Suchergebnisse

The Blue Nile originates from Lake Tana in the Ethiopian Highlands and contributes about 60–69% of the main Nile discharge. Previous studies investigated the relationship of sea surface temperature (SST) in the Pacific Ocean (Niño 3.4 region) to occurrence of meteorological and hydrological droughts in the Nile Basin. In this paper we focus on the dependence of occurrence of droughts and floods in the upper catchment of the Blue Nile on the timing of El Niño and La Niña events. Different events start at different times of the year and follow each other, exhibiting different patterns and sequences. Here we study the impact of these timing and temporal patterns on the Blue Nile droughts and floods. The comparison between the discharge measurements (1965–2012) at the outlet of the upper catchment of the Blue Nile and the El Niño index shows that when an El Niño event is followed by a La Niña event, there is a 67% chance for occurrence of an extreme flood. Furthermore, we also found that 83% of El Niño events starting in April–June resulted in droughts in the upper catchment of the Blue Nile. Although the current study is limited by the reduced number of samples, we propose that observations as well as global model forecasts of SST during this season could be used in seasonal forecasting of the Blue Nile flow. ; Abdus Salam International Centre for Theoretical Physics (Earth System Physics) ; European Union (DEWFORA project) ; European Union (STEPS project)

We simulate the observed statistical relationship between ENSO and the rainfall regime of the upper Blue Nile using the tropical-band version of the regional climate model RegCM4 (or Reg-TB). An ensemble of nine simulations for the 28-year period 1982–2009 is completed to investigate the role of ENSO in modulating rainfall over the upper Blue Nile catchment. Reg-TB shows a good skill in simulating the climatology of temperature, outgoing long-wave radiation patterns as well as related atmospheric circulation features during the summer season (i.e. the rainy season over the Blue Nile catchment). The model also succeeds in reproducing the observed negative correlation between Pacific SST and rainfall anomalies over the Blue Nile catchment, and in particular the association of droughts over the Blue Nile with El Niño events that start in April–June. We thus propose that observations and model forecasts of Pacific SST during this season could be used in seasonal forecasting of summer rainfall over the upper Blue Nile region. ; Abdus Salam International Centre for Theoretical Physics. Earth System Physics ; Abdus Salam International Centre for Theoretical Physics. Sandwich Training Educational Programme ; European Union (DEWFORA Project)

The SuperB asymmetric e+ - e− collider has been recently approved by the Italian Government. With a design luminosity two orders of magnitude greater than the past B-Factories and by exploiting the low-energy beam polarization, within few years it is expected to start the study of rare B and D meson decays, where New Physics might show up, and lepton flavour violation in tau decays. Due to the reduced center of mass boost, the vertex resolution must be improved to achieve the same proper-time difference resolution for B decays obtained in BaBar. Thus, based on the layout of the BaBar vertex detector, the SuperB Silicon Vertex Tracker must be equipped with an extra innermost layer (the Layer0), very close to the interaction point. The most stringent physics requirements concern the low material budget and the high-background working conditions of the Layer0: striplets modules, with short strips on high resistivity silicon sensors, are the baseline solution foreseen for the beginning of data taking; an upgrade to pixel sensors, more robust against high background occupancy, is planned at the full luminosity. The latest results on the various pixel options explored by a specific R&D program on different pixel technologies will be described: CMOS MAPS, pixel sensors realized on multiple layers with a vertical integration technology and hybrid pixels.