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Ernest M. Agee

Abstract

The tornado taxonomy presented by Agee and Jones is revised to account for the new definition of a tornado provided by the American Meteorological Society (AMS) in October 2013, resulting in the elimination of shear-driven vortices from the taxonomy, such as gustnadoes and vortices in the eyewall of hurricanes. Other relevant research findings since the initial issuance of the taxonomy are also considered and incorporated, where appropriate, to help improve the classification system. Multiple misoscale shear-driven vortices in a single tornado event, when resulting from an inertial instability, are also viewed to not meet the definition of a tornado.

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Ernest M. Agee

Evidence has been presented and discussed to show a cooling trend over the Northern Hemisphere since around 1940, amounting to over 0.5°C, due primarily to cooling at mid- and high latitudes. Some regions of the middle latitudes have actually warmed while others, such as the central and eastern United States, have experienced sharp cooling. A representative station for this latter region is Lafayette, Ind., which has recorded a drop of 2.2°C in its mean annual temperature from 1940 through 1978. The cooling trend for the Northern Hemisphere has been associated with an increase of both the latitudinal gradient of temperature and the lapse rate, as predicted by climate models with decreased solar input and feedback mechanisms.

Observations and interpretation of sunspot activity have been used to infer a direct thermal response of terrestrial temperature to solar variability on the time scale of the Gleissberg cycle (~90 years, an amplitude of the 11-year cycles). Measurements at the Greenwich Observatory and the Kitt Peak National Observatory, as well as other supportive information and arguments, are presented to hypothesize a physical link between the sunspot activity and the solar parameter. On the time scale of the Gleissberg cycle when the mean annual sunspot number exceeds 50 it is proposed that global cooling may be initiated due to the decreased insolation. This is also supported by umbral-to-penumbral ratios computed and interpreted by Hoyt (1979a).

Observations of sensible heat flux by stationary planetary waves and transient eddies, as well as general circulation modeling results of these processes, have also been examined from the viewpoint of the hypothesis of cooling due to reduced insolation. The westerlies appear to have shifted southward and to have strengthened during the cooling period, which allows for arguments of a preferred wave number for stationary waves due to mountain interaction. This type of interaction may give rise to preferred regions of heat flux as seen observationally, e.g., the warming in the far west regions of the United States and the sharp cooling in central and eastern regions. Cyclone frequencies have also been observed to shift southward, with up to 25% reduction in January and July cyclone frequency during the cooling trend in the western border of the North America continent and in the Gulf of Alaska. This region corresponds to the location of the large amplitude ridge in the planetary wave that has been observed, especially during the winter season when the westerlies are stronger.

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Ernest M. Agee

Observational evidence of a locally induced snowfall is presented. Local snow cover patterns are shown along with accompanying meteorological data which suggest that the precipitation process was initiated by the introduction of power plant and factory effluents into a supercooled fog and stratus cloud. Such an event poses a condition favorable for the application of the Bergeron-Findeisen theory. Likely sources of nuclei involved in the precipitation process are examined in relation to the snow cover patterns.

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Ernest M. Agee
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ERNEST M. AGEE

Abstract

An examination of Applications Technology Satellite 3 photographs of the Atlantic intertropical convergence zone (ITCZ) for the period May through July of 1969 has revealed an excellent case of ITCZ wave instability that was responsible for the formation of tropical storm Anna. Photographs are presented to emphasize the argument that wavelike perturbations in the ITCZ, independent of easterly disturbances, are capable of amplifying, breaking, and shedding vortexes of hurricane proportions. Observational evidence of this means of hurricane genesis strongly suggests the need for a theoretical treatment of the problem.

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Ernest M. Agee

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.

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Ernest M. Agee

Abstract

Manifestations of both Rayleigh-Taylor instability and Kármán vortices in atmospheric flows are recognized, and existing theory is applied to infer some values for the horizontal and vertical eddy transport coefficients for momentum, Kh, and Kz, respectively.

Periodic protrusions of cloud material from beneath cirrus bands sometimes associated with warm frontal

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Ernest M. Agee

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.

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Marina Zivković and Ernest M. Agee

Abstract

In this paper we present the results of numerical investigation of a two-dimensional nonlinear set of Boussinesq equations governing Bénard–Rayleigh convection using spectral representation in the horizontal direction and finite-difference formulation in the vertical direction. Integrations were characterized by high resolution (up to 171 horizontal modes on 32 levels in the vertical direction) and large domain size (ten linear cells were represented). The results presented were obtained for moderate values of Rayleigh number (1150 < Ra < 33 000) that was varied in a near continuous fashion.

It is found that two-dimensional heat flux transitions lead to simulations of various temporal states when sufficient resolution and high aspect-ratio domain of integration are used. The change of slope of the time-averaged logarithmic heat flux curve (log Nu) is simulated in a gradual manner by means of a series of bifurcated solutions.

This study demonstrates that transition from steady to time-dependent convection in two-dimensional simulations is the generic property of the Boussinesq equations. The findings highlight the roles of scale truncation and large domain aspect-ratio in simulations of self-organizing properties of thermal convection. They also provide useful information for the application of nonlinear spectral models to the study of organized convection.

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Ernest M. Agee and Andrea Orton

Abstract

An initial phase of laboratory investigation has been completed in pursuit of a global-scale methodology for reduction of CO2 in ambient air through direct air capture (DAC). The methodology presented previously by Agee, Orton, and Rogers provides the background for this study. The laboratory prototype experiment presented has been designed to assess the potential for removing CO2 from ambient air by snow deposition. The approach consists of refrigeration to achieve the required CO2 deposition temperature of 135 K at 1 bar of pressure. The refrigerant of choice is liquid nitrogen (LN2) with cooling (77 K) at the top of a cylindrical 26.5-L Pyrex glass sequestration chamber. A highly conductive aluminum base with 14 instrumentation ports rests at the interface between the LN2 reservoir and the sequestration chamber. The cooling and mixing through Rayleigh–Taylor instability achieves uniform deposition temperature. Insulation to maintain the cooling process is provided to sustain CO2 depletion phase change at 135 K. The coldest temperature achieved in experimentation was 125 K. The required cooling period was 4.5 h, with an additional hour to achieve uniform chamber temperatures ≤ 135 K through top-down convective mixing. Experimental measurements showed a reduction of CO2 in the chamber air from initial values of ~500 ppmv down to 35 ppmv. Discussion is given to the issue of chamber CO2 frost versus CO2 snowflake formation, as well as the overall relevance of the experiment to DAC through refrigeration and storage in Antarctica to reduce atmospheric CO2.

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