Aerosols in the convective boundary layer: effects on the radiation field and the land-atmosphere system Eduardo Barbaro * with contributions of: Jordi Vila, Maarten Krol, Huug Ouwersloot, Henk Baltink, Fred Bosveld, Dave Donovan, Wouter Knap, Ping Wang eorology and air-quality group eningen University [email protected]CESAR DAY KNMI
Aerosols in the convective boundary layer : effects on the radiation field and the land-atmosphere system. Eduardo Barbaro * with contributions of: Jordi Vila, Maarten Krol, Huug Ouwersloot, Henk Baltink, Fred Bosveld, Dave Donovan, Wouter Knap, Ping Wang . CESAR DAY. KNMI. - PowerPoint PPT Presentation
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Aerosols in the convective boundary layer: effects on the radiation field and the land-atmosphere system
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]
CESAR DAYKNMI
This talk is about:
CBL dynamicsRadiation
Land surface
Scattering
Aerosols
Absorption
Soil propertie
s
Latent heat
Sensible heat
Heat
budget
CBL height
θ, q
Strategy to answer:
Research question
Combining observations and
numerical modeling
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
Comprehensive observation dataset
CBL heightθq
CBL dynamics
RadiationAerosols
Land surface
Radiation budget:(LW ↕and SW ↕)
Aerosol properties:AOD, ω, g
SEB:QNET, SH,LE,G0
Numerical modeling
CBLdynamic
s
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.
LESMXL
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!
CBL prototypes
t
h 25th September 2003
Aerosol layer
t
h 8th May 2008
Aerosol layer
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).
8th May 2008
t
h
Initial conditions: θ and q8th May 2008
Residual layer Aerosol layer
Radiation budget8th May 2008
R2 = 0.99RMSE = 8.4 Wm-2
R2 = 0.93RMSE = 9.7 Wm-2
LES
CESAR
SEB and CBL height8th May 2008
LES
CESAR
Thermodynamic variables8th May 2008
LES
CESAR
Entrainment of drier air
Sensitivity Analysis: AOD
CLEAR CONTROL AERO+
Cabauw BeijingBarcelona
OsloQuebec
τCONTROL = 0.2 τAERO = 0.6τCLEAR = 0.0
SW and SEB modificationsτ = 0.6
τ = 0.2
τ = 0.0
25th September 2003
- Aerosols directly reduce downward irradiance- Relatively constant reduction on LE (10-20%) - SH is influenced more strongly- Aerosols increase EF (up to 20%)
Vertical heat budget and θτ = 0.6
τ = 0.2
τ = 0.0
25th September 2003
Aerosols:- Morning (dotted lines):
reduce the surface fluxeswarm the residual layer
- Afternoon (solid lines):Heat the CBL
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
MXL: sensitivity analysis (τ x ω)
C A
25th September 2003
C AC AC A
AOD and SSA
IrradianceEvaporative
fraction
CBL height
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)
Aerosols on the land-atmosphere system
SH
Δθ
QNET
θ
ω τ+- +
-
τ-
ω+
τ-
ω+
LE
τ-ω
+
HR
zi
-+
τ-
ω+
(τ x ω)25th September 2003
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
Two-stream approximationTwo stream approach is an approximation of the RTE in which radiation is propagating in only two discrete directions.
Two-stream + Eddington’s approximationEddinton’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!.Example: Stellar atmospheres (Eddington, 1916).
The DELTA-Eddington principleThe Eddinton-two stream approach produces very good results for thick layers but is inaccurate for thin layers andwhen 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)