as at the source, and outside of this area the spectrum is zero. 
In all three filters, the © cuteff values are given by the same 
expression. In each of the three filters the # cutoff values 
are slightly different. The determination of the 86 cutoff values 
and the ©-band width will be described first; then the various 
ft -band width determinations will be describeds and finally 
some sample filters will be graphed. 
Determination of the 0-band width and the 6 cutoff points 
The angles ®p, A®,, and Ae, are functions of x, y, and 
Wee For a storm of given width, the values of x and y then deter- 
mine these angles. If the width of the storm is doubled, and if 
the values of x and y are doubled, the same values for the angles 
result. Consequently, if x and y are measured in units of We» 
the angular cutoff values are in a sense independent of the 
actual width of the storm. In figure 24, lines of constant 6), 
Ae, and A 8, are shown on an x,y coordinate system with units 
marked off in terms of the width of the storm. Note that A 8; 
is slightly greater at each point than A@,. Given [a,(# ,e)]° 
and the point in the x,y plane at which the forecast is to be 
made, measure x and y in terms of Wy and enter the point on figure 
24 to read off @), Ao, and Ae,. Then in the  ,© polar co- 
ordinate plane draw a line through # equals zero along a radius 
at the value 8p- Mark off an angular increment in the positive 
6 direction equal to Ae, units from the values 9p, and a decre- 
ment in the negative © direction equal to Ae,.- Draw the two 
radii obtained. The two outside lines then cut off a sector of 
=239- 
