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Abstract
Time-dependent features of the wall static pressure field beneath vortices modeled in a Ward-type vortex simulator have been investigated with emphasis on measurements of maximum surface pressure deficit. A pressure-measuring system was devised for this purpose which is capable of resolving important transient features of the surface pressure field in an essentially undistorted form, and measurement techniques were employed which reduced the influence of vortex wander. Measurements of maximum surface pressure deficits and their dependence on flow rate and geometry are presented, as well as a detailed study of the magnitudes of the maximum surface pressure deficits as a function of swirl ratio. Also presented are surface pressure distributions in individual subsidiary vortices in a multiple vortex flow.
The greatest deficit pressures are found to be associated with the penetration of the vortex breakdown to the surface. The magnitude of the surface pressure deficit is closely related to the. square of the mean vertical velocity of the upflow and also is dependent on swirl ratio. The pressure deficits in the subsidiary vortices presented are variable but range up to three times that found at the center of the “parent” vortex.
Abstract
Time-dependent features of the wall static pressure field beneath vortices modeled in a Ward-type vortex simulator have been investigated with emphasis on measurements of maximum surface pressure deficit. A pressure-measuring system was devised for this purpose which is capable of resolving important transient features of the surface pressure field in an essentially undistorted form, and measurement techniques were employed which reduced the influence of vortex wander. Measurements of maximum surface pressure deficits and their dependence on flow rate and geometry are presented, as well as a detailed study of the magnitudes of the maximum surface pressure deficits as a function of swirl ratio. Also presented are surface pressure distributions in individual subsidiary vortices in a multiple vortex flow.
The greatest deficit pressures are found to be associated with the penetration of the vortex breakdown to the surface. The magnitude of the surface pressure deficit is closely related to the. square of the mean vertical velocity of the upflow and also is dependent on swirl ratio. The pressure deficits in the subsidiary vortices presented are variable but range up to three times that found at the center of the “parent” vortex.
Abstract
The wall static pressure fields beneath tornado-like vortices have been investigated using a large vortex generator especially designed to model tornado cyclone airflow. Presented in nondimensional form, the data include both a series of radial profiles across the mean pressure field under a variety of flow conditions, and a detailed investigation of the magnitude of the central pressure as a function of swirl. The profiles clearly show the development of the intense vortical core from the no-swirl state, and the evolution of the core from a one-celled into a two-celled flow. For the experimental range examined, it is found that the greatest pressure deficits and largest pressure gradients (in the mean field) are associated with single-celled vortices. Strong evidence is found for the existence of a dynamically induced downdraft in the two-celled vortex.
Abstract
The wall static pressure fields beneath tornado-like vortices have been investigated using a large vortex generator especially designed to model tornado cyclone airflow. Presented in nondimensional form, the data include both a series of radial profiles across the mean pressure field under a variety of flow conditions, and a detailed investigation of the magnitude of the central pressure as a function of swirl. The profiles clearly show the development of the intense vortical core from the no-swirl state, and the evolution of the core from a one-celled into a two-celled flow. For the experimental range examined, it is found that the greatest pressure deficits and largest pressure gradients (in the mean field) are associated with single-celled vortices. Strong evidence is found for the existence of a dynamically induced downdraft in the two-celled vortex.
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.
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.
Abstract
An observational study of the West Lafayette, Ind., tornado of 20 March 1976 has been made that presents photographic evidence of tornado formation accompanied by suction “debris” vortices in the surface boundary layer that produced a cycloidal debris pattern. Furthermore, four case studies of cycloidal debris analysis form this pattern using aerial photography support the multiple-suction vortex model proposed by Agee et al. (1975). Average values of the tangential speed of a suction vortex according to loop shift estimates ranged from 26.4 to 44 m s−1 and maximum values according to loop width estimates ranged from 44.0 to 61.6 m s−1 as the tornado grew to its most intense stage. The aerial and ground surveys of the damage track also showed that the cycloidal debris pattern corresponded to a region of F3 and F4 wind-speed damage.
Photographic evidence also documented a tail-cloud formation similar to the Fargo tornado (Fujita, 1959) that rotated cyclonically through the northeast to northwest sector of the tornado cyclone with a tangential speed of 16 m s−1 at a distance of 3 km from the tornado funnel.
Analysis of cloud photography further showed the features of the tornado system at various stages of intensity. Notable was the formation of a broad descending bowl-shaped cloud accompanied by multiple “condensation” funnels that corresponded to the region of strongest tornado intensity with F4 structural damage. This study also illustrates that multiple-suction debris vortices in the surface boundary layer can occur with only one condensation funnel present. This event is recognized as a similar but slightly different and smaller multiple-vortex phenomenon than that required for multiple-condensation funnels that fully extend through the planetary boundary layer.
Features unique to cyclodial debris patterns and the role of suction vortices in producing certain types of damage are also brought out in this study. Also a concentrated region of damage along a pathline of the southerly flow into the multiple-vortex region may be associated with a strong vorticity feeder band similar to that reported by Golden and Purcell (1975). Several such feeder bands may concentrate the vorticity into the core of the tornado cyclone. The tail-cloud phenomenon appears to be related to this flow feature in the tornado cyclone wind field.
