Objectives
Within the World Climate Research Program (WCRP) and its Global Energy and
Water Cycle Experiment (GEWEX), the GEWEX Radiation Panel was organized to
review theoretical and experimental knowledge of radiative processes in and
for the study of the climate system. In climate research, radiative processes
play two key roles. First, these processes are central to the climate's
energy cycle: climate is determined by the imbalances of solar radiative
heating and longwave radiative cooling. The circulation of the atmosphere
and ocean, the environment on land, and the biosphere are all driven by
local radiative imbalances. Changes in climate can be caused by alterations
of the radiation budget at the top of the atmosphere or at the surface, such
as those induced by changing amounts of greenhouse gases or aerosols in the
atmosphere or by changing land surface properties. The sensitivity of the
climate response to a change in radiative forcing is determined by many
feedback processes that alter the radiation budget, especially those
involving clouds and water vapor. Second, the main source of global
information about the climate system comes from the analysis of satellite
remote sensing data which requires detailed models of the interaction of
radiation with the atmosphere and the ocean-land-ice surfaces, including the
effects of vegetation, as a function of wavelength, polarization state and
observing geometry.
THUS, radiation is a central process of the climate system to
be understood, and a critical tool to obtain that understanding.
One of the most peculiar features of Earth's climate, which sets it apart
from the other planets in our solar system, is the presence on the surface
of large amounts of water in liquid and solid form. Together with water
vapor in the atmosphere, these reservoirs of water are continually exchanging
mass. Water evaporates from the ocean and land surfaces, is transported by the
atmosphere, forms clouds and returns to the surface as precipitation. Rainfall
on land can return to the sea via rivers or be stored in lakes and aquifers.
Snowfall on land can melt into rivers or build up into ice sheets, which can
melt into rivers later. The ocean's surface can freeze and sea ice can melt.
Since water in all its forms affects radiative exchanges and transformations
of water from one phase to another can absorb or emit heat energy, the action
of all these "water processes" profoundly changes the Earth's climate. In
fact, the cycle of water is inextricably linked with the cycle of energy by
clouds, water vapor and precipitation, so it makes sense to study these water
processes together with radiation processes.
THUS, THE GRP FOCUSES ON TRYING TO ANSWER THESE QUESTIONS:
How can we better measure and characterize the state and the variations of
the climate using satellite observations?
What are the changes in radiative forcing that cause climate change?
How do the interactions of radiation with changes of the internal state of
the climate (a.k.a. radiative feedbacks) affect the climate's
sensitivity?
How do the internal water exchange and transport processes in the climate
(a.k.a. water feedbacks) affect the climate's sensitivity?
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