Export 5 results:
Sort by: Author Title Type [ Year  (Desc)]
Conant, WC, Seinfeld JH, Wang J, Carmichael GR, Tang YH, Uno I, Flatau PJ, Markowicz KM, Quinn PK.  2003.  A model for the radiative forcing during ACE-Asia derived from CIRPAS Twin Otter and R/V Ronald H. Brown data and comparison with observations. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003260   AbstractWebsite

Vertical profiles of aerosol size, composition, and hygroscopic behavior from Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter and National Oceanic and Atmospheric Administration R/V Ronald H. Brown observations are used to construct a generic optical model of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) aerosol. The model accounts for sulfate, black carbon, organic carbon, sea salt, and mineral dust. The effects of relative humidity and mixing assumptions (internal versus external, coating of dust by pollutants) are explicitly accounted for. The aerosol model is integrated with a Monte Carlo radiative transfer model to compute direct radiative forcing in the solar spectrum. The predicted regional average surface aerosol forcing efficiency (change in clear-sky radiative flux per unit aerosol optical depth at 500 nm) during the ACE-Asia intensive period is -65 Wm(-2) for pure dust and -60 Wm(-2) for pure pollution aerosol (clear skies). A three-dimensional atmospheric chemical transport model (Chemical Weather Forecast System (CFORS)) is used with the radiative transfer model to derive regional radiative forcing during ACE-Asia in clear and cloudy skies. Net regional solar direct radiative forcing during the 5-15 April 2001 dust storm period is -3 Wm(-2) at the top of the atmosphere and -17 Wm(-2) at the surface for the region from 20degreesN to 50degreesN and 100degreesE to 150degreesE when the effects of clouds on the direct forcing are included. The model fluxes and forcing efficiencies are found to be in good agreement with surface radiometric observations made aboard the R. H. Brown. Mean cloud conditions are found to moderate the top of atmosphere (TOA) radiative forcing by a factor of similar to3 compared to clear-sky calculations, but atmospheric absorption by aerosol is not strongly affected by clouds in this study. The regional aerosol effect at the TOA ("climate forcing") of -3 Wm(-2) is comparable in magnitude, but of opposite sign, to present-day anthropogenic greenhouse gas forcing. The forcing observed during ACE-Asia is similar in character to that seen during other major field experiments downwind of industrial and biomass black carbon sources (e.g., the Indian Ocean Experiment (INDOEX)), insofar as the primary effect of aerosol is to redistribute solar heating from the surface to the atmosphere.

Flatau, PJ, Flatau M, Zaneveld JRV, Mobley CD.  2000.  Remote sensing of bubble clouds in sea water. Quarterly Journal of the Royal Meteorological Society. 126:2511-2523.   10.1256/smsqj.56807   AbstractWebsite

We report on the influence of submerged bubble clouds on the remote-sensing properties of water. We show that the optical effect of bubbles on radiative transfer and on the estimate of the ocean colour is significant. We present a global map of the volume fraction of air in water derived from daily wind speed data. This map. together with the parametrization of the microphysical properties, shows the possible significance of bubble clouds on the albedo to incoming solar energy.

Valero, FPJ, Bucholtz A, Bush BC, Pope SK, Collins WD, Flatau P, Strawa A, Gore WJY.  1997.  Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE): Experimental and data details. Journal of Geophysical Research-Atmospheres. 102:29929-29937.   10.1029/97jd02434   AbstractWebsite

Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) was conducted to study the magnitude and spectral characteristics of the absorption Of solar radiation by the clear and cloudy atmosphere. Three aircraft platforms, a Grob Egrett, a NASA ER-2, and a Twin Otter, were used during ARESE in conjunction with the Atmospheric Radiation Measurements (ARM) central and extended facilities in north central Oklahoma. The aircraft were coordinated to simultaneously measure solar irradiances in the total spectral broadband (0.224-3.91 mu m), near infrared broadband (0.678-3.3 mu m), and in seven narrow band-pass (similar to 10 nm width) channels centered at 0.500, 0.862, 1.064, 1.249, 1.501, 1.651, and 1.750 mu m. Instrumental calibration issues are discussed in some detail, in particular radiometric power, angular, and spectral responses. The data discussed in this paper are available at the ARM ARESE data archive via anonymous FTP to

Draine, BT, Flatau PJ.  1994.  Discrete-Dipole Approximation for Scattering Calculations. Journal of the Optical Society of America a-Optics Image Science and Vision. 11:1491-1499.   10.1364/josaa.11.001491   AbstractWebsite

The discrete-dipole approximation (DDA) for scattering calculations, including the relationship between the DDA and other methods, is reviewed. Computational considerations, i.e., the use of complex-conjugate gradient algorithms and fast-Fourier-transform methods, are discussed. We test the accuracy of the DDA by using the DDA to compute scattering and absorption by isolated, homogeneous spheres as well as by targets consisting of two contiguous spheres. It is shown that, for dielectric materials (Absolute value of m less than or similar to 2), the DDA permits calculations of scattering and absorption that are accurate to within a few percent.

Maslowska, A, Flatau PJ, Stephens GL.  1994.  On the Validity of the Anomalous Diffraction Theory to Light-Scattering by Cubes. Optics Communications. 107:35-40.   10.1016/0030-4018(94)90099-x   AbstractWebsite

The extinction and absorption efficiencies of a cube at light incidence normal to its four-fold symmetry axis are calculated using the anomalous diffraction theory (ADT). The results are compared with those based on the discrete dipole approximation (DDA). It is shown that for certain cases of the orientation of a cube relative to the direction of the incident light the extinction efficiency calculated using DDA and ADT do not agree. However, the ADT-based absorption efficiencies for the cases studied are dependent on a particle volume and exhibit smaller errors. Hence the validity of the ADT for cubes is not as good as for spheres.