Abstract
Black-sky cloud albedo (BCA) is derived from satellite UV 340 nm observations from NOAA and NASA satellites to infer long-term (1980–2018) shortwave cloud albedo variations induced by volcano eruptions, the El Niño–Southern Oscillation, and decadal warming. While the UV cloud albedo has shown no long-term trend since 1980, there are statistically significant reductions over the North Atlantic and over the marine stratocumulus decks off the coast of California; increases in cloud albedo can be seen over Southeast Asia and over cloud decks off the coast of South America. The derived BCA assumes a C-1 water cloud model with varying cloud optical depths and a Cox–Munk surface BRDF over the ocean, using radiances calibrated over the East Antarctic Plateau and Greenland ice sheets during summer.
Highlights
Uncertainty in the shortwave (SW) cloud radiative feedback to surface temperature variations is a key uncertainty in global temperature prediction for the future climate [1,2]
EcNisSeOcomparison, we converted the UV Black-sky cloud albedo (BCA) to a proxy shortwave cloud albedo using a set of empiricallyStdudeiersivheavde pfoounlydncoonmsisitaenlst ctlhouadt rveasproinesdeswtoiEthNScOlovuardiabpilhityasaemo(Fngigshuipre-ba8sbed).clTouhdese polynomials data, Clouds and the Earth’s Radiant Energy System (CERES) satellite data, and climate models
The BCA time-series from the second box showed a compensating reduction of cloudiness during each El Niño event This is consistent with enhanced subsidence in the Western Pacific during El Niño conditions
Summary
Uncertainty in the shortwave (SW) cloud radiative feedback to surface temperature variations is a key uncertainty in global temperature prediction for the future climate [1,2]. LER is the reflectivity derived for the Earth’s surface, bounding a purely Rayleigh atmosphere, consistent with measured the top of atmosphere (TOA) radiance; an assumption is that the surface is Lambertian, and the effects of aerosols and clouds are included in the LER of the scene. It is only a proxy for the SW flux at the top of atmosphere (TOA), the longer-term UV record includes the El Chichón and Mt. Pinatubo volcanic events and three additional ENSO events, and covers two decades (1980–2000), when global temperatures warmed 0.3 ◦C [7,8]. An additional refinement is an empirical adjustment that accounts for the cloud diurnal cycle
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