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 )

http://rtweb.aer.com

http://rtweb.aer.com

http://rtweb.aer.com

Radiative Closure Experiments

Specification of Atmospheric Properties

RadiativeTransferModel

Flux/RadianceMeasurements

COMPARE

Longwave Example

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

High-Resolution ASTI Validation

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