Earth's Annual Global Mean Energy Budget
Kiehl, J. T. and Trenberth, K. E., 1997
Bull. Amer. Meteor. Soc., 78, 197-208.
The purpose of this paper is to put forward a new estimate, in the
context of previous assessments, of the annual global mean energy
budget. A description is provided of the source of each component to
this budget. The top-of-atmosphere shortwave and longwave flux of
energy is constrained by satellite observations. Partitioning of the
radiative energy throughout the atmosphere is achieved through the use
of detailed radiation models for both the longwave and shortwave
spectral regions. Spectral features of shortwave and longwave fluxes
at both the top and surface of Earth's system are presented. The
longwave radiative forcing of the climate system for both clear (125
W·m-2) and cloudy (155 W·m-2) conditions are
discussed. We find that for the clear sky case the contribution due to
water vapor to the total longwave radiative forcing is 75
W·m-2, while for carbon dioxide it is 32
W·m-2. Clouds alter these values, and the effects of clouds
on both the longwave and shortwave budget are addressed. In
particular, the shielding effect by clouds on absorption and emission
by water vapor is as large as the direct cloud forcing. Because the
net surface heat budget must balance, the radiative fluxes constrain
the sum of the sensible and latent heat fluxes which can also be
estimated independently.
Figures:
- Figure 1. Longwave Emission
- PostScript (40 Kb),
GIF (5 Kb)
- Figure 2. Greenhouse Effect
- PostScript (28 Kb),
GIF (5 Kb)
- Figure 3. Longwave Could Forcing
- PostScript (27 Kb),
GIF (5 Kb)
- Figure 4. Downward Shortwave
- PostScript (57 Kb),
GIF (5 Kb)
- Figure 5. Net Shortwave
- PostScript (74 Kb),
GIF (5 Kb)
- Figure 6. Shortwave Cloud Forcing
- PostScript (50 Kb),
GIF (5 Kb)
- Figure 7. Earth's energy budget (see above)
- PostScript (76 Kb),
GIF (13 Kb)
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Hongjun Zhang:
zhangho@ucar.edu