Is SBDART on Target?: An Analysis Is SBDART on Target?: An Analysis of the Radiative Transfer Model to of the Radiative Transfer Model to

ObservationsObservationsDaniel P. TyndallDaniel P. Tyndall

Department of Marine and Environmental SystemsDepartment of Marine and Environmental SystemsFlorida Institute of TechnologyFlorida Institute of Technology

20 July 200520 July 2005

OverviewOverview

What is radiative transfer?What is radiative transfer? What is SBDART?What is SBDART? How did we evaluate SBDART?How did we evaluate SBDART? How well does SBDART do?How well does SBDART do? What can we conclude?What can we conclude?

What is radiative transfer?What is radiative transfer?

Transfer of radiant (or electromagnetic) energy Transfer of radiant (or electromagnetic) energy through a mediumthrough a medium

The four types of basic radiative transfer The four types of basic radiative transfer processes:processes:– TransmissionTransmission– AbsorptionAbsorption– ReflectionReflection– ScatteringScattering

All radiative transfer processes are based on All radiative transfer processes are based on these four processesthese four processes

1.1. Solar radiation strikes Solar radiation strikes cloud dropletcloud droplet

2.2. ReflectionReflection

3.3. ScatteringScattering

4.4. AbsorptionAbsorption

5.5. Transmission as infrared Transmission as infrared radiationradiation

Components of Radiative TransferComponents of Radiative Transfer

SBDARTSBDART

Why do we care about radiative transfer?Why do we care about radiative transfer?– Radiative transfer drives the weatherRadiative transfer drives the weather

Computing all interactions for the entire thickness Computing all interactions for the entire thickness of atmosphere is impossibleof atmosphere is impossible

SSanta anta BBarbara arbara DDISORT ISORT AAtmospheric tmospheric RRadiative adiative TTransfer modelransfer model– Written by P. Ricchiazzi et al. at the Institute of Written by P. Ricchiazzi et al. at the Institute of

Computational Earth Systems Science, University of Computational Earth Systems Science, University of California, Santa BarbaraCalifornia, Santa Barbara

– FORTRAN code first compiled in 1998FORTRAN code first compiled in 1998– Code continuously improvedCode continuously improved

SBDART Input ParametersSBDART Input Parameters

75 input parameters75 input parameters Atmospheric profile sounding inputAtmospheric profile sounding input

– Changes in temperature, pressure, water vapor and Changes in temperature, pressure, water vapor and ozone concentrations with heightozone concentrations with height

Cloud layer inputCloud layer input Particulate pollution inputParticulate pollution input Aerosol profile inputAerosol profile input Ground albedo parametersGround albedo parameters Geographical location, date, and time inputGeographical location, date, and time input

SBDART OutputSBDART Output

Verification of the ModelVerification of the Model

Goal: Verification of SBDARTGoal: Verification of SBDART– Clear skyClear sky– Cloudy sky (well developed cumulus)Cloudy sky (well developed cumulus)

Methods of verificationMethods of verification– Measuring total downward flux using a Measuring total downward flux using a

radiometerradiometer– Measuring the effective temperature of an Measuring the effective temperature of an

object in a specific wavelengthobject in a specific wavelength

Cloud and Sky Temperature Cloud and Sky Temperature MeasurementsMeasurements

Heitronics KT15.85 IIP infrared Heitronics KT15.85 IIP infrared pyrometer (pyrometer (supported by 2005 supported by 2005 ACITC faculty grantACITC faculty grant))

Sensitive to radiation between Sensitive to radiation between 9.6 and 11.5 micrometers9.6 and 11.5 micrometers

Pyrometer pointed to clouds Pyrometer pointed to clouds and clear skyand clear sky

Temperatures recorded every Temperatures recorded every secondsecond

Source: Heitronics

Pyrometer CalibrationPyrometer Calibration

Calculating Temperature from SBDARTCalculating Temperature from SBDART

Downward Flux per Wavelength14 June 2005 - Melbourne, FL - Clear Skies

0

100

200

300

400

500

600

0.1 1 10 100

Wavelength (μm) - Logarithmic Scale

Do

wn

war

d F

lux

(W/m

²)

