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Coupled vs. Decoupled Boundary Layers in VOCALS- REx

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 http:// www.atmos-chem-phys-discuss.net /11/8431/2011/.

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Coupled vs. Decoupled Boundary Layers in VOCALS- REx

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  1. 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 http://www.atmos-chem-phys-discuss.net/11/8431/2011/ VOCALS RF05, 72W 20S

  2. Two decoupling criteria Profiles: Δq = qt (<0.25zi) - qt(0.75-1zi) > 0.5 g kg-1 Coupled Decoupled Subcld legs: Δzb = Leg-mean lidarzb – LCL > 100 m

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

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

  5. Decoupling not correlated with inversion jumps • Lock (2009) and others have suggested high values of κ = 1 + cpΔθl/LΔqt 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

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