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William J. Schulz Jr., Richard P. Mied, and Charlotte M. Snow

Abstract

The authors address the propagation of continental shelf waves in the Mid-Atlantic Bight. An analytical model of the bathymetry in the region is constructed by representing the continental shelf as a gently sloping bottom, which deepens linearly with offshore distance to the place where it meets the continental slope. Seaward of that point, the bathymetry is modeled with an exponentially decaying function of distance. The linearized, barotropic equations of hydrostatic motion, subject to the long-wave approximation, yield separate shelf and slope solutions, which are matched at the shelf break to specify the eigenfunctions. The associated eigenvalues define the dispersion relations for each of the modes. Wavenumber–frequency pairs derived from NOAA sea surface height stations along the coast are plotted on the first-mode dispersion curve, and the agreement is good. The theory also shows good agreement with the wave data of D. P. Wang.

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Joseph M. Moran, David R. Smith, and John T. Snow

The Fourth International Conference on School and Popular Meteorological and Oceanographic Education was held 22–26 July 1996 in Edinburgh, Scotland. Conference attendees included 125 educators, meteorologists, oceanographers, and government officials representing 19 nations. The themes of the conference were the roles of meteorology and oceanography in science education and the benefits derived from improved environmental awareness and scientific literacy, particularly weather awareness, meteorological literacy, and understanding of the ocean. Formal presentations, workshops, poster sessions, and demonstrations provided information on programs for teacher enhancement, computer-aided instruction, and classroom access to real-time weather information through the World Wide Web.

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C. R. Church, J. T. Snow, and E. M. Agee

A 4 m wide and 7 m tall tornado vortex generator (including exhaust fan and duct work) has been constructed at Purdue University that operates on a principle similar to that of the earlier machine modeled by Ward (1972). Characteristics of the Purdue simulator are described, as well as the corresponding modifications and improvements that have been made to Ward's machine. Selected photographs of vortex configurations obtained in the simulator demonstrate the ability of the machine to achieve vortex breakdown and multiple vortex configuration. A radial-axial profile of velocity magnitudes (using hot-film anemometry) has been obtained for the state of vortex breakdown characterized by two interlocking helical spiral vortices. This preliminary result shows the potential that the experimental system offers for obtaining quantitative information about the flow field of selected vortex configurations. Multiple vortex phenomena in the thunderstorm-tornado system are examined in light of the laboratory simulation and the similarity concept.

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E. M. Agee, J. T. Snow, and P. R. Clare

Abstract

Analyses are presented of the tornado tracks for four tornado families affecting Indiana and neighboring states on 3 April 1974. The study by Agee et al.(1975)on the occurrence of multiple suction vortices in the tornado has been used by further extending Ward's (1972) multiple vortex phenomenon to the scale of the tornado cyclone. This has allowed an interpretation of multiple tornado events by means of which consecutive tornado damage paths may be frequently recognized as segments of cycloidal tracks for multiple vortices occurring within the larger tornado cyclone.

A tornado cyclone, most likely within the right rear quadrant of the severe thunderstorm, may contain two, three, or more smaller scale vortices (mini tornado cylones) that revolve cyclonically about the center of the. parent tornado cyclone as the entire system translates along with the thunderstorm. It is shown that these centers of action have cycloidal tracks that can be matched with the damage paths of tornado families. Tornadoes are observed to be left-turners or right-turners, depending on what portion along the cycloidal track touchdown and demise occur. A tornado family may he associated with a single vortex parent tornado cyclone which tends to produce longer tornado tracts that do not undergo appreciable turning. Tornado families, however, may be generated by multiple vortex tornado cyclone systems, and in this case tornado tracks follow a curtate cycloid, eventually turning into the cold air and dissipating. Another tornado can reappear, however, as the parent vortex caster returns cyclonically (along the cycloidal path) to more favorable environmental conditions for redevelopment. Finally, a summary is presented depicting the scales of possible multiple vortex systems associated with the tornado producing thunderstorm.

