ALBERT

Beschreibung: ABSTRACT In this observational research, the seasonally stratified (October to December) Indian Ocean Dipole mode (IOD) behaviour in the tropical Indian Ocean since 1870 is investigated. Three significant climate shifts manifested themselves in the Indian Ocean during the years 1918, 1961 and 1997. Each shift is preceded by a 3-year sequence of IOD events that are unique in the entire time series. The order is such that a relatively moderate negative sea surface temperature (SST) anomaly gradient intensifies to an extreme negative IOD event which then reverses in the shift year to an extreme positive event. The last two extreme IOD events reach record-breaking magnitudes during each shift implying intensification of the shift process with time. During the year before the shift, the Mascarene High (MH) is anomalously displaced poleward and westward, while it intensifies as it anomalously moves equatorward during the shift year. Therefore the maximum contrast of south Indian Ocean pressure pattern and hence the intensity of the MH, from one year to the other within an epoch, is achieved during the shift years. The intensity of this process has been escalating during each of the three successive shifts. Despite involving to a greater extent the IOD dynamics, these IOD shifts may primarily be an expression of the south Indian Ocean basinwide dynamics rather than a direct response to internal tropical influences.

Beschreibung: ABSTRACT Monthly total precipitation and mean temperature climate surfaces, gridded to 30-arcseconds (≈1 km at the equator) and available for all global land areas, are presented. These datasets are generated with a Delta downscaling method, using the 30-arcsecond WorldClim climatologies to scale monthly anomaly grids. For monthly mean temperature, the anomalies are constructed from both the Climate Research Unit (CRU) and Willmott & Matsuura (W&M) 0.5 degree time-series datasets, whereas for monthly precipitation Global Precipitation Climatology Centre (GPCC) data are also used. The 0.5 degree anomalies are then interpolated to the 30-arcsecond resolution. Use of piecewise cubic Hermite interpolating polynomials (PCHIP) to interpolate the anomaly grids results in more physically representative Delta downscaled surfaces, compared to bilinear and cubic spline interpolation. The Delta downscaled products are compared to Global Historical Climatology Network (GHCN) station records for six test regions distributed globally. In this analysis, the Delta grids produced using the W&M time-series dataset perform better than grids produced using GPCC or CRU. Using Oregon, USA as a test region, the Delta downscaled datasets are compared to the Parameter-elevation Regressions on Independent Slopes Model (PRISM) datasets. For monthly precipitation, PRISM performs better than each of the three Delta downscaled datasets, but for mean temperature both Delta downscaled datasets outperform PRISM. Through computing the Pearson product–moment correlation coefficient between GHCN station delineated errors in the WorldClim climatologies and the Delta downscaled W&M data, it is shown that performance of the Delta grids corresponds strongly to performance of the reference climatologies. Therefore, future improvement of the 30-arcsecond Delta grids described in this article is strongly tied to advances in the high-resolution climatological data for all global land surfaces. The Delta downscaled datasets discussed herein are open-source and freely distributed at http://www.globalclimatedata.org .

Beschreibung: The generation of gaseous singlet oxygen by gas-liquid reaction of chlorine with alkaline solution of hydrogen peroxide in spray form was studied experimentally on the originally designed device with a fast separation of reacted liquid from gas. The singlet oxygen yield, residual chlorine, and water vapor content in gas were measured under different experimental conditions of the centrifugal spray singlet oxygen generator (CSSOG) using nitrogen as a dilution gas. A characteristic feature of the CSSOG is a high utilization of the chemicals and production of singlet oxygen at a very high total pressure even near the atmospheric pressure. This generator developed originally for driving a chemical oxygen-iodine laser (COIL) could be employed also as an efficient singlet oxygen source in material science, chemical synthesis, and others. A centrifugal spray generator of singlet oxygen was optimized for operation with nitrogen buffer gas and high total pressure. This generator is able to successfully operate at much higher pressure compared to other types. Due to the very high hydrogen peroxide utilization the consumption of input liquid chemicals is substantially reduced.

Beschreibung: Ionic liquids (ILs) are recyclable acid catalysts for transesterification reactions. In the present study, different acidic ILs were examined in this reaction, with special focus on their recyclability. Furthermore, the IL-catalyzed transesterification reaction was realized in continuous operation. A miniplant reactor with technically representative design and operating characteristics was used for this study. The applied rig has a volume of 5 L and an external thermosyphon reboiler. The miniplant reactor can be operated in batch and in continuous mode. ILs functionalized with a sulfonic acid group were found to be the most suitable IL catalysts for the transesterification reactions under investigation. Using these ILs, reaction rates as high as for H 2 SO 4 could be realized. Moreover, the IL catalyst was demonstrated to be active for at least 1000 h of operation time. Ionic liquids are suitable catalysts for acid-catalyzed transesterifications. Acidic ionic liquids were used as recyclable and durable catalysts for this reaction. The performances of the benchmark catalysts were obtained for at least 1000 h of operation in a miniplant reactor, which is representative of industrial processes.

