The role of cloud phase in Earth's radiation budget

Abstract

The radiative impact of clouds strongly depends on their partitioning between liquid and ice phases. Until recently, however, it has been challenging to unambiguously discriminate cloud phase in a number of important global regimes. CloudSat and CALIPSO supply vertically resolved measurements necessary to identify clouds composed of both liquid and ice that are not easily detected using conventional passive sensors. The capability of these active sensors to discriminate cloud phase has been incorporated into the fifth generation of CloudSat's 2B‐FLXHR‐LIDAR algorithm. Comparisons with Clouds and the Earth's Radiant Energy System fluxes at the top of atmosphere reveal that an improved representation of cloud phase leads to better agreement compared to earlier versions of the algorithm. The RMS differences in annual mean outgoing longwave (LW) radiation gridded at 2.5° resolution are 4.9 W m−2, while RMS differences in outgoing shortwave (SW) are slightly larger at 8.9 W m−2 due to the larger diurnal range of solar insolation. This study documents the relative contributions of clouds composed of only liquid, only ice, and a combination of both phases to global and regional radiation budgets. It is found that mixed‐phase clouds exert a global net cloud radiative effect of −3.4 W m−2, with contributions of −8.1 W m−2 and 4.7 W m−2 from SW and LW radiation, respectively. When compared with the effects of warm liquid clouds (−11.8 W m−2), ice clouds (3.5 W m−2), and multilayered clouds consisting of distinct liquid and ice layers (−4.6 W m−2), these results reinforce the notion that accurate representation of mixed‐phase clouds is essential for quantifying cloud feedbacks in future climate scenarios.