Radar data from Marseilles, Ill., and Grissom Air Force Base, Ind., were analyzed for a portion of the lifetime of the parent thunderstorm system to determine the relationship between the path of the tornado cyclone and the Sadorus, Ill., and West Lafayette tornado tracks. Finally, a pressure drop of 44.6 mb was recorded in the path of the tornado cyclone at the time the West Lafayette tornado funnel was developing.
Abstract
An observational study of the West Lafayette, Ind., tornado of 20 March 1976 has been made that presents photographic evidence of tornado formation accompanied by suction “debris” vortices in the surface boundary layer that produced a cycloidal debris pattern. Furthermore, four case studies of cycloidal debris analysis form this pattern using aerial photography support the multiple-suction vortex model proposed by Agee et al. (1975). Average values of the tangential speed of a suction vortex according to loop shift estimates ranged from 26.4 to 44 m s−1 and maximum values according to loop width estimates ranged from 44.0 to 61.6 m s−1 as the tornado grew to its most intense stage. The aerial and ground surveys of the damage track also showed that the cycloidal debris pattern corresponded to a region of F3 and F4 wind-speed damage.
Photographic evidence also documented a tail-cloud formation similar to the Fargo tornado (Fujita, 1959) that rotated cyclonically through the northeast to northwest sector of the tornado cyclone with a tangential speed of 16 m s−1 at a distance of 3 km from the tornado funnel.
Analysis of cloud photography further showed the features of the tornado system at various stages of intensity. Notable was the formation of a broad descending bowl-shaped cloud accompanied by multiple “condensation” funnels that corresponded to the region of strongest tornado intensity with F4 structural damage. This study also illustrates that multiple-suction debris vortices in the surface boundary layer can occur with only one condensation funnel present. This event is recognized as a similar but slightly different and smaller multiple-vortex phenomenon than that required for multiple-condensation funnels that fully extend through the planetary boundary layer.
Features unique to cyclodial debris patterns and the role of suction vortices in producing certain types of damage are also brought out in this study. Also a concentrated region of damage along a pathline of the southerly flow into the multiple-vortex region may be associated with a strong vorticity feeder band similar to that reported by Golden and Purcell (1975). Several such feeder bands may concentrate the vorticity into the core of the tornado cyclone. The tail-cloud phenomenon appears to be related to this flow feature in the tornado cyclone wind field.
Radar data from Marseilles, Ill., and Grissom Air Force Base, Ind., were analyzed for a portion of the lifetime of the parent thunderstorm system to determine the relationship between the path of the tornado cyclone and the Sadorus, Ill., and West Lafayette tornado tracks. Finally, a pressure drop of 44.6 mb was recorded in the path of the tornado cyclone at the time the West Lafayette tornado funnel was developing.
Abstract
Twentieth-century regional sea level changes are estimated from 12 climate models from phase 5 of the Climate Model Intercomparison Project (CMIP5). The output of the CMIP5 climate model simulations was used to calculate the global and regional sea level changes associated with dynamic sea level, atmospheric loading, glacier mass changes, and ice sheet surface mass balance contributions. The contribution from groundwater depletion, reservoir storage, and dynamic ice sheet mass changes are estimated from observations as they are not simulated by climate models. All contributions are summed, including the glacial isostatic adjustment (GIA) contribution, and compared to observational estimates from 27 tide gauge records over the twentieth century (1900–2015). A general agreement is found between the simulated sea level and tide gauge records in terms of interannual to multidecadal variability over 1900–2015. But climate models tend to systematically underestimate the observed sea level trends, particularly in the first half of the twentieth century. The corrections based on attributable biases between observations and models that have been identified in Part I of this two-part paper result in an improved explanation of the spatial variability in observed sea level trends by climate models. Climate models show that the spatial variability in sea level trends observed by tide gauge records is dominated by the GIA contribution and the steric contribution over 1900–2015. Climate models also show that it is important to include all contributions to sea level changes as they cause significant local deviations; note, for example, the groundwater depletion around India, which is responsible for the low twentieth-century sea level rise in the region.
Abstract
Twentieth-century regional sea level changes are estimated from 12 climate models from phase 5 of the Climate Model Intercomparison Project (CMIP5). The output of the CMIP5 climate model simulations was used to calculate the global and regional sea level changes associated with dynamic sea level, atmospheric loading, glacier mass changes, and ice sheet surface mass balance contributions. The contribution from groundwater depletion, reservoir storage, and dynamic ice sheet mass changes are estimated from observations as they are not simulated by climate models. All contributions are summed, including the glacial isostatic adjustment (GIA) contribution, and compared to observational estimates from 27 tide gauge records over the twentieth century (1900–2015). A general agreement is found between the simulated sea level and tide gauge records in terms of interannual to multidecadal variability over 1900–2015. But climate models tend to systematically underestimate the observed sea level trends, particularly in the first half of the twentieth century. The corrections based on attributable biases between observations and models that have been identified in Part I of this two-part paper result in an improved explanation of the spatial variability in observed sea level trends by climate models. Climate models show that the spatial variability in sea level trends observed by tide gauge records is dominated by the GIA contribution and the steric contribution over 1900–2015. Climate models also show that it is important to include all contributions to sea level changes as they cause significant local deviations; note, for example, the groundwater depletion around India, which is responsible for the low twentieth-century sea level rise in the region.
