get_pblh()

subroutine module_bl_mynn::get_pblh	(	integer, intent(in)	KTS,
		integer, intent(in)	KTE,
		real, intent(out)	zi,
		real, dimension(kts:kte), intent(in)	thetav1D,
		real, dimension(kts:kte), intent(in)	qke1D,
		real, dimension(kts:kte+1), intent(in)	zw1D,
		real, dimension(kts:kte), intent(in)	dz1D,
		real, intent(in)	landsea,
		integer	kzi
	)

NOTES ON THE PBLH FORMULATION: The 1.5-theta-increase method defines PBL heights as the level at. which the potential temperature first exceeds the minimum potential. temperature within the boundary layer by 1.5 K. When applied to. observed temperatures, this method has been shown to produce PBL- height estimates that are unbiased relative to profiler-based. estimates (Nielsen-Gammon et al. 2008 [143]). However, their study did not include LLJs. Banta and Pichugina (2008) [156] show that a TKE-based. threshold is a good estimate of the PBL height in LLJs. Therefore, a hybrid definition is implemented that uses both methods, weighting the TKE-method more during stable conditions (PBLH < 400 m). A variable tke threshold (TKEeps) is used since no hard-wired value could be found to work best in all conditions.

GSD get_pblh General Algorithm

• FIND MIN THETAV IN THE LOWEST 200 M AGL
• FIND THETAV-BASED PBLH (BEST FOR DAYTIME).
• FOR STABLE BOUNDARY LAYERS, USE TKE METHOD TO COMPLEMENT THE THETAV-BASED DEFINITION (WHEN THE THETA-V BASED PBLH IS BELOW ~0.5 KM). THE TANH WEIGHTING FUNCTION WILL MAKE THE TKE-BASED DEFINITION NEGLIGIBLE WHEN THE THETA-V-BASED DEFINITION IS ABOVE ~1 KM.
• With TKE advection turned on, the TKE-based PBLH can be very large in grid points with convective precipitation (> 8 km!), so an artificial limit is imposed to not let PBLH_TKE exceed the theta_v-based PBL height +/- 350 m. This has no impact on 98-99% of the domain, but is the simplest patch that adequately addresses these extremely large PBLHs.