redemann, icartt workshop, durham, nh, aug.9-12, 2005 airborne measurements of spectral direct...

Redemann, ICARTT workshop, Durham, NH, Aug.9-12, 2005Redemann, ICARTT workshop, Durham, NH, Aug.9-12, 2005

Airborne measurements of spectral direct aerosol radiative forcing - a new aerosol gradient method applied to data

collected in INTEX/ITCT/ICARTT, 2004

J. Redemann(1), P. Pilewskie(2), P. Russell(4), J. Livingston(3), S. Howard(1), J.

Pommier(1), B. Schmid(1), W. Gore(4), J. Eilers(4), M. Wendisch(5)

(1) Bay Area Environmental Research Institute, Sonoma, USA, (2) University of Colorado, Boulder, USA,

(3) SRI International, Menlo Park, USA, (4) NASA Ames Research Center, Moffett Field, USA,

(5) Institute for Tropospheric Research, Leipzig, Germany


Contents

Description of the airborne instrumentation

used in this study

Methodology for an observationally-based

estimate of aerosol radiative effects

Comparison of results to ground-based

methods

Summary


Jetstream-31 (J31) in ITCT-INTEXIntercontinental Transport and Chemical Transformation-Intercontinental

Chemical Transport Experiment


Methodology for radiative effect studies from AOD gradientsMethodology for radiative effect studies from AOD gradients


Methodology for studying aerosol radiative forcing from horizontal AOD gradients

Measure simultaneous change in spectral aerosol optical depth

(AATS-14) and spectral net irradiance (SSFR) →

Fnet/AOD = aerosol radiative forcing efficiency

Observationally-based estimate of aerosol radiative effect

Advantage over ground-based methods – quasi-instantaneous –

because of short horizontal distances

Need to check (and correct for) effects of changing solar zenith

angle and changing column water vapor contents


18.25 18.3 18.35 18.4

0.08

0.09

0.1ICARTT 21. 7.2004 JRF12-R21Jul04.AB 18.25-18.37 UT

Alti

tud

e (

km) GPS alt

Press alt

18.25 18.3 18.35 18.40

0.5

UT

AO

D s

cre

en

ed

0.3535

0.38

0.4526

0.4994

0.5194

0.6044

0.6751

0.7784

0.8645

1.0191

1.2413

1.5578

2.1393

18.25 18.3 18.35 18.4860

880

900

920

940

UT

Do

wn

-we

llin

g F

lux

350-700nm350-1700nm


J31 Flight 12, 21 July 2004

Slope yields measure Slope yields measure of forcing efficiency, of forcing efficiency, i.e. forcing=f(AOD)i.e. forcing=f(AOD)


Full spectrum of Full spectrum of absoluteabsolute and and relativerelative forcing efficiency forcing efficiency


DateFlight Index

Case Index

incr./decr.Distance

[km] cos()

