Robert G. Ellingson and the ARESE II Science Team

Department of MeteorologyUniversity of Maryland

College Park, MD

ARESE II: Description and Initial Results

(ARM Enhanced Shortwave Experiment)

Motivation• Knowledge of the amount and location of solar energy

absorption is key to understanding the general circulation of the ocean and atmosphere and to our understanding and prediction of climate change.

• Measurements of the amount of solar radiation absorbed within clouds have yielded conflicting results. Many studies show much more absorption than can be explained by theory.

• If excess or enhanced absorption is true - we must:• reexamine our knowledge of the basic physics • modify climate models, AND • change remote sensing techniques.

The ARESE Experiments - Objectives

• Directly measure the absorption of solar radiation by the clear and cloudy atmosphere and

• investigate the causes of any absorption in excess of model predictions.

ARESE I - 25 September - 1 November 1995ARESE II - 15 February - 15 April 2000

ARESE I - A Thumbnail Sketch

• Used three aircraft platforms, as well as satellites and the ARM central and extended facilities in North Central Oklahoma

• Measured solar radiative fluxes at different altitudes and at the surface with spectral broadband, partial bandpass, and narrow bandpass filters

• Measurements obtained from aircraft flying in stacked formation over horizontal legs extending over several hundred kilometers

25 September - 1 November 1995

ARESE I - broadband absorptance increases with cloud fraction

Courtesy of R. Cess - SUNY Stonybrook

10 km10 km

Fluctuations of cloud liquid water

aerosol & water vapor

are assumed to be

horizontally homogeneous

Flight patterns : to fly over the CF with REVISIT times of

4 -5 min ., about 10 ind. samples/h., or 30 per 3 h. flight.

Central Facility

1 min 3 min 3 min 1 min

A schematic plot of the Observing System Simulation

with one aircraft above clouds and ground-based

radiometers

ARESE-II Conducted During Feb -Apr ‘00

Simulation by A. Marshak

ARESE-II was coordinated with an ARM Cloud IOP - insitu measurements of cloud microphysics

• Major Features• Unique sampling strategy - single

aircraft overflying SGP CART site on only overcast days

• Multiple independent instruments making same measurements with different technologies (aircraft and ground)

• Extensive pre- and post- experiment calibrations

• Long duration during a period of climatologically high frequency of extensive overcast (~ 6 cases)

• Science Team with considerably different pre-experiment views

The ARESE-II Measurement Strategy Differed Significantly From ARESE-I

• Used single aircraft (Twin Otter) repeatedly overflying surface instruments

• Single aircraft reduced cost, makes long deployment possible

• ARESE-I showed thick stratus approach uniform case

• 2 years CART data 4-6 uniform stratus cases in 6-week period

• Consistent with simulations by R. Cess and by A. Marshak

One of 2 flight patterns(6 min revisit, 83% duty cycle)

Ingress

Central facility

Continue on

Blue=data flight legRed=data not valid

DHC-6 Twin-Otter

Photos courtesy of Tim Tooman

Conditional Sampling(theory)

from Marshak et al., 1999: On the Removal of the Effect of Horizontal Fluxes in Two-Aircraft Measurements of Cloud Absorption. Quart. J. Roy. Meteor. Soc., 558, 2153-2170.

Atrue(x) =(1−ϖ0)σ (x) I(Ω,x,z)dΩdz4π∫

zbase

ztop

∫ Aapp(x) =[1−R(x)]−[T(x)−0] =

1− ΩI(Ω,x,ztop)dΩ− ΩI(Ω,x,zbase)dΩ2π −∫

2π +∫

H(x) =Aapp(x) −Atrue(x)

Uε = x:H500nm(x) ≤ε{ }

x: Atrue(x)∩ Aapp(x) ≠∅{ }= x:H500nm≈0{ }

x:HBroadBand(x) =0{ }?

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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Aapp

(x)

Atrue

(x)

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0

0.5

1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

all x∈[0,L]x∈U

ε,ε=0.01

Aapp

(x)

Atruε

(x) Courtesy ofAlexander Marshak

Extensive Spectral and Broadband Calibrations Were Performed Before and After ARESE II

• Spectral calibrations at Ponca City airport using lamps traceable to the ARM working standard

• Broadband calibrations at Blackwell-Tonkawa airport• Broadband calibrations at SGP site• Surface measurements at SGP 19 February through 6

April 2000

ARESE II Broadband Calibration Facility at Blackwell-Tonkawa Airport

Photos courtesy of Joe MichalskyPNNL/SUNY

Direct Measurement Uncertainty

3 W/m2

Diffuse Measurement Uncertainty

5 W/m2

But ...Slide courtesy of Joe MichalskyPNNL/SUNY

The Twin Otter Payload Was Significantly Enhanced Over ARESE I

3 sets of spectral and broadband nadir and zenith viewing radiometersScripps, RAMS total solar broadband hemispheric (224-3910 nm) ValeroScripps, RAMS fractional solar broadband hemispheric (680-3300 nm)Scripps, RAMS total direct-diffuse hemispheric; seven bands(495-505; 400-450; 450-500; 500-550; 550-600; 600-650; 650-700 nm)

NASA ARC SSFR (300-2500 nm in ~300 channels) PilewskieCSU SSP2 (400-2500 nm in ~100 channels) StephensMRI, CM21 broadband hemispheric (3350-2200 nm) AsanoSNL, CM22 broadband hemispheric (3350-2200 nm) ToomanCloud and meteorological measurementsJPL/UMASS ACR nadir viewing radar SekelskyBNL total temperature ToomanBNL static pressureBNL chilled mirror hygrometer

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aQuickDraw decompressorare needed to see this picture.

