Geoscience Reference
In-Depth Information
Figure 5.8.
Mean monthly net allwave radiation at the surface (Wm
−2
) for the four mid-
season months based on ISCCP-D data (courtesy of J. Key, NOAA, Madison, WI).
5.7
Cloud Radiative Forcing
5.7.1
Definition and Characteristics
Cloud radiative forcing represents the change in the net radiation budget because of
clouds. It can be broken into longwave and shortwave (solar) forcing components,
the sum of the two being the net cloud radiative forcing. V. Ramanathan et al. (
1989
)
formalized the forcing components as:
Longwave Forcing = LW
all
- LW
clear
(5.5)
Shortwave Forcing = SW
all
- SW
clear
(5.6)
where LW
all
and SW
all
are the net longwave and net solar fluxes under “all sky”
conditions (combining data for all conditions, whether clear or cloudy conditions),
and LW
clear
and SW
clear
represent the fluxes for clear-sky conditions. Cloud forcing
