shortwave radiative transfer in the earth’s atmosphere...
TRANSCRIPT
Jennifer Delamere, Eli Mlawer, and Tony CloughAtmospheric & Environmental Research, Inc.
Shortwave Radiative Transfer in theEarth’s Atmosphere:
Current Models and Validation
RapidRT Calculations
RRTM
Summary
• AER builds radiative transfer models suitable for Earth’s atmosphere– Longwave and shortwave– Validated against high-resolution
radiance/irradiance measurements
• RT models require:– Solar spectral irradiance– Complete spectral range– Sufficient spectral resolution
• Consensus data from solar community would ultimately be transferred into global climate and numerical weather prediction models
Line-by-LineRT Calculations
LBLRTM/CHARTS
Inclusioninto
GCMs/NWPs
AER Products & Services
• Community Radiative TransferModels
• Community Databases
• Spectral line parameters (input)
• Solar source function (input)
• Reference RT Cases (output)
• Web-sites
http://www.aer.com
http://rtweb.aer.com
Radiative Transfer: Line-by-Line
Line-by-Line Radiative Transfer Model (LBLRTM)• Calculations valid from ultra-violet to sub-millimeter spectral regions• Multiple-scattering option available (CHARTS)• Validated extensively against high-resolution measurements
MLS Profile
TOA: 1368.2
SFC: 1084.0
Required Parameters for SW RT
Spectral line and continuum parameters • MT_CKD Continuum Model• HITRAN database (38 molecules)
Surf
ace
Abs
orpt
ion
Coef
ficie
nt(c
m-1
)
Required Parameters for SW RT
Solar Spectral Irradiance • Kurucz (1992) provided desired resolution and spectral
range for RT calculations• Formulation based on Kitt Peak Solar Flux Atlas and
solar RT calculations
Required Parameters for SW RT
Solar Spectral Irradiance• Kurucz (1992)• Other Options (Gueymard, Thullier, etc.)
Figure provided by J. Michalsky
Radiative Transfer: GCM-suitableRRTM Longwave & Shortwave Correlated-k Models
• Accelerates calculations of fluxes• Uses small set of absorption coefficients to represent
absorption coefficients at all frequencies in the spectral band
• Achieves accuracy comparable to line-by-line method
MLS Profile
SFC: 1084.0
SFC: 1084.8
∆ SFC: -0.8
Users of RRTM Models
• Global GCMs1. ECMWF forecast model (using LW and testing SW)2. NCEP Global Forecast System (GFS) (using LW and testing SW)3. Max Planck Institute climate model (ECHAM5) (using LW)4. NCAR atmosphere model (CAM3) (using LW and SW at AER)5. GFDL climate model (testing LW and SW)
• Mesoscale/Regional Models1. Penn State/NCAR (MM5) (using LW)2. NCAR Weather Research and Forecasting (WRF) (using LW in NCAR/EM)3. UC/CIRES Arctic regional climate model (ARCSyM) (using LW)
• Dept. of Energy ARM Program1. Various Single Column Models (Scripps, LLNL, etc.) (using LW)2. BBHRP (using LW and SW )3. McICA (implemented in LW and SW)
• NPOESS (algorithm component; clear sky only)1. AER/NGST VIIRS net heat flux and ocean albedo (using LW and SW )
Radiative Closure Experiments
Specification of Atmospheric Properties
RadiativeTransferModel
Flux/RadianceMeasurements
COMPARE
RSS Validation
• Ground-based Rotating Shadowband Spectroradiometer (SUNY Albany) (Harrison et al., 1999)
• Deployed at ARM Southern Great Plains site from 1996 onward
• Spectrally resolved direct-normal, diffuse-horizontal, and total-horizontal irradiances
• 9000-28,900 cm-1 (1.1 - 0.35 µm)
• 512 channels (instrument now has 1024 channels)
• Spectral resolution from 91 cm-1 (IR) to 65 cm-1 (UV)
