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- Author or Editor: Duncan C. Blanchard x
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Abstract
A modification of Millikan's classic oil-drop experiment was used to determine the electric charge and radius of drops that were ejected from a bursting bubble at an air-sea water interface. Charge measurements were made of both the natural and the induced charge. Drops of 2 to 20 microns in radius carry natural charges of at least 2 × 102 to 5 × 103 elementary units, respectively. The induced charges are considerably higher, reaching 106 elementary units on drops of 50 microns radius. The sign of the natural charge is positive on drops < about 4 microns. For larger drops both the sign and magnitude of the charge appear to be a function of the depth of water through which the bubble rises.
The meteorological significance stems from the fact that rain and snow, as well as whitecaps, can produce great numbers of small bubbles in the surface waters of the oceans. Both laboratory and field work suggest that the majority of these bubbles produce positively charged drops that contribute to the atmospheric space-charge. Of special significance is the fact that, for positive induction fields less than about 25 v cm−1, a positive charge is found on the small drops. For fields greater than 25 v cm−1 the induced negative-charge exceeds the natural positive-charge and so the drops carry a net negative-charge. Consequently, small bubbles breaking at the surface of the sea in the presence of the earth's fair-weather positive field of about 1 v cm−1 will produce drops that carry a positive charge. Calculations based on measurements of the bubble spectrum produced by whitecaps indicate that the charge on the drops may, under some conditions, provide a counter-current of the same order of magnitude as the fair-weather conduction current. Thus the sea may be a source as well as a sink for the charge that maintains the earth's positive electric-field.
Abstract
A modification of Millikan's classic oil-drop experiment was used to determine the electric charge and radius of drops that were ejected from a bursting bubble at an air-sea water interface. Charge measurements were made of both the natural and the induced charge. Drops of 2 to 20 microns in radius carry natural charges of at least 2 × 102 to 5 × 103 elementary units, respectively. The induced charges are considerably higher, reaching 106 elementary units on drops of 50 microns radius. The sign of the natural charge is positive on drops < about 4 microns. For larger drops both the sign and magnitude of the charge appear to be a function of the depth of water through which the bubble rises.
The meteorological significance stems from the fact that rain and snow, as well as whitecaps, can produce great numbers of small bubbles in the surface waters of the oceans. Both laboratory and field work suggest that the majority of these bubbles produce positively charged drops that contribute to the atmospheric space-charge. Of special significance is the fact that, for positive induction fields less than about 25 v cm−1, a positive charge is found on the small drops. For fields greater than 25 v cm−1 the induced negative-charge exceeds the natural positive-charge and so the drops carry a net negative-charge. Consequently, small bubbles breaking at the surface of the sea in the presence of the earth's fair-weather positive field of about 1 v cm−1 will produce drops that carry a positive charge. Calculations based on measurements of the bubble spectrum produced by whitecaps indicate that the charge on the drops may, under some conditions, provide a counter-current of the same order of magnitude as the fair-weather conduction current. Thus the sea may be a source as well as a sink for the charge that maintains the earth's positive electric-field.
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Abstract
A brief survey of the major techniques of raindrop size-sampling is given. The filter-paper technique, finally adopted for use in this study, adapts itself admirably to the sampling of Hawaiian orographic rains.
The change in the drop-size distribution of rain as it falls from cloud to ground may be considerable. It is affected by wind shear, gravity separation, evaporation and drop collision. The evaporation error alone can be appreciable. The many small drops of the Hawaiian orographic rains may completely evaporate in a sub-cloud fall of only 1000 m. The evaporation problem was eliminated, and the others minimized, by sampling all the orographic rain at cloud base or within the cloud itself.
Drop-size distributions were obtained in such non-orographic rains as thunderstorms and cyclonic storms. The pertinent meteorological parameters, such as liquid-water content, median drop diameter, and radar reflectivity, agree reasonably well with the values given by other investigators.
