THE PRECIPITATION OF SLEET AND THE FORMATION OF GLAZE IN THE EASTERN UNITED STATES, JANUARY 20 TO 25, 1920, WITH REMARKS ON FORECASTING
1920; American Meteorological Society; Volume: 48; Issue: 2 Linguagem: Inglês
10.1175/1520-0493(1920)48 2.0.co;2
ISSN1520-0493
Autores Tópico(s)Arctic and Antarctic ice dynamics
ResumoSYNOPSIS An attempt is made by means of accurate charts of precipitation during the previous 12 hours, current temperature, pressure, and lines of wind flow, in combination with such aerological data as could be obtained, to construct cross-sections of the lower 3 kilometers of the atmosphere, during the period January 20 to 25, 1920. From such charts are shown the actual processes which produce rain, sleet, and snow, separately and in combination, in such a manner as to produce the ice cover, which is called an “ice storm.” The condition is, briefly, a cold northerly wind underrunning a warm southerly current forcing the latter aloft. The vertical distribution of temperature, shown in the crass-sections, indicates the manner in which the isotherms in that, territory covered by the northerly wind rise normally until the level of the overrunning southerly wind is attained, where the isotherm swerves sharply northward. The distance that the isotherm of freezing reaches is indicated by the northern limit of the precipitation of sleet. An empirical relation was obtained between the distance from the wind-shift line to the 32° isotherm and (1) the width of the glaze belt, (2) the width of the sleet belt, (3) the distance of the center of the sleet belt north of the 32° isotherm, (4) the width of the glaze belt on a meridian 4° east 12 hours later, and (4) the width of the glaze belt on a meridian 8° east 24 hours later. These values are presented with the full realization that they may be true for this particular storm only, and are as follows: (1) The width of the glaze belt=the distance between the 32° isotherm and the wind-shift line; (2) The width of the sleet belt=0.7 × the distance between the 32° isotherm and the wind-shift line; (3) The distance between the 32° isotherm and the center of the sleet belt=0.8 × the distance between the 32° isotherm and the wind-shift line; (4) The width of the glaze belt 4° east, 12 hours later=0.9 × the distance between the 32° isotherm and the wind-shift line; and, (5) The width of the glaze belt 8° east., 24 hours later=0.8 × the distance between the 32° isotherm and the wind-shift line. The importance of the wind-shift line in forecasting the region over which sleet or glaze are likely to occur is strongly emphasized, since it marks the point of ascent of the southerly wind and hence is the basis upon which rests the location of this type of precipitation.
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