yang_2008()

subroutine module_sf_mynn::yang_2008	(	real, intent(in)	Z_0,
		real, intent(out)	Zt,
		real, intent(out)	Zq,
		real, intent(in)	ustar,
		real, intent(in)	tstar,
		real, intent(in)	qst,
		real, intent(in)	Ren,
		real, intent(in)	visc
	)

The original formulation relates the thermal roughness length (Zt) to u* and T*:

Zt = ht * EXP(-beta*(ustar**0.5)*(ABS(tstar)**0.25))

where ht = Renc*visc/ustar and the critical Reynolds number (Renc) = 70. Beta was originally = 10 (2002 paper) but was revised to 7.2 (in 2008 paper). Their form typically varies the ratio Z0/Zt by a few orders of magnitude (1-1E4).

This modified form uses beta = 1.5 and a variable Renc (function of Z_0), so zt generally varies similarly to the Zilitinkevich form (with Czil = 0.1) for very small or negative surface heat fluxes but can become close to the Zilitinkevich with Czil = 0.2 for very large HFX (large negative T*). Also, the exponent (0.25) on tstar was changed to 1.0, since we found Zt was reduced too much for low-moderate positive heat fluxes.

This should only be used over land!

Referenced by sfclay1d_mynn().

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