ARESE II Summary• High quality data obtained on several clear and overcast days

(03/03, 03/17, 03/18, 03/21, 03/29 {best ones})• b1 data released by instrument PIs to ARESE II Science Team

in Sept 2000 (some data in better state than others)• ARESE II ST data discussion meeting 24-26 Oct 2000• Reprocessing with common calibration Nov-Dec 2000• ARESE II ST meeting 8-9 Feb 2001 - preliminary findings• Data released to science community 17 March 2001• Publication of ARESE II Science Team papers in progress

For additional information see the ARM UAV Homepagehttp://armuav.atmos.colostate.edu/

Looking for the Right Stuff

March 29, 2000 - An Excellent Example

NCEP Forecasts Are A Must!!!!

What Did We See From Space?

Alti

tude

(km

AG

L)

CART MMCR Reflectivty

Otter Cloud Radar

1800 20001900Time (UTC)

0

3

5

Alti

tude

(km

MSL

)

Flight Track

Latit

ude

(°N

)(°E )

What Did We See From the Aircraft and Ground?

Diffuse Field Camera

Image courtesy of Tim Tooman

Spectral Distribution of Fluxes From the SSFR

SSFR Upwelling Fluxes - 03/29/00W

avel

engt

h (n

m)

Time (hours)

QuickTime™ and aTIFF (Uncompressed) decompressor

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400

600

800

1000

1200

1400

1600

18.5 20.519.5

Preliminary SSFR Data From 29 March 2000

Wavelength (nm)

400 600 800 1000 1200 1400 1600

Alb

edo

Irra

dian

ce (W

 m-2 n

m-1)

Nadir irradiance

Albedo

1930 UTC

Data courtesy of Peter Pilewskie, NASA Ames

Broadband Fluxes

500

600

700

800

18.5 19 19.5 20 20.5

RAMSCM22

Time (GMT)

900

1000

1100

1200RAMSCM22

Downwelling Flux

Upwelling Flux

March 29, 2000

ARMARMAtmospheric Radiation MeasurementAtmospheric Radiation Measurement

Defined as the layer absorption divided by the downwelling solar flux at the top of layer (aircraft level)

Absorptance

Slide courtesy of Tom Ackerman

Conditional Sampling(March 29)

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500nm_abs_329liq

absorptance liq (cm)

GMT (h)

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500nm_abs_329BB_abs_329 liq

absorptance liq (cm)

GMT (h)

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500nm_abs_329BB_abs_329500nm_abs_329

liq

absorptance liq (cm)

GMT (h)

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Conditional sampling and LWP3_29_00

500nm_abs_329

BB_abs_329

500nm_abs_329

BB_abs_329

liq

absorptance liq (cm)

GMT (h)0

2

4

6

8

10

12

14

0.205 0.21 0.215 0.22 0.225 0.23 0.235 0.24 0.245

BB absorptionHistogram

March 29, 2000

frequ

ency

BB absorption

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500nm_abs_329

BB_abs_329

500nm_abs_329

BB_abs_329 CART siteoverpass

absorptance

GMT (h)

Courtesy ofAlexander Marshak

Analysis courtesy of Bob Cess using data from 10/00

Analysis courtesy of Bob Cess using data from 10/00

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02270303032003210329

TSBR absorptance

ARESE II: absorptance

Pope, Valero et al. 2001

These data are from the five days for which absorptance measurements from the CM22 radiometers and the TSBR radiometers can be compared.

There are two clear days, 0227 and 0320, with low absorptance values, and three cloudy days with higher absorptances. Agreement between the two types of radiometers is very good. (A 3% difference in the upwelling at 7 km on 0303 accounts for the offset in absorptance on that day.)Conclusion: The two different types of radiometers yield the same measured absorptance in both clear and cloudy conditions.Results courtesy of Pope et al.

Preliminary Comparisons of Model Calculations with

Observations

ARMARMAtmospheric Radiation MeasurementAtmospheric Radiation Measurement

ARESE2 March 2000, Cloudy-sky Flights

0

50

100

150

200

250

300

March 3 March 21 March 29

TSBRCM22SBDART

Results courtesy of Ackerman et al.

