ARESE II: Description and Initial Results
(ARM Enhanced Shortwave Experiment)
Robert G. Ellingson and the ARESE II Science Team
Department of Meteorology
University of Maryland
College Park, MD
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 ARESE II -
25 September - 1 November 1995
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
ARESE-II Conducted During Feb -Apr ‘00
A schematic plot of the Observing System Simulation
with one aircraft above clouds and ground-based
radiometers
• Major Features
• Unique sampling strategy - single
aircraft overflying SGP CART site
on only overcast days
Flight patterns
: to f ly ov er the CF with REVISIT times of
4 -5 min ., about 10 ind. samples/h., or 30 per 3 h. f light.
1 min
10 km
3 min
10 km
3 min
Fluctuationsof cloud liquid water
aerosol & w ater vapor
are assum ed to be
horizontally hom ogeneous
Central Facility
Simulation by A. Marshak
1 min
• 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
ARESE-II was coordinated with an ARM Cloud IOP insitu measurements of cloud microphysics
The ARESE-II Measurement Strategy
Differed Significantly From ARESE-I
Ingress
• Used single aircraft (Twin
Otter) repeatedly overflying
surface instruments
Central facility
Blue=data flight leg
Red=data not valid
Continue on
One of 2 flight patterns
(6 min revisit, 83% duty cycle)
• 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 6week period
• Consistent with simulations
by R. Cess and by A. Marshak
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 TwoAircraft Measurements of Cloud Absorption. Quart. J. Roy. Meteor. Soc., 558, 2153-2170.
z top
Atrue( x)  (1  0 ) (x)

I( , x,z)ddz
zbase 4 
Aapp (x )  [1 R(x )]  [T (x )  0] 
1

I( , x ,z top )d 
2 
 I(, x, z
base )d
2 
H(x )  A app( x)  Atrue( x )
x : HBroadBand(x)  0?
1
all x[0,L]
xU , =0.01

