Evidence for Hemispheric Spectral Albedo Inequality
- 1Lawrence Berkeley National Laboratory, Climate & Ecosystem Sciences Division, Berkeley, California, United States of America (wdcollins@lbl.gov)
- 2Dept. of Earth and Planetary Science, University of California, Berkeley, Berkeley, California, United States of America
In this study, we examine whether the interhemispheric symmetry observed
in broadband shortwave albedos also applies to the
hemispheric-mean visible and near-infrared albedos. While
several recent exploratory studies have examined this question
using climate models, we explore this
question using direct observations of the visible and
near-infrared albedos collected by the Nimbus-7 satellite. This
study builds upon earlier intercomparisons of cloud spectral
albedos from Nimbus-7 and from climate models using the same
combinations of Nimbus-7 measurements used here (Collins, 1998).
We find that the hemispheric-mean spectral partitioning of albedo is
consistently and statistically significantly different between the two
hemispheres. Consistent with prior studies, the origin of these
differences is due to interhemispheric differences in cloud cover.
Over oceans, the regional daily-mean differences between visible and
near-IR albedos are closely correlated with cloud amount. The
relative differences are maximized for clear-sky conditions and
minimized for overcast conditions.
Background: The shortwave broadband albedo is a weighted sum of the albedos
in the visible and near-infrared bands. Under condensate-free
conditions, the interactions of solar insolation in these bands
with the atmosphere and surface are quite different. To an
excellent approximation, the condensate-free atmosphere is a
conservative Rayleigh-scattering medium in the visible. Solar
radiation that is not reflected back to space is, to leading
order, transmitted to the surface. In the near-infrared, the
interactions of sunlight with the atmosphere are dominated by
absorption, primarily with water vapor. Additional absorption is
contributed by well-mixed greenhouse gases, oxygen, and other
gaseous constituents. The solar radiation
reaching the surface has therefore been reduced both by
reflection to space (from atmospheric condensates and the surface
albedo) and by absorption in the atmosphere. Hence, the relative
partitioning of net TOA insolation between the visible and
near-infrared bands will affect the relative partitioning between
atmospheric absorption and transmission to the surface.
How to cite: Collins, W. and Feldman, D.: Evidence for Hemispheric Spectral Albedo Inequality, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12, https://doi.org/10.5194/egusphere-egu23-12, 2023.
