A Radiation Closure Study at Both Surface and Top of Atmosphere Using Radiative Transfer Model

Dong, X., University of Arizona

Radiation Processes

High Latitude Processes

Dong X, B Xi, S Qiu, P Minnis, S Sun-Mack, and F Rose. 2016. "A radiation closure study of Arctic stratus cloud microphysical properties using the collocated satellite-surface data and Fu-Liou radiative transfer model." Journal of Geophysical Research: Atmospheres, 121(17), 10.1002/2016jd025255.


Figure 1. The ARM North Slope of Alaska (NSA) site (a) centered in 100km by 100km box, the red box shows the domain of 30-km x 30-km for this study, (b) the MODIS true color image over this region on 22:15 UTC, October 13 2003, (c) MODIS true color image on 22:40 UTC, June 5 2004.


Figure 10. Fu-Liou RTM calculated (a) SW↓sfc flux and (b) transmission γ at the surface, (c) SW↑TOA flux and (d) albedo RTOA with input of ARM, CERES Ed2 and Ed4 retrieved re and optical depth. The corresponding observations (OBS) are the ARM PSP surface measurements and the CERES Single Scanner Footprint (SSF) instantaneous reflected SW flux at the TOA. (e-h) for Aqua cases.


Figure 1. The ARM North Slope of Alaska (NSA) site (a) centered in 100km by 100km box, the red box shows the domain of 30-km x 30-km for this study, (b) the MODIS true color image over this region on 22:15 UTC, October 13 2003, (c) MODIS true color image on 22:40 UTC, June 5 2004.

Figure 10. Fu-Liou RTM calculated (a) SW↓sfc flux and (b) transmission γ at the surface, (c) SW↑TOA flux and (d) albedo RTOA with input of ARM, CERES Ed2 and Ed4 retrieved re and optical depth. The corresponding observations (OBS) are the ARM PSP surface measurements and the CERES Single Scanner Footprint (SSF) instantaneous reflected SW flux at the TOA. (e-h) for Aqua cases.

Science

Cloud macrophysical and microphysical properties have a significant impact on the radiative energy budgets at both the surface and top of atmosphere (TOA). The cloud-radiative interactions in the Arctic are even more complex due to large solar zenith angles, highly reflective snow and ice surfaces, and multiple reflections of solar radiation between the cloud layer and the surface. Minimal visual and thermal contrast exists between Arctic clouds and the snow- and ice-covered surfaces beneath them, which can lead to difficulties in passive satellite retrievals of cloud properties.

Impact

Retrievals of cloud microphysical properties based on passive satellite imagery are especially difficult over snow-covered surfaces because of the bright and cold surface. To help quantify their uncertainties, single-layered overcast liquid-phase Arctic stratus cloud microphysical properties retrieved using the CERES Ed2 and Ed4 algorithms are compared with ground-based retrievals at the ARM NSA site at Barrow, AK during the period from March 2000 to December 2006. A total of 206 and 140 snow-free cases (Rsfc ≤ 0.3), and 108 and 106 snow cases (Rsfc > 0.3), respectively, were selected from Terra and Aqua satellite passes over the ARM NSA site.

Summary

The CERES Ed4 and Ed2 optical depth (τ) and LWP retrievals from both Terra and Aqua are almost identical and have excellent agreement with ARM retrievals under snow-free and snow conditions. In order to reach a radiation closure study for both the surface and TOA radiation budgets, the ARM PSP-measured surface albedos were adjusted (63.6% and 80% of the ARM surface albedos for snow-free and snow cases, respectively) to account for the water and land components of the domain of 30-km x 30-km. Most of the RTM calculated SW↓sfc and SW↑TOA fluxes using ARM and CERES cloud retrievals and the domain mean albedos as input agree with the ARM and CERES flux observations within 10 W m-2 for both snow-free and snow conditions. Sensitivity studies show that the ARM LWP and re retrievals are less dependent on solar zenith angle (SZA), but all retrieved optical depths increase with SZA.