Global Change Abstracts The Swiss Contribution - SCNAT

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42 08.1-17 Atmospheric blocking: space-time links to the NAO and PNA Croci Maspoli M, Schwierz C, Davies H C Switzerland Meteorology & Atmospheric Sciences , Oceanography In the Northern hemisphere, regions characterized by an enhanced frequency of atmospheric blocking overlap significantly with those associated with the major extra-tropical patterns of largescale climate variability-namely the North Atlantic Oscillation (NAO) and the Pacific North American (PNA) pattern. There is likewise an overlap in the temporal band-width of blocks and these-climate patterns. Here the nature of the linkage between blocks and the climate patterns is explored by using the ERA-40 re-analysis data set to examine (1) their temporal and spatial correlation and (2) the interrelationship between blocks and the NAO/ PNA. It is shown that a strong anti-correlation exists between blocking occurrence and the phase of the NAO (PNA) in the North Atlantic (western North Pacific), and that there are distinctive interbasin differences with a clear geographical (over North Atlantic) and quantitative (over North Pacific) separation of typical blocking genesis/lysis regions during the opposing phases of the climate patterns. An Empirical Orthogonal Function (EOF) analysis points to a significant influence of blocking upon the NAO pattern (identifiable as the leading EOF in the Euro- Atlantic), and a temporal analysis indicates that long-lasting blocks are associated with the development of negative NAO/ PNA index values throughout their life-time. In addition an indication of a cause-and effect relationship is set-out for the North Atlantic linkage. Climate Dynamics, 2007, V29, N7-8, DEC, pp 713-725. 08.1-18 FinROSE - middle atmospheric chemistry transport model Damski J, Thlix L, Backman L, Taalas P, Kulmala M Finland, Switzerland Meteorology & Atmospheric Sciences , Modelling In this paper we describe the development and performance of a three- dimensional global middle atmospheric chemistry transport model Fin ROSE. The FinROSE chemistry transport model includes a numerical scheme for stratospheric chemistry with parameterizations for heterogeneous processing on polar stratospheric clouds (PSC) and on liquid binary aerosols together with a parameterisation of large nitric acid trihydrate Global Change Abstracts – The Swiss Contribution | Atmosphere particles (i.e. NAT-rocks) and PSC sedimentation. The total number of trace species in the model is 34 and the total number of gas-phase reactions, photodissociation processes and heterogeneous reactions is about 150. The model is forced by external wind and temperature fields. The simulations are normally performed in a 5 degrees x 10 degrees (lat. x long.) grid from the surface up to around 0.1 hPa, with a vertical resolution of ca. 1.5 km in the stratosphere. Long-term simulations (40 to 50 years) have been done using winds and temperatures from ECMWF ERA40 analyses. The performance of the model in describing the stratospheric composition and chemistry is shown and evaluated in this paper. In general, the FinROSE results show a good comparison with measured total ozone. Also the timing, the depth and the deepening of the Antarctic ozone hole, and the responsible processes are captured well in the model simulations. Boreal Environment Research, 2007, V12, N5, OCT 24, pp 535-550. 08.1-19 Doubled length of western European summer heat waves since 1880 Della Marta P M, Haylock M R, Luterbacher J, Wanner H Switzerland, Australia, England Meteorology & Atmospheric Sciences (1) We analyzed a new data set of 54 high-quality homogenized daily maximum temperature series from western Europe (Austria, Belgium, Croatia, Czech Republic, Denmark, Finland, France, Germany, Ireland, Netherlands, Portugal, Spain, Sweden, Switzerland, United Kingdom) to define more accurately the change in extreme warm Daily Summer Maximum Temperature (DSMT). Results from the daily temperature homogeneity analysis suggest that many instrumental measurements in the late 19th and early 20th centuries were warm- biased. Correcting for these biases, over the period 1880 to 2005 the length of summer heat waves over western Europe has doubled and the frequency of hot days has almost tripled. The DSMT Probability Density Function (PDF) shows significant changes in the mean (+ 1.6 +/- 0.4 degrees C) and variance (+ 6 +/- 2%). These conclusions help further the evidence that western Europe’s climate has become more extreme than previously thought and that the hypothesized increase in variance of future summer temperature has indeed been a reality over the last 126 years. Journal of Geophysical Research Atmospheres, 2007, V112, ND15, AUG 3 ARTN: D15103.