Visible to pyrometer

9.6-11.5 μm

Integrated Total Downward Flux

(visible to pyrometer)

Changing Incoming Flux to Changing Incoming Flux to TemperatureTemperature

Plank’s EquationPlank’s Equation– Plank’s equation used Plank’s equation used

to change flux to to change flux to temperaturetemperature

– Integrating over range Integrating over range of pyrometerof pyrometer

– Solved for the term Solved for the term TT, , temperature, using temperature, using iterative approachiterative approach

d

e

hcW

kT

hc

μm 5.11

μm 6.9 5

2μm 5.11

μm 6.91

2

Simulating the Melbourne Simulating the Melbourne AtmosphereAtmosphere

How do we simulate the Melbourne atmosphere?How do we simulate the Melbourne atmosphere?– XMR 1500Z (Cape Canaveral) sounding usedXMR 1500Z (Cape Canaveral) sounding used

TemperatureTemperature PressurePressure HumidityHumidity

– Tropical ozone profile built in to SBDART also usedTropical ozone profile built in to SBDART also used– CloudsClouds

Droplet sizeDroplet size Optical depthOptical depth Cloud height and thicknessCloud height and thickness

STID = XMR STNM = 74794 TIME = STID = XMR STNM = 74794 TIME = 050608/1500 050608/1500

PRES HGHT TMPC VAPRPRES HGHT TMPC VAPR 1014.00 3.00 27.20 31.671014.00 3.00 27.20 31.67 1000.00 131.00 25.40 30.931000.00 131.00 25.40 30.93 980.47 305.00 24.04 29.39980.47 305.00 24.04 29.39 977.00 336.29 23.80 29.12977.00 336.29 23.80 29.12 974.00 363.32 23.40 27.92974.00 363.32 23.40 27.92 946.94 610.00 22.32 22.50946.94 610.00 22.32 22.50 944.00 637.20 22.20 21.96944.00 637.20 22.20 21.96 914.42 914.00 20.05 22.08914.42 914.00 20.05 22.08 911.00 946.56 19.80 22.10911.00 946.56 19.80 22.10 882.61 1219.00 18.34 19.64882.61 1219.00 18.34 19.64 850.00 1543.00 16.60 17.04850.00 1543.00 16.60 17.04

Estimating Cloud ParametersEstimating Cloud Parameters

Cloud bases estimated Cloud bases estimated from the pyrometer from the pyrometer temperatures and temperatures and temperature profile from temperature profile from soundingssoundings

Clouds treated as Clouds treated as blackbodies (e.g. M. blackbodies (e.g. M. Griggs 1968)Griggs 1968)– Maximum droplet radiusMaximum droplet radius– Maximum optical depthMaximum optical depth

Cloud thickness set at 1 Cloud thickness set at 1 kilometerkilometer

Output from SNLIST, showing sounding Output from SNLIST, showing sounding information. If we were evaluating a cloud that information. If we were evaluating a cloud that measured 22measured 22°C on the pyrometer, we would °C on the pyrometer, we would estimate its base to be at 637.20 m.estimate its base to be at 637.20 m.

Two SBDART Model RunsTwo SBDART Model Runs

Clear Sky Temperature Cloud Base Temperature

Clear Sky Temperature VerificationClear Sky Temperature Verification

Cloud Base Temperature VerificationCloud Base Temperature Verification

Why the difference in temperatures?Why the difference in temperatures?

