HR: 1340h
AN: A33D-0095    [Abstracts]
TI: Passive Remote Sensing Of Aerosol Fine Mode Fraction: A Comparison With In-Situ Measurements During The ACE-Asia Field Campaign.
AU: * Gass\'{o}, S
AF: GEST/UMBC, 3.002 South Campus University of Maryland Baltimore County, Baltimore, MD 21250 United States
AU: O'Neill, N T
AF: CARTEL, Universite de Sherbrooke, Sherbrooke, QU J1K 2R1 Canada
AU: Redemann, J
AF: BAERI, NASA Ames Research Center MS 245-5, Moffett Field, CA 94035-1000 United States
AB: The contribution of the aerosol accumulation mode optical depth to the total optical depth ($\eta$) has become more relevant in recent years since it is a parameter that can be retrieved from satellite (MODIS) and sunphotometry (AERONET). $\eta$ has been defined in terms of optical properties and it assumes that the aerosol size distribution in the atmospheric column can be represented by two modes. A necessary method to interpret and validate $\eta$ is the comparison of retrievals with in-situ data. However, these comparisons are difficult due to several factors, for example aircraft in-situ measurements are frequently dominated by a variety of sampling issues. The purpose of this work is to address some of the issues related to the definition and interpretation of $\eta$: 1) How does the retrieved $\eta$ scale with the different ratios derived from the in-situ size distributions? 2) When multiple layers and mixed aerosols are present (such as pollution and dust layers frequently observed during ACE-Asia), is the retrieved $\eta$ characteristic of any particular layer or of all layers? 3) Can $\eta$, a parameter defined from optical properties, be related to a physical property such as total columnar or layer aerosol mass? Specifically, we compare collocated measurements of sun photometer derived $\eta$ and profiles of aerosol size distributions and scattering coefficients measured by the NOAA C-130 aircraft during the ACE-Asia field campaign. Appropriate corrections are applied to in-situ measurements in order to account for sampling drying and unknown index of refraction of the ambient aerosol. Several definitions of in-situ $\eta$ are tested including ratios defined in terms of the aerosol size distribution (ratio of accumulation mode to total surface and volume) as well as the ratio of measured scattering coefficient for particles up to 1 um (aerodynamic diameter) to total scattering. An inversion scheme based on the spectral dependence of the optical depth (O'Neill method) is used to derive $\eta$ from the AATS-6 sunphotometer onboard (bands 380,450,525 and 1020 nm). Initial comparisons indicate that retrieved $\eta$ scales reasonably well with the ratios of accumulation mode to total integrated area and volume. Further comparisons will be shown at the meeting.
DE: 3337 Numerical modeling and data assimilation
DE: 3359 Radiative processes
DE: 3360 Remote sensing
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting