Abstract. Linear particle depolarization ratio is presented for three case studies from the NASA Langley airborne High Spectral Resolution Lidar-2 (HSRL-2). Particle depolarization ratio from lidar is an indicator of non-spherical particles and is sensitive to the fraction of non-spherical particles and their size. The HSRL-2 instrument measures depolarization at three wavelengths: 355, 532, and 1064 nm. The three measurement cases presented here include two cases of dust-dominated aerosol and one case of smoke aerosol. These cases have partial analogs in earlier HSRL-1 depolarization measurements at 532 and 1064 nm and in literature, but the availability of three wavelengths gives additional insight into different scenarios for non-spherical particles in the atmosphere. A case of transported Saharan dust has a spectral dependence with a peak of 0.30 at 532 nm with smaller particle depolarization ratios of 0.27 and 0.25 at 1064 and 355 nm, respectively. A case of aerosol containing locally generated wind-blown North American dust has a maximum of 0.38 at 1064 nm, decreasing to 0.37 and 0.24 at 532 and 355 nm, respectively. The cause of the maximum at 1064 nm is inferred to be very large particles that have not settled out of the dust layer. The smoke layer has the opposite spectral dependence, with the peak of 0.24 at 355 nm, decreasing to 0.09 and 0.02 at 532 and 1064 nm, respectively. The depolarization in the smoke case may be explained by the presence of coated soot aggregates. We note that in these specific case studies, the linear particle depolarization ratio for smoke and dust-dominated aerosol are more similar at 355 nm than at 532 nm, having possible implications for using the particle depolarization ratio at a single wavelength for aerosol typing.

Since 1995, the Intergovernmental Panel on Climate Change (IPCC) assessment reports have highlighted, as leading uncertainties in understanding Earth's climate, the direct impact of airborne particles on the planetary energy balance and the indirect effects they have on clouds, atmospheric stability, regional circulation, and the hydrologic cycle. For example, the confidence with which future climate can be predicted depends to first order on the relationship between the near-surface warming response and the radiative forcing, primarily by greenhouse gases and aerosol effects. This relationship is characterized, in its simplest form, as a linear factor-the climate sensitivity. The quantity is determined using presentday and retrospective values of forcing and response; AFFILIATIONS: Kahn and hansiCo-Earth Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland; BeRKoff, Chen, and feRRaRe-NASA Langley Research Center, Hampton, Virginia; BRoCK and muRphy-Chemical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado; Ghan-Department of Energy, Pacific Northwest National Laboratory, Richland, Washington; heGG-Department of Atmospheric Sciences, University of Washington, Seattle, Washington; maRTins-Department of Physics, and Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, Maryland; mCnauGh- 2215OCTOBER 2017 AMERICAN METEOROLOGICAL SOCIETY | currently, the largest uncertainty in climate sensitivity is due to uncertainty in the aerosol forcing (IPCC 2013;Schwartz et al. 2014;Forster 2016).Further, the presence of aerosols often necessitates large corrections to other space-based measurements of independent parameters, such as ocean color and productivity (e.g., Gordon 1997), and they cause greater premature mortality than ozone, NO x , or other pollutants (Lelieveld et al. 2015). Frequent, global aerosol airmass-type mapping, of value itself for air quality, material transport, and other applications, also represents critical test, validation, and constraint data for climate modeling. Here, we expand the definition of "aerosol type" normally used in satellite remote sensing, which covers those categorical distinctions among particle components and mixtures that can be made from optical constraints, of varying sensitivity, to particle size, shape, and spectral absorption. To these we add particle hygroscopicity, mass, and composition, which are critical for treating aerosol direct and indirect forcing in climate models and for air quality applications. These additional characteristics cannot be derived from remote sensing alone and thus require in situ measurement. Further, measurements of these quantities make it possible to better represent aerosol light-absorption properties needed to address many radiative and dynamical questions, yet cannot be retrieved with sufficient accuracy from satellite observations alone.Single-view satellite instruments, such as the NASA EOS Moderate Resolution Imaging Spectroradiometer (MODIS) and the ...

No abstract

Abstract. Particle depolarization ratio is presented for three case studies from the NASA Langley airborne High Spectral Resolution Lidar-2 (HSRL-2). Particle depolarization ratio from lidar is an indicator of non-spherical particles and is sensitive to the fraction of non-spherical particles and their size. The HSRL-2 instrument measures depolarization at three wavelengths: 355, 532, and 1064 nm. The three measurement cases presented here include two cases of dust aerosol and one case of smoke aerosol. These cases have partial analogs in earlier HSRL-1 depolarization measurements at 532 and 1064 nm and in literature, but the availability of three wavelengths gives additional insight into different scenarios for non-spherical particles in the atmosphere. A case of transported Saharan dust has a spectral dependence with a peak of 0.30 at 532 nm with smaller particle depolarization ratios of 0.27 and 0.25 at 1064 and 355 nm, respectively. A case of locally generated wind-blown North American dust has a maximum of 0.38 at 1064 nm, decreasing to 0.37 and 0.24 at 532 and 355 nm, respectively. The cause of the maximum at 1064 nm is inferred to be very large particles that have not settled out of the dust layer. The smoke layer has the opposite spectral dependence, with the peak of 0.24 at 355 nm, decreasing to 0.09 and 0.02 at 532 and 1064 nm. The depolarization in the smoke case is inferred to be due to the presence of coated soot aggregates. We also point out implications for the upcoming EarthCARE satellite, which will measure particle depolarization ratio only at 355 nm. At 355 nm, the particle depolarization ratios for all three of our case studies are very similar, indicating that smoke and dust may be more difficult to separate with EarthCARE measurements than heretofore supposed.

No abstract