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Christopher R. Church and John T. Snow

Abstract

The results of a series of measurements of centerline pressure deficit in tornado-like vortices are described. These measurements were undertaken for the purpose of determining 1) how the magnitude of the central pressure deficit in a columnar vortex varies with height, and 2) what functional relationships exist between them deficits and the dynamic and geometric parameters characterizing the flow. The results graphically show the complicated variation of central pressure deficit with height in both laminar and turbulent vortices In low-swirl vortices, the largest deficits are found aloft, not at surface. Further, the low-swirl vortices have generally greater central pressure deficits than moderate-swirl events. The greatest deficits are tied to the approach of the vortex breakdown to the lower surface. The data also indicate a cubic dependence of the central pressure deficit on applied circulation.

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Glenn L. Baker and Christopher R. Church

Abstract

Measurements in a tornado simulator have yielded quantitative data on certain aspects of the mean flow of a variety of modeled vortices. The radius of maximum velocity in the vortex core has been measured using a hot-film anemometer for swirl ratio values from zero to 6. A simple model of the turbulent core radius as a function of swirl ratio shows good agreement with the experimental data. The magnitude of the mean total velocity vector at the core radius has also been determined for the same range of swirl ratios and for a range of Reynolds numbers. The measurements indicate that for laminar vortices the peak velocity is strongly dependent on swirl ratio, whereas for turbulent vortices the swirl ratio dependence is weak. For both laminar and turbulent vortices, peak velocities are directly proportional to the mean vertical velocity in the updraft region. The application of the experimental measurements to the estimation of actual tornadic velocities is demonstrated.

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Christopher R. Church, John T. Snow, and Jean Dessens

Observations of vortices of various types produced in a large thermal plume are described. The apparatus used to generate the plume is the Météotron, an array of 105 fuel oil burners with a total heat output of approximately 1000 MW. Three types of vortices have been observed: 1) large counter-rotating rolls in the downstream plume, 2) intense small-scale vortices resembling very strong dust devils seen at the surface on the downwind side of the plume, and 3) very large columnar vortices produced when the lower portion of the plume goes into rotation as a whole. Three mechanisms leading to the concentration of vorticity necessary to produce these vortex types are discussed. These include tilting and stretching of horizontal vorticity present in the environmental wind field, generation of vorticity within the plume by the action of buoyancy and drag forces, and convergence of preexisting background vorticity from the environment. It is concluded, based on these observations and physical considerations, that the generation of vortices of moderate intensity is to be expected in large plumes, be their source a forest fire or an industrial operation.

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Aimée B. A. Slangen, Benoit Meyssignac, Cecile Agosta, Nicolas Champollion, John A. Church, Xavier Fettweis, Stefan R. M. Ligtenberg, Ben Marzeion, Angelique Melet, Matthew D. Palmer, Kristin Richter, Christopher D. Roberts, and Giorgio Spada

Abstract

Sea level change is one of the major consequences of climate change and is projected to affect coastal communities around the world. Here, global mean sea level (GMSL) change estimated by 12 climate models from phase 5 of the World Climate Research Programme’s Climate Model Intercomparison Project (CMIP5) is compared to observational estimates for the period 1900–2015. Observed and simulated individual contributions to GMSL change (thermal expansion, glacier mass change, ice sheet mass change, landwater storage change) are analyzed and compared to observed GMSL change over the period 1900–2007 using tide gauge reconstructions, and over the period 1993–2015 using satellite altimetry estimates. The model-simulated contributions explain 50% ± 30% (uncertainties 1.65σ unless indicated otherwise) of the mean observed change from 1901–20 to 1988–2007. Based on attributable biases between observations and models, a number of corrections are proposed, which result in an improved explanation of 75% ± 38% of the observed change. For the satellite era (from 1993–97 to 2011–15) an improved budget closure of 102% ± 33% is found (105% ± 35% when including the proposed bias corrections). Simulated decadal trends increase over the twentieth century, both in the thermal expansion and the combined mass contributions (glaciers, ice sheets, and landwater storage). The mass components explain the majority of sea level rise over the twentieth century, but the thermal expansion has increasingly contributed to sea level rise, starting from 1910 onward and in 2015 accounting for 46% of the total simulated sea level change.

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