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Experimental wind-speed-dependent betamax for ST4 - new codebase #20

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Experimental wind-speed-dependent betamax for ST4 - new codebase #20

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69a15d1
Changes to WW3 to allow for a wind-dependent betamax calculation. Spe…
pieterbartsmit Jun 16, 2026
f9637e5
Rebase onto the new ww3 codebase.
pieterbartsmit Jun 29, 2026
c374e15
Added realistic values from our calibration for the parameters. Also …
pieterbartsmit Jun 29, 2026
5ae8660
Updated to latest estimates for slope/intercept.
pieterbartsmit Jun 30, 2026
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2 changes: 1 addition & 1 deletion VERSION
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@@ -1 +1 @@
7.14
7.14.2
20 changes: 17 additions & 3 deletions model/src/w3src4md.F90
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Expand Up @@ -551,6 +551,13 @@ SUBROUTINE W3SIN4 (A, CG, K, U, USTAR, DRAT, AS, USDIR, Z0, CD, &
REAL :: COSU, SINU, TAUX, TAUY, USDIRP, USTP
REAL :: TAUPX, TAUPY, UST2, TAUW, TAUWB
REAL , PARAMETER :: EPS1 = 0.00001, EPS2 = 0.000001

REAL :: BBETA_EFF !PBS: The effective "betamax" after we apply a linear approximation.
! Part of SOFAR enhancements to be able to better calibrate betamax
! Estimated as BBETA_EFF= BETAMAX_INTERCEPT + BETAMAX_SLOPE * U
REAL , PARAMETER :: BETAMAX_INTERCEPT=1.134 ! Intercept of the linear betamax relation
REAL , PARAMETER :: BETAMAX_SLOPE=0.0157 ! Slope of the linear betamax relation

#if defined(W3_T) || defined(W3_STAB3)
REAL :: Usigma !standard deviation of U due to gustiness
REAL :: USTARsigma !standard deviation of USTAR due to gustiness
Expand Down Expand Up @@ -602,9 +609,12 @@ SUBROUTINE W3SIN4 (A, CG, K, U, USTAR, DRAT, AS, USDIR, Z0, CD, &
STRESSSTABN =0.
!
! Coupling coefficient times density ratio DRAT
!
CONST1=BBETA/KAPPA**2 ! needed for the tail
CONST0=CONST1*DRAT ! needed for the resolved spectrum
! PBS: Instead of a constant betamax we use a betamax linearly dependent on wind speed to allow for more flexibility
! in calibration. (SOFAR SPECIFIC)
BBETA_EFF = MAX( MIN( BETAMAX_INTERCEPT + BETAMAX_SLOPE * U, 1.5 ), 1.25)

CONST1=BBETA_EFF/KAPPA**2 ! needed for the tail
CONST0=CONST1*DRAT ! needed for the resolved spectrum
!
! 1.a estimation of surface roughness parameters
!
Expand Down Expand Up @@ -957,6 +967,10 @@ SUBROUTINE W3SIN4 (A, CG, K, U, USTAR, DRAT, AS, USDIR, Z0, CD, &
TAU1 =(TAUHFT(IND,J)*DELI2+TAUHFT(IND+1,J)*DELI1 )*DELJ2 &
+(TAUHFT(IND,J+1)*DELI2+TAUHFT(IND+1,J+1)*DELI1)*DELJ1
END IF

! PBS - SOFAR: Because we recompute betamax based on windspeed we have to reschale the tabulated tail
! contributions with the new betamax value
TAU1 = TAU1 * (BBETA_EFF / BBETA)
!
TAUHF = LEVTAIL0*UST**2*TAU1
END IF ! End of test on use of table
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