used in the model itself.
Postprocessing within the model allows to use the most effective and optimized computer environment for calculations, which is not always the case in the users own environment. The HIRLAM libraries for handling the grib files are also automatically available in this environment.
Maintenance of the postprocessing code as one of the HIRLAM libraries is easier and more reliable than maintenance of separate programs written by different users. The code might be separated from the model for stand-alone postprocessing purposes.

At the moment postprocessing within HIRLAM allows users to produce model level and pressure level data in GRIB format and time series data in a BUFR-like format. The set of available variables has been developed during the history of HIRLAM and contains the most essential model variables, although not always handled in the most systematic way. Postprocessed variables are requested in the namelists defined by the user.

In the following the variables available from the latest reference HIRLAM 4.9.0 version are listed together with some enhancements under development at FMI (in italics). The enhancements are mainly concerned with deriving variables for constant height levels and isentropic levels. In addition to writing new subroutines some of the existing code has been modified (not shown in italics). Adding of other new variables should be quite straightforward. At the moment time series data and stand-alone postprocessing remain as defined for the earlier reference versions, thus not touched by the enhancements.

An overview of the enhanced code structure and available variables are given in Tables below.

Some components of the enhanced postprocessing code

grdy	POSTP	call OMCOMP	to calculate model level omega
	POSTP	call EDCOMP	to calculate model level etadot
	POSTP	call POSTPP	for all postprocessing
prpo	POSTPP	call METRIC,MFXCOMP	to calculate metric coefficients and mass flux components
	POSTPP	call WCOMP	to calculate model level w
	WCOMP	call VERADV,HORADV	for calculation of advection
	VERADV	call HORDIV	for calculation of divergence
	POSTPP	call PVCOMP	to calculate model level IPV
	PVCOMP	call VORTIC	for calculation of vorticity
	POSTPP	call GPOCOM	to calculate model full and half level geopotentials
	POSTPP	call INTPRE	for pressure level interpolation
	INTPRE	call FIPINT,TPINT,XPINT,OMINT	to interpolate variables to pressure levels
	INTPRE	call PSLCOM	to calculate mean sea level pressure
	POSTPP	call INTHGT	for constant height level interpolation
	INTHGT	call PHGCAL	to calculate pressure on the height level
	INTHGT	call XZINT XTRHGT	to interpolate/extract nearest model level variables to height levels
	POSTPP	call PTHCAL	to calculate pressures of isentropic surfaces
	PTHCAL	call XPINT0	pressure interpolation in one point x,y
	POSTPP	call INTTHE	for isentropic level interpolation
	INTTHE	call XPINT1,FIPINT1,TPINT1,UPINT1,VPINT1	to interpolate variables to isentropic levels
	POSTPP	call XTRETA	for extraction of model level data
	XTRETA	call XTR,VINT	to extract needed model level data

Possible output from the HIRLAM model

State variables and diagnostics on model surfaces:

GRIB-code

Variable unit IPAR LTYP LEV note

		GRIB-code
Variable	unit	IPAR	LTYP	LEV	note

isentropic potential vorticity	Ks^-1Pa^-1	004	109
temperature	K	011	109
potential temperature	K	013	109
dew point temperature	K	017	109
u-component of wind	ms^-1	033	109	relative to the rotated coordinates, given at u-points
v-component of wind	ms^-1	034	109	relative to the rotated coordinates, given at v-points
vertical velocity (sigma coordinates)	s^-1	038	109	used to store hybrid coordinate etadot
vertical velocity (pressure coordinates)	Pas^-1	039	109
geometric vertical velocity	ms^-1	040	109
absolute vorticity	s-¹	041	109	given at vorticity points
relative vorticity	s-¹	043	109	given at vorticity points
specific humidity	kg kg^-1	051	109
relative humidity	fraction	052	109
total precipitation	kg m^-2	061	109	accumulated
specific cloud condensate	kg kg^-1	076	109
total cloud cover	fraction	071	109
convective cloud cover	fraction	072	109
kinetic energy of turbulence	J kg^-1	200	109

State variables and diagnostics on pressure levels

GRIB-code

Variable unit IPAR LTYP LEV note

		GRIB-code
Variable	unit	IPAR	LTYP	LEV	note

geopotential	J kg^-1	006	100
temperature	K	011	100
potential temperature	K	013	100
dew point temperature	K	017	100
u-component of wind	ms^-1	033	100	relative to the rotated coordinates, given at u-points
v-component of wind	ms^-1	034	100	relative to the rotated coordinates, given at v-points
vertical velocity (pressure coordinates)	Pas^-1	039	100
relative humidity	fraction	052	100
total cloud cover	fraction	071	100
specific cloud condensate	kg kg^-1	076	100
kinetic energy of turbulence	J kg^-1	200	100

State variables and diagnostics on constant height levels

GRIB-code

Variable unit IPAR LTYP LEV note

pressure	Pa	001	103
isentropic potential vorticity	Ks^-1Pa^-1	004	103
temperature	K	011	103
potential temperature	K	013	103
dew point temperature	K	017	103
u-component of wind	ms^-1	033	103	relative to the rotated coordinates, given at u-points
v-component of wind	ms^-1	034	103	relative to the rotated coordinates, given at v-points
geometric vertical velocity	ms^-1	040	103
absolute vorticity	s-¹	041	103	given at vorticity points
relative vorticity	s-¹	043	103	given at vorticity points
relative humidity	fraction	052	103
total cloud cover	fraction	071	103
specific cloud condensate	kg kg^-1	076	103
kinetic energy of turbulence	J kg^-1	200	103