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Thomas A. Jones, Kevin M. McGrath, and John T. Snow

Abstract

Nearly 100 000 vortex detections produced by the Mesocyclone Detection Algorithm (MDA) are analyzed to gain insight into the effectiveness of the detection algorithm in identifying various types of tornado-producing events. Radar and algorithm limitations prevent raw vortex detections from being very useful without further discrimination. Filtering techniques are developed to remove spurious vortex detections and discriminate between vortices that are and are not related to mesocyclones.

To investigate whether various vortex detections (and their attributes) are associated with severe weather phenomena, they are compared with available tornado reports to determine if detections with certain types of attributes can be associated with tornadic events. Tornado reports are used since the ground truth tornado set is more reliable than other databases of severe weather phenomena. Basic skill scores and more advanced principal component methods are used to quantify the correlation between vortex detection attributes and tornadoes.

The results of this analysis reveal that only a very small percentage (<5%) of vortex detections, using the most basic definition, are associated with the occurrence of a tornado. Percentages increase to approximately 10% as the criteria for defining a vortex detection as a mesocyclone detection become more strict; however, many tornadic events are only associated with weaker detections and are “missed” when the detection threshold is increased. Several velocity-derived detection attributes are shown to have weak to moderate predictive ability when determining whether a detection is (or is not) tornadic.

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Kate Snow, Andrew McC. Hogg, Bernadette M. Sloyan, and Stephanie M. Downes

Abstract

The influence of freshwater and heat flux changes on Antarctic Bottom Water (AABW) properties are investigated within a realistic bathymetry coupled ocean–ice sector model of the Atlantic Ocean. The model simulations are conducted at eddy-permitting resolution where dense shelf water production dominates over open ocean convection in forming AABW. Freshwater and heat flux perturbations are applied independently and have contradictory surface responses, with increased upper-ocean temperature and reduced ice formation under heating and the opposite under increased freshwater fluxes. AABW transport into the abyssal ocean reduces under both flux changes, with the reduction in transport being proportional to the net buoyancy flux anomaly south of 60°S.

Through inclusion of shelf-sourced AABW, a process absent from most current generation climate models, cooling and freshening of dense source water is facilitated via reduced on-shelf/off-shelf exchange flow. Such cooling is propagated to the abyssal ocean, while compensating warming in the deep ocean under heating introduces a decadal-scale variability of the abyssal water masses. This study emphasizes the fundamental role buoyancy plays in controlling AABW, as well as the importance of the inclusion of shelf-sourced AABW within climate models in order to attain the complete spectrum of possible climate change responses.

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O. Coddington, J. L. Lean, P. Pilewskie, M. Snow, and D. Lindholm

Abstract

We present a new climate data record for total solar irradiance and solar spectral irradiance between 1610 and the present day with associated wavelength and time-dependent uncertainties and quarterly updates. The data record, which is part of the National Oceanic and Atmospheric Administration’s (NOAA) Climate Data Record (CDR) program, provides a robust, sustainable, and scientifically defensible record of solar irradiance that is of sufficient length, consistency, and continuity for use in studies of climate variability and climate change on multiple time scales and for user groups spanning climate modeling, remote sensing, and natural resource and renewable energy industries. The data record, jointly developed by the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP) and the Naval Research Laboratory (NRL), is constructed from solar irradiance models that determine the changes with respect to quiet sun conditions when facular brightening and sunspot darkening features are present on the solar disk where the magnitude of the changes in irradiance are determined from the linear regression of a proxy magnesium (Mg) II index and sunspot area indices against the approximately decade-long solar irradiance measurements of the Solar Radiation and Climate Experiment (SORCE). To promote long-term data usage and sharing for a broad range of users, the source code, the dataset itself, and supporting documentation are archived at NOAA’s National Centers for Environmental Information (NCEI). In the future, the dataset will also be available through the LASP Interactive Solar Irradiance Data Center (LISIRD) for user-specified time periods and spectral ranges of interest.

