HR: 14:10h
AN: A32C-02    [PDF]
TI: Analysis of Measurement Requirements for the Aerosol Indirect Effect: A Synthesis of Observations and Modeling
AU: * Feingold, G
EM: graham.feingold@noaa.gov
AF: NOAA/ETL, 325 Broadway, Boulder, CO 80305 United States
AU: Previdi, M
EM: mprevidi@envsci.rutgers.edu
AF: Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901 United States
AU: Veron, D E
EM: veron@envsci.rutgers.edu
AF: Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901 United States
AB: The aerosol indirect effect has been measured for some time now by satellite remote sensors, and more recently by surface-based remote sensors. The indirect effect is often expressed in terms of a relative change in drop size for a relative change in aerosol optical depth or extinction. Here we present some recent results of surface based remote sensing of the indirect effect and assess whether aerosol optical depth or extinction is a suitable proxy for the aerosol affecting drop formation. To do so, we use multiple realizations of a cloud model to investigate the sensitivity of cloud drop effective radius $r_e$ to aerosol parameters (size distribution and composition) and dynamical parameters (updraft and liquid water content). A breakdown of the individual aerosol terms contributing to drop size change shows that use of aerosol extinction as a proxy for size distribution and composition tends to underestimate the magnitude of the first indirect effect. The use of the aerosol index alleviates this problem somewhat. We show that $r_e$ is most sensitive to cloud liquid water, a parameter often ignored in indirect effect analyses. The relative importance of the other parameters varies for different conditions but aerosol concentration $N_a$ is consistently important. Updraft plays an increasingly important role under high aerosol loadings. Requirements for measuring the indirect effect over polluted continents are shown to be more stringent than those over cleaner, remote oceans. This may influence interpretation of current satellite and surface remote measurements of the indirect effect.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 1640 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting