/[MITgcm]/MITgcm/pkg/land/land_stepfwd.F
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Revision 1.3 - (hide annotations) (download)
Fri May 14 16:14:48 2004 UTC (20 years ago) by jmc
Branch: MAIN
CVS Tags: checkpoint53b_pre, checkpoint53b_post
Changes since 1.2: +117 -59 lines
* only liquid water diffuse or run-off.
* threshold on snow thickness (excess goes into run-off).

1 jmc 1.3 C $Header: /u/gcmpack/MITgcm/pkg/land/land_stepfwd.F,v 1.2 2004/03/11 14:42:00 jmc Exp $
2 jmc 1.1 C $Name: $
3    
4     #include "LAND_OPTIONS.h"
5    
6     CBOP
7     C !ROUTINE: LAND_STEPFWD
8     C !INTERFACE:
9     SUBROUTINE LAND_STEPFWD(
10     I land_frc, bi, bj, myTime, myIter, myThid)
11    
12     C !DESCRIPTION: \bv
13     C *==========================================================*
14     C | S/R LAND_STEPFWD
15     C | o Land model main S/R: step forward land variables
16     C *==========================================================*
17     C \ev
18    
19     C !USES:
20     IMPLICIT NONE
21    
22     C == Global variables ===
23     C-- size for MITgcm & Land package :
24     #include "LAND_SIZE.h"
25    
26     #include "EEPARAMS.h"
27     #include "LAND_PARAMS.h"
28     #include "LAND_VARS.h"
29    
30     C !INPUT/OUTPUT PARAMETERS:
31     C == Routine arguments ==
32     C land_frc :: land fraction [0-1]
33     C bi,bj :: Tile index
34     C myTime :: Current time of simulation ( s )
35     C myIter :: Current iteration number in simulation
36     C myThid :: Number of this instance of the routine
37     _RS land_frc(1-OLx:sNx+OLx,1-OLy:sNy+OLy,nSx,nSy)
38     INTEGER bi, bj, myIter, myThid
39     _RL myTime
40     CEOP
41    
42     #ifdef ALLOW_LAND
43     C == Local variables ==
44     C i,j,k :: loop counters
45     C kp1 :: k+1
46 jmc 1.2 C grd_HeatCp :: Heat capacity of the ground [J/m3/K]
47 jmc 1.3 C enthalpGrdW :: enthalpy of ground water [J/m3]
48 jmc 1.1 C fieldCapac :: field capacity (of water) [m]
49 jmc 1.2 C mWater :: water content of the ground [kg/m3]
50 jmc 1.3 C groundWnp1 :: hold temporary future soil moisture []
51     C grdWexcess :: ground water in excess [m/s]
52 jmc 1.1 C fractRunOff :: fraction of water in excess which leaves as runoff
53 jmc 1.2 C flxkup :: downward flux of water, upper interface (k-1,k)
54     C flxdwn :: downward flux of water, lower interface (k,k+1)
55 jmc 1.3 C flxEngU :: downward energy flux associated with water flux (W/m2)
56     C upper interface (k-1,k)
57     C flxEngL :: downward energy flux associated with water flux (W/m2)
58     C lower interface (k,k+1)
59 jmc 1.2 C temp_af :: ground temperature if above freezing
60     C temp_bf :: ground temperature if below freezing
61     C mPmE :: hold temporary (liquid) Precip minus Evap [kg/m2/s]
62     C enWfx :: hold temporary energy flux of Precip [W/m2]
63     C enGr1 :: ground enthalpy of level 1 [J/m2]
64     C mSnow :: mass of snow [kg/m2]
65     C dMsn :: mass of melting snow [kg/m2]
66     C snowPrec :: snow precipitation [kg/m2/s]
67     C hNewSnow :: fresh snow accumulation [m]
68 jmc 1.3 C dhSnowMx :: potential snow increase [m]
69     C dhSnow :: effective snow increase [m]
70     C mIceDt :: ground-ice growth rate (<- excess of snow) [kg/m2/s]
71 jmc 1.2 C ageFac :: snow aging factor [1]
72 jmc 1.3 _RL grd_HeatCp, enthalpGrdW
73     _RL fieldCapac, mWater
74     _RL groundWnp1, grdWexcess, fractRunOff
75 jmc 1.1 _RL flxkup(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
76     _RL flxkdw(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
77 jmc 1.3 _RL flxEngU(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
78     _RL flxEngL, temp_af, temp_bf, mPmE, enWfx, enGr1
79     _RL mSnow, dMsn, snowPrec
80     _RL hNewSnow, dhSnowMx, dhSnow, mIceDt, ageFac
81 jmc 1.1 INTEGER i,j,k,kp1
82    
83 jmc 1.2 IF (land_calc_grT .AND. .NOT.land_impl_grT ) THEN
84 jmc 1.1 C-- Step forward ground temperature:
85    
86     DO k=1,land_nLev
87     kp1 = MIN(k+1,land_nLev)
88    
89     IF (k.EQ.1) THEN
90     DO j=1,sNy
91     DO i=1,sNx
92     flxkup(i,j) = land_HeatFlx(i,j,bi,bj)
93     ENDDO
94     ENDDO
95     ELSE
96     DO j=1,sNy
97     DO i=1,sNx
98     flxkup(i,j) = flxkdw(i,j)
99     ENDDO
100     ENDDO
101     ENDIF
102    
103     DO j=1,sNy
104     DO i=1,sNx
105     IF ( land_frc(i,j,bi,bj).GT.0. ) THEN
106     C- Thermal conductivity flux, lower interface (k,k+1):
107     flxkdw(i,j) = land_grdLambda*
108     & ( land_groundT(i,j,k,bi,bj)
109     & -land_groundT(i,j,kp1,bi,bj) )
110     & *land_rec_dzC(kp1)
111    
112 jmc 1.2 C- Step forward ground enthalpy, level k :
113     land_enthalp(i,j,k,bi,bj) = land_enthalp(i,j,k,bi,bj)
114     & + land_deltaT * (flxkup(i,j)-flxkdw(i,j))/land_dzF(k)
115 jmc 1.1
116     ENDIF
117     ENDDO
118     ENDDO
119    
120     ENDDO
121     C-- step forward ground temperature: end
122     ENDIF
123    
124 jmc 1.2 C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
125    
126     #ifdef LAND_OLD_VERSION
127     IF ( .TRUE. ) THEN
128     #else
129 jmc 1.3 IF ( land_calc_grW ) THEN
130 jmc 1.2 #endif
131 jmc 1.3 C-- Initialize run-off arrays.
132     DO j=1,sNy
133     DO i=1,sNx
134     land_runOff(i,j,bi,bj) = 0. _d 0
135     land_enRnOf(i,j,bi,bj) = 0. _d 0
136     ENDDO
137     ENDDO
138 jmc 1.2 C-- need (later on) ground temp. to be consistent with updated enthalpy:
139     DO k=1,land_nLev
140     DO j=1,sNy
141     DO i=1,sNx
142     IF ( land_frc(i,j,bi,bj).GT.0. ) THEN
143     mWater = land_rhoLiqW*land_waterCap
144     & *land_groundW(i,j,k,bi,bj)
145     grd_HeatCp = land_heatCs + land_CpWater*mWater
146     temp_bf = (land_enthalp(i,j,k,bi,bj)+land_Lfreez*mWater)
147     & / grd_HeatCp
148     temp_af = land_enthalp(i,j,k,bi,bj) / grd_HeatCp
149     land_groundT(i,j,k,bi,bj) =
150     & MIN( temp_bf, MAX(temp_af, 0. _d 0) )
151     ENDIF
152     ENDDO
153     ENDDO
154     ENDDO
155     ENDIF
156    
157     IF ( land_calc_snow ) THEN
158     C-- Step forward Snow thickness (also account for rain temperature)
159     ageFac = 1. _d 0 - land_deltaT/timeSnowAge
160     DO j=1,sNy
161     DO i=1,sNx
162     IF ( land_frc(i,j,bi,bj).GT.0. ) THEN
163     mPmE = land_Pr_m_Ev(i,j,bi,bj)
164     enWfx = land_EnWFlux(i,j,bi,bj)
165     enGr1 = land_enthalp(i,j,1,bi,bj)*land_dzF(1)
166     C- snow aging:
167     land_snowAge(i,j,bi,bj) =
168     & ( land_deltaT + land_snowAge(i,j,bi,bj)*ageFac )
169     IF ( enWfx.LT.0. ) THEN
170     C- snow precip in excess (Snow > Evap) :
171     C => start to melt (until ground at freezing point) and then accumulate
172     snowPrec = -enWfx -MAX( enGr1/land_deltaT, 0. _d 0 )
173     snowPrec = MAX( snowPrec*recip_Lfreez , 0. _d 0 )
174     mPmE = mPmE - snowPrec
175 jmc 1.3 flxEngU(i,j) = enWfx + land_Lfreez*snowPrec
176 jmc 1.2 hNewSnow = land_deltaT * snowPrec / land_rhoSnow
177     C- refresh snow age:
178     land_snowAge(i,j,bi,bj) = land_snowAge(i,j,bi,bj)
179     & *EXP( -hNewSnow/hNewSnowAge )
180 jmc 1.3 C- update snow thickness:
181     c land_hSnow(i,j,bi,bj) = land_hSnow(i,j,bi,bj) + hNewSnow
182     C glacier & ice-sheet missing: excess of snow put directly into run-off
183     dhSnowMx = MAX( 0. _d 0,
184     & land_hMaxSnow - land_hSnow(i,j,bi,bj) )
185     dhSnow = MIN( hNewSnow, dhSnowMx )
186     land_hSnow(i,j,bi,bj) = land_hSnow(i,j,bi,bj) + dhSnow
187     mIceDt = land_rhoSnow * (hNewSnow-dhSnow) / land_deltaT
188     land_runOff(i,j,bi,bj) = mIceDt/land_rhoLiqW
189     land_enRnOf(i,j,bi,bj) = -mIceDt*land_Lfreez
190 jmc 1.2 ELSE
191     C- rain precip (whatever Evap is) or Evap exceeds snow precip :
192     C => snow melts or sublimates
193     c snowMelt = MIN( enWfx*recip_Lfreez ,
194     c & land_hSnow(i,j,bi,bj)*land_rhoSnow/land_deltaT )
195     mSnow = land_hSnow(i,j,bi,bj)*land_rhoSnow
196     dMsn = enWfx*recip_Lfreez*land_deltaT
197     IF ( dMsn .GE. mSnow ) THEN
198     dMsn = mSnow
199     land_hSnow(i,j,bi,bj) = 0. _d 0
200 jmc 1.3 flxEngU(i,j) = enWfx - land_Lfreez*mSnow/land_deltaT
201 jmc 1.2 ELSE
202 jmc 1.3 flxEngU(i,j) = 0. _d 0
203 jmc 1.2 land_hSnow(i,j,bi,bj) = land_hSnow(i,j,bi,bj)
