Baltic Sea

Depth (m)
50
100
150
200
a
250
2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
θ ( o C)
8 x 10−3 Days since 31 August 1997
Var θ , (K 2 )
6
4
2
b
0
0 50 100 150 200 250 300 350 400 450
4
x 10 −5
c
κ θ
(m 2 /s)
2
0
0 1 2 3 4 5 6 7 8 9 10
L (m)
Figure 3.11: (a) Potential temperature prole from 27 March 1998, ltered with a cut-o length of 3
m (grey stars) and 50 m (black dots). Horizontal lines indicate the intrusion layer (90-170 m) used for
the analysis; (b) time series of 〈θ ′2 〉 (stars) for all available temperature proles between 31 August 1997
and 7 November 1998, and exponential t (dashed line); (c) vertical intrusion scale, L, vs. diusivity of
heat, κ θ .
variance associated with the intrusions,
∂〈θ ′2 〉
∂t
〈 ( ) ∂θ
′ 2 〉
= −2κ θ
∂z
≈ −2κ θ
〈θ ′2 〉
L 2 , (3.9)
where in the last step we have assumed that vertical gradients are characterised by the standard
42