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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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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

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
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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

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

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

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 and Alyssa Hendricks

Abstract

The placement of operational Doppler radar at National Weather Service offices in Florida in 1994 and 1995 has produced a distinct climatological discontinuity in archived records of hurricane-induced tornado (HIT) events. During the period of this study (1979–2010), Florida experienced 91 named tropical cyclones (omitting years 1994 and 1995) that produced a total of 300 HITs, as recorded in the NOAA Storm Data climatological publication. The 30 years of records examined for 1979–2010 consisted of 15 years as the pre-Doppler period (1979–93) and 15 years as the Doppler period (1996–2010) and produced an average of 1.92 HITs per tropical cyclone for the pre-Doppler period and 3.85 HITs per tropical cyclone for the Doppler period. Additionally, the HIT statistics were further compiled as the number of HITs per potential HIT day, which yielded values of 0.52 and 1.14, respectively, for the pre-Doppler and Doppler periods. Normalized statistics are based on the total accumulated number of potential HIT days for each period (96 for pre-Doppler and 219 for Doppler). Further, it has been determined that (a) no HITs were recorded in the pre-Doppler period for hurricanes greater than category-2 intensity, ostensibly because of the inability to separate hurricane wind damage from tornado damage, whereas (b) the Doppler period averaged 5.0 and 11.7 HITs per category-3 and category-4 storms, respectively. Finally, this study has clearly documented the magnitude (and effect) of Doppler technology on HITs reported in Florida Storm Data archives. The Doppler era is much more accurate, whereas the pre-Doppler era HIT occurrences are severely underestimated.

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Jeffry Rothermel and Ernest M. Agee

Abstract

The 1 s data set collected by the NCAR Electra research aircraft in the presence of closed mesoscale cellular convection (MCC) has been examined for the purpose of determining the convective wind field and horizontal profiles of temperature and specific humidity. Two flight legs during AMTEX (16 February 1975) were selected for study: one at the 100 m level (case 1) and the other at the 970 m level (case 2), 30 m below cloud base

Two closed cells with diameters of 39,0 and 33.0 km were traversed in case 1. Filtered virtual temperature data showed a double-cycle variation, with an average difference between warm and cool regions of 0.32 K. The difference in specific humidity between moist cell center and dry cell wag was ∼1.0 g kg−1. The vertical velocity power spectrum showed no MCC-scale energy. Horizontal wind velocity data indicated convergence toward cell center with mesoscale wind velocity components ∼15 m s−1. The data for case 2 encompassed two closed cells, with traverse lengths ∼32 km each. The difference between dry cell wall and moist cell center was ∼0.7 g kg −1 Filtered vertical velocity showed downward motion in cell walls and upward motion near cell center, the difference being ∼1.0 m s−1 Filtered virtual temperature data indicated a weak single-cycle variation. Horizontal convective velocities were 0.75 m s−1

A physical explanation of the double-cycle temperature profile at the 100 m level is offered based on the combined effects of 1) warm air entrainment from an overlying inversion layer; 2) radiative cooling at cloud-top level, side-wall mixing and evaporative cooling, and subsequent (partial) moist adiabatic descent of air; and 3) sensible heating at cell center due to the warm sea surface.

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