DIFFUSION FROM A C'ONTINUOUS SOURCE A T SEA
31 9
I
1 - - - - I
10
SO
100
Diffusion Time
t (mind
Pic;. 2. Change of n,' with I for a dye plume in Red Wharf Bay, 21 June 1969.
other 12 releases, the value of m lay between I .2 and 2.7. The constants in the
power law equation were evaluated and the value of K, computed for a
standard diffusion time of 30 min, so that the values of K, were comparable.
They ranged from 240 cm2/sec to 4100 cm2/sec with a median value of
1 200 cm2/sec.
In most of the experiments the data could be fitted to the power laws
m = 1.5 or m = 2 without loss of significance, but a considerable loss of
significance occurred if laws rn = 1 or It) = 3 were fitted. The implication of
rn > 1 is that diffusion took place at a faster rate than that corresponding to
a constant K , , i.e., to an eddy scale small cornpard with the width of the
plume. On the other hand, since m < 3, diffusion was slower than would
correspond to an inertial subrange in turbulence that was locally isotropic in
the horizontal plane.
( 5 )
of = B2t2
and (3) as
(6 1
K , = B2t
where B is a constant diffusion velocity.
If m = 2, Eq. (2) may be written