cos()/

07/17/04 JRF10 1 ↓ 0.016 (25.2%) 15.32 0.016 0.50% 0.31

07/21/04 JRF12 2 ↑ 0.134 (41.5%) 30.24 0.134 0.50% 0.04

07/22/04 JRF13 3 ↓ 0.069 (14.7%) 13.23 0.069 0.31% 0.05

07/23/04 JRF14 4 ↑ 0.201 (40.0%) 22.49 0.201 0.47% 0.02

07/23/04 JRF14 5 ↓ 0.070 (11.0%) 7.99 0.070 0.17% 0.02

07/23/04 JRF14 6 ↑ 0.039 (5.1%) 6.84 0.039 0.13% 0.03

07/29/04 JRF16 7 ↓ 0.143 (38.1%) 18.69 0.143 0.22% 0.02

07/29/04 JRF16 8 ↑ 0.378 (91.3%) 28.38 0.378 0.67% 0.02

07/29/04 JRF16 9 ↓ 0.177 (35.1%) 6.46 0.177 0.01% 0.00

08/02/04 JRF19 10 ↓ 0.245 (124.6%) 42.85 0.245 0.67% 0.03

08/02/04 JRF19 11 ↑ 0.219 (111.8%) 44.70 0.219 1.09% 0.05

08/03/04 JRF21 12 ↑ 0.095 (25.5%) 33.06 0.095 2.19% 0.23

08/07/04 JRF22 13 ↓ 0.02 (27.6%) 64.35 0.020 1.99% 1.00

08/08/04 JRF24 14 ↑ 0.036 (66.5%) 108.30 0.036 2.05% 0.58

Summary of 14 gradient casesSummary of 14 gradient cases


RR22-statistic – univariate vz. multivariate regressor model-statistic – univariate vz. multivariate regressor model


350-700nm net flux change for 10 ICARTT cases, assuming ssa=0.9-1, g=0.65-0.7

Conversion from instantaneous to 24h-average forcing efficiency


Bush and Bush and Valero, 2003 Valero, 2003 ACE-AsiaACE-Asia

Previous methodologies for aerosol radiative forcing studiesPrevious methodologies for aerosol radiative forcing studies

Flu

x 40

0-70

0nm

F

lux

400-

700n

m

[Wm

[Wm

-2]]

GMT on Day 106

AOD (500nm)

Flu

x 40

0-70

0nm

F

lux

400-

700n

m

[Wm

[Wm

-2]]


Comparison of 24h-avg. forcing efficiencies at the surface to previous work

Author 24h-ARFE @ surface

[Wm-2]

Spectral range region comments

This work 45.8±13.1

82.9±23.1

0.35 – 0.7m

0.35 – 1.67m

Gulf of Maine airborne

Kim et al., 2005 69 - 90 (non-dust)

91 - 104 (dust)

0.3 – 4.0m Korean peninsula + East China Sea

surface

Kim et al., 2005 55 - 76 0.3 – 4.0m East Asia surface

Meywerk and Ramanathan, 1999

48* (84 at noon) 0.4 – 0.7m East Asia, INDOEX-1

ship

Bush and Valero, 2002

38.5±4.0

72.2±5.5

0.4 – 0.7m

0.3 – 3.81m

Kaashidhoo, INDOEX

surface

Bush and Valero, 2003

42.2±4.8

73.0±9.6

0.4 – 0.7m

0.3 – 3.81m

Gosan,

ACE-Asia

surface

* Converted from reported value at solar noon


Summary

1. In INTEX/ICARTT/ITCT, we observed a total of 14 horizontal AOD gradients, with 10 gradients well suited for an analysis using the gradient forcing method.

2. More than half of the AOD gradients (at a wavelength of 499 nm) were greater than 0.1 and extended over distances less than 40 km.

3. We found cos()/«1 && nm>0.05 to be necessary criteria for the gradient forcing method.

4. Within the 10 case studies we found a high variability in the derived instantaneous aerosol forcing efficiencies (forcing per unit optical depth) for the visible wavelength range (350-700nm), with a mean of -79.6Wm-2 and a standard deviation of 21.8Wm-2(27%).

5. The mean instantaneous forcing efficiency for the visible plus near-IR wavelength range (350-1670nm) was derived to be ‑135.3Wm-2 with a standard deviation of 36.0Wm-2(27%).

6. An analytical conversion of the instantaneous forcing efficiencies to 24h-average values based on a 2-stream approximation yielded -45.8±13.1Wm-2 (mean±std) for the visible and -82.9±23.1Wm-2 (mean±std) for the visible plus near-IR wavelength range, respectively.


Acknowledgements

Funding for the J-31 aircraft modifications through NASA RSP, TCP + SSP, and for ICARTT measurements and data analysis through NOAA ACCP are gratefully acknowledged.

redemann, icartt workshop, durham, nh, aug.9-12, 2005 airborne measurements of spectral direct...

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