Download presentation

Presentation is loading. Please wait.

1
**Wind-driven circulation II**

●Wind pattern and oceanic gyres ●Sverdrup Relation ●Vorticity Equation

3
**Surface current measurement from ship drift**

Current measurements are harder to make than T&S The data are much sparse.

4
**Surface current observations**

5
**Surface current observations**

8
**Drifting Buoy Data Assembly Center, Miami, Florida**

Atlantic Oceanographic and Meteorological Laboratory, NOAA

9
**Annual Mean Surface Current Pacific Ocean, 1995-2003**

Drifting Buoy Data Assembly Center, Miami, Florida Atlantic Oceanographic and Meteorological Laboratory, NOAA

11
**Schematic picture of the major surface currents of the world oceans**

Note the anticyclonic circulation in the subtropics (the subtropical gyres)

12
**Relation between surface winds and subtropical gyres**

13
**Surface winds and oceanic gyres: A more realistic view**

Note that the North Equatorial Counter Current (NECC) is against the direction of prevailing wind.

14
**Mean surface current tropical Atlantic Ocean**

Note the North Equatorial Counter Current (NECC)

16
**Consider the following balance in an ocean of depth h of flat bottom**

Sverdrup Relation Consider the following balance in an ocean of depth h of flat bottom (1) (2) Integrating vertically from –h to 0 for both (1) and (2), we have (neglecting bottom stress and surface height change) (3) (4) where are total zonal and meridional transport of mass sum of geostrophic and ageostropic transports

17
**(3) and (4) can be written as**

Define We have (3) and (4) can be written as (6) (5) Differentiating , we have

18
**We have Sverdrup equation**

Using continuity equation And define We have Sverdrup equation Vertical component of the wind stress curl If The line provides a natural boundary that separate the circulation into “gyres”

19
**is the total meridional mass transport**

Geostrophic transport Ekman transport Order of magnitude example: At 35oN, -4 s-1, 2 m-1 s-1, assume x10-1 Nm-2 y=0

20
**Alternative derivation of Sverdrup Relation**

Construct vorticity equation from geostrophic balance (1) Assume =constant (2) Integrating over the whole ocean depth, we have

21
where is the entrainment rate from the surface Ekman layer at 45oN The Sverdrup transport is the total of geostrophic and Ekman transport. The indirectly driven Vg may be much larger than VE.

22
then

23
**set x =0 at the eastern boundary,**

Since , we have set x =0 at the eastern boundary, Further assume In the trade wind and equatorial zones, the 2nd derivative term dominates:

26
**Mass Transport Since Let , , where is stream function.**

Problem: only one boundary condition can be satisfied.

27
1 Sverdrup (Sv) =106 m3/s

Similar presentations

© 2020 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google