HR: 09:00h
AN: C51C-05    [Abstracts]
TI: Transmission of Solar Radiation Through Summer Melt Ponds
AU: * Light, B
EM: bonnie@apl.washington.edu
AF: Applied Physics Laboratory Polar Science Center University of Washington, 1013 NE 40th St, Seattle, WA 98105 United States
AU: Grenfell, T C
EM: tcg@atmos.washington.edu
AF: Department of Atmospheric Sciences University of Washington, Box 351640 University of Washington, Seattle, WA 98195 United States
AU: Perovich, D K
EM: Donald.K.Perovich@erdc.usace.army.mil
AF: USA CRREL ERDC, 72 Lyme Rd, Hanover, NH 03755 United States
AB: During the summer melt cycle, the sea ice cover exhibits large changes in the amount of solar radiation backscattered to the atmosphere, absorbed, and transmitted to the ocean. These changes in radiative partitioning are, in part, driven by changes in the optical properties of the surface. Relatively high albedo areas of bare ice and remnant snow and relatively low albedo areas of open water and surface ponding create a spatially inhomogeneous surface with significant optical property variability on meter to decameter scales. Understanding how the complex surface partitions radiation requires understanding how individual surface types partition radiation. Measurements of spectral albedo, transmittance, and extinction were made at bare and ponded multiyear sea ice sites during the SHEBA summer. A radiative transfer model is used to simulate the optical property observations. Modeled and observed spectral albedos were compared and used to infer vertical profiles of scattering coefficients for each site. For bare multiyear ice, scattering coefficients were generally between 1 and 10 cm-1 (assuming g = 0.94) for the uppermost 10 -30 cm and between 0.25 and 0.9 cm-1 within the ice interior. For ponded multiyear ice, scattering coefficients were approximately uniform with depth and generally between 0.1 and 0.2 cm-1. The inferred inherent optical properties are then used in the radiative transfer model to predict spectral transmittance and extinction. For bare ice, the good agreement between observed and modeled transmittance suggests that the optical property observations are consistent. For ponded ice, the transmittances predicted by the model were significantly larger than those observed. Although the inferred model has some uncertainty, it is highly likely that the measurements are biased by the horizontal inhomogeneity of the ice cover. Monte Carlo radiative transfer simulations performed on an azimuthally symmetric domain indicate that transmittance measurements made under the center of ponds with diameter less than approximately four times the ice thickness can be strongly influenced by the optical properties of the surrounding ice. When the surrounding ice has higher extinction, transmittance measurements made at specific locations beneath ponds may underestimate the amount of shortwave energy reaching the ocean. The radiative transfer model is used to estimate and correct these biases in the measurements.
DE: 4504 Air/sea interactions (0312)
DE: 4552 Ocean optics
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting