Study made of corrosion resistance of stainless steel and nickel alloys in nuclear reactor superheaters

Experiments performed under conditions found in nuclear reactor superheaters determine the corrosion rate of stainless steel and nickel alloys used in them. Electropolishing was the primary surface treatment before the corrosion test. Corrosion is determined by weight loss of specimens after defilming

A systematic comparison of tropical waves over northern Africa. Part II: Dynamics and thermodynamics

This study presents the first systematic comparison of the (thermo-)dynamics associated with all major tropical wave types causing rainfall modulation over northern tropical Africa: Madden Julian Oscillation (MJO), Equatorial Rossby waves (ERs), mixed Rossby-gravity waves (MRGs), Kelvin waves, tropical disturbances (TDs, including African Easterly Waves), and eastward inertio-gravity waves (EIGs). Reanalysis and radiosonde data were analyzed for the period 1981--2013 based on space-time filtering of outgoing longwave radiation. The identified circulation patterns are largely consistent with theory. The slow modes, MJO and ER, mainly impact precipitable water, whereas the faster Kelvin waves, MRGs, and TDs primarily modulate moisture convergence. Monsoonal inflow intensifies during wet phases of the MJO, ERs, and MRGs, associated with a northward shift of the intertropical discontinuity for MJO and ERs. During passages of vertically tilted imbalanced wave modes, such as MJO, Kelvin waves, and TDs, and partly MRGs, increased vertical wind shear and improved conditions for up- and downdrafts facilitate the organization of convection. The balanced ERs are not tilted and rainfall is triggered by large-scale moistening and stratiform lifting. The MJO and ERs interact with intraseasonal variations of the Indian monsoon and extratropical Rossby wave trains. The latter causes a trough over the Atlas Mountains associated with a tropical plume and rainfall over the Sahara. Positive North Atlantic and Arctic Oscillation signals precede tropical plumes in case of the MJO. The results unveil which dynamical processes need to be modeled realistically to represent the coupling between tropical waves and rainfall in northern tropical Africa.Comment: 33 pages, 11 figures, supplementary material; submitted to Journal of Climat

A systematic comparison of tropical waves over northern Africa. Part I: Influence on rainfall

Low-latitude rainfall variability on the daily to intraseasonal timescale is often related to tropical waves, including convectively coupled equatorial waves, the Madden-Julian Oscillation (MJO), and tropical disturbances. Despite the importance of rainfall variability for vulnerable societies in tropical Africa, the relative influence of tropical waves for this region is largely unknown. This article presents the first systematic comparison of the impact of six wave types on precipitation over northern tropical Africa during the transition and full monsoon seasons, using two satellite products and a dense rain gauge network. Composites of rainfall anomalies in the different datasets show} comparable modulation intensities in the West Sahel and at the Guinea Coast, varying from less than 2 to above 7 mm/d depending on the wave type. African Easterly Waves (AEWs) and Kelvin waves dominate the 3-hourly to daily timescale and explain 10-30% locally. On longer timescales (7-20d), only the MJO and equatorial Rossby (ER) waves remain as modulating factors and explain about up to one third of rainfall variability. Eastward inertio-gravity waves and mixed Rossby-gravity (MRG) waves are comparatively unimportant. An analysis of wave superposition shows that low-frequency waves (MJO, ER) in their wet phase amplify the activity of high-frequency waves (TD, MRG) and suppress them in the dry phase. The results stress that more attention should be paid to tropical waves when forecasting rainfall over northern tropical Africa.Comment: 34 pages, 12 figures, supplementary material; submitted to Journal of Climat