1. Estuarine Variability
 Tidal
 Subtidal
Wind and Atmospheric Pressure
 Fortnightly
M2 and S2
 Monthly
M2 and N2
 Seasonal (River Discharge)

2. Estuarine Variability
 Tidal
 Subtidal
Wind and Atmospheric Pressure
 Fortnightly
M2 and S2
 Monthly
M2 and N2
 Seasonal (River Discharge)

3. Tidal Straining
River
Ocean
Slack Before Ebb
Ocean
Ebb
Tidal Flow

4. End of Ebb
Flood
Tidal Flow

7. z (m)
z (m)
z (m)
z (m)
z (m)
z (m)

8. Influence of tidal asymmetries in mixing
Jay & Musiak (1994)
MacCready & Geyer (2010) A A

9. Magnitude (cm/s) of circulation induced by asymmetries in mixing
Ratio of circulation induced by asymmetries in mixing vs. density-driven flow

10. Estuarine Variability
 Tidal
 Subtidal
Wind and Atmospheric Pressure
 Fortnightly
M2 and S2
 Monthly
M2 and N2
 Seasonal (River Discharge)

11. Subtidal Variability
Produced by direct forcing on estuary (local forcing) or on the coastal ocean, which in turn influences estuary (remote forcing - coastal waves)
Wind forcing may:
produce mixing
induce circulation
generate surface slopes

12. But at the air-water interface it is:
Wind-produced mixing
The energy per unit area per unit time or power per unit area generated by the wind to mix the water column is proportional to W3
At a height of 10 m, the power per unit area generated by the wind stress is:
But at the air-water interface it is:
The wind power at the air water interface is only 0.1 % of the wind power at a height of 10 m.
Acts from the surface downward
May destratify the entire water column when forcing is large and buoyancy is low

13. s s Wind-induced circulation
The wind-induced circulation can compete with estuarine circulation, or act in concert
The wind-induced circulation will depend on stratification:
depth-dependent under stratified conditions
weak depth-dependence under homogeneous conditions s
Weak
Depth-Averaged
Transport s
Large
Depth-Mean
Transport

16. sx Wind-Induced Surface Slope
Can be assessed from the vertical integration of the linearized u momentum equation,
with no steady state:
Note that a westward sx (negative) produces a negative slope.
sx x1 x2 y x x1 x2 
Wind will pile up water in the direction toward which it blows.

18. The perturbation produced by the wind propagates into the estuary and may cause seiching if the period of the perturbation is close to the natural period of oscillation:

19. Estuarine Variability
 Tidal
 Subtidal
Wind and Atmospheric Pressure
 Fortnightly
M2 and S2
 Monthly
M2 and N2
 Seasonal (River Discharge)

20. Tides in PONCE DE LEON INLET

21. Example:
Hudson River

22. Hudson River
MacCready & Geyer, 2010, Ann Rev Fluid Mech

23. Fortnightly variability in the Richardson Number

24. Mean or Residual Flow Mean or Residual Salinity (Density)
Depth
Mean or
Residual
Flow
Can you see this modulation from the analytical solution?
Ocean
Neap
Spring
Mean or
Residual
Salinity
(Density)
Depth
Increasing salinity

25. Estuarine Variability
 Tidal
 Subtidal
Wind and Atmospheric Pressure
 Fortnightly
M2 and S2
 Monthly
M2 and N2
 Seasonal (River Discharge)

28. Salt Intrusion vs. River Discharge
(Journal of Physical Oceanography, 2007, 2133)
Salt Intrusion vs. River Discharge
Model

29. Strong outflow from both River Discharge and NW winds1 2 3 4 5 6
2 / 3 of volume outflow associated with river input
1 / 3 to wind forcing

31. Forcing from Atmospheric Pressure Gradients
Another mechanism that may cause subtidal variability in estuaries comes from atmospheric or barometric pressure.

32. Hurricane Felix
 = P/(g)
P of 1 mb (100 Pa) =  of 0.01 m

33. Example of Tidal interaction
with density gradient
Chilean Inland Sea
Pitipalena Estuary

34. CTD
Time
Series 1 2

35. 1 2

36. N C N C C N

37. Slopes produced by different winds in Chesapeake Bay

38. Forcing from Atmospheric Pressure Gradients
Another mechanism that may cause subtidal variability in estuaries comes from atmospheric or barometric pressure.
mouth B A
head
Indirectly through sea level slope B A
head
mouth
depth z x