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J. D. SARTOR

Abstract

Narrow band slices have been taken of the radio emission spectrum from convective clouds in the frequency range from 30 mc./sec. to 550 mc./sec. and at 7.5 kc./sec. to monitor long and short range lightning discharges. Despite the careful choice of the bands to avoid interference from manmade sources, a major problem is the identification of spurious noise. In spite of these interferences, radiation apparently associated with growing convective clouds has been observed from an aircraft. The number of discharges per km.2 per sec. observed at the different frequencies is a function of receiver sensitivity, suggesting that “atmospherics” vary greatly in spectral intensity. The number of discharges observed generally exceeds previous estimates. A relation between the occurrence of sporadic E and major thunderstorm precipitation areas is reported and evaluated in light of previous observations of the similar relationships. Together, the concepts suggest a linkage between strong solar flare activity and anomolous thunderstorm rainfall.

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J. D. Sartor

Abstract

The growth of electric fields in clouds resulting from charge rearrangement due to particle interaction and translation is calculated under the assumption that the initial electrification is provided by the fair weather charge distribution of the atmosphere or by some other basic charge separating process. The results demonstrate that particle interaction must be taken into account in the electrification process during the precipitation formation period. In fact, they show that, starting with the normal fair weather field, it is possible to explain qualitatively and quantitatively many of the presently known observations of the electrical growth and field recovery behavior of thunderstorms.

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J. D. Sartor

Abstract

The physical factors governing the induction charge separation mechanism in thunderstorms are discussed. Evidence is presented indicating that rebounding collisions between hailstones and cloud droplets are not (as suggested by Moore, 1975) restricted to grazing collisions near the hailstone equator. Collisions between hailstones and cloud droplets can therefore he expected to play an important part in the charge separation process in thunderstorms.

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J. D. Sartor and C. E. Abbott

Abstract

The lack of detailed information of the drag forces of cloud droplets during accelerated motion has made it necessary to assume that steady-state drag forces can be used to predict their motion at all times. This assumption is made implicitly in the calculations of collision efficiencies of cloud droplets even though theory and experiment demonstrate that drops accelerate while hydrodynamically interacting. Interaction of droplets in turbulent motion should be particularly sensitive to discrepancies between accelerated drag and steady state.

We have observed the motion of small water drops (Reynolds number R≲5) accelerating from rest in a still air chamber. The drag coefficients of the accelerated motion of small droplets, obtained in this manner, are compared with observations of steady-state drag coefficients and are found to agree within experimental error. Using the steady-state drag coefficients obtained by Le Clair et al. from wind tunnel studies and numerical solutions to the Navier-Stokes equation of motion, we analytically integrated the equations of motion (R≲5) for accelerating and decelerating drops to obtain analytic prediction equations for their velocity and position as functions of time. Calculations from these equations are compared with our observations and found to agree within experimental error, usually much less than 10%.

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J. D. Sartor, I. Katz, and R. E. Katz

Interest of the radio-meteorologist centers on diffusion because the vertical structure and the non-homogeneity of the atmosphere, in terms of refractive index, play a vital part in radar propagation. A portable method of measuring diffusion consists of lifting smoke-puff generators aloft with tethered balloons, setting off puffs remotely and photographing them with two motion picture cameras. From the resulting records of the areal spread of the smoke and the distance it travels, one may compute values of diffusion coefficients. Preliminary experiments yield data in accord with values published by Sutton.

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