Possible flaws in approximating atmospherePossible flaws in approximating atmosphere– Impact of intervening water vaporImpact of intervening water vapor– Model uses plane parallel approximationsModel uses plane parallel approximations– Approximation of clouds as perfect blackbodiesApproximation of clouds as perfect blackbodies

Differences in temperature are not large in Differences in temperature are not large in both casesboth cases– At 20At 20°C, error of 2% causes a temperature °C, error of 2% causes a temperature

variance of 1°Cvariance of 1°C

ConclusionsConclusions

Difference between SBDART and measured Difference between SBDART and measured temperatures of low level cumulus clouds within a temperatures of low level cumulus clouds within a few degreesfew degrees

Model-observation clear sky comparisons are Model-observation clear sky comparisons are much greatermuch greater

Differences in model and observed temperaturesDifferences in model and observed temperatures– Problem with observed measurement, model, model Problem with observed measurement, model, model

input, or a combination of these?input, or a combination of these?

More analysis on SBDART encouragedMore analysis on SBDART encouraged

AcknowledgementsAcknowledgements

Rebecca Davis for cloud base estimatesRebecca Davis for cloud base estimates Melissa Martin for pyrometer calibration dataMelissa Martin for pyrometer calibration data ACITC for providing funding for pyrometerACITC for providing funding for pyrometer

ReferencesReferencesAestheimer, Robert W. Aestheimer, Robert W. Handbook of Infrared Radiation MeasurementHandbook of Infrared Radiation Measurement. Barnes Engineering Company, . Barnes Engineering Company,

Stamford, Connecticut, 82 pp., 1983.Stamford, Connecticut, 82 pp., 1983.

Hottel, H.C. and A.F. Sarofim. Hottel, H.C. and A.F. Sarofim. Radiative TransferRadiative Transfer. McGraw-Hill, New York/St. Louis/San . McGraw-Hill, New York/St. Louis/San Francisco/Toronto/London/Sydney, 520 pp., 1967.Francisco/Toronto/London/Sydney, 520 pp., 1967.

Griggs, M. Emissivities of Natural Surfaces in the 8- to 14-Micron Spectral Region. Griggs, M. Emissivities of Natural Surfaces in the 8- to 14-Micron Spectral Region. J. Geophys. Res.J. Geophys. Res., , 73(24): 1968.73(24): 1968.

Ricchiazzi, Paul et al. Santa Barbara DISORT Atmospheric Radiative Transfer. Ricchiazzi, Paul et al. Santa Barbara DISORT Atmospheric Radiative Transfer. <http://arm.mrcsb.com/sbdart/> 2001.<http://arm.mrcsb.com/sbdart/> 2001.

Ricchiazzi, Paul, Shiren Yang, and Catherine Gautier. SBDART: A Practical Tool for Plane Parallel Ricchiazzi, Paul, Shiren Yang, and Catherine Gautier. SBDART: A Practical Tool for Plane Parallel Radiative Transfer in the Earth’s Atmosphere. Earth Space Research Group, Santa Barbara, CA Radiative Transfer in the Earth’s Atmosphere. Earth Space Research Group, Santa Barbara, CA <http://www.crseo.ucsb.edu/esrg/pauls_dir/>, 2005.<http://www.crseo.ucsb.edu/esrg/pauls_dir/>, 2005.

Ricchiazzi, Paul, Shiren Yang, Catherine Gautier, and David Sowle. SBDART: A Research and Teaching Ricchiazzi, Paul, Shiren Yang, Catherine Gautier, and David Sowle. SBDART: A Research and Teaching Software Tool for Plane-Parallel Radiative Transfer in the Earth’s Atmosphere. Software Tool for Plane-Parallel Radiative Transfer in the Earth’s Atmosphere. Bull. Am. Meteorol. Bull. Am. Meteorol. Soc.Soc., 85(1): 2004., 85(1): 2004.

Wallace, John M. and Peter V. Hobbs. Wallace, John M. and Peter V. Hobbs. Atmospheric Science: An Introductory SurveyAtmospheric Science: An Introductory Survey . Academic Press, . Academic Press, San Diego/New York/Boston/London/Sydney/Tokyo/Toronto, 467 pp., 1977.San Diego/New York/Boston/London/Sydney/Tokyo/Toronto, 467 pp., 1977.

And now, And now, Wanda Reeves…