The measurements made in orographic rains from non-freezing clouds, however, lead to considerably different values of these factors. The raindrop distributions are narrow, with the largest drops rarely exceeding 2 mm in diameter. In general, the higher the intensity, the more numerous are the drops at the large end of the spectrum. At the small end of the drop spectrum (<0.4 mm), however, increased intensity is accompanied by a decrease in the drop count. Distributions of this type indicate the absence of any chain-reaction process.
Concentrations of drops less than 0.5 mm in diameter often are in excess of 40,000 m−3. These large numbers of small drops give low values for median drop diameter and radar reflectivity, but high values of liquid-water content.
All of the drop distributions have been put into three categories: (1) non-orographic rain, (2) orographic rain at cloud base, and (3) orographic rain within the cloud and near cloud top. In each case, regression equations have been developed to express the meteorological parameters as a function of rain intensity.
Abstract
A brief survey of the major techniques of raindrop size-sampling is given. The filter-paper technique, finally adopted for use in this study, adapts itself admirably to the sampling of Hawaiian orographic rains.
The change in the drop-size distribution of rain as it falls from cloud to ground may be considerable. It is affected by wind shear, gravity separation, evaporation and drop collision. The evaporation error alone can be appreciable. The many small drops of the Hawaiian orographic rains may completely evaporate in a sub-cloud fall of only 1000 m. The evaporation problem was eliminated, and the others minimized, by sampling all the orographic rain at cloud base or within the cloud itself.
Drop-size distributions were obtained in such non-orographic rains as thunderstorms and cyclonic storms. The pertinent meteorological parameters, such as liquid-water content, median drop diameter, and radar reflectivity, agree reasonably well with the values given by other investigators.
The measurements made in orographic rains from non-freezing clouds, however, lead to considerably different values of these factors. The raindrop distributions are narrow, with the largest drops rarely exceeding 2 mm in diameter. In general, the higher the intensity, the more numerous are the drops at the large end of the spectrum. At the small end of the drop spectrum (<0.4 mm), however, increased intensity is accompanied by a decrease in the drop count. Distributions of this type indicate the absence of any chain-reaction process.
Concentrations of drops less than 0.5 mm in diameter often are in excess of 40,000 m−3. These large numbers of small drops give low values for median drop diameter and radar reflectivity, but high values of liquid-water content.
All of the drop distributions have been put into three categories: (1) non-orographic rain, (2) orographic rain at cloud base, and (3) orographic rain within the cloud and near cloud top. In each case, regression equations have been developed to express the meteorological parameters as a function of rain intensity.
Abstract
Potential gradient and space charge measurements have been made along the shore on the island of Hawaii. Both of these atmospheric electric parameters were positive and considerably higher and more variable when the air came from over the sea as opposed to air that came from over the land. The nature of the fluctuations in the space charge and potential gradient suggests that some of the positive space charge found in the sea air originated from the sea in the surf zone a few meters upwind of the measuring site. It is suggested that intensive bubbling in the surf along the shore resulted in the ejection of positively charged droplets of sea water into the atmosphere. The flux of charge from the surface of the water was calculated to he about 3 × 104 elementary charges per square centimeter per second.
It is felt that a similar charge flux would be produced by bubbling processes associated with whitecaps on the open sea. The various factors that may modify the oceanic charge production are discussed.
Abstract
Potential gradient and space charge measurements have been made along the shore on the island of Hawaii. Both of these atmospheric electric parameters were positive and considerably higher and more variable when the air came from over the sea as opposed to air that came from over the land. The nature of the fluctuations in the space charge and potential gradient suggests that some of the positive space charge found in the sea air originated from the sea in the surf zone a few meters upwind of the measuring site. It is suggested that intensive bubbling in the surf along the shore resulted in the ejection of positively charged droplets of sea water into the atmosphere. The flux of charge from the surface of the water was calculated to he about 3 × 104 elementary charges per square centimeter per second.
It is felt that a similar charge flux would be produced by bubbling processes associated with whitecaps on the open sea. The various factors that may modify the oceanic charge production are discussed.
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