Post on 12-Jan-2016
description
How well can we measure the vertical profile of tropospheric aerosol extinction?
B. Schmid1, R. Ferrare2, C. Flynn3, R. Elleman4, D. Covert4, A. Strawa5, E. Welton6, D. Turner3, H. Jonsson7, J. Redemann1, J. Eilers5, K. Ricci8, A. Hallar5, M. Clayton9, J. Michalsky10, A. Smirnov11, B. Holben6, J. Barnard3
1Bay Area Environmental Research Institute, Sonoma, CA 2NASA Langley Research Center, Hampton, VA 3Pacific Northwest National Laboratory, Richland, WA4University of Washington, Seattle, WA 5NASA Ames Research Center, Moffett Field, CA 6NASA GSFC, Greenbelt, MD 7Center for Interdisciplinary Remotely-Piloted Aircraft Studies, Marina, CA
8Los Gatos Research Inc., Mountain View, CA 9SAIC/NASA Langley Research Center, Hampton, VA 10NOAA/ARL, Boulder, CO 11GEST/UMBC/ NASA GSFC, Greenbelt, MD
Goal
We assess the accuracy with which the vertical profile of aerosol extinction (a fundamental aerosol property) can currently be measured with state-of-the art instrumentation.
We cannot stress enough that for climate considerations it is the properties of the unaltered aerosol at its ambient concentration and thermodynamic state that are of interest.
We compare ambient aerosol extinction profiles obtained in coordinated field campaigns that include in situ and remote sensing measurements of aerosols aboard airborne platforms over surface-based lidars.
We start with the results of a recent campaign, the Department of Energy Atmospheric Radiation Measurement (ARM) Aerosol Intensive Operations Period (AIOP, May 2003), and then consider these results in the context of findings from other field campaigns conducted since 1996.
Conclusion
While we find that each of the methods investigated here has its strengths and weaknesses, there is no definitive proof that one of the methods is fundamentally flawed. From the biases found in AIOP and previous studies, we conclude that the systematic error associated with measuring the tropospheric vertical profile of the ambient aerosol extinction with current state-of-the art instrumentation is 15-20% at visible wavelengths and potentially larger in the UV and near-infrared. Random errors, as measured by rms differences are considerably larger, ranging from 26% to 98%.
How did we measure the vertical profile of aerosol extinction during AIOP?
Summary of AIOP Extinction ComparisonsRaman
Neph+PSAP
MPLNET
Cadenza
CadenzaNeph+PSAP
MPLARM
Neph+PSAP
-50%
-40%
-30%
-20%
-10%
0%
10%
20%
30%
40%
50%
Re
l. B
ias
to
AA
TS
-14
= 354 nm
= 453 nm
= 519 nm
= 675 nm = 1550 nm
Extinction comparisons in previous field campaigns
TARFOX, 1996
ACE-2, 1997
PRIDE, 2000
SAFARI, 2000
ACE-Asia, 2001
ARM Aerosol IOP, 2003
CLAMS, 2001
x y # profiles # data points
AATS-14 Neph+PSAP 26 3484AATS-14 Cadenza 26 2856
AATS-14 MPLNET 2.0 13 587AATS-14 MPLARM 19 2073
AATS-14 Raman Lidar 11 468
AATS-14 in-situ H2O 35 6705
Focus on data obtained in vertical profiles over SGP CF Altitudes: ~90 – 5600 m
CIRPAS Twin Otter
AATS-14
AATS-14 on UW CV-580 AATS-14 on CIRPAS Pelican
AATS-6
SPAWAR Navajo
UW C-131A
NCAR C-130
Future SGP Lidar Validation IOP
An unnoticed loss of sensitivity of the Raman lidar had occurred leading up to AIOP leading to a significant bias in derived aerosol extinction. The Raman lidar has recently been restored/upgraded. Therefore the ARM Aerosol Working group is proposing further validation using AATS-14 aboard a profiling aircraft (~20 flight hours, profiles 300 – 23,000 ft altitude, ~Sep 2005).
AATS-14 on Sky Research J-31
Photo courtesy Yin-Nan Lee, BNL
Airborne:• Nephelometer+PSAP• Cavity-Ring-Down (Cadenza) • Sunphotometry (AATS-14)
Ground based:• Raman Lidar (CARL)• MPLNET• MPLARM
0
1
2
3
4
5
6
0 0.1 0.2 0.3
Aerosol Extinction (1/km)
Alt
itu
de
(km
)
Neph+PSAP (453 nm) 18:34-18:52 UT
May 27, 2003