Global Change Abstracts The Swiss Contribution - SCNAT

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58 ability and various significant trends of the time series of seasonal cluster frequency. Tentative estimations of central European temperature changes based solely on seasonal cluster frequencies can explain between 33.9% (summer) and 59.0% (winter) of temperature variance on the seasonal time scale. However, the signs of long- term changes in temperature are correctly reproduced even on multidecadal - centennial time scales. Moreover, linear warming trends are reproduced, implying from one- third up to one- half of the observed temperature increase between 1851/ 52 and 2003 (except for summer, but with significant trends for spring and autumn), indicating that changes in daily circulation patterns contribute to the observed overall long- term warming in the central European region. Journal of Climate, 2007, V20, N16, AUG 17, pp 4065-4095. 08.1-57 Remote sensing of aerosol optical depth over central Europe from MSG- SEVIRI data and accuracy assessment with ground-based AERO- NET measurements Popp C, Hauser A, Foppa N, Wunderle S Switzerland, Germany Remote Sensing , Meteorology & Atmospheric Sciences In this study, the remote sensing of aerosol optical depth (tau(a)) from the geostationary Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) is demonstrated. The proposed method is based on the analysis of a time series of SEVIRI’s 0.6 µm channel images. Top-of-atmosphere reflectance is precorrected for the effect of atmospheric gases and a background aerosol amount. Subsequently, surface reflectance for each pixel is estimated by determining its lowest precorrected reflectance within the observed time period for each satellite observation time of the day. The resulting diurnal surface reflectance curve in combination with the radiative transfer code SMAC are finally used to derive ta. This approach is applied to SEVIRI subscenes of central Europe (40.8 - 51.3 degrees N, 0.3 degrees W - 19.9 degrees E) from August 2004, daily acquired between 0612 and 1712 UTC in intervals of 15 min. SEVIRI tau(a) are related to Aerosol Robotic Network (AERONET) Sun photometer measurements from nine sites. About 3200 instantaneous SEVIRI and Sun photometer tau(a) are compared. An overall correlation of 0.9 and a root mean square error of 0.08 are obtained. Further, the spatial distribution of SEVIRI tau(a) maps for August 2004 represent expectable features like higher concen- Global Change Abstracts – The Swiss Contribution | Atmosphere trations in industrialized regions or lower loading in higher altitudes. It is concluded that the described method is able to provide an estimate of tau(a) from MSG-SEVIRI data. Such aerosol maps of high temporal frequency could be of interest to atmospheric related sciences, e. g., to track aerosol particle transport. Journal of Geophysical Research Atmospheres, 2007, V112, ND24, NOV 9 ARTN: D24S11. 08.1-58 Hydrological aspects of the Mesoscale Alpine Programme: Findings from field experiments and simulations Ranzi R, Zappa M, Bacchi B Italy, Switzerland Modelling , Hydrology , Meteorology & Atmospheric Sciences The Mesoscale Alpine Programme (MAP) was a unique initiative to improve the understanding of processes involved in orographically influenced precipitation events and in the related emergence and mitigation of floods in the Alps. This study presents a summary of the results from investigations of hydrological relevance in areas to the south (Lago Maggiore watershed) and north (Ammer watershed) of the Alps. A special focus is given to the 1999 Special Observing Period (SOP) experiment. MAP has been an important dialogue platform between the hydrological and meteorological communities. A common goal has been the verification and the assessment of errors and sources of uncertainty of new coupled techniques for flood forecasting in mountainous environments. The ensemble multi-model error in the hydrometeorological forecast, two days in advance, was 30% of the observed peaks and 15% of the observed runoff volumes, on average. To provide some insight on the relative importance and priority of observation strategies of hydrological factors such as soil moisture and reservoir volume in contributing to the flood intensity, the MAP project ‘Hydrology’ focused also on the role and magnitude of water storage in reservoirs. The presented analyses indicate that for the investigated basins and flood events, the storage reservoirs may retain, on average, up to 10% of the event runoff volume and are key elements contributing to the mitigation of peak runoff. The observed variability of soil moisture is large and therefore it has been confirmed that severe difficulties remain in instrumental monitoring of soil moisture in mountainous environments. The sensitivity of floods to soil moisture in the physiogeographic context analysed here seems, however, to be minor, due to the shallow soil layer covering