204     & - dMsn / land_rhoSnow
205     ENDIF
206     c IF (mPmE.GT.0.) land_snowAge(i,j,bi,bj) = timeSnowAge
207     mPmE = mPmE + dMsn/land_deltaT
208     ENDIF
209     flxkup(i,j) = mPmE/land_rhoLiqW
210     c land_Pr_m_Ev(i,j,bi,bj) = mPmE
211     IF ( land_hSnow(i,j,bi,bj).LE. 0. _d 0 )
212     & land_snowAge(i,j,bi,bj) = 0. _d 0
213     C- avoid negative (but very small, < 1.e-34) hSnow that occurs because
214     C of truncation error. Might need to rewrite this part.
215     c IF ( land_hSnow(i,j,bi,bj).LE. 0. _d 0 ) THEN
216     c land_hSnow(i,j,bi,bj) = 0. _d 0
217     c land_snowAge(i,j,bi,bj) = 0. _d 0
218     c ENDIF
219     ENDIF
220     ENDDO
221     ENDDO
222     ELSE
223     DO j=1,sNy
224     DO i=1,sNx
225     flxkup(i,j) = land_Pr_m_Ev(i,j,bi,bj)/land_rhoLiqW
226 jmc 1.3 flxEngU(i,j) = 0. _d 0
227 jmc 1.2 ENDDO
228     ENDDO
229     ENDIF
230    
231     C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
232    
233 jmc 1.1 IF (land_calc_grW) THEN
234     C-- Step forward ground Water:
235    
236     DO k=1,land_nLev
237     IF (k.EQ.land_nLev) THEN
238     kp1 = k
239     fractRunOff = 1. _d 0
240     ELSE
241     kp1 = k+1
242     fractRunOff = land_fractRunOff
243     ENDIF
244     fieldCapac = land_waterCap*land_dzF(k)
245    
246     DO j=1,sNy
247     DO i=1,sNx
248     IF ( land_frc(i,j,bi,bj).GT.0. ) THEN
249 jmc 1.3
250     #ifdef LAND_OLD_VERSION
251     IF ( .TRUE. ) THEN
252     IF ( k.EQ.land_nLev ) THEN
253     #else
254     IF ( land_groundT(i,j,k,bi,bj).LT.0. _d 0 ) THEN
255     C- Frozen level: only account for upper level fluxes
256     IF ( flxkup(i,j) .LT. 0. _d 0 ) THEN
257     C- Step forward soil moisture (& enthapy), level k :
258     land_groundW(i,j,k,bi,bj) = land_groundW(i,j,k,bi,bj)
259     & + land_deltaT * flxkup(i,j) / fieldCapac
260     IF ( land_calc_snow )
261     & land_enthalp(i,j,k,bi,bj) = land_enthalp(i,j,k,bi,bj)
262     & + land_deltaT * flxEngU(i,j) / land_dzF(k)
263     ELSE
264     C- Frozen level: incoming water flux goes directly into run-off
265     land_runOff(i,j,bi,bj) = land_runOff(i,j,bi,bj)
266     & + flxkup(i,j)
267     land_enRnOf(i,j,bi,bj) = land_enRnOf(i,j,bi,bj)
268     & + flxEngU(i,j)
269     ENDIF
270     C- prepare fluxes for next level:
271     flxkup(i,j) = 0. _d 0
272     flxEngU(i,j) = 0. _d 0
273    
274     ELSE
275    
276     C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
277 jmc 1.2 C- Diffusion flux of water, lower interface (k,k+1):
278 jmc 1.3 IF ( k.EQ.land_nLev .OR.
279     & land_groundT(i,j,kp1,bi,bj).LT.0. _d 0 ) THEN
280     #endif /* LAND_OLD_VERSION */
281     C- no Diffusion of water if one level is frozen :
282     flxkdw(i,j) = 0. _d 0
283     flxEngL = 0. _d 0
284     ELSE
285     flxkdw(i,j) = fieldCapac*
286     & ( land_groundW(i,j,k,bi,bj)
287     & -land_groundW(i,j,kp1,bi,bj) )
288     & / land_wTauDiff
289     C- energy flux associated with water flux: take upwind Temp
290     IF ( flxkdw(i,j).GE.0. ) THEN
291     flxEngL = flxkdw(i,j)*land_rhoLiqW*land_CpWater
292     & *land_groundT(i,j,k,bi,bj)
293     ELSE
294     flxEngL = flxkdw(i,j)*land_rhoLiqW*land_CpWater
295     & *land_groundT(i,j,kp1,bi,bj)