0.5
0
A
app
(x)
U  x : H500nm (x)  
x : Atrue(x) Aapp(x)   x : H500nm  0
-0.5
-1
0
Courtesy of
Alexander Marshak
0.05
0.1
0.15
0.2
A
true
(x)
0.25
0.3
0.35
0.4
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 Michalsky
PNNL/SUNY
Direct Measurement Uncertainty
 3 W/m2
Diffuse Measurement Uncertainty
 5 W/m2
But ...
Slide courtesy of
Joe Michalsky
PNNL/SUNY
The Twin Otter Payload Was Significantly
Enhanced Over ARESE I
3 sets of spectral and broadband nadir and zenith viewing radiometers
Scripps, RAMS total solar broadband hemispheric (224-3910 nm)
Valero
Scripps, 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)
CSU SSP2 (400-2500 nm in ~100 channels)
MRI, CM21 broadband hemispheric (3350-2200 nm)
SNL, CM22 broadband hemispheric (3350-2200 nm)
Qu ic kTi me™ a nd a
TIFF (Unc om pres se d) de co mp re ss or
are n ee de d to s ee th is pi ctu re .
QuickTi me™ and a
QuickD raw decompressor
are needed to see thi s pi ctur e.
Pilewskie
Stephens
Asano
Tooman
Cloud and meteorological measurements
JPL/UMASS ACR nadir viewing radar
BNL total temperature
BNL static pressure
BNL chilled mirror hygrometer
Sekelsky
Tooman
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 Homepage
http://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?
What Did We See From the Aircraft and Ground?
CART MMCR Reflectivty
Latitude (°N)
Flight Track
Altitude (km MSL)
(°E )
Otter Cloud Radar
5
3
0
1800
1900
Time (UTC)
2000
Diffuse Field Camera
Image courtesy of
Tim Tooman
Spectral Distribution of
Fluxes From the SSFR
SSFR Upwelling Fluxes - 03/29/00
Wavelength (nm)
1600
1400
1200
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
1000
800
600
400
18.5
19.5
Time (hours)
20.5
Irradiance (W m-2 nm-1)
Preliminary SSFR Data From 29 March 2000
Nadir irradiance
Albedo
1930 UTC
Albedo
Data courtesy of
Peter Pilewskie,
NASA Ames
400
600
800
1000
1200
Wavelength (nm)
1400
1600
Broadband Fluxes
-2
)
March 29, 2000
Downwelling Flux
Upwelling Flux
Absorptance
Defined as the layer absorption divided
by the downwelling solar flux at the top
of layer (aircraft level)
ARM
Atmospheric Radiation Measurement
Slide courtesy of Tom Ackerman
Conditional Sampling
(March 29)
500nm_abs_329
500nm_abs_329
BB_abs_329
BB_abs_329
BB_abs_329
500nm_abs_329
500nm_abs_329
liq
CART site
overpass
BB_abs_329
0.4
0.1
0.3
0.08
0.2
0.06
liq (cm)
0.1
14
0.04
12
BB absorption
Histogram
March 29, 2000
10
0
0.02
frequency
absorptance
Conditional sampling and LWP
3_29_00
8
6
4
-0.1
18.5
19
19.5
20
GMT (h)
0
20.5
2
0
0.205 0.21 0.215 0.22 0.225 0.23 0.235 0.24 0.245
BB absorption
Courtesy of
Alexander Marshak
Analysis courtesy
of Bob Cess using
data from 10/00
Analysis courtesy
of Bob Cess using
data from 10/00
These data are from the five
days for which absorptance
measurements from the CM22
radiometers and the TSBR
radiometers can be compared.
ARESE II: absorptance
0.4
0227
0303
0320
0321
0329
CM22 absorptance
0.3
0.2
0.1
0.0
0.0
0.1
0.2
0.3
0.4
T SBR absorptance
Pope, Valero et al. 2001
Results courtesy of Pope et al.
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.
Preliminary Comparisons
of Model Calculations with
Observations
Bars represent leg to leg variability
Results courtesy of Ackerman et al.
ARM
Atmospheric Radiation Measurement
Absorptance in ARESE II Flights
TSBR
0.30
CM22
CM21
Model
Results courtesy of Ackerman et al.
(Bars indicate leg to leg variability)
0.25
Ignore
CM21
results
shown
here
0.20
Clear cases
0.15
0.10
0.05
0.00
27-Feb
20-Mar
3-Mar
21-Mar
29-Mar
ARESE II Р day averages
0.25
absorptance
0.20
0.15
range of
model
values
0.10
0.05
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).
0.00
0227
0303
0317
0320
0321
0329
0403
date
Pope, Valero et al. 2001
Results courtesy of Pope et al.
Conclusion: observed
cloudy-sky absorptances
are significantly greater
than model predictions.
O’Hirok and Gautier, 2001
MWR
BLC
MMCR
MPL
SMOS
AOS
TOMS
BBSS
CM21/22s
MFRSR
MFR
SSP
SSFR
TDDR
SB3D
MIE
aerosol
atm.
surface
cloud
model
 obs.
RAMS
 obs.
SBMOD
SHORTWAVE
ABSORPTION
COMPARISON
CLOUD RECIPE
 COMPUTE MMCR MODE 1 and 3
 COMPUTE CLOUD BASE
O’Hirok and Gautier, 2001
 MASK REFLECTANCE FIELD (min. threshold)
 COMPUTE ICE WATER CONTENT [Frisch et al. 1995, Platt, 1997]
 COMPUTE DRIZZLE [Liu and Illingworth, 2000]
 DERIVE CLOUD OPTICAL THICKNESS FROM MFRSR
 COMPUTE MEAN RE FROM TAU AND LWP (MWR)
 DERIVE LWC FROM MMCR AND LWP [Dong et al. 2000]
 DERIVE N FROM LWC AND MEAN RE –
 COMPUTE RE AT ALL CELLS –
 CONVERT TIME CONSTANT TO SPATIAL CONSTANT (wind)
 INTERPOLATE ONTO 1000 COLUMN x 150 LAYER GRID
 BAKE AT 350° FOR ONE HOUR AND ENJOY
9
03/29/2000
structure
km
0
120
60
 = 55
re = 7.5
optical thickness
0
within 2.5 km of cart site
17:30
0
21:30 UTC
75 km
O’Hirok and Gautier, 2001
March 03 2000
0.5
Model
RAMS
Cm22
Absorptance
0.4
0.3
+/-10%
0.2
+/-5%
0.1
0.0
visible
near-ir
total
O’Hirok and Gautier, 2001
March 21 2000
0.5
Absorptance
0.4
Model
RAMS
Cm22
+/-10%
+/-5%
0.3
0.2
0.1
0.0
visible
near-ir
total
O’Hirok and Gautier, 2001
March 29 2000
0.5
Absorptance
0.4
+/-10%
Model
RAMS
Cm22
+/-5%
0.3
0.2
0.1
0.0
visible
near-ir
total
O’Hirok and Gautier, 2001
March 29 2000 model sensitivity
0.06
visible absorptance
RAMS
Cm22
0.03
0.4
near-ir absorptance
0.3
0.25
total absorptance
0.15
ref
rnd
ipa
re x2
drz ice O’Hirok
x4
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
Pre-
Post-
courtesy of
Joe Michalsky
PNNL/SUNY
PostPre-