Global Change Abstracts – The Swiss Contribution | Atmosphere 59 the underlying rocks and the relatively high permeability of soils which reduce the ‘hydrological memory’ of the soil cover in the mountain basins investigated. Quarterly Journal of the Royal Meteorological Society, 2007, V133, N625, B, APR, pp 867-880. 08.1-59 Ice nucleation of ammonia gas exposed montmorillonite mineral dust particles Salam A, Lohmann U, Lesins G Canada, Bangladesh, Switzerland Meteorology & Atmospheric Sciences The ice nucleation characteristics of montmorillonite mineral dust aerosols with and without exposure to ammonia gas were measured at different atmospheric temperatures and relative humidities with a continuous flow diffusion chamber. The montmorillonite particles were exposed to pure (100%) and diluted ammonia gas (25 ppm) at room temperature in a stainless steel chamber. There was no significant change in the mineral dust particle size distribution due to the ammonia gas exposure. 100% pure ammonia gas exposure enhanced the ice nucleating fraction of montmorillonite mineral dust particles 3 to 8 times at 90% relative humidity with respect to water (RHw) and 5 to 8 times at 100% RHw for 120 min exposure time compared to unexposed montmorillonite within our experimental conditions. The percentages of active ice nuclei were 2 to 8 times higher at 90% RHw and 2 to 7 times higher at 100% RHw in 25 ppm ammonia exposed montmorillonite compared to unexposed montmorillonite. All montmorillonite particles are more efficient as ice nuclei with increasing relative humidities and decreasing temperatures. The activation temperature of montmorillonite exposed to 100% pure ammonia was 15 degrees C higher than for unexposed montmorillonite particles at 90% RHw. In the 25 ppm ammonia exposed montmorillonite experiments, the activation temperature was 10 degrees C warmer than unexposed montmorillonite at 90% RHw. Degassing does not reverse the ice nucleating ability of ammonia exposed montmorillonite mineral dust particles suggesting that the ammonia is chemically bound to the montmorillonite particle. This is the first experimental evidence that ammonia gas exposed montmorillonite mineral dust particles can enhance its activation as ice nuclei and that the activation can occur at temperatures warmer than -degrees C where natural atmospheric ice nuclei are very scarce. Atmospheric Chemistry and Physics, 2007, V7, N14, pp 3923-3931. 08.1-60 A trajectory-based estimate of the tropospheric ozone column using the residual method Schoeberl M R, Ziemke J R, Bojkov B, Livesey N J, Duncan B, Strahan S, Froidevaux L, Kulawik S, Bhartia P K, Chandra S, Levelt P F, Witte J C, Thompson A M, Cuevas E, Redondas A, Tarasick D W, Davies J, Bodeker G E, Hansen G, Johnson B J, Oltmans S J, Voemel H, Allaart M, Kelder H, Newchurch M, Godin Beekmann S, Ancellet G, Claude H, Andersen S B, Kyroe E, Parrondos M C, Yela M, Zablocki G, Moore D, Dier H, von der Gathen P, Viatte P, Stuebi R, Calpini B, Skrivankova P, Dorokhov V, de Backer H, Schmidlin F J, Coetzee G, Fujiwara M, Thouret V, Posny F, Morris G, Merrill J, Leong C P, König Langlo G, Joseph E USA, Netherlands, Spain, Canada, New Zealand, Norway, France, Denmark, Finland, Poland, England, Germany, Switzerland, Czech Republic, Russia, Belgium, South Africa, Japan, Malaysia Meteorology & Atmospheric Sciences , Modelling We estimate the tropospheric column ozone using a forward trajectory model to increase the horizontal resolution of the Aura Microwave Limb Sounder (MLS) derived stratospheric column ozone. Subtracting the MLS stratospheric column from Ozone Monitoring Instrument total column measurements gives the trajectory enhanced tropospheric ozone residual (TTOR). Because of different tropopause definitions, we validate the basic residual technique by computing the 200-hPato- surface column and comparing it to the same product from ozonesondes and Tropospheric Emission Spectrometer measurements. Comparisons show good agreement in the tropics and reasonable agreement at middle latitudes, but there is a persistent low bias in the TTOR that may be due to a slight high bias in MLS stratospheric column. With the improved stratospheric column resolution, we note a strong correlation of extratropical tropospheric ozone column anomalies with probable troposphere-stratosphere exchange events or folds. The folds can be identified by their colocation with strong horizontal tropopause gradients. TTOR anomalies due to folds may be mistaken for pollution events since folds often occur in the Atlantic and Pacific pollution corridors. We also compare the 200-hPa-to-surface column with Global Modeling Initiative chemical model estimates of the same quantity. While the tropical comparisons are good, we note that chemical model variations in 200hPa-to-surface column at middle latitudes are much smaller than seen in the TTOR. Journal of Geophysical Research Atmospheres, 2007, V112, ND24, DEC 19 ARTN: D24S49.
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