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David K. Hutchinson, Matthew H. England, Andrew M. Hogg, and Kate Snow

Abstract

Climate model projections and observations show a faster rate of warming in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). This asymmetry is partly due to faster rates of warming over the land than the ocean, and partly due to the ocean circulation redistributing heat toward the NH. This study examines the interhemispheric warming asymmetry in an intermediate complexity coupled climate model with eddy-permitting (0.25°) ocean resolution, and results are compared with a similar model with coarse (1°) ocean resolution. The models use a pole-to-pole 60° wide sector domain in the ocean and a 120° wide sector in the atmosphere, with Atlantic-like bathymetry and a simple land model. There is a larger high-latitude ocean temperature asymmetry in the 0.25° model compared with the 1° model, both in equilibrated control runs and in response to greenhouse warming. The larger warming asymmetry is caused by greater melting of NH sea ice in the 0.25° model, associated with faster, less viscous boundary currents transporting heat northward. The SH sea ice and heat transport response is relatively insensitive to the resolution change, since the eddy heat transport differences between the models are small compared with the mean flow heat transport. When a wind shift and intensification is applied in these warming scenarios, the warming asymmetry is further enhanced, with greater upwelling of cool water in the Southern Ocean and enhanced warming in the NH. Surface air temperatures show a substantial but lesser degree of high-latitude warming asymmetry, reflecting the sea surface warming patterns over the ocean but warming more symmetrically over the land regions.

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C. R. Church, J. T. Snow, G. L. Baker, and E. M. Agee

Abstract

The investigation of tornado vortex dynamics by means of a laboratory simulation is described. Based on observations from nature and an examination of the Navier-Stokes equations, a laboratory simulator of the Ward type has been constructed. This simulator generates various vortex configurations as a function of swirl ratio, radial Reynolds number and aspect ratio. Configurations which are described are 1) a single laminar vortex; 2) a single vortex with breakdown bubble separating the upper turbulent region from the lower laminar region; 3) a fully developed turbulent core, where the breakdown bubble penetrates to the bottom of the experimental chamber; 4) vortex transition to two intertwined helical vortices; and 5) examples of higher order multiple-vortex configurations that form in the core region.

Hot-film anemometry measurements of the magnitude of the velocity vector and inflow (swirl) angle have been obtained in a sequence of flows characterized by progressively increasing values of swirl ratio. These data include measurements in both the quasi-irrotational outer flow and the more complex core region. Due to the similarity that exists between the model and tornadoes, these observations provide insight into the flow fields likely to be encountered in real events.

Particularly significant findings include the mapping of the transition points at which the flow converts from a single to a double helical vortex configuration, and from a double to a triple pattern, as a function of system parameters. Additionally, the velocity measurements show the development of a cylindrical shear zone at the outer edge of the core, which, through inertial instability, may lead to the multiple-vortex phenomenon.

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D. R. Smith, R. S. Weinbeck, I. W. Geer, J. T. Snow, K. M. Ginger, and J. M. Moran

Project ATMOSPHERE, the K–12 educational program of the American Meteorological Society, has been involved in teacher enhancement for four years. Summer workshops for teachers have been a primary component of the AMS K–12 educational initiatives since its inception. During the summer of 1994, Project ATMOSPHERE conducted four workshops: two of the workshops were for teachers in the Atmospheric Education Resource Agent program; another was for K–12 teachers, including one teacher each from Canada and Australia; and the fourth was for faculty members at community colleges or four-year undergraduate institutions. These workshops provide teachers at all levels with instruction on a variety of atmospheric topics, an introduction to the operational and research activities of the meteorological community, and exposure to atmospheric scientists and their facilities. Such workshops provide enriching experiences for educators who teach about weather and climate topics in their science classrooms.

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