Bars represent leg to leg variability

Absorptance in ARESE II Flights

0.00

0.05

0.10

0.15

0.20

0.25

0.30

27-Feb 20-Mar 3-Mar 21-Mar 29-Mar

TSBR CM22 CM21 Model

Clear cases

(Bars indicate leg to leg variability)

Results courtesy of Ackerman et al.

Ignore CM21 results shown here

0.00

0.05

0.10

0.15

0.20

0.25

0227 0303 0317 0320 0321 0329 0403

ARESE II – day averages

date

range of modelvalues

Pope, Valero et al. 2001

Day averages of absorptance (from TSBR measurements) show values of 0.10 to 0.12 for the clear days and values of 0.20 to 0.23 for the cloudy days. A standard model gives absorptance values ranging from 0.10 for clear sky to 0.15 for cloudy sky (optical depth 60).

Conclusion: observed cloudy-sky absorptances are significantly greater than model predictions.

Results courtesy of Pope et al.

MMCR

AOS

MWR

MPLBLC

MFRSRMFR

SMOS

TOMSBBSS

SSPSSFR SB3D

MIE SBMOD

RAMS

CM21/22s

TDDR

SHORTWAVEABSORPTIONCOMPARISON

aerosol

surface

atm.

cloud

model obs. obs.

O’Hirok and Gautier, 2001

CLOUD RECIPE

Ø COMPUTE MMCR MODE 1 and 3

Ø COMPUTE CLOUD BASE

Ø MASK REFLECTANCE FIELD (min. threshold)

Ø COMPUTE ICE WATER CONTENT [Frisch et al. 1995, Platt, 1997]

Ø COMPUTE DRIZZLE [Liu and Illingworth, 2000]

Ø DERIVE CLOUD OPTICAL THICKNESS FROM MFRSR

Ø COMPUTE MEAN RE FROM TAU AND LWP (MWR)

Ø DERIVE LWC FROM MMCR AND LWP [Dong et al. 2000]

Ø DERIVE N FROM LWC AND MEAN RE –

Ø COMPUTE RE AT ALL CELLS –

Ø CONVERT TIME CONSTANT TO SPATIAL CONSTANT (wind)

Ø INTERPOLATE ONTO 1000 COLUMN x 150 LAYER GRID

Ø BAKE AT 350° FOR ONE HOUR AND ENJ OY

O’Hirok and Gautier, 2001

17:30 21:30 UTC0 75 km

03/29/2000

120

0

60

9

0

structure

within 2.5 km of cart site

optical thickness

km

t = 55re = 7.5

O’Hirok and Gautier, 2001

visible near-ir total

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ModelRAMSCm22

Absorptance

March 03 2000

+/-5%

+/-10%

O’Hirok and Gautier, 2001

0.1

0.2

0.3

0.4

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0.0

ModelRAMSCm22

Absorptance

March 21 2000

+/-5%

+/-10%

visible near-ir total O’Hirok and Gautier, 2001

visible near-ir total

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0.2

0.3

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0.0

ModelRAMSCm22

Absorptance

March 29 2000

+/-5%

+/-10%

O’Hirok and Gautier, 2001

ref rnd ipa re x2 drz ice x4

0.06

0.03

0.4

0.3

0.25

0.15

RAMSCm22

visible absorptance

near-ir absorptance

total absorptance

March 29 2000 model sensitivity

O’Hirok and Gautier, 2001

Summary conclusions to date

• Ackerman et al. - Differences between modeled and observed absorption on cloudy days are order 10%

• Pope et al. - observed cloudy-sky absorptances are significantly greater than model predictions.

• O’Hirok and Gautier - major differences between observations and calculations are in the near IR, but total differences are within the order 10% range.

Common to all

• Observed absorption is greater than calculated

• Smaller absorption and smaller discrepancies than ARESE I

Problems and Paths Forward• Apparent disagreement between different models -

use ICRCCM as an arbiter

• Causes of the discrepancies not yet identified - expanded use of the spectral data and extensive examination of all the data by the ARM Science Team and the general science community

• The data are there - Have at them!!!

ARESE-II has a broad-based Science Team

Ackerman, Tom (PNNL) Marshak, Sasha (Univ Maryland)

Asano, Shoji (Tohoku Univ) Michalsky, Joe (SUNY Albany)

Cahalan, Bob (NASA GSFC) Minnis, Pat (NASA LRC)

Cess, Bob (SUNY, Stony Brook) Sekelsky Steve (Univ Mass)

Ellingson, Bob* (Univ Maryland) Stephens, Graeme (CSU)

Gautier, Catherine (UCSB) Tooman, Tim (SNL)

Long, Chuck (PSU) Valero, Francisco (Scripps)

Mace, Jay (Univ Utah) Vitko, John (SNL)

Marchand, Roger (PNNL) Wiscombe, Warren (NASA GSFC)

* Mission Scientist

Pre- and Post- ARESE II Boadband Calibrations Data

courtesy of Joe MichalskyPNNL/SUNY

Pre-

Pre-

Post-

Post-