Satellite-based estimation of high-altitude ice cloud radiative forcing derived through a Rapid Contrail-RF Estimation Approach

Abstract. Contrails, anthropogenic ice clouds formed by aircraft at cruise altitudes, strongly influence the Earth’s radiation budget but the measurement of their radiative forcing (RF) remains poorly quantified at high temporal resolution. In this study, we present the Rapid Contrail-RF Estimation Approach, which uses geostationary satellite observations to estimate the radiative forcing of high-altitude ice clouds, including potential contrail cirrus clouds. Starting from a cloud retrieval product, we apply pre-computed Look-Up Tables (LUTs) to generate radiative forcing maps for high-altitude ice clouds. Specifically, observations from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) onboard Meteosat Second Generation (MSG) were used to visually identify days with potential contrails. For 6 selected days, ice clouds were characterized using the Optimal Cloud Analysis (OCA) product from MSG/SEVIRI data provided by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). The LUTs were constructed using the libRadtran radiative transfer model to quantify the radiative effect of ice clouds in the short-wave (SW) and long-wave (LW) spectral regions. A cloud top pressure filter was applied to isolate high-altitude ice clouds, including potential contrails. The resulting data set provides a quantification of SW, LW, and net radiative forcing at the top of the atmosphere due to potential contrails. We show that these clouds contribute to daytime cooling and nighttime warming, with a net effect that varies between diurnal cycles. We assess the validity of the Rapid Contrail-RF Estimation Approach through correlation exercises focusing on uncertainties in the use of LUTs, a single ice cloud parameterization, and a calculated cloud top height, supplemented by comparisons with polar orbiting satellite observations from the Clouds and the Earth's Radiant Energy System (CERES) instruments. In general, these correlative comparisons indicate that the proposed approach provides accurate data on the estimation of the radiative forcing of high-altitude ice clouds, including potential contrails, with an accuracy of approximately 15 %.