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Edwin Kessler

An apparent mesocyclone passed directly over a surface station that was equipped with both digital and strip chart recorders near Criner, Okla. Peak gusts were 18 m s−1 (35 kt); within 3 min the surface wind changed from strong southeasterly to strong westerly. The pressure dropped 5 mb in 52 min and recovered 4 mb in 6 min. There was only a trace of precipitation. The wind system was probably an inertial remnant of circulation formed with a thunderstorm whose peak intensity occurred about three hours before the cyclone was observed.

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Edwin Kessler

Abstract

The average length of echoes and a measure of pattern bandedness in digitized PPI displays are estimated from exponential-function approximations to the pattern autocorrelation coefficients. Average echo lengths estimated by the computer are correlated to actual lengths in 39 cases with a coefficient of 0.9. This processing of radar weather data may be useful for characterizing mesoscale transport processes and for operational problems such as air traffic control.

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Edwin Kessler

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Edwin Kessler

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The density of cloud and precipitation relates via simple approximations to the slope, vertical air speed, and diameter of moist updraft columns, and to the fallspeed and residence time of cloud and precipitation particles.

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Edwin Kessler

The prominent characteristics of tornadoes, their sociological and meteorological importance, aspects of the national weather service that pertain to storm forecasting and warning, observational and theoretical studies of tornadoes, and some prospects for modifying tornadoes, are briefly surveyed. Some paths for future development of the warning service and of scientific investigations are indicated.

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Edwin Kessler
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Edwin Kessler

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Oklahoma Mesonetwork data are used to illustrate important atmospheric features that are not well shown by the usual synoptic data. For example, some shifts of wind from south to north that are shown as cold fronts on synoptic charts are not cold fronts by any plausible definition. As previously discussed by Fred Sanders and others, such errors in analysis can be reduced by knowledge of the wide variety of weather phenomena that actually exists, and by more attention to temperatures at the earth's surface as revealed by conventional synoptic data. Mesoscale data for four cases reinforce previous discussions of the ephemeral nature of fronts and deficiencies in the usual analyses of cold fronts. One type of misanalyzed case involves post-cold-frontal boundary layer air that is warmer than the prefrontal air. A second type is usually nocturnal, with a rise of local temperature during disruption of an inversion and a wind shift with later cooling that accompanies advection of a climatological gradient of temperature.

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Edwin Kessler III

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If distributions of precipitation in the atmosphere could be understood in terms of their associated three-dimensional winds, then radar, radiosonde, and surface observations might be utilized in new ways as sources of information about the winds. In this paper, continuity equations for precipitation content of horizontally uniform updrafts, or to the cores of simple cells such as represented by showers formed in the absence of vertical wind shear. A parabolic profile of updrafts is assumed. When the precipitation profile is steady-state and the fall speed of precipitation is constant, the amount of precipitation per unit volume of air increases rapidly downward in mid-atmosphere. Near the surface, changes in the vertical are very small. Maxima of precipitation content occur aloft before steady conditions obtain throughout the updraft layer; in the steady case, maxima aloft may occur when the terminal fall speed of precipitation increases only slightly faster than the updrafts and with little increase of fall speed during their growth, as is often the case with snow. An explanation is offered for the difference between the vertical distributions of precipitation associated with widespread systems and with showers, and means for practical utilization of the results are suggested.

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Edwin Kessler III

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EDWIN KESSLER III

Abstract

Continuity equations are used to clarify relationships between air motions and distributions of accompanying precipitation. The equations embody simple modeling of condensation and evaporation with the following assumptions: (1) water vapor shares the motion of the air in all respects; (2) condensate shares horizontal air motion, but falls relative to air at a speed that is the same for all the particles comprising precipitation at a particular time and height; (3) the cloud phase is omitted.

After a review of one-dimensional models, the distributions of condensate in two-dimensional model wind fields are discussed with regard to instantaneous evaporation of condensate in unsaturated air and to no evaporation. The most nearly natural cases must lie between these extremes. The methods for obtaining solutions are instructive of basic interactions between air motion and water transport. The steady-state precipitation rate from a saturated horizontally uniform updraft column is shown to equal the sum of the vertically integrated condensation rate and a term that contains the horizontal divergence of wind. The latter term becomes relatively small as the ratio of precipitation fall speeds to updrafts becomes large. A basis for some studies of precipitation mechanisms, the equation N(V + w) = const., where N is the number of particles comprising precipitation at a particular point in space and time, V is their fall velocity, and w is the updraft, is shown to imply violation of continuity principles unless variations in w are quite small. Continuity equations are applied to radar-observed convective cells (generators) and their precipitation trails, and to radar-observed precipitation pendants (stalactites), and provide bases for estimating the strength, duration, and vertical extent of the associated vertical air currents. The stalactite study also discloses how horizontal variations of precipitation intensity arise during precipitation descent through a saturated turbulent atmosphere.

The continuity equations are powerful tools for illuminating fundamental properties of wind-water relationships. The conclusion discusses attractive paths along which this work should be extended.

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