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Grant L. Darkow

Abstract

The distribution in time and space of the total specific energy (cpT + gZ + Lq + V2 /2) of the environment of severe storms is examined. Comparison of the total energy profiles of tornado proximity soundings with the closest check soundings show pronounced differences. The tornado proximity sounding has substantially higher total energy values in the lower troposphere and lower values in the mid-troposphere than nearby stations. It is shown that the total specific energy may be approximated with negligible error by the static energy (cpT + gZ + Lw) and that this parameter is proportional to isobaric equivalent potential temperature and is similarly conservative.

A practical application of these results to severe storm forecasting is given in the form of a “Total Energy Index.” This index is readily and objectively determined from routinely transmitted upper air data. Unlike other widely used stability indices, the Energy Index indicates not only the energy release associated with the ascending, potentially warm air but also the possible contribution of the saturated descent of the evaporatively cooled, potentially cold mid-tropospheric air to the total energy release of the storm. Examples are shown of the Energy Index field on several recent tornado days.

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Henry Liu
and
Grant L. Darkow

Abstract

Wind generated Pressure inside buildings, normally referred to as “internal pressure” in engineering literature, has a profound effect on the atmospheric pressure measured with indoor barometers during severe storms. The magnitude of the internal pressure is proportional to the dynamic pressure (stagnation pressure) which in turn increases with the square of the wind speed. Normally, this pressure is negative, and it has a magnitude in the neighborhood of 50% of the stagnation pressure. Its value changes drastically when an opening such as a door or window is opened or broken in high winds. The internal pressure also fluctuates readily with the fluctuations of the external pressure when a large opening exists. Surface pressure measurements taken in severe storms may contain serious errors if this internal pressure effect is not corrected. The paper summarizes latest research findings on internal pressure reported in the literature, and explores their implications to meteorology—especially to the study of severe storms such as hurricanes and tornadoes. Measures to correct or reduce the error generated by internal pressure are also discussed.

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Grant L. Darkow
and
Owen E. Thompson

Abstract

An hypothesis is given for the cause of the observed diurnal oscillations in the mid- and upper-tropospheric wind field that occur in association with oscillations of the boundary layer wind field and low-level, nocturnal jet occurrences. A simple mathematical model of the middle and upper troposphere is solved using perturbation techniques subject to the condition that the three-dimensional velocity is continuous at a plane separating the boundary layer from the atmosphere above, and the vertical motion is zero at the tropopause height. Theoretical results are presented which show good agreement with previously published wind data from the surface to the region of the tropopause.

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Brynn W. Kerr
and
Grant L. Darkow

Abstract

Environmental flow relative to tornado-producing thunderstorms is examined through the use of the large tornado proximity sounding dataset compiled at the University of Missouri. It is believed that the 184 soundings gleaned from this collection represent the largest, most restrictive database of its kind with observed storm velocities, as determined from microfilm of conventional National Weather Service radar. Using these storm velocities, mean storm-relative wind profiles were derived for the entire data sample and sample subsets based on tornadic intensity, strength of the mean environmental flow, magnitude of CAPE, and direction of storm motion with respect to the mean environmental wind vector. Although it is apparent that a number of tornadoes occur independent of the larger-scale flow, the mean storm-relative wind profiles suggest that there is a preferred storm-relative flow structure for tornadic thunderstorms. Tornadic intensity in association with this structure appears to strengthen as 1) the magnitude of storm-relative helicity grows through an increasingly deep layer of the lower through midtroposphere and 2) mid- and upper-level storm-relative winds strengthen while possessing decreasing directional variability at their respective heights above ground level (4–12 km AGL).

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