Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 59). / This work takes an in depth look at acoustic propagation through double duct sound speed profiles in the Arctic. While the traditional Arctic sound speed profile has a single surface duct, some portions of the Arctic have a sound speed profile which includes a second, lower duct. These double duct systems are seen through out the Beaufort Sea, dating back to 2004, in data made available by the Ice-Tethered Profiler program at the Woods Hole Oceanographic Institutes. The acoustic propagation through the double duct system is analyzed using normal mode analysis, through the Kraken normal mode code. A simulated lower duct is introduced in order to isolate only those modes which travel within the lower duct. Propagation through the lower duct is compared to propagation in traditional Arctic sound speed profiles, and for certain ducts distinct increases in propagation strength are shown. / by Thomas Howe. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009. / Includes bibliographical references (leaf 51). / As the Arctic ice cover continues to retreat, the possibility of regular transit through the Arctic becomes an increasing reality. Liner companies could take advantage of distance savings (up to 4000 nautical miles less than existing routes) available from transit through the Arctic by offering faster port-to-port voyage times while simultaneously reducing voyage expenses. The purpose of the study is to investigate the economic feasibility of a liner service with shipping routes through the Arctic. To accomplish this, information pertaining to Arctic conditions, containerships and icebreakers, and container ports was collected and used to build a model that estimates the expense and time of port-to-port voyages through the Arctic. Different combinations of vessels, routes, and speeds through the Arctic were evaluated with the model. The expense and time of the Arctic voyages were then compared to the equivalent existing liner routes. The likelihood of year-round reliable containership service through the Arctic in the future depends on one's perspective. One the one hand, it won't happen for decades due to the presence of ice. Current predictions of a largely ice-free Arctic range from 2030 to later than 2100. On the other hand, if some favorable assumptions are made, it deserves serious consideration once minimally ice-strengthened containerships are able to be reliably escorted through the Arctic at a speed of 10kts. / by Russell Pollock. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Since the 1990's, greenhouse gas forcing has warmed the Arctic at twice the rate of lower latitudes, coinciding with a dramatic decline in Arctic sea ice extent. This manifestation of climate change has ignited a lively and ongoing debate regarding if Arctic warming will significantly influence extreme weather in the extra-tropics. This thesis offers three distinct contributions to the dialogue. Firstly, results are presented from a suite of targeted climate model experiments designed to establish how ice-forced and snow-forced anomalies interact and propagate through the atmosphere. Results suggest that high snow anomalies can suppress the October-November atmospheric response by interfering with the forcing of hemispheric (wave one) atmospheric dynamics. Intriguingly, the simulations do not force the persistent stratospheric response reported in similar experiments. This may be a consequence of transient or seasonally-restricted surface forcing. Secondly, multi-model projections of future wintertime North Atlantic and North Pacific tropospheric jets are analyzed using a novel Bayesian weighting technique. This approach is shown to reduce systematic bias and indicates that future forcing of the jets - due to greenhouse gas emissions - will be first order linear (i.e. independent of historical bias). Results suggest that the widely reported future poleward shift at the level of the eddy-driven jet is far from robust. Lastly, an attempt is made to distill the current level of consensus within the scientific community using expert elicitation. Results reveal a fairly evenly split on if Arctic warming has already had a significant impact on the mid-latitude jets, but a strong consensus that it will in the future. / by David Patrick Whittleston. / Ph. D.

Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 53-58). / The Arctic surface air temperature has warmed nearly twice as much as the global mean since the mid-20th century. Arctic sea ice has also been declining rapidly in recent decades. There is still discussion about how much of this Arctic amplification is caused by local factors, such as changes in surface albedo, versus remote factors, such as changes in heat transport from the midlatitudes. This thesis focuses mainly on the role of poleward heat transport on Arctic amplification. Most of the previous studies on this topic have defined ocean heat transport as the zonally averaged ocean heat transport at 65°N or 70°N, which ignores the physical pathways of heat into the Arctic and may include recirculation of heat in the North Atlantic. In this thesis, we define the ocean heat transport as the heat transport across five sections surrounding the Arctic, to create a closed domain in the Arctic. / Previous studies on Arctic amplification have used either a single model run or have compared results from a multi-model ensemble. While the multi-model ensemble approach may potentially average out biases in individual models, the ensemble spread confounds the model differences and the internal climate variability. In this thesis, we investigate the Arctic amplification in the Community Earth System Model version 1 (CESMi) Large Ensemble. The CESMI Large Ensemble includes 40 members that use the same model and external forcing, but different initializations. This simulates different climate trajectories that can occur in a given atmosphere-ocean-land-cryosphere system. We find that CESMI Large Ensemble projects a large increase towards the end of the 21st century in ocean heat transport into the Arctic, and that the increase in ocean heat transport is significantly correlated with Arctic amplification. / The main contributor to the increase in ocean heat transport is the increase across the Barents Sea Opening. The increase in Barents Sea Opening ocean heat transport is highly correlated with the decrease in sea ice in the Barents-Kara Sea region. We propose that this is because the increase in ocean heat transport melts the ice at the sea ice margin, which results in increased surface heat flux from the ocean and further local feedback through decreased surface albedo and increased cloud coverage. We also find that while the changes in atmosphere heat transport into the Arctic circle at 66.5 N are on the same order as the changes in ocean heat transport, they are not correlated with Arctic amplification. / by Laura Elizabeth Fleming. / S.M. / S.M. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis: S.M. in Oceanographic Engineering, Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2017. / Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 885-86). / A newly discovered double ducted acoustic environment present throughout much of the Beaufort Sea in the Arctic has a major effect on active acoustic transmissions. This work performs an in depth analysis of how the lower duct impacts the propagation of various active signals used commonly for acoustic communications or active sonar. First, this thesis performs a thorough modal analysis of the effect of the double ducted environment on long range propagation of a 300 Hz and 3500 Hz pulse. Signal excess is determined for the two different source pulses to quantify the effect of the lower duct on noise and SNR. Finally, channel capacity is calculated for the two frequency bands to evaluate operational impacts of the lower duct on acoustic communication systems in the Arctic. / by Scott Adams Carper / S.M. in Oceanographic Engineering / S.M.

Thesis: S.M., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2020 / Cataloged from student-submitted PDF of thesis. / Includes bibliographical references (pages 91-94). / The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate (ASTE), a regional, medium-resolution coupled ocean-sea ice state estimate, is analyzed for the first time using bounding isopycnals. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate (2004) and traverses the Arctic Ocean along boundary current pathways at approximately 2 cm/s. The surge also alters AW flow direction and speed including a significant reversal in flow direction along the Lomonosov Ridge. The surge results in a new quasi-steady AW flow from 2010 through the end of the state estimate period in 2017. The time-mean AW circulation during this time period indicates a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A three-layer depiction of ASTE's overturning circulation within the AO indicates AW is converted to colder, fresher Surface Layer water at a faster rate than is transformed to Bottom Water (1.2 Sv vs. 0.4 Sv). Observed AW properties compared to ASTE output indicate increasing misfit during the simulated period with ASTE's AW Layer generally being warmer and thicker than in observations. / by Jeffrey Scott Grabon. / S.M. / S.M. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references (p. 57-58). / The mid-to-deep Arctic Ocean is generally characterized by a cyclonic circulation, contained along shelves and ridges. Here we analyze the general Arctic circulation using an idealized numerical model consisting of a circular basin with two channels acting as inflow and outflow. We analyze the circulation (direction, strength and sensitivity) for wind forcing with and without bathymetry (ridges), and with and without stratification. We find that the circulation is modified drastically by both bathymetry and wind direction, where an altered wind field can change both the direction of the horizontal basin circulation as well as the strength of the inflow and outflow. The idealized circulations imply that the Arctic circulation, and the associated export of freshwater, can easily switch states in a changing climate. / by Peter Joseph Sugimura. / S.M.

No description available.

This thesis is a reconnaissance of the behavioural ecology of domestic cats. The principal subjects were two groups of farm cats. There was also a group of captive cats and a house cat. The study differs from all previous ones in that the cats were tame and therefore could be shadowed and observed for long periods at all hours. It deals with (1) activity patterns and activity budget, (2) use of space and social behaviour, (3) scent communication, (4) foraging and (5) population dynamics.

No description available.