- Cesar Observatory

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)

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