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Eduardo Barbaro * with contributions of: Jordi Vila, Maarten Krol, Huug Ouwersloot, Henk Baltink, Fred Bosveld, Dave Donovan, Wouter Knap, Ping Wang * Meteorology and air-quality group Wageningen University

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This talk is about: CBL dynamics Radiation Land surface Scattering Aerosols Absorption Soil properties Latent heat Sensible heat Heat budget CBL height θ, q

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Research question How do the CBL dynamics and the land-atmosphere system react to the SW radiation absorbed by the aerosols during the day ? CBL dynamics Radiation Land surface

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Comprehensive observation dataset CBL height θ q CBL dynamics Radiation Aerosols Land surface Radiation budget: (LW ↕and SW ↕) Aerosol properties: AOD, ω, g SEB: Q NET, SH,LE,G 0

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Numerical modeling CBL dynamics Surface fluxes Aerosols and radiation LES: 3-D high-resolution model able to reproduce detailed CBL dynamics. MXL: Simplified bulk model able to reproduce the most important CBL dynamics. Penman-Monteith: Land-surface model able to calculate the SEB. Delta-Eddington: Broadband radiative transfer code able to calculate SW radiation profiles accounting for the aerosol information. LES MXL Radiative transfer (Delta- Eddington) SEB (Penman- Monteith) The MXL model is used to perform 256 systematic runs (sensitivity analysis) varying the initial aerosol properties (AOD and ω). Broader quantification!

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CBL prototypes t h Aerosol layer t h

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Aerosol temporal evolution and vertical structure Similar to Wang et al 2009 We constrain the aerosol data in our LES and MXL models (red dashes). t h

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Initial conditions: θ and q Residual layer Aerosol layer

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Radiation budget R 2 = 0.99 RMSE = 8.4 Wm -2 R 2 = 0.93 RMSE = 9.7 Wm -2 LES CESAR

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SEB and CBL height LES CESAR

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Thermodynamic variables LES CESAR Entrainment of drier air

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Sensitivity Analysis: AOD CLEAR CONTROL AERO+ τ CONTROL = 0.2τ AERO = 0.6 τ CLEAR = 0.0

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SW and SEB modifications τ = 0.6 τ = 0.2 τ = Aerosols directly reduce downward irradiance - Relatively constant reduction on LE (10-20%) - SH is influenced more strongly - Aerosols increase EF (up to 20%)

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Vertical heat budget and θ τ = 0.6 τ = 0.2 τ = 0.0 Aerosols: -Morning (dotted lines): reduce the surface fluxes warm the residual layer -Afternoon (solid lines): Heat the CBL

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CBL height evolution -Aerosols shallow the CBL because of less entrainment -Aerosols delay/anticipate the CBL onset/collapse τ = 0.6 τ = 0.2 τ = 0.0

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MXL: sensitivity analysis (τ x ω) C A C A C A C A AOD and SSA Irradiance Evaporative fraction CBL height

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Take home message: Disrupt the land-atmosphere diurnal cycle Reduce irradiance, SH and LE Shallow and warm the CBL Aerosols will (in a nutshell): When also located above the CBL (I): Strongly shallow the CBL Delay the CBL onset When located within the CBL (II): Shallow the CBL (also reduce Δθ) Anticipate the CBL afternoon collapse t h(I) (II)

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Aerosols on the land-atmosphere system SH ΔθΔθ Q NET θ ω τ τ - ω + τ - ω + LE τ - ω + HR zizi - + τ - ω +

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(τ x ω)

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Two-stream approximation N=1 Two stream approach is an approximation of the RTE in which radiation is propagating in only two discrete directions. Diffuse radiance production by simple scattering of direct solar radiation Diffuse radiance production by scattering of diffuse radiation available in dτ. The multiple scattering contribution is represented by up(down)ward intensities weighted by the appropriated asymmetry factor

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Two-stream approximation Two stream approach is an approximation of the RTE in which radiation is propagating in only two discrete directions. Diff (2) and filling (1) in we have: Boundary conditions: TOP -> I ↓ = 0 SURF -> I ↑ = albedo*I ↓

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Two-stream + Eddington’s approximation Eddinton’s approximation is an improvement on two-stream approach. It can be used to obtain the radiance in a plane-parallel medium with ISOTROPIC SCATTERING. frequency-independen The scattering is also assumed frequency-independent (representative λ) ->not true for aerosols!. Example: Stellar atmospheres (Eddington, 1916). OPS! Boundary conditions: TOP -> I ↓ = 0 SURF -> I ↑ = albedo*I ↓ I μ

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The DELTA-Eddington principle The Eddinton-two stream approach produces very good results for thick layers but is inaccurate for thin layers and when significant absorption is involved. f, fraction of scattered energy residing in the forward peak We remove f=g 2 (f≈0.5) from τ, ω, and g in order to better define the phase function.

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A complex system: ( Interconnection between radiation – land surface – CBL dynamics - Aerosols ) Almost no mass here! BL height (<2km) TOA (100km) 870 Wm -2 Mie scattering + absorption -> attenuates shortwave radiation! Big particles (both absorption + scattering) H LE (39 km) 25% θ CBL ↑ T surf ↓ 800 Wm -2 CABAUW TOA Rayleigh scattering Diffuse Direct

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