154 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



The chart (fig. no) gives the vertical component of specific momentum in the 

 height where pressure is one unit smaller than at the ground. The sheet can have a 

 thickness defined by the decrease of pressure of one m-bar, of one c-bar, or of one 

 d-bar. The numbers added to the curves will then represent the vertical specific 

 momentum respectively in the units o. i gram per square meter per second, i gram 

 per square meter per second, or 10 grams per square meter per second. 



Instead of defining the sheets by the decrease of pressure, we can define them 

 as sheets of a thickness of 10, ioo, or iooo meters. The numbers added to the curves 

 on the chart of fig. no will then approximately represent vertical velocity, in the 

 following units: in tenths of millimeters if the sheet has a thickness of 10 meters, 

 in millimeters if the sheet has a thickness of ioo meters, and in centimeters if the 

 sheet has a thickness of iooo meters. This rule will be very convenient for getting 

 a qualitative picture of the vertical motion which the chart of fig. no describes 

 quantitatively by vertical specific momentum. 



The chart is seen to give an ascending velocity which has its greatest values near 

 the point and along the lines of convergence. But areas of descending velocity are 

 also found, even near the point of convergence and between two lines of convergence. 



189. Complete Kinematic Diagnosis. Kach of the three methods of represent- 

 ing free vertical motion, by areas of equal vertical transport, by topographic repre- 

 sentation of surfaces of flow, or by charts of the vertical component, will have its 

 special advantages in special cases. But the question will now be which of them will 

 work best as a link in a complete kinematic diagnosis of atmospheric motions. 



The construction of a chart of areas which represent equal vertical transport 

 will be easy for each single atmospheric sheet. But inasmuch as the lines of flow 

 have a different course in the different sheets, the summation of the transports 

 produced in the different sheets will be circumstantial. For this reason we shall 

 not make a general use of this method. 



When the topographic method is applied, we shall not meet with this difficulty. 

 We can pass by simple graphical addition from the relative topographies which we 

 find by the solenoidal condition to the corresponding absolute topographies. But 

 the drawback of the topographic method will be the great complication of the sur- 

 faces of flow. In the neighborhood of the initial curve C used to define the surface 

 it will be relatively simple. But the farther we follow it the more complicated will 

 be the course of the contour-lines. Finally we shall always come to places where 

 the surface folds itself so as to be cut by a vertical line at more than one point. The 

 topographic method of representation will then become complicated, and will lose 

 its conspicuity. While the method may do good service for special investigations, 

 we shall not try to take it as the base for a universal method. 



We shall therefore base the complete kinematic diagnosis upon the representa- 

 tion of the vertical motion by charts of the vertical components. The production 

 of these charts is a little more laborious than that of the preceding ones, but as soon 

 as they are produced all further operations will be easy to perform upon them. 



