[1] The rapid temperature increase of 1°C over mainland Europe since 1980 is considerably larger than the temperature rise expected from anthropogenic greenhouse gas increases. Here we present aerosol optical depth measurements from six specific locations and surface irradiance measurements from a large number of radiation sites in Northern Germany and Switzerland. The measurements show a decline in aerosol concentration of up to 60%, which have led to a statistically significant increase of solar irradiance under cloud-free skies since the 1980s. The measurements confirm solar brightening and show that the direct aerosol effect had an approximately five times larger impact on climate forcing than the indirect aerosol and other cloud effects. The overall aerosol and cloud induced surface climate forcing is $+1 W m À2 dec À1 and has most probably strongly contributed to the recent rapid warming in Europe. Citation: Ruckstuhl, C., et al.

Abstract. The Satellite Application Facility on Climate Monitoring (CM-SAF) aims at the provision of satellite-derived geophysical parameter data sets suitable for climate monitoring. CM-SAF provides climatologies for Essential Climate Variables (ECV), as required by the Global Climate Observing System implementation plan in support of the UNFCCC. Several cloud parameters, surface albedo, radiation fluxes at the top of the atmosphere and at the surface as well as atmospheric temperature and humidity products form a sound basis for climate monitoring of the atmosphere. The products are categorized in monitoring data sets obtained in near real time and data sets based on carefully intercalibrated radiances. The CM-SAF products are derived from several instruments on-board operational satellites in geostationary and polar orbit as the Meteosat and NOAA satellites, respectively. The existing data sets will be continued using data from the instruments on-board the new joint NOAA/EUMETSAT Meteorological Operational Polar satellite. The products have mostly been validated against several ground-based data sets both in situ and remotely sensed. The accomplished accuracy for products derived in near real time is sufficient to monitor variability on diurnal and seasonal scales. The demands on accuracy increase the longer the considered time scale is. Thus, interannual variability or trends can only be assessed if the sensor data are corrected for jumps created by instrument changes on successive satellites and more subtle effects like instrument and orbit drift and also changes to the spectral response function of an instrument. Thus, a central goal of the recently started Continuous Development and Operations Phase of the CM-SAF (2007–2012) is to further improve all CM-SAF data products to a quality level that allows for studies of interannual variability.

[1] Naked-eye observation of sky cloud cover has widely resisted automation. Automatic cloud cover detection systems suitable also for nighttime operation often demand large equipment investments and expensive data processing. An automatic partial cloud amount detection algorithm (APCADA) is presented, based only on accurate measurements of longwave downward radiation, temperature, and relative humidity at screen level height. APCADA provides cloud cover estimates every 10 min during daytime and nighttime and is applicable to radiation stations without knowledge of synoptic cloud observations. Naked-eye observations from seven radiation sites spanning from arctic to tropical climates have been compared to APCADA estimates. Results show that about 86% of all cases agree within ±1-octa cloud amount difference for sites with moderate climate, 82% for sites with arctic climate, and 78% for the site with tropical climate. For a maximum ±2-octa cloud amount difference, average site percentages range from 90% up to 95%.

[1] Europe's temperature increases considerably faster than the northern hemisphere average. Detailed month-bymonth analyses show temperature and humidity changes for individual months that are similar for all Europe, indicating large-scale weather patterns uniformly influencing temperature. However, superimposed to these changes a strong west-east gradient is observed for all months. The gradual temperature and humidity increases from west to east are not related to circulation but must be due to non-uniform water vapour feedback. Surface radiation measurements in central Europe manifest anthropogenic greenhouse forcing and strong water vapor feedback, enhancing the forcing and temperature rise by about a factor of three. Solar radiation decreases and changing cloud amounts show small net radiative effects. However, high correlation of increasing cloud-free longwave downward radiation with temperature (r = 0.99) and absolute humidity (r = 0.89), and high correlation between ERA-40 integrated water vapor and CRU surface temperature changes (r = 0.84), demonstrates greenhouse forcing with strong water vapor feedback. Citation: Philipona, R., B. Durr, A. Ohmura, and C. Ruckstuhl (2005), Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe,

[1] The Intergovernmental Panel of Climate Change (IPCC) confirmed concentrations of atmospheric greenhouse gases and radiative forcing to increase as a result of human activities. Nevertheless, changes in radiative forcing related to increasing greenhouse gas concentrations could not be experimentally detected at Earth's surface so far. Here we show that atmospheric longwave downward radiation significantly increased (+5.2(2.2) Wm À2 ) partly due to increased cloud amount (+1.0(2.8) Wm À2 ) over eight years of measurements at eight radiation stations distributed over the central Alps. Model calculations show the cloud-free longwave flux increase (+4.2(1.9) Wm À2 ) to be in due proportion with temperature (+0.82(0.41)°C) and absolute humidity (+0.21(0.10) g m À3 ) increases, but three times larger than expected from anthropogenic greenhouse gases. However, after subtracting for two thirds of temperature and humidity rises, the increase of cloud-free longwave downward radiation (+1.8(0.8) Wm À2 ) remains statistically significant and demonstrates radiative forcing due to an enhanced greenhouse effect.