Abstract
Abstract. Measurements from ground-based cloud radar, high spectral resolution lidar and microwave radiometer are used in conjunction with a column version of the Rapid Radiative Transfer Model (RRTMG) and radiosonde measurements to derive the surface radiative properties under mixed-phase cloud conditions. These clouds were observed during the United States Department of Energy (US DOE) Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Clouds Experiment (M-PACE) between September and November of 2004. In total, sixteen half hour time periods are reviewed due to their coincidence with radiosonde launches. Cloud liquid (ice) water paths are found to range between 11.0–366.4 (0.5–114.1) gm−2, and cloud physical thicknesses fall between 286–2075 m. Combined with temperature and hydrometeor size estimates, this information is used to calculate surface radiative flux densities using RRTMG, which are demonstrated to generally agree with measured flux densities from surface-based radiometric instrumentation. Errors in longwave flux density estimates are found to be largest for thin clouds, while shortwave flux density errors are generally largest for thicker clouds. A sensitivity study is performed to understand the impact of retrieval assumptions and uncertainties on derived surface radiation estimates. Cloud radiative forcing is calculated for all profiles, illustrating longwave dominance during this time of year, with net cloud forcing generally between 50 and 90 Wm−2.
Highlights
The radiative impacts of clouds remain one of the largest uncertainties in the simulation and understanding of global climate change (IPCC, 2007)
All parameters were found to be strongly tied to liquid cloud droplet size distributions assumed and cloud liquid water path (LWP)
Shupe and Intrieri (2004) provide cloud radiative forcing calculations for an annual cycle of clouds observed during the Surface Heat Budget of the Arctic (SHEBA; Uttal et al, 2002), analyzing individual contributions of cloud properties on long and shortwave forcing for observed clouds
Summary
The radiative impacts of clouds remain one of the largest uncertainties in the simulation and understanding of global climate change (IPCC, 2007). As discussed in Shupe et al (2008a), observation of these clouds is inherently difficult due to the need to capture multiple phases of water simultaneously Despite these challenges, several previous efforts have provided estimates of Arctic stratiform cloud radiative characteristics and forcing. Shupe and Intrieri (2004) provide cloud radiative forcing calculations for an annual cycle of clouds observed during the Surface Heat Budget of the Arctic (SHEBA; Uttal et al, 2002), analyzing individual contributions of cloud properties on long and shortwave forcing for observed clouds They found that clouds with significant longwave impacts were generally low clouds with warmer base temperatures, with longwave cloud forcing impacted strongly by LWP.
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