• Model-measurement intercomparison provided means to look at clear-sky anomalous absorption issue
Solar Irradiance in RSS Validations
• Extraterrestrial irradiances implied from RSS langley regressions do not agree in all spectral regions with the Kurucz solar irradiances (Harrison et al., 1999)• Approach: RSS irradiances adjusted to Kurucz solar irradiances
• Implication: Measurement-model comparisons are effectively between measured and calculated transmittances
RSS Radiative Closure
• Model LBLRTM/CHARTS calculations (Mlawer et al., 2000) include:
- Atmospheric thermodynamic profile specified by observations- Spectrally dependent surface albedo derived from measurements- Aerosols- Instrument cosine response
Direct
Diffuse
October 2, 1997 @ 11:32 AM
High-Resolution ASTI Validation
• Absolute Solar Transmittance Interferometer (U. Denver)
• Measures solar radiance from 2000 - 10,000 cm-1 (1 - 5 µm) with 0.6 cm-1 resolution
• Field of View: central 16% of the solar disk
• Deployed at the Southern Great Plains ARM site
• Opportunity to look in detail at processes in the near-infrared
• Validation resulted in parameterization of collision-induced O2 continuum for RT models
BBHRP at ARM SGP Site
• Radiative Closure Studies for: • broadband• shortwave• cloudy skies• ‘grid cell’• TOA• all ARM sites
• Generate heating rate profiles based on in-situ measurements using validated radiative transfer model (for use bymodelers)• Generate dataset of measured and modeled radiation for all ARM sites• Provide a ‘test suite’ for researchers evaluating new parameterizations and data sources
-20 -16 -12 -8 -4 0 4 8 12 16 200
0.05
0.1
0.15
0.2
0.25
0.3
Per
cent
age
of c
ases
Diffuse Irradiance Residual (W/m 2)
2-km
10-km
Laser CloudRadar
Base
RadarEcho
Top
LowRadar
Sensitivity
MicrowaveRadiometer
Emission
BroadbandRadiometers
Retrieved Cloud Microphysics
Radiative Transfer Model
(RRTM)
Satellite TOAMeasurement
Modeled TOAFluxes
Modeled Surface Broadband
Fluxes
BBHRP Project
RapidRT Calculations
RRTM
Wrap-Up
• Consensus data from solar community would ultimately be transferred into global climate and numerical weather prediction models
• AER hosts a web-site with models and their associated inputs and reference output cases– http://rtweb.aer.com
• Opportunity for future high-resolution radiometric measurements in Chile (proposed RHUBC-II experiment)
Line-by-LineRT Calculations
LBLRTM/CHARTS
Inclusioninto
GCMs/NWPs
RRTM_LW Band Data
CFC-12,CFC-22
CFC-11,CFC12
CCl4
Halocarbons
CH4H2O,CH43250.02600.016
H2OH2O1480.01390.010
-N2O,CO2, H2O*,N2*2600.02380.015
CO2CO22380.02250.014
O3 *H2O,N2O,CO2*,CO*2250.02080.013
-H2O,CO22080.01800.012
H2O,O2*H2O,O2*1800.01480.011
CH4,N2OH2O,CH4,N2O*1390.01180.09
O3,CO2*, N2O*H2O,O3*,CO2*,N2O*1180.01080.08
O3,CO2H2O,O3,CO2*1080.0980.07
-H2O,CO2*980.0820.06
CO2,O3H2O,CO2 ,O3*820.0700.05
CO2,O3H2O,CO2700.0630.04
H2O,CO2,N2O*H2O,CO2,N2O*630.0500.03
H2OH2O500.0350.02
H2O, N2*H2O,N2350.010.01
96 - 0.01 mb1050 - 96 mbEnding (cm-1)Starting (cm-1)Band
* Included as Minor Species
RRTM_SW Band Data
CO2H2O2600.0820.014
O3,O2O3,O250000.038000.013
O3O338000.029000.012
--29000.022650.011
O3 *H2O,O3*22650.016000.010
O2,O3*H2O,O2,O3*16000.012850.09
-H2O12850.08050.08
O2H2O,O28050.07700.07
H2O,CO2H2O,CO27700.06150.06
H2O,CH4*H2O,CH4*6150.05150.05
CO2H2O,CO25150.04650.04
CH4H2O,CH44650.04000.03
H2O,CO2H2O,CO24000.03250.02
CH4H2O,CH43250.02600.01
96 - 0.01 mb1050 - 96 mbEnding (cm-1)Starting (cm-1)Band #
* Included as Minor Species