Clear Air Turbulence (CAT) is the turbulence experienced at high altitude on board an aircraft. The main mechanisms for its generation are often said to be Kelvin-Helmholtz instability and mountain waves. CAT is an issue to the aviation industry in the sense that it is hard to predict its magnitude and exact location. Mostly, it is just a nuisance for the crew and passengers, but occasionally it causes serious injuries and aircraft damage. It also prevents air-to-air refuelling to be conducted in a safe manner. The micro scale nature of CAT makes it necessary to describe it with turbulence indices. The first part of this study presents a verification of the two commonly used turbulence indices, TI1 and TI2, developed by Ellrod and Knapp in 1992. The verification is done with AMDAR (Aircraft Meteorological Data Relay) reports and computed indices from ERA-Interim data. The second part presents a 33-year climatology of the indices for describing CAT. Results show that the index TI1 is generally the better of the two indices based on hit rate, but TI2 performs better based on false alarm rate. The climatology suggests that CAT is more frequent at the northern east coast of the U.S., over the island of Newfoundland and east of Greenland. In the vertical, CAT seems to occur most frequently at the 225 hPa level but also occur frequently at the 300 hPa level at the aforementioned areas. Based on AMDAR reports from 2011, only 0.014% of the reports were positive turbulence observations. The low amount of reports suggests that CAT can be avoided effectively with current CAT predicting skills and flight planning. / Clear Air Turbulence (CAT) är den turbulens på hög höjd som upplevs ombord på flygplan och orsaken till denna turbulens sägs ofta vara Kelvin-Helmholtz-instabilitet och lävågor. På grund av svårigheten att förutsäga dess styrka och exakta position är CAT ett problem inom flygbranschen. Ofta är CAT bara ett irritationsmoment för besättning och passagerare, men kan ibland orsaka personskador och flygplansskador. Den mikroskaliga strukturen som CAT har gör det nödvändigt att beskriva den med turbulensindex. Den första delen av denna studie tar upp pålitligheten av två ofta använda turbulensindex, TI1 och TI2, utvecklade av Ellrod och Knapp år 1992. Verifikationen görs med hjälp av AMDAR-rapporter (Aircraft Meteorological Data Relay) och turbulensindex beräknade med data från ERA-Interim. Den andra delen består av en 33-års klimatologisk studie av CAT baserat på dessa index. Baserat på träffgrad presterar TI1 generellt bättre än TI2, men TI2 presterar bättre än TI1 vad gäller falsklarmsgrad. Den klimatologiska studien tyder på att CAT är mer frekvent över USAs norra ostkust, över Newfoundland och öster om Grönland. I vertikalled verkar CAT förekomma mest frekvent omkring 225 hPa-nivån, men även runt 300 hPa-nivån över de geografiska områden som nämnts ovan. AMDARrapporter från 2011 visar att endast 0.014% av rapporterna observerade turbulens. Den låga andelen antyder att man effektivt kan undvika CAT över nordatlanten med branschens nuvarande förmåga att förutse CAT och god färdplanering. / Research on a CRuiser Enabled Air Transport Environment, RECREATE

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Canada consistently balances competing inclinations for proximity and distance with the United States. Yet the extant literature on Canadian foreign policy has rarely focused on this particular behaviour trait or readily accepted that such an ambiguous stance is actually underpinned by a strategic logic, let alone the crux of a purported grand strategy. And the few that that are open to the notion of a Canadian grand strategy often overlook the domestic decision-making determinants of behaviour, are largely empirical-descriptive in content, or are chronologically limited to either the early Cold War or a few key foreign policy episodes. This dissertation rectifies these shortcomings by providing a theoretical-explanatory and empirically-informed account of Canada’s post-war grand strategy, in which its domestic origins, strategic policies, and cultural predispositions are all carefully explored. It does so by applying the cultural-cybernetic model of behaviour, which combines strategic cultural factors that guide policy-makers on security matters with cybernetic policy processes, through which beliefs, inclinations, and policy choices are standardized and regularized as distinct doctrines across a range of foreign, defence, and security policies. It tests this model on two key cases of Canadian grand strategy in the post-war period: (1) Canada’s policy responses to American preferences on strategic (air and missile) defence over some six decades, and (2) its policy responses to US – and to a lesser extent British – strategic preferences on NATO defence strategy during the Cold War. The findings reveal that Canada’s strategic policies fluctuated between the two Standing Operational Doctrines in its policy repertoire: continental soft-bandwagoning and defensive weak-multilateralism. These two doctrines span the range of feasible policy options – the “goldilocks zone” – required to ensure that any trade-offs between security and sovereignty, as the central values being pursued in the cybernetic process, are minimized. It is for this reason that Canada’s strategic behaviour has a high degree of policy continuity, patterned consistency, and is best described as the goldilocks grand strategy.

