Characterizing the Vertical Distribution of Aerosols over the ARM SGP Site

Richard Ferrare(a), David Turner (b), Marian Clayton(c),Mian Chin(d), Sarah Guibert(e), Michael Schulz(e)

(a) NASA Langley Research Center, Hampton, Virginia (b) Pacific Northwest National Laboratory, Richland, Washington(c) Science Applications International Corporation, Hampton, Virginia(d) NASA Goddard Space Flight Center, Greenbelt, Maryland(e) Laboratorie des Sciences du Climat et de l’Environment, CEA/CNRS-LSCE, France

AEROCOM Meeting, December 3, 2004

• DOE ARM SGP CRF Raman Lidar System• Aerosol and Water Vapor Measurements• AEROCOM comparisons• Additional aerosol measurements at ARM SGP

Outline

AcronymsDOE = Department of EnergyARM = Atmospheric Radiation MeasurementSGP = Southern Great PlainsCRF = Climate Research FacilityCARL = CRF Raman Lidar

• DOE ARM SGP CF site (Lamont , Oklahoma) (36o 37 ' N, 97o 30 ' W)

• Nd:YAG (355 nm) (day/night)• Wavelengths

– Rayleigh/Mie (355 nm)– Depolarization (355 nm)– Raman water vapor (408 nm)– Raman nitrogen (387 nm)

• 39 meter range resolution• water vapor and aerosol profiles• precipitable water vapor and

aerosol optical thickness• aerosol and cloud depolarization• designed for continuous,

autonomous operation

Additional information: http://www.arm.gov/docs/instruments/static/rl.html

CART Raman Lidar (CARL)

(Turner et al., JAOT, 2002)

Data: available via ftp from ARM Experiment Center (http://www.arm.gov)Color images at: http://playground.arm.gov/~turner/raman_lidar_quicklooks.html

CART Raman Lidar/AERI+Model Clear-Sky Product

Measurement Altitude Range

Vertical Resolution

Nominal Temporal Resolution

Error Precision Detection Limit

Aerosol Backscattering (355 nm)

0.060-8 km 78 m 10 min 0.0005 (km-sr)-1

5-10%

2% 0.0002-0.0004 km-sr-1

Aerosol Extinction (355 nm)

0.1-8 km 150-500 m 10 min 0.03 km-1

5-10% 5% 0.02-0.03 km-1

Aerosol Optical Thickness (355 nm)

- - 10 min 5% or 0.03

5% 0.03

Water Vapor Mixing Ratio

0.060-8 km (night) 0.060-4 km (day)

78 m 2-10 min 5% 2% 0.002 g/kg

Relative Humidity 0.060-8 km (night) 0.060-4 km (day)

78 m 2-10 min 5% 5% 1%

Precipitable Water Vapor

- - 10 min 5% 5% 2 mm

Linear Depolarization 1-14 km 39 m 1-10 min 10% 2% Temperature (AERI+Model)

0-3 km (AERI) 3-15 (Model)

100 m - 1 km

8 min 1 K 1 K

Cloud Base Height 0.060-14 km 78 m 1-10 min 78 m 39 m 0.060 km

Automated algorithms for routine retrievals of water vapor and aerosol profiles

Data: available via ftp from ARM Experiment Center (http://www.arm.gov)Color images at: http://playground.arm.gov/~turner/raman_lidar_quicklooks.html

CARL Aerosol and Water Vapor Profiles

Water Vapor Mixing Ratio

Relative Humidity

Aerosol BackscatterDecember 3, 1998

Aerosol Extinction

(Turner et al., J. Atmos. Oceanic Tech., 19, 2002)

EARLINET EARLINET

Continuous vs. Periodic Measurements

CARL

CARL

CARL – continuousEARLINET – periodicMonthly Yearly

CARL

Winter

SummerA

eros

ol E

xtin

ctio

n (k

m-1

)

Average Diurnal Variation of Aerosol Extinction Profiles and AOT

• Large changes in vertical profile• Smaller changes in AOT

(st. dev ~ 10%)

Sunrise

Sunrise

Sunset

Sunset

Ter

ra

0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.1

0.2

0.3

0.4

0.5

0.6

Aqua

Aqu

a

Terr

a Fall (day) Fall (night) Winter (day) Winter (night)Ae

roso

l Opt

ical

Thi

ckne

ss (3

55 n

m)

Time (UT)

Summer (day) Summer (night) Spring (day) Spring (night)

Aqu

a

AOT

Spring

Aer

osol

Ext

inct

ion

(km

-1)

Correlation between Aerosol Extinction and Relative Humidity• CARL aerosol extinction profiles averaged over 946 days (Mar. 1, 1998 – Dec. 31, 2001)• Higher extinction concentrated over smaller vertical extent at night• Highest aerosol extinction and RH found near surface at night

