Measurement Report: Observed Increase in Southern Hemisphere Reflected Energy from Clouds During December 2020 and 2021





Citation of Original Publication

Herman, J., Huang, L., Hafner, D., and Szabo, A.: Measurement Report: Observed Increase in Southern Hemisphere Reflected Energy from Clouds During December 2020 and 2021, Atmos. Chem. Phys. Discuss. [preprint],, in review, 2022.


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Measured backscattered UV radiances at 388±1.5 nm are converted to Lambert Equivalent Reflectivity (LER) are from EPIC (Earth Polychromatic Imaging Camera) onboard the DSCOVR spacecraft (Deep Space Climate Observatory) orbiting about the Sun-Earth Lagrange-1 (L1) gravitational balance point. The average percent of reflected solar energy in the 388±1.5 nm band is 29.2 % of the global incident solar energy in that band. Maximum reflected 388 nm solar energy RSE, mostly from clouds, occurs during the summer solstice in each hemisphere, December in the Southern Hemisphere SH and June in the Northern Hemisphere NH. The global average RSE (90° S to 90° N) has a maximum in December and a minimum in June showing that the SH cloud reflected energy is greater than that in the NH. Backscattering from land and oceans at 388 nm is small since the average clear-sky reflectivity of the Earth’s surface free of snow and ice is about 0.05. Calculations of RSE based on the 388 nm LER show a 7 % increase during December 2020 in RSE at 40° S to 50° S when the backscattering angle BA was 178.05°, and 6 % at 30° S to 40° S in November 2021 when BA = 177.5° compared to previous years, 2015–2019, with a smaller BA. Comparison of 380 nm RSE at 40° S to 50° S during December 2020 from the low Earth polar-orbiting nadir mapper in the Ozone Mapping and Profiler Suite (OMPS-NM) near 13:30 local solar time suggests that there has been a 5 % increase in SH cloud reflection during December 2020 compared to previous years. This suggests that the observed increase by EPIC is mostly from an increase in cloud cover and not from enhanced backscatter. In the NH RSE values at large EPIC BA (177.5° in June 2020 and 178.2° in June 2021) between 30° N to 60° N show a percent decrease 4.8 % in RSE at 45° N during June 2021 and a 6 % increase during June 2020 at 55° N compared to the previous 4 years. This also suggests that the increase and decrease in RSE are probably related to changes in cloud cover and not backscatter angle effects. Annual integrals of percent reflected solar energy over complete years are almost constant at all latitudes.