Abstract
The Earth’s spherical albedo describes the ratio of light reflected from the Earth to that incident from the Sun, an important variable for the Earth’s radiation balance. The spherical albedo has been previously estimated from satellites in low-Earth orbits, and from light reflected from the Moon. We developed a method to derive the Earth’s spherical shortwave albedo using the images from the Earth Polychromatic Imaging Camera (EPIC) on board National Oceanic and Atmospheric Administration’s (NOAA) Deep Space Climate Observatory (DSCOVR). The satellite is located in the Lagrange 1 point between the Earth and the Sun and observes the complete illuminated part of the Earth at once. The method allows us to provide continuously updated spherical albedo time series data starting from 2015. This time series shows a systematic seasonal variation with the mean annual albedo estimated as 0.295±0.008 and an exceptional albedo maximum in 2020, attributed to unusually abundant cloudiness over the Southern Oceans.
Highlights
Solar radiation is the primary energy source of the Earth and largely determines Earth’s climate
We introduce first the Earth Polychromatic Imaging Camera (EPIC) imagery and the methods that we use to derive the albedo in Materials and Methods
The reason for this is that the angular resolution of the tabulated angular distribution models (ADM) available at the Clouds and the Earth’s Radiant Energy System (CERES) project web pages2 is only 10°, and we want to interpolate with a finer resolution in the backscattering direction and combining similar surface types gives us more robust estimation
Summary
Solar radiation is the primary energy source of the Earth and largely determines Earth’s climate. The proportion of the incoming solar radiation reflected back to space by the Earth is described by the spherical (i.e., Bond) albedo. It depends on the reflective properties of the Earth and it is affected by the proportion of the highly reflective areas relative to darker areas. The Earth’s spherical albedo is an indicator of the radiation budget and driving the global weather and climate processes. Since 1997 the albedo is being overseen by the Clouds and the Earth’s Radiant Energy System (CERES), which includes five satellites and seven CERES radiometers (see Wielicki et al, 1996). The CERES albedo product is a combination of observations from several instruments seeing different parts of the Earth, and as it takes numerous hours for the CERES to scan the entire Earth while the cloud cover of the Earth evolves in a matter of minutes, the spherical albedo evaluation method by the CERES instruments
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