The practical use of meteorological reports and weather-maps . ithin the areas of low barometer, occur thesmaller areas of low iDressure with which cyclones, tornadoes,and thunder-storms are associated. It is the study of theseareas, of high and low barometer, that is now of particularinterest. The dimensions of these smaller areas vary from that of a fewsquare miles, as in tornadoes, to that of five hundred milessquare, as in extensive cyclones. The largest areas of highbarometer of interest to this country, are those of the Tropicof Cancer and the South Atlantic and Pacific Oceans, and (inth
The practical use of meteorological reports and weather-maps . ithin the areas of low barometer, occur thesmaller areas of low iDressure with which cyclones, tornadoes,and thunder-storms are associated. It is the study of theseareas, of high and low barometer, that is now of particularinterest. The dimensions of these smaller areas vary from that of a fewsquare miles, as in tornadoes, to that of five hundred milessquare, as in extensive cyclones. The largest areas of highbarometer of interest to this country, are those of the Tropicof Cancer and the South Atlantic and Pacific Oceans, and (inthe winter) that which exists in the interior of the I^^orthAmerican continent. While carefully studying the every-day variations of thebarometer, the meteorologist will not forget each day diligentlyto compare the days Isobars with the mean monthly Isobars onhis isobarometric chart. These differ widely from the Isobarsfor the year as shown in the accompanying chart. ISOBAKOJIETRIC LINES, SHOWING, IN INCHES, MEAN ANNUAL ATMOSPHERIC PRESSURE FOR lAlITED 30 60 10 2 0 15 THE WINDS AND THEIR LAW. Whether considered as the indices, or as the causes of com-ing changes of weather, no phenomenon is more importantthan that of the winds. Upon the direction and force of thewinds, some meteorologists lay very great stress in everyattempt at storm forecasting; and, in order to determine these,it is necessary to draw the Isobars. Assuming the lines of equal barometric pressure to be drawnon the Weather-Chart, it is at once perceived that, in well-understood accordance with the laws of mechanics, the atmos-phere must be x)ushing from the regions of higher to those oflower xjressure. The resulting movement of the air, modifiedby the forces of inertia and friction, and by the rotation of theearth and local obstructions, is converted into the local windswhose directions are indicated by the arrows upon the maps,and whose velocities are given in miles per hour. These windsmay be called loc
Size: 2000px × 1249px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubj, booksubjectmeteorology
