Coupled vs. Decoupled Boundary Layers in VOCALS-REx Chris Jones and Chris Bretherton Department of Atmospheric Sciences University of Washington Dave Leon.

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Presentation transcript:

Coupled vs. Decoupled Boundary Layers in VOCALS-REx Chris Jones and Chris Bretherton Department of Atmospheric Sciences University of Washington Dave Leon Department of Atmospheric Sciences University of Wyoming VOCALS RF05, 72W 20S

Two decoupling criteria Profiles: Δq = q t ( 0.5 g kg -1 Coupled Decoupled Subcld legs: Δz b = Leg-mean lidar z b – LCL > 100 m

Decoupling correlates with well-mixed cloud thickness Open symbols = POC leg segments …as does drizzle, but causality unclear.

Decoupling uncorrelated to wind speed Bretherton and Wyant (1997) suggested stronger latent heat fluxes should promote decoupling – not seen in our results.

Decoupling not correlated with inversion jumps Lock (2009) and others have suggested high values of κ = 1 + c p Δθ l /LΔq t induce strong entrainment and Sc cloud breakup. Strong entrainment might also favor decoupling. Use REx C-130 profiles to calculate jumps/decoupling, adjacent subcloud legs to calculate cloud fraction. κ > 0.4 often (but not always) goes with broken cloud. For κ < 0.5 there is no obvious correlation of κ and decoupling. POC and non-POC distributions overlap Red: POCs Dash: Lock LES results