Sunrise

Sunrise

Sunset

Sunset

Rel

ativ

e H

umid

ity (%

)

SpringSunriseSunset

Aerosol Extinction Relative Humidity

Month

Aer

osol

Opt

ical

Thi

ckne

ss

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

GOCART (355 nm)CART Raman Lidar (355 nm)Cimel Sun photometer (340 nm)

carlaot>0 and carlnum>10 and alt<0.04 and ci340>0Box: Mean-2*SE, Mean+2*SE Whisker: Mean-SD, Mean+SD

Observed versus Modeled Aerosol Optical Thickness

• SGP data from 2000-2001• GOCART reproduces AOT during Fall-Spring but misses Summer peak• INCA shows Summer peak

Initial Comparisons with GOCART and INCA (LSCE) models

Note change in scales

Observed versus Modeled Aerosol Profiles• GOCART mean aerosol profiles show smaller vertical

variability than the mean CARL observation

September 2000

September 2000

September 2000

November 2000 November 2000November 2000

CARL INCA

MATCH PNNL

Measured versus Modeled Monthly Average Aerosol Profiles

KYU

MOZGN

UTO_CTM

CARL

Measured versus Modeled Monthly Average Aerosol Profiles

September 2000 November 2000

Observed versus Modeled Aerosol Profiles• Considerable variation in model profiles near the surface

Measured versus Modeled Aerosol Profiles• Large differences in vertical distributions of aerosols from models• Model AOT is slightly lower than AOT measured by CARL and CimelSun photometer• Model aerosol extinction is considerably lower than CARL near surface

Diurnal variation in aerosol extinction profiles• Measured profiles show larger variation near surface• Measured variation is highly correlated with relative humidity• Modeled variation near surface is smaller

Diurnal Variation in Aerosol Profiles

CARL INCA

Relative Humidity Aerosol Extinction

Measured versus Modeled RH and Aerosol Profiles

Retrievals of Boundary Layer Height

**

* **

** *

Percentage of AOT below BL Height Median; Box: 25%, 75%; Whisker: 5%, 95%

Time (UT)

Perc

enta

ge

0102030405060708090

100

2 4 6 8 10 12 14 16 18 20 22 24

WinterSummer

Box Plot (copy of 01011998-12312003_aot_addv5.sta 60v*35976c)

• Amount of AOT within PBL- varies with time of day- does not vary significantly with season or AOT

• Significant fraction of AOT (>25%) is above PBL

Aerosol Observing System (AOS)

Four-Year Climatology (1996-2000) of Aerosol Optical Properties at Surface

Aerosol Scattering Single Scattering Albedo

Fine mode fraction Angstrom exponent

Aerosol Hygroscopic Growth at SGP

Sheridan et al., 2001 JGR

In Situ Aerosol Profile (IAP) – Cessna 172• Primary Measurements

- Aerosol scattering (3 λ) (dry)- Aerosol absorption (1 λ) (dry)- Hemispheric backscatter fraction (dry)- Aerosol scattering (1 λ) (high RH)

• Derived Parameters– Aerosol single scatter albedo– Aerosol optical thickness– Angstrom exponents

Aerosol Profiling

2-3 profiles/week

Two-Year Climatology (2000-2002) of Aerosol Optical Properties over SGP

(dry, submicron) (Andrews et al., JGR, 2004)

IAP Aerosol Profiling

Vertical Variability of Aerosols – IAP Measurements

• Examined vertical variability of aerosol parameters using more than 300 IAP profiles from Mar. 2000-June 2003• Computed range of values for each profile and weighted by aerosol scattering• SSA varied by 0.12 or more in ~25% of cases• Angstrom exponent varied by 0.5 or more in ~25% of cases

cross – medianbox – 25-75%bar – 5-95%

cross – medianbox – 25-75%bar – 5-95%

April 4, 2000

Aerosol Extinction (km-1)

(Peppler et al., Bull. AMS, 81, 2000)(Ferrare et al., J. Geophys. Res., 106, 2001)

• Aerosol extinction/backscatter ratio (“lidar ratio”) varies with altitude due to changes in aerosol size, composition, and shape• Raman lidar measurements of lidar ratio indicate that large variations in these aerosol properties with altitude occur ~30% of the time

CARL observations of the aerosol vertical variability

17.0 17.5 18.0 18.5 19.0 19.5 20.0

7

6

5

4

3

2

1

Date (May, 1998)

Alti

tude

(km

)

0

1

2

3

4

5

6

7

0.0 0.1 0.2 0.3 0.4 0.5

Aerosol Extinction (km-1)

Alti

tude

(km

)

30 40 50 60 70 80 90 100 110 120

May 18, 1998 19:50-20:20 UTExtinction/Backscatter Ratio

Extinction

Aerosol Extinction/Backscatter Ratio Sa (sr)

Elevated layer of smoke from fires in Central America (May, 1998)

Aerosol Chemistry Measurements

• What? ARM Sponsors aerosol chemistry measurements• Who? Dr. Patricia Quinn - NOAA/PMEL• Why?

