How much did Glacial North Atlantic Water shoal?

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 29 (2014): 190-209, doi:10.1002/2013PA002557.Observations of δ13C and Cd/Ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the Last Glacial Maximum, with the degree of shoaling being significant enough for the water mass to be renamed Glacial North Atlantic Intermediate Water. These nutrient tracers, however, may not solely reflect changes in water mass distributions. To quantify the distribution of Glacial North Atlantic Water, we perform a glacial water mass decomposition where the sparsity of data, geometrical constraints, and nonconservative tracer effects are taken into account, and the extrapolation for the unknown water mass end-members is guided by the modern-day circulation. Under the assumption that the glacial sources of remineralized material are similar to that of the modern day, we find a steady solution consistent with 241 δ13C, 87 Cd/Ca, and 174 δ18O observations and their respective uncertainties. The water mass decomposition indicates that the core of Glacial North Atlantic Water shoals and southern source water extends in greater quantities into the abyssal North Atlantic, as previously inferred. The depth of the deep northern-southern water mass interface and the volume of North Atlantic Water, however, are not grossly different from that of the modern day. Under this scenario, the vertical structure of glacial δ13C and Cd/Ca is primarily due to the greater accumulation of nutrients in lower North Atlantic Water, which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial Atlantic.G.G. is supported by NSF grants OIA-1124880 and OCE-1301907, and the WHOI Ocean and Climate Change Institute.2014-09-1

Experimental study of the Subsonic Aerodynamics of a Blended Wing Body Air Vehicle with a Focus on Rapid Technology Assessment

The subsonic aerodynamic performance of a blended wing body aircraft constructed using selective laser sintering was assessed in the AFIT low-speed wind tunnel. The scaled-down model of a strike tanker aircraft consisted of a shaped fuselage and sweptback wings. The Reynolds number, based on mean wing chord, during testing was on the order of 105 while the Mach number ranged from 0.10 to 0.20. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure data measured with 8 taps located on the model’s upper surface, a comparison to computational fluid dynamics (CFD) solutions acquired in a parallel study conducted by AFRL/VAAC, and global pressure sensitive paint (PSP) measurements. Paint measurements were compared to pressure tap data to ensure their accuracy while lift and drag coefficients, as well as pitching and rolling moments were examined to determine performance characteristics, including stability attributes and aircraft stall. One of the most interesting results was the striking difference in the force and moment measurements before and after the paint was applied to the surface. The average surface roughness, Ra, was measured with a profilometer and was found to have increased from approximately 0.3μm to 0.7μm when the paint was applied. When traditional 2-D boundary layer approaches to assessing the effect of roughness, the 0.7μm value falls well below the threshold at which one would anticipate roughness to have any effect. There is support in archival literature for the notion that roughness effects are more pronounced in a 3-D boundary layer, and the pitching moment data and the PSP data indicate that the for the painted model, there is a gradual onset of wing stall marching inward from the wingtips toward the body. By contrast, the force and, in particular, the pitching moment data suggests that the onset of wing stall is sudden across the entire wing for the unpainted case. Interestingly, the CFD data compared well with the data corresponding to the measurements of the rougher, painted model. Notably, the grid used in CFD would require at least an order of magnitude higher resolution in the boundary layer region to accurately depict the submicron roughness effects