This is the entity of GFS Noah LSM model of physics subroutines. It is a soil/veg/snowpack land-surface model to update soil moisture, soil ice, soil temperature, skin temperature, snowpack water content, snowdepth, and all terms of the surface energy balance and surface water balance (excluding input atmospheric forcings of downward radiation and precipitation ). More...

Detailed Description

The land-surface model component was substantially upgraded from the Oregon State University (OSU) land surface model to EMC's new Noah Land Surface Model (Noah LSM) during the major implementation in the NCEP Global Forecast System (GFS) on May 31, 2005. Forecast System (GFS). The Noah LSM embodies about 10 years of upgrades (see [11]; [50]; [20]) to its ancestor, the OSU LSM. The Noah LSM upgrade includes:

An increase from two (10, 190 cm thick) to four soil layers (10, 30, 60, 100 cm thick)
Addition of frozen soil physics
Add glacial ice treatment
Two snowpack states (SWE, density)
New formulations for infiltration and runoff account for sub-grid variability in precipitation and soil moisture
Revised physics of the snowpack and its influence on surface heat fluxes and albedo
Higher canopy resistance
Spatially varying root depth
Surface fluxes weighted by snow cover fraction
Improved thermal conduction in soil/snow
Improved seasonality of green vegetation cover.
Improved evaporation treatment over bare soil and snowpack

Parameters

[in]	nsoil	integer, number of soil layers (>=2 but <=nsold)
[in]	couple	integer, =0:uncoupled (land model only), =1:coupled with parent atmos model
[in]	icein	integer, sea-ice flag (=1: sea-ice, =0: land)
[in]	ffrozp	real, flag for snow-rain detection (1.=snow, 0.=rain)
[in]	dt	real, time step (<3600 sec)
[in]	zlvl	real, height abv atmos ground forcing vars ( \(m\))
[in]	sldpth	real, thickness of each soil layer ( \(m\)), nsoil
[in]	swdn	real, downward SW radiation flux ( \(W/m^2\))
[in]	swnet	real, downward SW net (dn-up) flux ( \(W/m^2\))
[in]	lwdn	real, downward LW radiation flux ( \(W/m^2\))
[in]	sfcems	real, sfc LW emissivity (fractional)
[in]	sfcprs	real, pressure at height zlvl above ground( \(Pa\))
[in]	sfctmp	real, air temp at height zlvl above ground ( \(K\))
[in]	sfcspd	real, wind speed at height zlvl above ground ( \(m s^{-1}\))
[in]	prcp	real, precipitation rate ( \(kgm^{-2}s^{-1}\))
[in]	q2	real, mixing ratio at hght zlvl above ground ( \(kgkg^{-1}\))
[in]	q2sat	real, sat mixing ratio at zlvl above ground ( \(kgkg^{-1}\))
[in]	dqsdt2	real, slope of sat specific humidity curve at t=sfctmp ( \(kgkg^{-1}k^{-1}\))
[in]	th2	real, air potential temperature at zlvl above ground ( \(K\))
[in]	ivegsrc	integer, sfc veg type data source UMD or IGBP
[in]	vegtyp	integer, vegetation type (integer index)
[in]	soiltyp	integer, soil type (integer index)
[in]	slopetyp	integer, class of sfc slope (integer index)
[in]	shdmin	real, min areal coverage of green veg (fraction)
[in]	alb	real, background snow-free sfc albedo (fraction)
[in]	snoalb	real, max albedo over deep snow (fraction)
[in,out]	tbot	real, bottom soil temp ( \(K\)) (local yearly-mean sfc air temp)
[in,out]	cmc	real, canopy moisture content ( \(m\))
[in,out]	t1	real, ground/canopy/snowpack eff skin temp ( \(K\))
[in,out]	stc	real, soil temp ( \(K\))
[in,out]	smc	real, total soil moisture (vol fraction)
[in,out]	sh2o	real, unfrozen soil moisture (vol fraction), note: frozen part = smc-sh2o
[in,out]	sneqv	real, water-equivalent snow depth ( \(m\)), note: snow density = snwqv/snowh
[in,out]	ch	real, sfc exchange coeff for heat & moisture ( \(ms^{-1}\)), note: conductance since it's been mult by wind
[in,out]	cm	real, sfc exchange coeff for momentum ( \(ms^{-1}\)), note: conductance since it's been mult by wind
[in,out]	z0	real, roughness length ( \(m\))
[out]	nroot	integer, number of root layers
[out]	shdfac	real, aeral coverage of green veg (fraction)
[out]	snowh	real, snow depth ( \(m\))
[out]	albedo	real, sfc albedo incl snow effect (fraction)
[out]	eta	real, downward latent heat flux ( \(W/m^2\))
[out]	sheat	real, downward sensible heat flux ( \(W/m^2\))
[out]	ec	real, canopy water evaporation ( \(W/m^2\))
[out]	edir	real, direct soil evaporation ( \(W/m^2\))
[out]	et	real, plant transpiration ( \(W/m^2\))
[out]	ett	real, total plant transpiration ( \(W/m^2\))
[out]	esnow	real, sublimation from snowpack ( \(W/m^2\))
[out]	drip	real, through-fall of precip and/or dew in excess of canopy water-holding capacity ( \(m\))
[out]	dew	real, dewfall (or frostfall for t<273.15) ( \(m\))
[out]	beta	real, ratio of actual/potential evap
[out]	etp	real, potential evaporation ( \(W/m^2\))
[out]	ssoil	real, upward soil heat flux ( \(W/m^2\))
[out]	flx1	real, precip-snow sfc flux ( \(W/m^2\))
[out]	flx2	real, freezing rain latent heat flux ( \(W/m^2\))
[out]	flx3	real, phase-change heat flux from snowmelt ( \(W/m^2\))
[out]	runoff1	real, surface runoff ( \(ms^{-1}\)) not infiltrating sfc
[out]	runoff2	real, sub sfc runoff ( \(ms^{-1}\)) (baseflow)
[out]	runoff3	real, excess of porosity for a given soil layer
[out]	snomlt	real, snow melt ( \(m\)) (water equivalent)
[out]	sncovr	real, fractional snow cover
[out]	rc	real, canopy resistance (s/m)
[out]	pc	real, plant coeff (fraction) where pc*etp=transpi
[out]	rsmin	real, minimum canopy resistance (s/m)
[out]	xlai	real, leaf area index (dimensionless)
[out]	rcs	real, incoming solar rc factor (dimensionless)
[out]	rct	real, air temperature rc factor (dimensionless)
[out]	rcq	real, atoms vapor press deficit rc factor
[out]	rcsoil	real, soil moisture rc factor (dimensionless)
[out]	soilw	real, available soil moisture in root zone
[out]	soilm	real, total soil column moisture (frozen+unfrozen) ( \(m\))
[out]	smcwlt	real, wilting point (volumetric)
[out]	smcdry	real, dry soil moisture threshold (volumetric)
[out]	smcref	real, soil moisture threshold (volumetric)
[out]	smcmax	real, porosity (sat val of soil mois)

