examples of secondary flows and lateral variability
TRANSCRIPT
Examples of secondary flows and lateral variability
U-UU-U
S1
S2
S3
S4
U+UU-U
S1
S2
S3
S4
Differential Advection in channel with deep middle andShallow flanks Producing along channel salinity gradient
U+UU-U
Salty
FreshFresh
Effects of Differential Advection on Flood TideNunes and Simpson (1985)
What’s the effect on stratification?What’s the effect on the along channel momentum balance?What happens on Ebb?
Pressure gradient centrifugal acceleration
022
zR
uU
Kalkwijk and Booij (1986)Geyer (1993)
Requires Secondary flowsto balance forcing
z
vAz
Secondary flows due to flow curvatureFrom Geyer (1993)
Pressure gradient centrifugal acceleration
022
zy
gR
uU
Baroclinic balance arrests lateral flows
Chant and Wilson (1997)Seim and Gregg (1997)
Current VectorsUpper layer
Lower layer
CTD section
NYNJ
NY
NJ
CTD section
Chant and Wilson, 1997
Red - Surface
Blue -Middle
Purple- Bottom
ADCP mooring
Average ebb-dry periodSecondary circulation
Average ebb-wet periodNo secondary circulation
Current Vectors
NOAA/NOS - PORTS mooring data.
Wet Period
Wet Period
1 m/s
1m 2 m1.5 m
Currents during Maximum ebbWet Period
Dry Period1 m/s
Tidal Range
1m 2 m1.5 m
Red Surface Blue Bottom
Max Ebb
vs.
Tidal Range
Dry Period
Tidal Range
Dep
thD
epth
Tidal Range
Along Channel Flow
Cross Channel Flow
Neap Tides
Tidal RangeD
epth
Dep
th
Tidal Range
Along Channel Flow
Cross Channel Flow
Max Ebb vs. Tidal Range Wet Period
Spring tides
Wet Period - Maximum Ebb binned vs Tidal Range
Stronger shear in alongchannel flow but weaker
cross channel flows.
Tidal Range
Str
atif
icat
ion
Moderate Strong
WeakComplex
Lateral Sloshing??
Secondary flows driven by Coriolis (Lerczak and Geyer, 2004)
Lerczak and Geyer (2004) model set up.
Az=22*10-4 m2/s
Uf=0.25 cm/s
Max(V)=10 cm/s
Az=3.3*10-4 m2/s
Uf=7.0 cm/s
Max(V)= 2.6 cm/s
vdAA
1v
Lerczak and Geyer (2004)
As stratification increases Secondary flows decrease
Flood-ebb asymmetry in Secondary flows
V~1/S(z)
ranges from 1 for weaklyStratified case and approaces100 during strongly case
(represents ratio of isopycnal tiltingTo differential advection)
Tidally mean vuy+wuz
Is dominated by flood Tide.
Note where velocity maxIs on flood (red line)
0 5 10 15 20 25 30 35 40 45 50-20
-15
-10
-5
0
m
Salinity May 4th 2002
5
0 5 10 15 20 25 30 35 40 45 50-15
-10
-5
0
km north of the Battery
m
May 26th, 2002
5
10
20
Figure 4 Salt section along Hudson during moderate to high flow condition during spring tide (upper panel) and neap tide (Lower panel). See figure 2 for timing of transects relative to river flow and tidal range
Figure 5. (upper panel) along channel currents averaged between 1.35 and 6.1 meters above the bottom water from site 4 (blue line) and its low passed filtered component (green line). (lower panel) surface (green line) and bottom (blue line) salinity during the spring of 2002.
April May June
Exchange flow drops off more slowly than H&R predicts becauseH&R neglected the effect of lateral circulation that becomes moreImportant as mixing increases.
Including Coriolis produces lateral asymmetries. This would tend to transportSediment to the right (looking seaward) and thus produce a laterally asymmetricChannel such as the Hudson.
Channel Cross-section at mooring array
1 2 3 4
In the afternoon we’ll look at aspects of lateral circulation basedOn data from the Hudson
Laterally Asymmetric Channel in Hudson
James Neap
James Spring
Hudson Neap
Hudson Spring
Vertically Sheared
Laterally Sheared
Figure 3) Schematic showing movement of Hudson and James river estuary throughKevlin/Ekman number space over the spring neap cycle. Laterally sheared estuaries lie in the upper right quadrant, while vertically sheared estuaries lie in the lower left quadrant
U1,V1U2,V2
s1s
s1b
s2s
Full mooring deployment (Lerczak et al. 2006) and locations ofData used in afternoon experiment