Scattering of longwave radiation by cloud particles has been regarded
unimportant and hence commonly neglected in global climate models.
However, it has been demonstrated by recent studies that cloud longwave
scattering plays an unignorable role in modulating the energy budget of
the Earth System. Offline radiative transfer calculation showed that
excluding cloud longwave scattering could overestimate outgoing longwave
radiation and underestimate downward irradiance to the surface, and thus
impose excessive cooling onto the atmosphere column. How this physical
process interacts with other processes in the Arctic climate system,
however, has not been thoroughly evaluated yet. Given the fact that the
melting of ice and snow that cover the vast surface of the Arctic region
is sensitive to energy budget, and such melting may trigger further
feedback mechanisms, the neglection of cloud longwave scattering could
bias the regional climate simulations to a considerable extent. We have
incorporated cloud longwave scattering into the NCAR CESM and the DoE
E3SM and this study analyzed the impact on the simulated polar climates
in both earth system models. Cloud longwave scattering leads to a warmer
surface air temperature in both models, especially over the wintertime.
A detailed surface energy budget analysis is performed, for both the
mean state and the temporal variability. Preliminary results suggest
that the leading change is downward longwave flux and upward longwave
flux, followed by the changes of turbulent heat flux. How the longwave
scattering treatments can couple with cloud microphysics and
precipitation physics to affect Arctic precipitation is further
explored.