Cut-off Lows in the South Africa region and their contribution to precipitation

The contribution of Cut-off Lows (CoLs) to precipitation and extreme rainfall frequency in South Africa has been quantified from 402 station records over the period 1979–2006. Firstly, 500 hPa CoL trajectories over Southern Africa and surrounding oceans were determined and their features thoroughly analyzed. In a second step, using daily precipitable water, outgoing long wave radiation data and station rainfall records, an area was defined where the occurrence of CoLs is associated with rainfall over South Africa. CoLs transiting in the 2.5°E–32.5°E/20°S–45°S are more likely to produce precipitation over the country. When 500 hPa CoLs are centered just off the west coast of the country (around 15°E/32.5°S) their impact is substantial in term of daily rainfall intensity and spatial coverage. CoL rainy days have been studied and it is shown that they significantly contribute to precipitation in South Africa, more strongly along the south and east coasts as well as inland, over the transition zone between the summer and winter rainfall domains where they contribute between 25 to more than 35 % of annual accumulation. At the country scale, CoL rainfall is more intense and widespread in spring than during other seasons. Over the analyzed period, a significant trend in annual CoLs’ frequency shows an increase of about 25 %. This increase is mainly realized in spring and in a lesser extent in summer. This trend is accompanied by a significant increase in the frequency of CoL rainy days specifically along the south coast and over the East of the country during the spring–summer period. In parallel, it is shown that from late spring until summer CoLs’ frequency varies significantly accordingly with large scale circulation modes of the Southern Hemisphere such as the Pacific South American pattern (PSA). This positive trend in CoLs’ frequency may be related with the positive trend in the PSA during the spring–summer period over the three last decades.     

Can well-being between Sub-Saharan Africa (SSA) and Organization for Economic Cooperation and Development (OECD) member countries converge?

This study investigates the convergence of well-being between Sub Saharan Africa (SSA) and Organization for Economic Cooperation and Development (OECD) member countries during the period 1980–2014. The gap in living standard was examined from a steady state represented by the average income of OECD countries. Applying the unit root estimation technique to test for convergence with and without structural breaks, the result shows that; among a total of 43 countries studied, about 14 % are converging towards the average of OECD average. When the shock caused by the economic crisis of 2008 was factored into the analysis, the gains of about five countries out of the six converging disappeared. These results are disturbing owing to the fact that countries in the Asian region that started almost at the same level with SSA have converged to form a convergence club. Therefore, a lot more effort is needed from the government and stake holders in most countries in SSA to improve on the determinants of growth like good health care, quality institutions, better education and commitments to pursue developmental programmes which will boost the income of an average African to acquire better life.     

Validation of a field filtration technique for characterization of suspended particulate matter from freshwater. Part II. Minor, trace and ultra trace elements

A field filtration method for the concentration and separation of suspended particulate matter (SPM) from freshwater systems and the subsequent determination of minor, trace and ultra trace elements (As, Ba, Be, Cd, Co, Cr, Cs, Cu, Ga, Hf, Mo, Nb, Ni, Pb, Rb, Sb, Sc, Sn, Sr, Ta, Th, Tl, U, V, W, Zn and Zr) is validated with respect to detection limits, precision and bias. The validation comprises the whole procedure including filtration, sample digestion and instrumental analysis. The method includes two digestion procedures (microwave acid digestion and alkali fusion) in combination with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). Total concentrations of these 27 trace and minor elements have been determined in suspended particulate matter (SPM) from lake and river water with low levels of suspended solids (<2 mg L⁻¹ DW), and a wide range of element concentrations. The precision of the method including filtration, digestion and instrumental determination ranges between 8% and 18% RSD for most elements on a dry weight basis. Higher recovery after acid digestion is found for some elements, probably because of volatilization or retention losses in the fusion procedure. Other elements show higher recovery after fusion, which is explained by more efficient decomposition of refractory mineral phases relative to the non-total acid digestion. Non-detectable concentrations of some elements are reported due to small differences between blank filter levels and the amounts of elements present on the filters after sampling. The method limits of detection range between 0.7 ng and 2.65 μg, as estimated from the blank filter samples. These detection limits are 10–550 times higher compared to the corresponding instrumental limits of detection. The accuracy and bias of the overall analytical procedure was assessed from replicate analysis of certified reference materials. A critical evaluation of the instrumental capabilities of the ICP-QMS instrumentation in comparison with a double focusing sector field plasma mass spectrometry technique (ICP-SFMS) is also included. It was found that a modified microwave acid digestion procedure in combination with ICP-SFMS could replace ICP-AES determinations and fusion digestions for most of the investigated elements. Guidelines and limitations for this time- and labour- efficient procedure, offering accurate results for the majority of elements studied are discussed.     

Spektrographische Untersuchungen des magnetischen Sterns α2CVn

The main purpose of this paper was the examination of the Cassegrain-spectrograph of the 2-m-universaltelescope at Tautenburg for investigations of magnetic stars. Therefore from 26 spectrograms of the well known magnetically variable star α²CVn taken with a reciprocal linear dispersion of 10 Å/mm variations of radial velocity and magnetic field strength for some lines of Eu II, Cr II, Si II, Mg II were determined. The results agree well with those of Babcock [5] and Struve and Swings [2], derived from spectrograms of higher dispersion. The large variation in the radial velocity of Eu II and Cr II is confirmed. In the oblique rotator model this requires a very strong concentration of Eu II at the poles and of Cr II at the equator.