Beschreibung: ABSTRACT This study demonstrates the capability of the Weather Research and Forecasting (WRF) model with four-dimensional data assimilation (WRF-FDDA) to produce a high-resolution climatography of seasonal precipitation over Israel and the surrounding areas. The system was used to dynamically downscale global Climate Forecast System (CFS) reanalysis with continuous assimilation of conventional and unconventional observations. Precipitation seasons (December-January-February) in 7 years, including two extreme dry and wet seasons observed in the past decades, were generated at 2-km spatial resolution. Verification against rain-gauge observations shows that the WRF-FDDA system effectively reproduces the spatial and inter-annual variability, as well as the timing, intensity, and length of wet and dry spells. The best agreement between model and observations was obtained at areas dominated by complex terrain, illustrating the benefit of the high-resolution lower boundary forcing in the dynamical downscaling process. In contrast, some biases were observed over coastal-flat terrain. The model was able to reproduce some of the extreme events, but exhibited limitations in the case of rare events. This specific discrepancy between the model and observations suggests that further fine tuning and different model configurations may be needed to correctly simulate extreme events. The use of an objective weather-regimes verification procedure reveals the skill of the climatography for different types of extra-tropical cyclones: while biases are larger at coastal-flat areas under shallow-cyclonic conditions, deep-cyclonic conditions lead to more significant biases in complex terrain regions. The weather-regimes dependent information may be used for further calibration of the downscaled precipitation.

Beschreibung: ABSTRACT The source region of Yangtze River in China is a part of Tibet Plateau where the hydrological processes are sensitive to climatic change. The impacts of precipitation, air temperature and evapotranspiration on annual runoff in the source region of Yangtze River during 1957–2009 are investigated in the time-period domain using wavelet analysis method and multiple regression method. Annual evapotranspiration is calculated with data of precipitation and air temperature based on Takahashi's empirical equation. This approximation of actual evapotranspiration successfully matches the mean annual water balance. Significant periods of runoff, 7–8 year, 20–21 year and 42–43 year, are revealed by using Morlet wavelet. Different significant periods are found for annual precipitation, air temperature and evapotranspiration, whereas the 7–8 year and 42–43 year periods are the same of the runoff. It is indicated by wavelet correlation coefficients that the correlations between runoff and these climatic components depends on periods. Change in the summation of runoff wavelet coefficients at different period can approximately represents the change pattern of real runoff and is correlated with the wavelet coefficients of the climatic components. The correlation can be expressed with a linear multiple regression equation which indicates that the change in annual runoff is contributed by change in annual precipitation rather than change in air temperature. This relationship between runoff and climatic components are different from that in the source region of Yellow River, in China.

Beschreibung: A mathematical model based on 34 days continuous operation of an industrial isomerization unit was developed. The unit involves a radial-flow reactor with a catalyst capable of converting xylenes and ethylbenzene to mixed xylenes. The catalyst contains EU-1 zeolite, platinum, and alumina as binder. Two reactions are considered, i.e., ethylbenzene isomerization and xylene isomerization. The rates are based on the Hougen-Watson model according to the literature. An optimization procedure based on the trust-region-reflective algorithm was carried out in order to obtain new kinetic constants that minimize the difference between the actual and the calculated values. The standard error of the parameters estimated was calculated through the deleted-one Jackknife method. A simplified mathematical model for simulating the reactor operation of an industrial isomerization unit was developed. A relatively new type of catalyst allowed milder conditions to reduce side reactions. The kinetic constants were obtained through an optimization procedure. The model may be applied to simulate larger systems due to its simplicity.

Beschreibung: An industrial-scale reactor for ethylene production was modeled using the oxidative dehydrogenation of ethane (ODHE) in a multi-tubular reactor system, examining a variety of parameters affecting reactor performance. The model showed that a double-bed multi-tubular reactor with intermediate air injection scheme was superior to a single-bed design, due to the increased ethylene selectivity while operating under lower oxygen partial pressures. The optimized reactor length for 100 % oxygen conversion was theoretically determined for both reactor designs. The use of a distributed oxygen feed with a limited number of injection points indicated a significant improvement on the reactor performance in terms of ethane conversion and ethylene selectivity. This concept also overcame the reactor runaway temperature problem and enabled operations over a wider range of conditions to obtain enhanced ethylene production. High demands for ethylene call for more efficient reactor designs. This model for the oxidative dehydrogenation of ethane for a Ni-Nb-O mixed-oxide catalyst showed that a double-bed multi-tubular reactor with air injection is superior to a single-bed design, due to an increased ethylene selectivity while operating under lower oxygen partial pressures.