• Determine mass scattering efficiencies of major aerosol components (Cl-, NO3-, SO4-2, Na+, NH4+, K+, Mg2+, Ca+2)• Validate the output from chemical transport models• Link aerosol sources to aerosol radiativeproperties.

• When? Period: 2000 – present• Daily submicron samples• Weekly supermicron sample

• How?• Measure concentrations of aerosol mass and inorganic ions• Differencing aerosol mass and ion data, derive “residual” mass composed of dust and/or carbonaceous aerosol

• Future funding in question – requires endorsements (AEROCOM?)

Summary• CARL routinely provides continuous profiles of aerosol

backscattering and extinction, depolarization, RH• Seasonal average profiles

– Aerosol vertical distributions and scale heights vary with AOT and season• Diurnal variability

– Large changes in vertical profile, smaller changes in integrated values– Correlations in aerosol extinction, relative humidity

• PBL variability– Amount of AOT within PBL varies with time of day– Amount of AOT within PBL does not vary significantly with season– Significant fraction of AOT (>25%) is above PBL

• Model mean aerosol profiles typically show smaller vertical variability than the mean CARL observations

• In situ aerosol measurements on periodic small aircraft flights provide additional profiles of aerosol intensive properties

• Additional surface measurements of aerosol size, chemistry can be used to evaluate model performance

Backup slides

Routine Aerosol-Related Measurements at SGP

Measured versus Modeled Aerosol Profiles• Large differences in vertical distributions of aerosols from models• Model AOT is slightly lower than AOT measured by CARL and CimelSun photometer• Model aerosol extinction is considerably lower than CARL near surface

Aerosol Optical Thickness (355 nm)

GOCART INCACimel

CARL

Aerosol Extinction (355 nm)

GOCART

INCA

CARL

• Four-day backtrajectories were computed using NOAA/ARL HYSPLIT4* model• These trajectories were divided into distinct clusters corresponding to large scale transport patterns using the methods described by Dorling et al. (1992)†

• CARL profiles show enhanced water vapor and aerosols from southerly and southeasterly flow

0

1

2

3

4

5

6

7

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Summer

GF D

C

E A B

Percentage ofTrajectories

A 22% B 10% C 23% D 23% E 3% F 4% G 6% H 10%

Aerosol Extinction (km-1)

Altit

ude

(km

)

Summer

Backtrajectories - Summer

AOT>0.4

Backtrajectories - Winter• Majority of trajectories from west and northwest• CARL profiles show low water vapor and aerosols from westerly and northwesterly flow

0

1

2

3

4

5

6

7

0.0 0.1 0.2 0.3 0.4 0.5

Winter

H

GD

C

BA

FE

Percentage ofTrajectories

A 32% B 15% C 13% D 11% E 3% F 1% G 7% H 17%

Aerosol Extinction (km-1)

Altit

ude

(km

)

Winter

AOT<0.1

Slope = 0.90Intercept = -0.028R = 0.88N = 2304rms error = 0.068 (30%)Bias diff = 0.011 (5%)

Raman lidar/Cimel AOT comparison

April-May 1998August 1998-January 2000

Average aerosol extinction and water vapor profiles

• Aerosol vertical distributions and scale heights vary with AOT and season• Water vapor vertical distributions and scale heights are relatively constant

Average aerosol extinction profiles andhistograms of aerosol optical thickness

Average water vapor profiles and histograms of precipitable water vapor

(Turner et al., Geophys. Res. Letters, 28, 2001)

0 6 12 18 24 30 36 42 480.0

0.2

0.4

0.6

0.8

1.0

Altitude (km) 0.06 0.47 0.98 1.48 2.00

Water Vapor Mixing Ratio

Auto

corr

elat

ion

Lag (hours)

0 6 12 18 24 30 36 42 480.0

0.2

0.4

0.6

0.8

1.0

Altitude (km) 0.06 0.47 0.98 1.48 2.00

Relative Humidity

Auto

corr

elat

ion

Lag (hours)

0 6 12 18 24 30 36 42 480.0

0.2

0.4

0.6

0.8

1.0Aerosol backscatter

Auto

corr

elat

ion

Lag (hours)

Altitude (km) 0.06 0.47 0.98 1.48 2.00

0 6 12 18 24 30 36 42 480.0

0.2

0.4

0.6

0.8

1.0

Altitude (km) 0.06 0.47 0.98 1.48 2.00

Aerosol Extinction

Auto

corr

elat

ion

Lag (hours)

Autocorrelation Functions• CART Raman Lidar data from 2000-2001• Water vapor shows less variability than aerosol, particularly near surface

*Anderson, T., et al., Mesoscale Variations of Tropospheric Aerosols, J. Atmos. Sci., 60, 119-137, 2003.

