Bruno Dürr

Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe

Europes temperature increases considerably faster than the northern hemisphere average. Detailed month- by-month 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.

Verification of CM-SAF and MeteoSwiss satellite based retrievals of surface shortwave irradiance over the Alpine region

Verification results from different satellite-based surface shortwave irradiance retrievals and sensitivity runs for key input parameters are presented for the Alpine region. Overall the uncertainty of the hourly retrievals at the Federal Office of Meteorology and Climatology (MeteoSwiss) validated with high-quality surface measurements is comparable with results from the standard Heliosat-3 model, but clearly improved for situations with snow-cover. The sensitivity study reveals that it is recommended to precisely georeference the High Resolution Visible (HRV) and the Spinning Enhanced Visible and Infrared Imager (SEVIRI) channels of the Meteosat Second Generation (MSG) satellites to obtain accurate surface shortwave irradiance estimates. They also confirm the benefit of terrain corrections for sites located in deep Alpine valleys. Monthly mean shortwave irradiance retrievals provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM-SAF) are verified with the MeteoSwiss products. For the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR)-based product about 60% of all satellite 15 km × 15 km grid cells match the MeteoSwiss product, if locally dependent 90% confidence intervals are applied. This percentage decreases to 52%, if the standard CM-SAF 90% confidence interval of 20 Wm−2 is used. Taking the local spatial variability of the shortwave irradiance field into account therefore allows obtaining more realistic verification results over heterogeneous terrain such as the Alpine region.

Comparison of modeled and observed cloud-free longwave downward radiation over the Alps

Differences between computed and observed cloud-free longwave downward radiation (LDR) were examined both for Payerne and six further radiation sites of the Alpine Surface Radiation Budget (ASRB) network. LDR was computed by the complex radiative transfer model (RTM) MODTRAN v4.0 and by a simplified RTM used in the numerical weather prediction model alpine model (aLMo). MODTRAN computed LDR in Payerne using sounding data and ASRB observed LDR show an average difference of 1.5 W m -2 (±3.5 W m -2 ), and -3.2 W m -2 ±3.6 W m -2 ) for night- and daytime respectively from 1996 to 2001. Nighttime LDR is underestimated by the aLMo RTM in the order of -20 W m-2 compared to ASRB measurements both at Payerne and at six further ASRB sites. However LDR bias is strongly reduced in Payerne during daytime. For comparison MODTRAN computed LDR using aLMo forecasted atmospheric profiles shows mean differences in the order of -3 W m -2 both for night- and daytime. Hence the comprehensive radiation scheme used in aLMo is mainly responsible for the substantial underestimation of cloud-free LDR.