Report

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 [email protected] * This talk is about: Radiation CBL dynamics Absorption Land surface Latent heat Aerosols Sensible heat Scattering Soil properties CBL height θ, q Heat budget Research question Radiation CBL dynamics Land surface How do the CBL dynamics and the land-atmosphere system react to the SW radiation absorbed by the aerosols during the day ? Comprehensive observation dataset Radiation Aerosols CBL dynamics Radiation budget: (LW ↕and SW ↕) Aerosol properties: AOD, ω, g CBL height θ q Land surface SEB: QNET, SH,LE,G0 Numerical modeling Radiative transfer (DeltaEddington) LES MXL SEB (PenmanMonteith) • LES: 3-D high-resolution model able to reproduce detailed CBL dynamics. Aerosols and radiation • MXL: Simplified bulk model able to reproduce the most important CBL dynamics. Surface fluxes CBL dynamics Broader quantification! The MXL model is used to perform 256 systematic runs (sensitivity analysis) varying the initial aerosol properties (AOD and ω). • 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. CBL prototypes h h Aerosol layer Aerosol layer t t Aerosol temporal evolution and vertical structure h We constrain the aerosol data in our LES and MXL models (red dashes). t Similar to Wang et al 2009 Initial conditions: θ and q Residual layer Aerosol layer LES CESAR Radiation budget R2 = 0.99 RMSE = 8.4 Wm-2 R2 = 0.93 RMSE = 9.7 Wm-2 LES CESAR SEB and CBL height LES CESAR Thermodynamic variables Entrainment of drier air Sensitivity Analysis: AOD τCLEAR = 0.0 CLEAR τCONTROL = 0.2 CONTROL τAERO = 0.6 AERO+ τ = 0.6 τ = 0.2 τ = 0.0 SW and SEB modifications - Aerosols directly reduce downward irradiance Relatively constant reduction on LE (10-20%) SH is influenced more strongly Aerosols increase EF (up to 20%) τ = 0.6 Vertical heat budget and θ Aerosols: - Morning (dotted lines): reduce the surface fluxes warm the residual layer - Afternoon (solid lines): Heat the CBL τ = 0.2 τ = 0.0 τ = 0.6 CBL height evolution - Aerosols shallow the CBL because of less entrainment - Aerosols delay/anticipate the CBL onset/collapse τ = 0.2 τ = 0.0 MXL: sensitivity analysis (τ x ω) AOD CBL and height SSA CC AA Irradiance Evaporative fraction Take home message: Aerosols will (in a nutshell): h Disrupt the land-atmosphere diurnal cycle • Reduce irradiance, SH and LE • Shallow and warm the CBL When also located above the CBL (I): • Strongly shallow the CBL • Delay the CBL onset (I) (II) t When located within the CBL (II): • Shallow the CBL (also reduce Δθ) • Anticipate the CBL afternoon collapse Aerosols on the land-atmosphere system θ Δθ ω τ zi ω τ - + ω τ HR + - ω + - + + τ SH + - ω τ + QNET LE (τ x ω) Two-stream approximation Two stream approach is an approximation of the RTE in which radiation is propagating in only two discrete directions. N=1 The multiple scattering contribution is represented by up(down)ward intensities weighted by the appropriated asymmetry factor Diffuse radiance production by simple scattering of direct solar radiation Diffuse radiance production by scattering of diffuse radiation available in dτ. 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 ↓ 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. The scattering is also assumed frequency-independent (representative λ) ->not true for aerosols!. OPS! Example: Stellar atmospheres (Eddington, 1916). I μ Boundary conditions: TOP -> I↓ = 0 SURF -> I↑ = albedo*I ↓ 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=g2 (f≈0.5) from τ, ω, and g in order to better define the phase function. A complex system: (Interconnection between radiation – land surface – CBL dynamics - Aerosols) CABAUWTOA TOA (100km) Almost no mass here! (39 km) Rayleigh scattering Diffuse Direct 870 Wm-2 800 Wm-2 25% H LE BL height Mie scattering + absorption -> attenuates shortwave radiation! Big particles (both absorption + scattering) θCBL↑ Tsurf ↓ (<2km)