Global Daytime Variability of Clouds From DSCOVR/EPIC Observations

Abstract

Knowledge of the daytime variability of cloud fraction is pivotal for the accurate determination of the atmosphere's energy balance. Yet, polar orbiting satellites are unable to fully capture daytime variability and individual geostationary satellites only provide measurements for portions of the Earth. In addition, diurnal cloud fraction variations analyzed with General Circulation Models provide results that cannot be reconciled with observations in many situations. Here, we show that the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) satellite presents a unique opportunity to examine changes in daytime global cloud fraction resolved at one‐hour frequency. For the first time, we characterize the global daytime variability of clouds with a single sensor, presenting evidence that the fraction of liquid clouds reaches its maximum over continental areas and its minimum over ocean around noon. We compare our results with previous global and regional studies and examine implications for the Earth's energy budget.

Cloud Height Daytime Variability From DSCOVR/EPIC and GOES-R/ABI Observations

“…We then average the cloud height of all the local time maps across the number of observations for each grid cell and across all years for a particular season, obtaining thus seasonally-averaged maps of cloud height at all local times. This methodology has proven useful in determining diurnal cycles with EPIC data and quantifying the diurnal variability of cloud fraction for low and high clouds consistently with previous research (Delgado-Bonal et al, 2021). Due to EPIC's location at the L1 point, the best pixel resolution is achieved at nadir ( ~8 km); off nadir the pixels become elliptical with the long axis larger by a factor of about 1/ cos(SZA) and the short axis unaffected.…”

“…In this case, a positive correlation between high cloud fraction and cloud height is observed for most of the globe. High cloud fraction evolves diurnally regardless of the surface type, with higher cloud fraction values in the afternoon than in the morning and noon (see discussion and appendixes in Delgado-Bonal et al, 2021). The diurnal cloud height cycles obtained in this paper (see Figures 2, 3) follow a similar behavior during the day, with cloud height increasing from morning to evening, hence resulting in mostly positive regional correlations.…”

“…In this study, we use retrievals from both EPIC and ABI aboard GOES-R to quantify the diurnal evolution of cloud top height for their overlapping coverage area. Previous analyses of cloud fraction from EPIC and ISCCP showed that the diurnal evolution of high and low cloud fractions is different (Cairns 1995;Delgado-Bonal et al, 2021), However, the accompanying cycles of cloud top heights have hitherto not been examined. Here, we apply a separation between high and low clouds to resolve more meaningfully the diurnal cycle of height for different kinds of clouds.…”

“…Over land, as the sun heats the surface, cloud cover starts increasing early in the morning as the boundary layer deepens, reaching a maximum around noon and early afternoon and continuing with a decrease of cloud cover later in the afternoon. Over ocean, cloud cover evolution follows a diametrically opposite cycle: peak cloud fraction during nighttime, followed by decrease during the morning, a minimum around noon, and a steady increase during the afternoon (Delgado-Bonal et al, 2020a;Delgado-Bonal et al, 2021).…”

Non‐Gaussian Distributions of TOA SW Flux as Observed by MISR and CERES

“…A recent study showed that the SW diurnal variation from the CERES EBAF is somewhat different from the one inferred from the DSCOVR/EPIC observation (Lim et al., 2021). In addition, the rate of daytime cloud fraction changes from DSCOVR/EPIC observations is not symmetric about noon either (Delgado‐Bonal et al., 2021). The diurnal variation of albedo estimated from the Earth Radiation Budget Experiment (ERBE) also shows that the albedo variations are not always symmetric with respect to noon due to variations of cloudiness throughout the day, which are asymmetric about noon (Rutan et al., 2014).…”