Global Change Abstracts – The Swiss Contribution | Atmosphere 43 08.1-20 Summer heat waves over western Europe 1880-2003, their relationship to large-scale forcings and predictability Della Marta P M, Luterbacher J, von Weissenfluh H, Xoplaki E, Brunet M, Wanner H Switzerland, Australia, Spain Meteorology & Atmospheric Sciences We investigate the large-scale forcing and teleconnections between atmospheric circulation (sea level pressure, SLP), sea surface temperatures (SSTs), precipitation and heat wave events over western Europe using a new dataset of 54 daily maximum temperature time series. Forty four of these time series have been homogenised at the daily timescale to ensure that the presence of inhomogeneities has been minimised. The daily data have been used to create a seasonal index of the number of heat waves. Using canonical correlation analysis (CCA), heat waves over western Europe are shown to be related to anomalous high pressure over Scandinavia and central western Europe. Other forcing factors such as Atlantic SSTs and European precipitation, the later as a proxy for soil moisture, a known factor in strengthening land-atmosphere feedback processes, are also important. The strength of the relationship between summer SLP anomalies and heat waves is improved (from 35%) to account for around 46% of its variability when summer Atlantic and Mediterranean SSTs and summer European precipitation anomalies are included as predictors. This indicates that these predictors are not completely collinear rather that they each have some contribution to accounting for summer heat wave variability. However, the simplicity and scale of the statistical analysis masks this complex interaction between variables. There is some useful predictive skill of summer heat waves using multiple lagged predictors. A CCA using preceding winter North Atlantic SSTs and preceding January to May Mediterranean total precipitation results in significant hindcast (1972-2003) Spearman rank correlation skill scores up to 0.55 with an average skill score over the domain equal to 0.28 +/- 0.28. In agreement with previous studies focused on mean summer temperature, there appears to be some predictability of heat wave events on the decadal scale from the Atlantic Multidecadal Oscillation (AMO), although the long-term global mean temperature is also well related to western European heat waves. Combining these results with the observed positive trends in summer continental European SLP, North Atlantic SSTs and indications of a decline in European summer precipitation then possibly these long-term changes are also related to increased heat wave occurrence and it is important that the physical processes controlling these changes be more fully understood. Climate Dynamics, 2007, V29, N2-3, AUG, pp 251-275. 08.1-21 Effects of convective ice lofting on H 2O and HDO in the tropical tropopause layer Dessler A E, Hanisco T F, Füglistaler S USA, Switzerland, England Meteorology & Atmospheric Sciences , Modelling We have added convective ice lofting to a Lagrangian trajectory model of tropical tropopause layer (TTL) water vapor (H 2O) and its stable isotopologue, HDO. The Lagrangian model has been previously shown to accurately simulate H 2O in the TTL and lower stratosphere. We show here that the model does a poor job reproducing the observed HDO depletion (delta D) in the TTL. When convective ice lofting to altitudes below the cold point (the point where air experiences its lowest H 2O saturation mixing ratio) is added to the model, there is little change in H 2O in the lower stratosphere, but a large change in delta D throughout the TTL that brings the model into better agreement with measurements. Thus convective ice lofting has the capacity to improve the model’s delta D simulation while not significantly degrading the agreement between simulated and measured H 2O. Convective ice lofting to altitudes above the cold point, on the other hand, has a large effect on lower stratospheric H 2O, suggesting that changes in convection reaching these altitudes could drive changes in lower stratospheric H 2O. This suggests a mechanism by which lower stratospheric H 2O trends may be at least partially decoupled from tropopause temperature trends. Such a disconnection was suggested by previous observations of simultaneously increasing stratospheric H 2O and a cooling tropical tropopause. Journal of Geophysical Research Atmospheres, 2007, V112, ND18, SEP 26 ARTN: D18309. 08.1-22 Some factors in the design of a regional prediction model: an examination based upon two MAP events Didone M, Lüthi D, Davies H C Switzerland Modelling , Meteorology & Atmospheric Sciences Consideration is given to the impact of both synoptic-scale flow features and different model configurations upon the performance of an Alpine-encompassing regional NWP model. The so-called regional LM forecast model is used to
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