Hygroscopic Aerosol Growth

• Preliminary study• Used 20 cases (1998) near

top of daytime BL• αa(RH=80%)/ αa(RH=30%) ~ 1.9

• Measurements are consistent with results from humidified nephelometer at surface

Raman lidar

Humidified nephelometer at surface

0.1 1 10 100 1000 10000

0.1

1

10

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

1.2

ζ(q)

q

Altitude (km) 0.47 2.00q=2

q=1

q=1

q=2

0.47 km

2.0 km

Stru

ctur

e Fu

nctio

ns, S

q(r)

Lag (hours)

Aerosol Extinction Structure Functions• Changes in structure function slopes at 6-8 hours (~200-280 km) indicate scale break associated with transition to stationary regime• Power law spectral slope β = ζ(2)+1 varies between 1.6-1.8• Spectral exponent decreases with altitude

Cimel Sun Photometer (CSPOT)

• Primary Measurements- Aerosol optical thickness (multiwavelength)- Sky radiance in principal plane and almucantar

• Derived Parameters– Angstrom exponents– Aerosol size distribution– Aerosol single scattering albedo– Aerosol refractive index

• Primary Measurements- Direct spectral irradiance- Diffuse spectral irradiance

• Derived Parameters– Aerosol optical thickness (λ)

Rotating Shadowband Radiometer (RSS)

Aerosol Optical Thickness and Radiative Influences

Multiple-year record of aerosol optical depth at ARM SGP site in north-central Oklahoma (Michalsky et al., 2001)

• Primary Measurements- Aerosol optical thickness

(multiwavelength)• Derived Parameters

– Angstrom exponents– Direct/diffuse ratio

MultiFilter Rotating Shadowband Radiometer (MFRSR)

Aerosol Optical Thickness and Radiative Influences

Aerosol Optical Thickness (550 nm)

Micropulse Lidar (MPL)• Primary Measurements

- Relative aerosol backscatter• Derived Parameters

– Aerosol backscatter profiles– Aerosol extinction profiles

CART Raman Lidar (CARL)• Primary Measurements

- Aerosol backscatter profiles- Aerosol extinction profiles- Aerosol optical thickness- Water vapor mixing ratio- Precipitable water vapor- Depolarization ratio profiles

• Derived Parameters– Relative humidity– Cirrus optical thickness

Aerosol Profiling

John Ogren, Elisabeth Andrews NOAA/CMDL

Vertical Variability of Aerosols – IAP Measurements

• IAP flights often show large vertical variability in intensive parameters• Surface measurements often differ from column averages

y = 0.52x + 1.00R2 = 0.35

y = 1.02x1

1.5

2

2.5

3

1 1.5 2 2.5 3

Surface Angstrom

Col.

Avg.

Ang

stro

m y = 0.45x + 0.52R2 = 0.39

y = 1.00x0.8

0.85

0.9

0.95

1

0.8 0.85 0.9 0.95 1

Surface ωo

Col.

Avg.

ωo

April 4, 2000

Boundary Layer Height (1998-2003)Median; Box: 25%, 75%; Whisker: 5%, 95%

Time (UT)

Alti

tude

(m)

0

500

1000

1500

2000

2500

3000

2 4 6 8 10 12 14 16 18 20 22 24

Aerosol Backscatter (Lidar)Water Vapor Mixing Ratio (Lidar)Potential Temperature (Sonde)

Box Plot (copy of 01011998-12312003_aot_addv5.sta 59v*35976c)

• PBL Height Methods:• Radiosonde - Potential temperature -(Heffter, 1980)

• Raman Lidar - Aerosol backscatter, water vapor via Haar wavelet – (Brooks, 2003)

• Best agreement during afternoon, early evening

Raman Lidar Retrieval of Boundary Layer Height and AOT

Percentage of AOT below BL Height Median; Box: 25%, 75%; Whisker: 5%, 95%

Time (UT)

Perc

enta

ge

0102030405060708090

100

2 4 6 8 10 12 14 16 18 20 22 24

WinterSummer

Box Plot (copy of 01011998-12312003_aot_addv5.sta 60v*35976c)

• Amount of AOT within PBL- varies with time of day- does not vary significantly with season or AOT

• Significant fraction of AOT (>25%) is above PBL