Abstract
Uncertainty in Arctic top-of-atmosphere (TOA) radiative flux
observations stems from the low sun angles and the heterogeneous scenes.
Advancing our understanding of the Arctic climate system requires
improved TOA radiative fluxes. We compare Cloud and Earth’s Radiant
Energy System (CERES) TOA radiative fluxes with Arctic
Radiation-IceBridge Sea and Ice Experiment (ARISE) airborne measurements
using two approaches: grid box averages and instantaneously-matched
footprints. Both approaches indicate excellent agreement in the longwave
and good agreement in the shortwave, within 2 uncertainty considering
all error sources (CERES and airborne radiometer calibration, inversion,
and sampling). While the SW differences are within 2 uncertainty, both
approaches show a ~‑10 W m‑2 average
CERES-aircraft flux difference. Investigating the source of this
negative difference, we find a substantial sensitivity of the flux
differences to the sea ice concentration dataset. Switching from
imager-based to passive microwave-based sea ice data in the CERES
inversion process reduces the differences in the grid box average fluxes
and in the sea ice partly cloudy scene anisotropy in the matched
footprints. In the long-term, more accurate sea ice concentration data
are needed to reduce CERES TOA SW flux uncertainties. Switching from
imager to passive microwave sea ice data, in the short-term, could
improve CERES TOA SW fluxes in polar regions, additional testing is
required. Our analysis indicates that calibration and sampling
uncertainty limit the ability to place strong constraints
(<±7%) on CERES TOA fluxes with aircraft measurements.