296     ENDIF
297     ENDIF
298 jmc 1.1
299     C- Step forward soil moisture, level k :
300 jmc 1.3 groundWnp1 = land_groundW(i,j,k,bi,bj)
301 jmc 1.2 & + land_deltaT * (flxkup(i,j)-flxkdw(i,j)) / fieldCapac
302 jmc 1.3
303     C- Water in excess will leave as run-off or go to level below
304     land_groundW(i,j,k,bi,bj) = MIN(1. _d 0, groundWnp1)
305     grdWexcess = ( groundWnp1 - MIN(1. _d 0, groundWnp1) )
306     & *fieldCapac/land_deltaT
307 jmc 1.1
308     C- Run off: fraction 1-fractRunOff enters level below
309 jmc 1.3 land_runOff(i,j,bi,bj) = land_runOff(i,j,bi,bj)
310     & + fractRunOff*grdWexcess
311     C- prepare fluxes for next level:
312     flxkup(i,j) = flxkdw(i,j)
313     & + (1. _d 0-fractRunOff)*grdWexcess
314    
315     IF ( land_calc_snow ) THEN
316     enthalpGrdW = land_rhoLiqW*land_CpWater
317     & *land_groundT(i,j,k,bi,bj)
318     C-- Account for water fluxes in energy budget: update ground Enthalpy
319     land_enthalp(i,j,k,bi,bj) = land_enthalp(i,j,k,bi,bj)
320     & + ( flxEngU(i,j) - flxEngL - grdWexcess*enthalpGrdW
321     & )*land_deltaT/land_dzF(k)
322    
323     land_enRnOf(i,j,bi,bj) = land_enRnOf(i,j,bi,bj)
324     & + fractRunOff*grdWexcess*enthalpGrdW
325     C- prepare fluxes for next level:
326     flxEngU(i,j) = flxEngL
327     & + (1. _d 0-fractRunOff)*grdWexcess*enthalpGrdW
328     ENDIF
329 jmc 1.2 ENDIF
330 jmc 1.3 C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
331 jmc 1.2
332 jmc 1.1 ENDIF
333     ENDDO
334     ENDDO
335    
336     ENDDO
337     C-- step forward ground Water: end
338 jmc 1.2 ENDIF
339    
340     C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|
341    
342 jmc 1.3 IF ( land_calc_grT ) THEN
343     C-- Compute ground temperature from enthalpy (if not already done):
344 jmc 1.2
345     DO k=1,land_nLev
346     DO j=1,sNy
347     DO i=1,sNx
348     C- Ground Heat capacity, layer k:
349     mWater = land_rhoLiqW*land_waterCap
350     & *land_groundW(i,j,k,bi,bj)
351     grd_HeatCp = land_heatCs + land_CpWater*mWater
352     C temperature below freezing:
353     temp_bf = (land_enthalp(i,j,k,bi,bj)+land_Lfreez*mWater)
354     & / grd_HeatCp
355     C temperature above freezing:
356     temp_af = land_enthalp(i,j,k,bi,bj) / grd_HeatCp
357     #ifdef LAND_OLD_VERSION
358     land_enthalp(i,j,k,bi,bj) =
359     & grd_HeatCp*land_groundT(i,j,k,bi,bj)
360     #else
361     land_groundT(i,j,k,bi,bj) =
362     & MIN( temp_bf, MAX(temp_af, 0. _d 0) )
363     #endif
364     ENDDO
365     ENDDO
366     ENDDO
367    
368     IF ( land_impl_grT ) THEN
369     DO j=1,sNy
370     DO i=1,sNx
371     IF ( land_hSnow(i,j,bi,bj).GT.0. _d 0 ) THEN
372     land_skinT(i,j,bi,bj) = MIN(land_skinT(i,j,bi,bj), 0. _d 0)
373     ELSE
374     land_skinT(i,j,bi,bj) = land_groundT(i,j,1,bi,bj)
375     ENDIF
376     ENDDO
377     ENDDO
378     ELSE
379     DO j=1,sNy
380     DO i=1,sNx
381     land_skinT(i,j,bi,bj) = land_groundT(i,j,1,bi,bj)
382     ENDDO
383     ENDDO
384     ENDIF
385    
386     C-- Compute ground temperature: end
387 jmc 1.1 ENDIF
388    
389     #endif /* ALLOW_LAND */
390    
391     RETURN
392     END

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