Tracing The Physical Signatures Among The Calculated Global Clear-Sky Spectral Shortwave Radiative Flux Distribution
Presenter: Xiang Zhong P301
Co-Author(s): Xiquan Dong, Baike Xi, Jordann Brendecke
Advisor(s): Xiquan Dong
1Hydrology & Atmospheric Sciences
This study utilized the MODerate resolution atmospheric TRANsmission (MODTRAN6.0.2.5, M6.0) model to compute global clear-sky shortwave (SW) radiative flux and compared it with NASA's Clouds and the Earth's Radiant Energy System (CERES) Synoptic Radiative Fluxes and Clouds (SYN1deg) product. The global distributions of clear-sky downwelling SW fluxes at the surface yielded similar annual means of 246.51 W m-2 for M6.0 and 242.42 W m-2 for SYN1deg. Differences indicate slightly higher M6.0 values in low to mid-latitudes, notably in the Northern Hemisphere (NH), but lower in higher latitudes compared to SYN1deg. However, most differences fall within CERES' estimated uncertainty (~ 6 W m-2). The sensitivities of clear-sky SW/μ0 fluxes to change in Precipitable Water Vapor (PWV), the clear-sky water vapor radiative kernel, are approximately -0.7 W m-2/(kg m-2) over oceans, consistent between M6.0 and CERES SYN1deg, except for SYN1deg over the Southern Hemisphere (SH) ocean. Zonal means of land coverage and SW/VIS/NIR albedos from M6.0 calculations reveal that Visible (VIS) albedos are highest, followed by SW and Near-Infrared (NIR) albedos in polar regions (>60º), while NIR albedos dominate from low to mid-latitudes (<60º). Albedos and their differences increase monotonically with increased land coverage from 60 ºS to 60 ºN. Consistent clear-sky water vapor radiative kernels from both products exceed expectations, offering insights for climate model calculations. More robust kernels should be derived from longer datasets in the future.