10 Aug 2022
10 Aug 2022
Status: this preprint is currently under review for the journal ACP.

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

Jay Herman1, Liang Huang2, David Hafner2, and Adam Szabo3 Jay Herman et al.
  • 1University of Maryland Baltimore County JCET, Baltimore, Maryland USA
  • 2Science Systems and Applications, Lanham, Maryland, USA
  • 3NASA Goddard Space Flight Center, Greenbelt, Maryland USA

Abstract. 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.

Jay Herman et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-481', Anonymous Referee #1, 23 Dec 2022
    • AC1: 'Reply on RC1', Jay Herman, 17 Jan 2023
  • RC2: 'Comment on acp-2022-481', Anonymous Referee #2, 08 Jan 2023
    • AC2: 'Reply on RC2', Jay Herman, 17 Jan 2023

Jay Herman et al.

Data sets

Measurements of Cloud Reflected Energy Jay Herman and Liang Huang

Jay Herman et al.


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Short summary
The research object is to see if reflections from clouds by the DSCOVR satellite at the Earth-Sun Lagrange point are enhanced as the backscattering angle nears 180 degrees. The 388 nm wavelength channel sees almost nothing from the Earth's surface. The result is that the Southern Hemisphere radiance increase in December 2020 and 2021 is likely caused by cloud amount increase and not by enhanced reflectivity at a 178-degree backscatter angle.