GFS Noah LSM General Algorithm

Functions/Subroutines
subroutine	gfssflx (nsoil, couple, icein, ffrozp, dt, zlvl, sldpth, swdn, swnet, lwdn, sfcems, sfcprs, sfctmp, sfcspd, prcp, q2, q2sat, dqsdt2, th2, ivegsrc, vegtyp, soiltyp, slopetyp, shdmin, alb, snoalb, tbot, cmc, t1, stc, smc, sh2o, sneqv, ch, cm, z0, nroot, shdfac, snowh, albedo, eta, sheat, ec, edir, et, ett, esnow, drip, dew, beta, etp, ssoil, flx1, flx2, flx3, runoff1, runoff2, runoff3, snomlt, sncovr, rc, pc, rsmin, xlai, rcs, rct, rcq, rcsoil, soilw, soilm, smcwlt, smcdry, smcref, smcmax)

subroutine	alcalc
	This subroutine calculates albedo including snow effect (0 -> 1).

subroutine	canres
	This subroutine calculates canopy resistance which depends on incoming solar radiation, air temperature, atmospheric water vapor pressure deficit at the lowest model level, and soil moisture (preferably unfrozen soil moisture rather than total).

subroutine	csnow
	This subroutine calculates snow termal conductivity.

subroutine	nopac
	This subroutine calculates soil moisture and heat flux values and update soil moisture content and soil heat content values for the case when no snow pack is present.