State variables and diagnostics on isentropic levels

GRIB-code

Variable unit IPAR LTYP LEV note

pressure	Pa	001	113
isentropic potential vorticity	Ks^-1Pa^-1	004	113
geopotential	J kg^-1	006	113
temperature	K	011	113
dew point temperature	K	017	113
u-component of wind	ms^-1	033	113	relative to the rotated coordinates, given at mass points
v-component of wind	ms^-1	034	113	relative to the rotated coordinates, given at mass points
Montgomery stream function	J kg^-1	037	113
absolute vorticity	s-¹	041	113	given at vorticity points
relative vorticity	s-¹	043	113	given at vorticity points
relative humidity	fraction	052	113
total cloud cover	fraction	071	113
specific cloud condensate	kg kg^-1	076	113
kinetic energy of turbulence	J kg^-1	200	113

Surface and soil variables

GRIB-code

Variable unit IPAR LTYP LEV note

surface pressure	Pa	001	105	0	not the mean sea level pressure
surface pressure tendency	Pa s^-1	003	105	0
surface geopotential	J kg^-1	006	105	0	geopotential relative to mean sea level
sea surface temperature	K	011	102	0
land surface temperature	K	011	105	0
intermediate soil temperature	K	011	105	999
deep soil temperature	K	011	105	998	monthly climatology
water equivalent of snowpack	m	066	105	0
fraction of land		081	105	0	fraction of grid-box covered by land
climatological roughness length	m	083	105	0	analysis files contain a background-value
roughness length over sea	m	083	102	0	analysis files contain a background-value
background albedo	m	084	105	0	used by the forecast model to generate the actual albedo
land surface wetness	m	086	105	0
intermediate soil wetness	m	086	105	999
deep soil wetness	m	086	105	998	monthly climatology
fraction of ice		091	102	0	fractional ice coverage in non-land part of grid-box
fraction of forest		197	105	0	fractional forest coverage in land part of grid-box

Near-surface diagnostics

GRIB-code

Variable unit IPAR LTYP LEV note

mean sea level pressure	Pa	002	105	0	Old non-standard code definition: 001,103,0
screen level temperature	K	011	105	2	2 m above ground
screen level dew point temperature	K	017	105	2	2 m above ground
u-component of wind at 10 m height	ms^-1	033	105	10	relative to the rotated coordinates, given at mass-points
v-component of wind at 10 m height	ms^-1	034	105	10	relative to the rotated coordinates, given at mass-points
screen level specific humidity	kg kg^-1	051	105	2	2 m above ground
screen level relative humidity	fraction	052	105	2	2 m above ground
depth of the boundary layer	m	067	105	0
total cloud cover	fraction	071	105	0
low level cloud cover	fraction	073	105	0
medium level cloud cover	fraction	074	105	0
high level cloud cover	fraction	075	105	0

Accumulated surface fluxes

GRIB-code

Variable unit IPAR LTYP LEV note

total precipitation	kg m^-2	061	105
grid-scale precipitation	kg m^-2	062	105
sub grid-scale precipitation	kg m^-2	063	105
total snowfall	kg m^-2	065	105
grid-scale snowfall	kg m^-2	079	105
sub grid-scale snowfall	kg m^-2	078	105
evaporation	kg m^-2	057	105
net short-wave radiation	J m^-2	111	105
net long-wave radiation	J m^-2	112	105
downwelling long-wave radiation	J m^-2	115	105
downwelling (global) short-wave radiation	J m^-2	117	105
latent heat flux	J m^-2	121	105
sensible heat flux	J m^-2	122	105
momentum flux (u-component)	N m^-2s	124	105	relative to the rotatated grid, given at mass-points
momentum flux (v-component)	N m^-2s	125	105	relative to the rotatated grid, given at mass-points

Accumulated fluxes at the top of the atmosphere

GRIB-code

Variable unit IPAR LTYP LEV note

net short-wave radiation	J m^-2	113	008
net long-wave radiation	J m^-2	114	008
downwelling short-wave radiation	J m^-2	117	008

Vertically-integrated quantities

GRIB-code

Variable unit IPAR LTYP LEV note

precipitable water	kg m^-2	054	105
cloud condensate	kg m^-2	076	105
change of temperature due to parametrized processes	K kg m^-2	210	200
change of temperature due to vertical diffusion	K kg m^-2	211	200
change of temperature due to radiation	K kg m^-2	212	200
change of specific humidity due to parameterized processes	kg m^-2	220	200
change of specific humidity due to vertical diffusion	kg m^-2	221	200
change of specific cloud condensate due to parameterized processes	kg m^-2	230	200
change of specific cloud condensate due to vertical diffusion	kg m^-2	231	200
change of u-component due to parametrized processes	kg m^-1s^-1	240	200
change of u-component due to vertical diffusion	kg m^-1s^-1	241	200
change of v-component due to parametrized processes	kg m^-1s^-1	245	200
change of v-component due to vertical diffusion	kg m^-1s^-1	246	200

Accumulated diagnostic variables on model levels

GRIB-code

Variable unit IPAR LTYP LEV note

change of temperature due to parameterized processes	K s^-1	210	109
change of temperature due to vertical diffusion	K s^-1	211	109
change of temperature due to radiation	K s^-1	212	109
change of specific humidity due to parameterized processes	kg kg^-1s^-1	220	109
change of specific humidity due to vertical diffusion	kg kg^-1s^-1	221	109
change of specific cloud condensate due to parameterized processes	kg kg^-1s^-1	230	109
change of specific cloud condensate due to vertical diffusion	kg kg^-1s^-1	231	109
change of u-component due to parametrized processes	m s^-2	240	109
change of u-component due to vertical diffusion	m s^-2	241	109
change of v-component due to parametrized processes	m s^-2	245	109
change of v-component due to vertical diffusion	m s^-2	246	109