Detalles de publicación
PP 07037
Shortwave forcing of the earth's climate: modern and historical variations in the sun's irradiance and the earth's reflectance
Big Bear Solar Observatory, New Jersey Institute of Technology, Big Bear City, 92314, USA.
Instituto de Astrofisica de Canarias, La Laguna, E38205, Spain.
Changes in the Earth's radiation budget are driven by changes in
the balance between the thermal emission from the top of the
atmosphere and the net sunlight absorbed. The shortwave radiation
entering the climate system depends on the Sun's irradiance and the Earth's reflectance. Often, studies replace the net sunlight by proxy measures of solar irradiance, which is an oversimplification used in efforts to probe the Sun's role in past climate change. With new helioseimic data and new measures of the
Earth's reflectance, we can usefully separate and constrain the relative roles of the net sunlight's two components, while probing the degree of their linkage. First, this is possible because helioseismic data provide the most precise measure ever of the solar cycle, which ultimately yields more profound physical limits on past irradiance variations. Since irradiance variations are
apparently minimal, changes in the Earth's climate that seem to be associated with changes in the level of solar activity -- the Maunder Minimum and the Little Ice age for example -- would then seem to be due to terrestrial responses to more subtle changes in the Sun's spectrum of radiative output. This leads naturally to a linkage with terrestrial reflectance, the second component of
the net sunlight, as the carrier of the terrestrial amplification of the Sun's varying output. Much progress has also been made in determining this difficult to measure, and not-so-well-known quantity. We review our understanding of these two closely linked, fundamental drivers of climate.
the balance between the thermal emission from the top of the
atmosphere and the net sunlight absorbed. The shortwave radiation
entering the climate system depends on the Sun's irradiance and the Earth's reflectance. Often, studies replace the net sunlight by proxy measures of solar irradiance, which is an oversimplification used in efforts to probe the Sun's role in past climate change. With new helioseimic data and new measures of the
Earth's reflectance, we can usefully separate and constrain the relative roles of the net sunlight's two components, while probing the degree of their linkage. First, this is possible because helioseismic data provide the most precise measure ever of the solar cycle, which ultimately yields more profound physical limits on past irradiance variations. Since irradiance variations are
apparently minimal, changes in the Earth's climate that seem to be associated with changes in the level of solar activity -- the Maunder Minimum and the Little Ice age for example -- would then seem to be due to terrestrial responses to more subtle changes in the Sun's spectrum of radiative output. This leads naturally to a linkage with terrestrial reflectance, the second component of
the net sunlight, as the carrier of the terrestrial amplification of the Sun's varying output. Much progress has also been made in determining this difficult to measure, and not-so-well-known quantity. We review our understanding of these two closely linked, fundamental drivers of climate.