Das Projekt "Towards an improved understanding of the Global Energy Balance: absorption of solar radiation" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Atmosphäre und Klima durchgeführt. The genesis and evolution of Earth's climate is largely regulated by the balance between inflow of solar energy (received from the Sun) and outflow of thermal energy (emitted by the Earth). Human interference with climate occurs first of all through a perturbation of this energy balance, as a result of anthropogenic modification of greenhouse gas and aerosol concentration. Changes in the global energy balance affect not only global warming, but also other aspects of climate change, such as the intensity of the water cycle, snow cover and glacier retreat, plant productivity and terrestrial carbon uptake. Despite the central importance of the global energy balance for the climate system and climate change, substantial uncertainties still exist in the quantification of its different components and their decadal variations. The long-term research goal of the investigators aims at an improved understanding of the mean state and the spatio-temporal variations of the global energy balance. While our knowledge on the energy exchange between Sun, Earth and space has recently been improved through new satellite programs, the distribution of radiative energy within the climate system, which cannot directly be measured by satellites, is still afflicted with large uncertainties. The present project aims at reducing the uncertainties in the absorption of solar radiation within the climate system, a crucial component of the global energy balance, through an optimal usage of the information contained in worldwide surface and satellite measurements. These investigations should allow for the best possible estimates on the disposition of solar radiation in the climate system. Such estimates are urgently needed for a better understanding and representation of the global energy balance in the framework of the 5th IPCC assessment report, and for the assessment and improvement of climate models.
Das Projekt "A Century of Atmospheric Transmission over Davos" wird vom Umweltbundesamt gefördert und von Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD,WRC) durchgeführt. A Century of Atmospheric Transmission over Davos Measurements of the solar radiation at the Physikalisch-Meteorologisches Observatorium Davos (PMOD) started in 1909 and are continued to present time. Radiometry and its application in meteorology have been a focal point of research activities at PMOD and have lead to the establishment of the World Radiation Center (WRC) in 1971 by the World Meteorological Organization. This long-term measurement series provides not only a detailed climatology of the insolation at Davos, including secular trends, but also contains information about the atmospheric transmission and its variability over the past century. The current scientific discussion about 'Global Dimming' starting in the late 50's and subsequent 'Brightening' after the late 80's, refers to the observed world-wide changes of insolation since the second half of the 20th century and their impact on global warming. The proposed causes for these variations, changing atmospheric transmission and cloudiness, are not separable from global (directed + diffuse) radiation alone. Additional observations of the direct solar radiation are required that can be evaluated in terms of apparent atmospheric transmission which in turn is dominated by aerosol extinction and water vapor absorption. Aerosol extinction of sun light represents a negative or cooling effect that is compensating to some extent the climate warming by greenhouse gases. This SNF project will compile the historic and recent solar measurement at PMOD, supplemented by observation available from Meteo Swiss (MCH), into a homogeneous time series spanning 100 years. Apparent atmospheric transmission will be inferred from these data by a proven method and analyzed for secular and decadal trends. Based on the high quality of measurements at Davos and modern radiative transfer calculations the project will model the total atmospheric transmission in terms of aerosol extinction and water vapor absorption. This project will retrieve time series of atmospheric parameters through reanalysis of existing observational data that are valuable in the assessment of climatic change in Switzerland.
