Impacts of Active Satellite Sensors' Low-level Cloud Detection Limitations on Cloud Radiative Forcing
- Center for Satellite Applications and Research, NOAA/NESDIS, Madison, WI, USA
Abstract. Previous studies revealed that satellites sensors with the best detection capability identify 25–40 % and 0–25 % fewer clouds below 0.5 km and between 0.5–1.0 km, respectively, over the Arctic land. Quantifying the impacts of cloud detection limitations on the radiation flux are critical especially over the Arctic Ocean considering the dramatic changes in Arctic sea ice. In this study, the proxies of the space-based radar, CloudSat, and lidar, CALIPSO, cloud masks are derived based on simulated radar reflectivity and cloud optical thickness using retrieved cloud properties from surface-based radar and lidar during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Limitations in low-level cloud detection by the space-based active sensors, and the impact of these limitations on the radiation fluxes at the surface and the top of atmosphere (TOA), are estimated. The results show that the combined CloudSat and CALIPSO product generally detects all clouds above 1 km, while detecting 25 % (9 %) fewer in absolute values below 600 m (600 m to 1 km) than surface observations. These detection limitations lead to uncertainties in the monthly mean cloud radiative forcing (CRF), with maximum absolute monthly mean values of 2.7 Wm−2 and 4.0 Wm−2 at the surface and TOA, respectively. The uncertainties for individual cases are larger – up to 30 Wm−2. Cloud information from only the CALIPSO or the CloudSat leads to larger cloud detection differences compared to the surface observations, and larger CRF uncertainties with absolute monthly means larger than 10.0 Wm−2. These uncertainties need to be considered when radiation flux products from CloudSat and CALIPSO are used in climate and weather studies.
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