subroutine	penman
	This subroutine calculates potential evaporation for the current point. various partial sums/products are also calculated and passed back to the calling routine for later use.

subroutine	redprm
	This subroutine internally sets default values or optionally read-in via namelist i/o, all soil and vegetation parateters requied for the execusion of the Noah LSM.

subroutine	sfcdif
	This subroutine calculates surface layer exchange coefficients via iterative process(see [12]).

subroutine	snfrac
	This subroutine calculates snow fraction (0->1).

subroutine	snopac
	This subroutine calculates soil moisture and heat flux values and update soil moisture content and soil heat content values for the case when a snow pack is present.

subroutine	snow_new
	This subroutine calculates snow depth and densitity to account for the new snowfall. new values of snow depth & density returned.

subroutine	snowz0
	This subroutine calculates total roughness length over snow.

subroutine	tdfcnd
	This subroutine calculates thermal diffusivity and conductivity of the soil for a given point and time.

subroutine	evapo
	This subroutine calculates soil moisture flux. The soil moisture content (smc - a per unit volume measurement) is a dependent variable that is updated with prognostic equations. The canopy moisture content (cmc) is also updated. Frozen ground version: new states added: sh2o, and frozen ground correction factor, frzfact and paramter slope.

subroutine	shflx
	This subroutine updates the temperature state of the soil column based on the thermal diffusion equation and update the frozen soil moisture content based on the temperature.

subroutine	smflx
	This subroutine calculates soil moisture flux. The soil moisture content (smc - a per unit vulume measurement) is a dependent variable that is updated with prognostic equations. The canopy moisture content (cmc) is also updated. Frozen ground version: new states added: sh2o and frozen ground correction factor, frzx and parameter slope.

subroutine	snowpack
	This subroutine calculates compaction of a snowpack under conditions of increasing snow density, as obtained from an approximate solution of E. Anderson's differential equation (3.29),NOAA technical report NWS 19, by Victor Koren, 03/25/95. subroutine will return new values of snowh and sndens .

subroutine	devap
	This subrtouine calculates direct soil evaporation.

subroutine	frh2o
	This subroutine calculates amount of supercooled liquid soil water content if temperature is below 273.15K (t0). It requires Newton-type iteration to solve the nonlinear implicit equation given in eqn 17 of [50]. More...

subroutine	hrt
	This subroutine calculates the right hand side of the time tendency term of the soil thermal diffusion equation. Also to compute (prepare) the matrix coefficients for the tri-diagonal matrix of the implicit time scheme.

subroutine	hrtice
	This subroutine calculates the right hand side of the time tendency term of the soil thermal diffusion equation for sea-ice (ice = 1) or glacial-ice (ice).

subroutine	hstep
	This subroutine calculates/updates the soil temperature field.

subroutine	rosr12
	This subroutine inverts (solve) the tri-diagonal matrix problem.

subroutine	snksrc
	This subroutine calculates sink/source term of the termal diffusion equation.

subroutine	srt
	This subroutine calculates the right hand side of the time tendency term of the soil water diffusion equation. Also to compute (prepare) the matrix coefficients for the tri-diagonal matrix of the implicit time scheme.

subroutine	sstep
	This subroutine calculates/updates soil moisture content values and canopy moisture content values.

subroutine	tbnd
	This subroutine calculates temperature on the boundary of the layer by interpolation of the middle layer temperatures.

subroutine	tmpavg
	This subroutine calculates soil layer average temperature (tavg) in freezing/thawing layer using up, down, and middle layer temperature (tup, tdn, tm), where tup is at top boundary of layer, tdn is at bottom boundary of layer. tm is layer prognostic state temperature.

subroutine	transp
	This subroutine calculates transpiration for the veg class.

subroutine	wdfcnd
	This subroutine calculates soil water diffusivity and soil hydraulic conductivity.

Function/Subroutine Documentation

subroutine gfssflx::frh2o ( )

New version (June 2001): much faster and more accurate Newton iteration achieved by first taking log of eqn cited above – less than 4 (typically 1 or 2) iterations achieves convergence. Also, explicit 1-step solution option for special case of paramter ck=0, which reduces the orginal implicit equation to a simpler explicit form, known as the "flerchinger eqn". Improved handling of solution in the limit of freezing point temperature t0.

