Export 3 results:
Sort by: Author Title Type [ Year  (Desc)]
Podgorny, I, Lubin D, Perovich DK.  2018.  Monte Carlo study of UAV-measurable albedo over Arctic Sea ice. Journal of Atmospheric and Oceanic Technology. 35:57-66.   10.1175/jtech-d-17-0066.1   AbstractWebsite

In anticipation that unmanned aerial vehicles (UAVs) will have a useful role in atmospheric energy budget studies over sea ice, a Monte Carlo model is used to investigate three-dimensional radiative transfer over a highly inhomogeneous surface albedo involving open water, sea ice, and melt ponds. The model simulates the spatial variability in 550-nm downwelling irradiance and albedo that a UAV would measure above this surface and underneath an optically thick, horizontally homogeneous cloud. At flight altitudes higher than 100 m above the surface, an airborne radiometer will sample irradiances that are greatly smoothed horizontally as a result of photon multiple reflection. If one is interested in sampling the local energy budget contrasts between specific surface types, then the UAV must fly at a low altitude, typically within 20 m of the surface. Spatial upwelling irradiance variability in larger open water features, on the order of 1000 m wide, will remain apparent as high as 500 m above the surface. To fully investigate the impact of surface feature variability on the energy budget of the lower troposphere ice-ocean system, a UAV needs to fly at a variety of altitudes to determine how individual features contribute to the area-average albedo.

Lubin, D, Vogelmann AM.  2010.  Observational quantification of a total aerosol indirect effect in the Arctic. Tellus Series B-Chemical and Physical Meteorology. 62:181-189.   10.1111/j.1600-0889.2010.00460.x   AbstractWebsite

We use 6 yr of multisensor radiometric data (1998-2003) from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program to provide an observational quantification of the short-wave aerosol first indirect effect in the Arctic. Combined with the previously determined long-wave indirect effect, the total (short-wave and long-wave) first indirect effect in the high Arctic is found to yield a transition from surface warming of +3 W m(-2) during March to a cooling of -11 W m(-2) during May, therefore altering the seasonal cycle of energy input to the Arctic Earth atmosphere system. These data also reveal evidence of a first indirect effect that affects optically thinner clouds during summer. which may represent an additional negative climate feedback that responds to a warming Arctic Ocean with retreating sea ice.

Berque, J, Lubin D, Somerville RCJ.  2004.  Infrared radiative properties of the Antarctic plateau from AVHRR data. Part I: Effect of the snow surface. Journal of Applied Meteorology. 43:350-362.   10.1175/1520-0450(2004)043<0350:irpota>;2   AbstractWebsite

The effective scene temperature, or "brightness temperature," measured in channel 3 (3.5-3.9 m m) of the Advanced Very High Resolution Radiometer (AVHRR) is shown to be sensitive, in principle, to the effective particle size of snow grains on the Antarctic plateau, over the range of snow grain sizes reported in field studies. In conjunction with a discrete ordinate method radiative transfer model that couples the polar atmosphere with a scattering and absorbing snowpack, the thermal infrared channels of the AVHRR instrument can, therefore, be used to estimate effective grain size at the snow surface over Antarctica. This is subject to uncertainties related to the modeled top-of-atmosphere bidirectional reflectance distribution function resulting from the possible presence of sastrugi and to lack of complete knowledge of snow crystal shapes and habits as they influence the scattering phase function. However, when applied to NOAA-11 and NOAA-12 AVHRR data from 1992, the snow grain effective radii of order 50 mum are retrieved, consistent with field observations, with no apparent discontinuity between two spacecraft having different viewing geometries. Retrieved snow grain effective radii are 10-20-mum larger when the snow grains are modeled as hexagonal solid columns rather than as spheres with a Henyey-Greenstein phase function. Despite the above-mentioned uncertainties, the retrievals are consistent enough that one should be able to monitor climatically significant changes in surface snow grain size due to major precipitation events. It is also shown that a realistic representation of the surface snow grain size is critical when retrieving the optical depth and effective particle radius of clouds for the optically thin clouds most frequently encountered over the Antarctic plateau.