The North Atlantic Oscillation (NAO) is one of the main components of atmospheric circulation variability within the middle and high latitudes of the Northern Hemisphere and largely affects winter weather in northeastern United States. This study examined the most recent decadal trend of the NAO as well as its influence on snowfall totals and storm track variability in the northeast U.S. over the previous 50-year period. Previous research has indicated greater snowfall totals in the Northeast during NAO negative phases due to repeated polar outbreaks. Nonetheless, past research has also shown connections between the NAO positive phase and active winter seasons in this region. This study provides insight on how both positive and negative NAO phases can produce significant snowfall in the Northeast. Statistical and graphical analysis were completed to assess the relationship between the NAO and seasonal snowfall (NDJFM) from 1961-2010 for stations within the Northeast (Virginia to Maine). In addition, two case studies of recent winter events with differing NAO phases were evaluated to provide insight on how both NAO phases can produce significant snowfall in the Northeast. The statistical analysis revealed inverse relationships between the NAO negative phase and seasonal snowfall. The composite analysis indicated an average positive NAO pattern from 1961-2010, yet the NAO negative years produced higher frequency of snowfall in the Northeast. The case studies highlighted variations in storm track and snowfall distribution of the two winter events in differing phases. This study shows that snowfall can occur in particular regions of the Northeast regardless of the NAO phase which has important implications for forecasters. This research also provides the necessary information to complete the most recent decadal trend of the NAO and determine its average pattern. The update of this record will assist climatologists and weather forecasters in predicting future northeast U.S. winter storms. / Department of Geography

The strength of the Atlantic meridional overturning circulation (AMOC) is believed to be associated with changes in surface buoyancy in the subpolar North Atlantic, which naturally leads to a notion that the AMOC has been weakening under global warming. Yet, a variety source of observations and its assimilation into ocean circulation models have not supported such an AMOC decline so far. In this study, an aspect that has not been paid attention, regarding the maintenance of the AMOC strength, is explored: storm activity in the subpolar North Atlantic (NA). An analysis using reanalysis data shows that the wintertime turbulent heat flux variability in the LS deep convection region is largely controlled by a small number of extreme heat flux event days, suggesting a pivotal role of winter storms in prompting LS deep-water formation. A set of forced ocean-ice model simulations, in which synoptic winter storm activity associated with these event days is either suppressed or doubled over the subpolar NA, confirms the above analysis as the altered storm activity results in a substantial change in LS convection and the AMOC strength. These experiments also show an upward AMOC trend during the late twentieth century, the degree of which is to some extent related to the intensity of storm activity in the LS. The upward AMOC trend found in the first part of the dissertation opposes to a downward AMOC trend in the twentieth century coupled model simulations employing the identical ocean component. An analysis suggests that contrast to the ocean-ice model, storm activity in the LS convection region and associated heat flux decreases during the late twentieth century. Although there is also a buoyancy increase over the LS, the wintertime heat flux decrease appears to be a more dominant factor for a decrease in convection in the LS, as an increasing freshwater input from Arctic/Subarctic Ocean bypasses the interior LS along the western boundary current. Therefore, the downward AMOC trend in the coupled model can be linked ultimately to the decreasing storm activity over the LS. This study therefore suggests that storm activity over the major convection regions needs to be paid further attention in assessing AMOC variations, including long-term trend in response to a warming scenario, in future studies.

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 77-86). / Microfiche. / ix, 86 leaves, bound ill. (some col.) 29 cm

Univ., Habil.-Schr.--Darmstadt. / Includes bibliographical references (p. 290 - 308) and index.

Zugl.: Frankfurt am Main, Univ., Diss. / Originally presented as the author's thesis (doctoral)--Universität Frankfurt am Main. Includes bibliographical references and index.

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