56 research outputs found
Seasonal cycle of circulation in the Antarctic Peninsula and the off-shelf transport of shelf waters into southern Drake Passage and Scotia Sea
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 90 (2013): 15-30, doi:10.1016/j.dsr2.2013.02.029.The seasonal cycle of circulation and transport in the Antarctic Peninsula shelf region is investigated using a high-resolution (~2km) regional model based on the Regional Oceanic Modeling System (ROMS). The model also includes a naturally occurring tracer with a strong source over the shelf (radium isotope 228Ra, t1/2=5.8 year) to investigate the sediment Fe input and its transport. The model is spun up for three years using climatological boundary and surface forcing and then run for the 2004-2006 period using realistic forcing. Model results suggest a persistent and coherent circulation system throughout the year consisting of several major components that converge water masses from various sources toward Elephant Island. These currents are largely in geostrophic balance, driven by surface winds, topographic steering, and large-scale forcing. Strong off-shelf transport of the Fe-rich shelf waters takes place over the northeastern shelf/slope of Elephant Island, driven by a combination of topographic steering, extension of shelf currents, and strong horizontal mixing between the ACC and shelf waters. These results are generally consistent with recent and historical observational studies. Both the shelf circulation and off-shelf transport show a significant seasonality, mainly due to the seasonal changes of surface winds and large-scale circulation. Modeled and observed distributions of 228Ra suggest that a majority of Fe-rich upper layer waters exported off-shelf around Elephant Island are carried by the shelfbreak current and the Bransfield Strait Current from the shallow sills between Gerlache Strait and Livingston Island, and northern shelf of the South Shetland Islands, where strong winter mixing supplies much of the sediment derived nutrients (including Fe) input to the surface layer.This project is supported by NOAA grant NA09OAR4310062. MZ and MJ 11 are also supported by NSF grant 0948378 and MAC by NSF grant 0948442
Winter mesoscale circulation on the shelf slope region of the southern Drake Passage
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 90 (2013): 4-14, doi:10.1016/j.dsr2.2013.03.041.An austral winter cruise in July-August 2006 was conducted to study the winter circulation and
iron delivery processes in the Southern Drake Passage and Bransfield Strait. Results from
current and hydrographic measurements revealed a circulation pattern similar to that of the
austral summer season observed in previous studies: The Shackleton Transverse Ridge (STR) in
the southern Drake Passage blocks a part of the eastward Antarctic Circumpolar Current (ACC)
which forces the ACC to detour southward, produces a Taylor Column over the STR, and forms
an ACC jet within the Shackleton Gap, a deep channel between the STR and the shelf of
Elephant Island. Observations show that to the west of the STR, the Upper Circumpolar Deep
Water (UCDW) intruded onto the shelf around the South Shetland Islands while to the east of the
STR, shelf waters were transported off the northern shelf of Elephant Island. Along a similar
west-east transect approximately 50 km off the shelf, the northward transport of shelf waters was
approximately 2.4 and 1.2 Sv in the austral winter and summer, respectively. The waters around
Elephant Island primarily consist of the UCDW that has been modified by local cooling and
freshening, unmodified UCDW that has recently intruded onto the shelf, and Bransfield Current
water that is a mixture of shelf and Bransfield Strait waters. Weddell Sea outflows were
observed which affect the hydrography and circulation in the Bransfield Strait and indirectly
affect the circulation patterns in the southern Drake Passage and around Elephant Island. Two
Fe enrichment and transport mechanisms are proposed that intrusions of the UCDW onto the
northern shelf region of the South Shetland Islands is considered as the results of Ekman
pumping due to prevailing westerly wind in the region while the offshelf transport of shelf
waters in the shelf region east of Elephant Island is due to acquisition of positive vorticity by
shelf waters from horizontal mixing with onshelf intruded ACC waters.This project was supported by the National Science Foundation grant numbers OPP-0229966,
ANT-0444040 and ANT-0948378 to M. Zhou, OPP0230445, ANT0443403 and ANT-0948357
to C. Measures, ANT0443869 and ANT-0948442 to M. Charette, and OPP0230443,
ANT0444134 and ANT0948338 to B.G. Mitchell
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Fe sources and transport from the Antarctic Peninsula shelf to the southern Scotia Sea
Development of an FBG Sensor Array for Multi-Impact Source Localization on CFRP Structures
We proposed and studied an impact detection system based on a fiber Bragg grating (FBG) sensor array and multiple signal classification (MUSIC) algorithm to determine the location and the number of low velocity impacts on a carbon fiber-reinforced polymer (CFRP) plate. A FBG linear array, consisting of seven FBG sensors, was used for detecting the ultrasonic signals from impacts. The edge-filter method was employed for signal demodulation. Shannon wavelet transform was used to extract narrow band signals from the impacts. The Gerschgorin disc theorem was used for estimating the number of impacts. We used the MUSIC algorithm to obtain the coordinates of multi-impacts. The impact detection system was tested on a 500 mm × 500 mm × 1.5 mm CFRP plate. The results show that the maximum error and average error of the multi-impacts’ localization are 9.2 mm and 7.4 mm, respectively
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