Ernest M. Agee

Characteristics of Tornado-Like Vortices as a Function of Swirl Ratio: A Laboratory Investigation

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...

a review of mesoscale cellular convection

Abstract A brief review of the classical theory for convective instability is presented, with primary emphasis on the more recent theoretical and experimental findings that pertain to mesoscale cellular convection in the atmosphere. Important physical and geometrical features of three-dimensional patterns of free convection commonly observed over the oceans are discussed, especially those features that point to distinct differences when compared to laboratory convection. Some suggestions for future study are offered with particular reference to the AMTEX program being planned by the Japanese Committee for GARP.

Observations from Space and Thermal Convection: A Historical Perspective

Abstract An abbreviated historical account of the evolution of the satellite meteorology program is presented. Emphasis is placed on the importance of the satellite and its space platform for observing and studying atmospheric convection. Particular attention is focused on the role of the space program in establishing atmospheric manifestations of Benard-Rayleigh convection, as well as on the applicability of classical thermal convection studies to atmospheric processes. Examples of mesoscale cellular convection and related convective phenomena are presented and discussed briefly.

Mesoscale cellular convection over the oceans

Abstract A review of the understanding and progress in the study of mesoscale cellular convection (MCC) in cloud-topped marine boundary layers is provided. A comparison is made between MCC and the classical study of Benard-Rayleigh convection, with noted similarities and differences. External physical forcing mechanisms in the atmosphere are identified and discussed, in view of their effect on convection development and structure. Onset, horizontal planform, circulation direction, aspect radio and scaling phenomena are explained in terms of atmospheric processes. The global climatology of MCC is also updated and briefly discussed in terms of GCM model development.

Tornado Vortex Simulation at Purdue University

Abstract 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 Wards 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 s...

Trends in Cyclone and Anticyclone Frequency and Comparison with Periods of Warming and Cooling over the Northern Hemisphere

Abstract Available datasets and pertinent climatological studies have been examined to show the statistical trends in frequency of cyclone and anticyclone events for the Northern Hemisphere during periods of warming and cooling this century (as determined from the NASA temperature dataset). Results tend to indicate a decrease in events during cooling and an increase during warming, although further study is warranted. A second objective of this study has been to show the discontinuity introduced by the National Meteorological Center in 1970–71 in the automated 500-mb map analysis of cyclone events.

Preliminary Results from the Air Mass Transformation Experiment (AMTEX)

The field phases of AMTEX, a GARP subprogram on air-sea interaction implemented by Japan, were conducted over the East China Sea in the environs of Okinawa, Japan, during the last two weeks of February in 1974 and 1975. Investigators from Australia, Canada, and the United States also participated in this experiment. The weather was generally very favorable for this study of air mass transformation processes in 1975 because of an extensive cold air outbreak during most of the experimental period. A basic synoptic data set was obtained from 6 h soundings from an array of aerological stations centered at Okinawa. In addition, satellite, hourly surface and surface marine, oceanographic, boundary layer, radiation, radar, cloud physics, and aircraft data were obtained and have been or will be available in published data reports or on magnetic tape. Preliminary results from 1974 and 1975 reported at the Fourth AMTEX Study Conference and joint United States–Japan Cooperative Science Program Seminar, “Air Mass Tra...

A Definitive Approach to Turbulence Statistical Studies in Planetary Boundary Layers

Abstract A method for comprehensive statistical data analysis is presented. It includes a procedure for selection of segments within a data record, where data can be considered stationary, allowing the computation of statistical parameters (from data over selected segments) and their confidence intervals (estimating the statistical reliability of the parameters). The method is illustrated by analysing the vertical component of the wind velocity data collected by research aircraft flights over Lake Michigan during Project LESS (Lake Effect Snow Studies). The results indicate that for skewness and kurtosis, the requirements for acceptable “averaging distances” are less limiting than the required distances for corresponding third- and forth-order moments.

Kinematic Analysis and Air-Sea Heat Flux Associated with Mesoscale Cellular Convection during AMTEX 75

Abstract Several excellent examples of open and closed mesoscale cellular convection (MCC) were observed in DMSP satellite imagery during the second field period of the Air Mass Transformation Experiment (AMTEX), conducted 14–28 February 1975 over the East China Sea in the vicinity of the Kuroshio current. The kinematic fields of horizontal divergence, vertical motion and vorticity of the large-scale flow producing the MCC and the associated heat flux at the air-sea interface were determined to starch for observational evidence as to the cause of circulation direction in the convection cells. None of these kinematic fields had features unique to open and closed cells, with predominantly downward vertical motion and diverging horizontal flow in the convecting layer. From the study of the kinematic fields determined for 14 cases of open cells and 20 cases of closed Cells a physical depiction has been made of the distribution of the vertical motion in the vertical plane of a mesoscale cell during its formati...

Multiple Vortex Features in the Tornado Cyclone and the Occurrence of Tornado Families

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 Wards (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. Tornado...