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Biomedical subjects

M A Wells

Publications and source records attributed to M A Wells.

At least 145 records · Page 8Linked to original sources
PubMed1973

Downwind and upwind effects in the Arizona cloud-seeding experiment.

The principal subject of this report is a comparison of precipitation on days with seeding with that without seeding, averaged over those rain gauges that on each particular day were "downwind," "upwind," or to the sides. Two estimates of relevant wind directions are used, based on successive radiosondes at Tucson that bracketed the scheduled time of seeding. By use of these radiosondes, the apparent effects of seeding on rain in downwind localities 90-180 miles (145-290 km) away from target were found to be an apparent 45% loss of rain (P = 0.002) and an apparent 34% loss of rain (P = 0.028), respectively. Other results indicate considerable geographic heterogeneity.

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PubMed1972

Re-evaluation of the Arizona cloud-seeding experiment.

The apparent effect of cloud seeding on the average 24-hr precipitation in the Santa Catalina Mountains during the two programs of the 7-year-long Arizona experiment was found to be a 30% loss of rain (P = 0.06). Considering rainy days only, the apparent effect is a 34% loss of rain (P = 0.03). On South-East days the apparent loss was 40% (P = 0.03). The analysis of the diurnal variation in the amounts of hourly precipitation brought out two suggestions: (i) more active silver iodide enters the clouds through seeding at their bases than at the -6 degrees C level; (ii) the population of experimental days includes two categories with opposite responses to seeding: augmentations of rain in one case and losses in the other. These suggestions require independent confirmation.

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PubMed1971

Further studies of the whitetop cloud-seeding experiment.

By means of two stratifications of experimental days of the Whitetop Project-into categories E and W and into categories air mass and frontal-the effects of cloud seeding on precipitation downwind, upwind, and to the sides, up to 180 miles from the seeding line, were investigated. No significant effects were found for W and frontal days. On the other hand, for E and airmass days, significant and highly significant apparent effects of seeding were found in all directions and in areas at distances up to 180 miles. All these significant apparent effects are negative, the largest of them indicating that seeding reduced precipitation to one quarter of its unseeded value.

Journal Article↗
PubMed1971

Hypothetical explanations of the negative apparent effects of cloud seeding in the whitetop experiment.

In order to explain the apparent losses of rain ascribable to seeding at the Whitetop trial, particularly large and highly significant in the stratum E (but not in the opposite stratum W) of experimental days, it has been hypothesized that seeding causes widespread cloudiness and subsequent lowering of ground temperatures. This hypothesis is flatly contradicted by the observations: the seeded E-days (but not W-days) were uniformly less cloudy and hotter than those without seeding. Curiously, these differences prevailed not only from the scheduled time of seeding but also for several hours beforehand. The average rainfall for the 10 hr that preceded the time of seeding was investigated in eight "cells", defined by the day's wind direction to be downwind, upwind, and to the sides and "far" and "near" the center of seeding. Highly significant decreases were found in the far-upwind and far-left cells, indicating an earlymorning disparity between those E-days that later were declared as experimental to be seeded and those E-days that were declared as experimental not to be seeded. This disparity, difficult to explain by chance variation, suggests that particular caution be used in treating differences in the rainfall between seeded and not-seeded days in the Whitetop trial as having been caused by seeding.

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