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TIME 1826 27 28 29 1830 32 
36 ©6038 1840 Gs) 1850 1900 CST 
Fic. 1—Life cycle of the Fargo Tornado of June 20, 1957, determined by using about 200 photographs 
taken by Fargo-Moorhead citizens during the time of the storm; the cone-shaped funnel reached the 
ground only a minute after its appearance at the base of the tornado-producing cloud; the entire life 
of the storm was about 30 minutes 
tornado is concerned, no way of computing wind 
speed inside or outside the funnel has been found. 
Tangential wind speed at the funnel edge is 
summarized in Figure 6 as a function of time and 
the radius of the funnel. The dashed line in the 
figure denotes the radius of the rounded portion 
of the funnel which appeared at 18h 28m CST, 
then increased rapidly in diameter. 
The slope of the rounded bottom funnel, which 
would have maintained the cyclostrophic wind 
speed obtained by using the movie taken by 
WDAY-TYV, should be at least five times steeper 
than it actually was. At one time the rounded 
bottom of the funnel was almost flat, yet it was 
rotating at over 100 mph. This suggested that the 
constant pressure surface should cut through the 
bottom of the funnel. 
Irreversible process taking place inside tornado 
inflow—The previous discussion indicates that 
the constant pressure surfaces maintaining the 
high-speed cyclostrophie wind at the base of the 
rounded bottom funnel must have been much 
steeper than the funnel itself. 
A schematic figure of constant pressure sur- 
faces in relation to a rounded bottom funnel is 
shown in Figure 7. We should reconsider the ther- 
modynamical process taking place inside the air 
flowing into the tornado funnel. 
The dry adiabatic process in the parcel method 
is an adiabatie reversible process in thermody- 
namics. No heat should be added or produced 
along the course of the expansion of a parcel. 
This would result in the same condensation pres- 
sure regardless of the path of the parcel so long 
as it starts expanding under the same initial con- 
ditions. 
Through an irreversible adiabatic process, how- 
ever, heat is continuously produced internally 
while the parcel expands. Parcel A, , for instance, 
will show a small rate of cooling when it flows 
into a tornado, because the parcel moves near the 
ground under the influence of frictional force 
which produces heat; meanwhile the parcel loses 
its mechanical energy. Thermodynamiecally, the 
line along which the parcel expands lies between 
isentrope and isenthalpe on adiabatic charts. 
