Environmental Engineering Reference
In-Depth Information
22-Sep-12
22-Sep-12
28:0 ʿ N
28:0 ʿ N
26:5 ʿ N
26:5 ʿ N
25:0 ʿ N
25:0 ʿ N
23:5 ʿ N
23:5 ʿ N
22:0 ʿ N
22:0 ʿ N
92:0 ʿ W
90:5 ʿ W
89:0 ʿ W
87:5 ʿ W
86:0 ʿ W
92:0 ʿ W
90:5 ʿ W
89:0 ʿ W
87:5 ʿ W
86:0 ʿ W
Fig. 3 ( left ) Fluid patches ( blue ) overlaid on backward FTLE normalized by the largest value in
the domain (from white to black in a gray scale, the FTLE changes from 0 to 1). ( right ) Backward
FTLE with attracting LCS obtained as squeezelines computed in backward time ( red )
suggested by ridges (locally maximizing curves) of the FTLE field (thin regions of
darkest gray tones in the figure). While FTLE ridges cannot be expected to coincide
with squeezelines or stretchlines (Haller 2011 ), they tend to run close to each other, at
least over some segments. This is illustrated in the right panel of Fig. 3 , which shows
the same backward FTLE field shown in the left panel with selected attracting LCS
obtained as squeezelines on t 0 = 22 September 2012 computed in backward time out
to t = 12 September 2012. These squeezelines are launched on t 0 = 22 September
2012 at locations lying on selected FTLE ridges. Note that, while departures are
evident, FTLE ridges run close to LCS over some segments.
The tendency of the FTLE to carry flow coherence imprints should not be taken
as implying that this flow diagnostic is capable of revealing the fundamental cause of
flow coherence. This is illustrated in Fig. 4 , which shows patches and corresponding
centerpiece LCS overlaid on backward FTLE computed at each t 0 shown using
|
t
t 0 |=
10 days. Note that these LCS are not well represented by nearby FTLE
15-Sep-12
17-Sep-12
22-Sep-12
28:0 o N
28:0 o N
28:0 o N
26:5 o N
26:5 o N
26:5 o N
25:0 o N
25:0 o N
25:0 o N
23:5 o N
23:5 o N
23:5 o N
22:0 o N
22:0 o N
22:0 o N
92:0 o W : o W : o W : o W : o W
92:0 o W : o W : o W 87:5 o W 86:0 o W
92:0 o W 90:5 o W 89:0 o W 87:5 o W 86:0 o W
Fig. 4 Selected snapshots of the evolution of fluid patches ( blue ) and centerpiece LCS ( red ), all
overlaid on backward FTLE on the corresponding date
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