Referenced by snksrc().

subroutine gfssflx	(	integer, intent(in)	nsoil,
		integer, intent(in)	couple,
		integer, intent(in)	icein,
		real (kind=kind_phys), intent(in)	ffrozp,
		real (kind=kind_phys), intent(in)	dt,
		real (kind=kind_phys), intent(in)	zlvl,
		real (kind=kind_phys), dimension(nsoil), intent(in)	sldpth,
		real (kind=kind_phys), intent(in)	swdn,
		real (kind=kind_phys), intent(in)	swnet,
		real (kind=kind_phys), intent(in)	lwdn,
		real (kind=kind_phys), intent(in)	sfcems,
		real (kind=kind_phys), intent(in)	sfcprs,
		real (kind=kind_phys), intent(in)	sfctmp,
		real (kind=kind_phys), intent(in)	sfcspd,
		real (kind=kind_phys), intent(in)	prcp,
		real (kind=kind_phys), intent(in)	q2,
		real (kind=kind_phys), intent(in)	q2sat,
		real (kind=kind_phys), intent(in)	dqsdt2,
		real (kind=kind_phys), intent(in)	th2,
		integer, intent(in)	ivegsrc,
		integer, intent(in)	vegtyp,
		integer, intent(in)	soiltyp,
		integer, intent(in)	slopetyp,
		real (kind=kind_phys), intent(in)	shdmin,
		real (kind=kind_phys), intent(in)	alb,
		real (kind=kind_phys), intent(in)	snoalb,
		real (kind=kind_phys), intent(inout)	tbot,
		real (kind=kind_phys), intent(inout)	cmc,
		real (kind=kind_phys), intent(inout)	t1,
		real (kind=kind_phys), dimension(nsoil), intent(inout)	stc,
		real (kind=kind_phys), dimension(nsoil), intent(inout)	smc,
		real (kind=kind_phys), dimension(nsoil), intent(inout)	sh2o,
		real (kind=kind_phys), intent(inout)	sneqv,
		real (kind=kind_phys), intent(inout)	ch,
		real (kind=kind_phys), intent(inout)	cm,
		real (kind=kind_phys)	z0,
		integer, intent(out)	nroot,
		real (kind=kind_phys), intent(out)	shdfac,
		real (kind=kind_phys), intent(out)	snowh,
		real (kind=kind_phys), intent(out)	albedo,
		real (kind=kind_phys), intent(out)	eta,
		real (kind=kind_phys), intent(out)	sheat,
		real (kind=kind_phys), intent(out)	ec,
		real (kind=kind_phys), intent(out)	edir,
		real (kind=kind_phys), dimension(nsoil), intent(out)	et,
		real (kind=kind_phys), intent(out)	ett,
		real (kind=kind_phys), intent(out)	esnow,
		real (kind=kind_phys), intent(out)	drip,
		real (kind=kind_phys), intent(out)	dew,
		real (kind=kind_phys), intent(out)	beta,
		real (kind=kind_phys), intent(out)	etp,
		real (kind=kind_phys), intent(out)	ssoil,
		real (kind=kind_phys), intent(out)	flx1,
		real (kind=kind_phys), intent(out)	flx2,
		real (kind=kind_phys), intent(out)	flx3,
		real (kind=kind_phys), intent(out)	runoff1,
		real (kind=kind_phys), intent(out)	runoff2,
		real (kind=kind_phys), intent(out)	runoff3,
		real (kind=kind_phys), intent(out)	snomlt,
		real (kind=kind_phys), intent(out)	sncovr,
		real (kind=kind_phys), intent(out)	rc,
		real (kind=kind_phys), intent(out)	pc,
		real (kind=kind_phys), intent(out)	rsmin,
		real (kind=kind_phys), intent(out)	xlai,
		real (kind=kind_phys), intent(out)	rcs,
		real (kind=kind_phys), intent(out)	rct,
		real (kind=kind_phys), intent(out)	rcq,
		real (kind=kind_phys), intent(out)	rcsoil,
		real (kind=kind_phys), intent(out)	soilw,
		real (kind=kind_phys), intent(out)	soilm,
		real (kind=kind_phys), intent(out)	smcwlt,
		real (kind=kind_phys), intent(out)	smcdry,
		real (kind=kind_phys), intent(out)	smcref,
		real (kind=kind_phys), intent(out)	smcmax
	)

For open-sea, sea-ice and glacial-ice cases, sflx() should not have been called (set green vegetation fraction (shdfac) =0.)
Calculate soil layer depth below ground (sigin of zsoil is negative).
Call redprm() to set the land-surface paramters, including soil-type and veg-type dependent parameters.
Over sea-ice or glacial-ice, if water-equivalent snow depth (sneqv) below threshold lower bound (0.01 m for sea-ice, 0.10 m for glacial-ice), then set at lower bound and store the source increment in subsurface runoff/baseflow (runoff2).
For sea-ice and glacial-ice cases, set smc and sh2o values = 1.0 as a flag for non-soil medium.
If input snowpack (sneqv) is nonzero, then call csnow() to compute snow density (sndens) and snow thermal conductivity (sncond).
Determine if it's precipitating and what kind of precipitation it is. if it's precipitating and the air temperature is colder than \(0^oC\), it's snowing! if it's precipitating and the air temperature is warmer than \(0^oC\), but the ground temperature is colder than \(0^oC\), freezing rain is presumed to be falling.
If either precipitation flag (snowng, frzgra) is set as true:
- Since all precip is added to snowpack, no precip infiltrates into the soil so that prcp1 is set to zero.
- Call snow_new() to update snow density based on new snowfall, using old and new snow.
- Call csnow() to update snow thermal conductivity.
If precipitation is liquid (rain), hence save in the precip variable that later can wholely or partially infiltrate the soil (along with any canopy "drip" added to this later).
Determine snowcover fraction and albedo fraction over sea-ice, glacial-ice, and land. For nonzero snow depth over land case:
- Call snfrac() to calculate snow fraction cover.
- Call alcalc() to calculate surface albedo modification due to snowdepth state.
Calculate thermal diffusivity (df1):
- For sea-ice case and glacial-ice case, this is constant( \(df1=2.2\)).
- For non-glacial land case, call tdfcnd() to calculate the thermal diffusivity of top soil layer ([69]).
  - For IGBP/urban, \(df1=3.24\).
  - Add subsurface heat flux reduction effect from the overlying green canopy, adapted from section 2.1.2 of [68].
Calculate subsurface heat flux, ssoil, from final thermal diffusivity of surface mediums,df1 above, and skin temperature and top mid-layer soil temperature.
For uncoupled mode, call snowz0() to calculate surface roughness (z0) over snowpack using snow condition from the previous timestep.
Calculate virtual temps and virtual potential temps needed by subroutines sfcdif and penman.
Calculate the total downward radiation (fdown) = net solar (swnet) + downward longwave (lwdn) as input of penman() and other surface energy budget calculations.
Call penman() to calculate potential evaporation (etp), and other partial products and sums for later calculations.
Call canres() to calculate the canopy resistance and convert it into pc if nonzero greenness fraction.
Now decide major pathway branch to take depending on whether snowpack exists or not:
- For no snowpack is present, call nopac() to calculate soil moisture and heat flux values and update soil moisture contant and soil heat content values.
- For a snowpack is present, call snopac().
Noah LSM post-processing:
- Calculate sensible heat (h) for return to parent model.
- Convert units and/or sign of total evap (eta), potential evap (etp), subsurface heat flux (s), and runoffs for what parent model expects.
- Convert the sign of soil heat flux so that:
  - ssoil>0: warm the surface (night time)
  - ssoil<0: cool the surface (day time)
- For the case of land (but not glacial-ice): convert runoff3 (internal layer runoff from supersat) from \(m\) to \(ms^-1\) and add to subsurface runoff/baseflow (runoff2). runoff2 is already a rate at this point.
- For the case of sea-ice (ice=1) or glacial-ice (ice=-1), add any snowmelt directly to surface runoff (runoff1) since there is no soil medium, and thus no call to subroutine smflx (for soil moisture tendency).
- Calculate total column soil moisture in meters (soilm) and root-zone soil moisture availability (fraction) relative to porosity/saturation.

References alcalc(), canres(), csnow(), nopac(), penman(), redprm(), sfcdif(), snfrac(), snopac(), snow_new(), snowz0(), and tdfcnd().

Referenced by lsm_noah::lsm_noah_run().

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Detailed Description

GFS Noah LSM General Algorithm

Functions/Subroutines

Function/Subroutine Documentation