Term Paper Guide• Find an oceanic or relevant atmospheric phenomenon you are

interested in (e.g., ENSO, PDO, AMO, TAV, IOD, NAO, hurricane activity, regional flood or drought, monsoon, etc)

• Describe the general pattern, life cycle, or probable mechanisms of the phenomenon you choose based on class material and/or literature

• Examine the real-time oceanic evolution through the NOAA briefings from August to November 2012

• Write a 2-4 page report (double space) in a research paper style to address the evolution of the chosen phenomenon during this period (a set of questions to be addressed is given in next slide)

• New ideas or approaches are encouraged

Questions to be addressed:

• Is 2011 a typical year for the phenomenon you have chosen? • What is the evidence for that? • What phase are we in during the past four months? • What are the main factors driving the development or persistence

or the phenomenon? • What do you expect about its development in the coming winter

and spring?• Is the information from the briefing adequate for you to trace the

developing event? • Are the course materials useful in understanding the

phenomenon?

Wind-driven circulation II

Wind pattern and oceanic gyres

Sverdrup Relation

Vorticity Equation

Surface current measurement from ship drift

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

Surface current observations

Surface current observations

A climatology of near-surface currents and SST for the world, at one degree resolution, derived from satellite-tracked surface drifting buoy observations. Most recent data included: 1 January 2011. Reference:Lumpkin, R. and Z. Garraffo, 2005: Evaluating the Decomposition of Tropical Atlantic Drifter Observations. J. Atmos. Oceanic Techn. I 22, 1403-1415.Lumpkin, R. and S. L. Garzoli, 2005: Near-surface Circulation in the Tropical Atlantic Ocean. Deep-Sea Res. I 52(3),495-518, 10.1016/j.dsr.2004.09.001.

http://www.aoml.noaa.gov/phod/dac/drifter_climatology.html

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

Annual Mean Surface CurrentPacific Ocean, 1995-2003

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

Schematic picture of the major surface currents of the world oceans

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

Relation between surface winds and subtropical gyres

Surface winds and oceanic gyres: A more realistic view

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

Sverdrup RelationConsider 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)

where

(3)

(4)

are total zonal and meridional transport of mass

sum of geostrophic and ageostropic transports

Differentiating , we have

Define We have

(3) and (4) can be written as

(5) (6)

Using continuity equation

And define

Vertical component of the wind stress curl

We have Sverdrup equation

If The line provides a natural boundary that separate the circulation into “gyres”

is the total meridional mass transport

Geostrophic transport

Ekman transport

Order of magnitude example:At 35oN, -4 s-1, 2 10-11 m-1 s-1, assume x10-1 Nm-2 y=0

then

Since , we have

set x =0 at the eastern boundary,

Further assume

In the trade wind and equatorial zones, the 2nd derivative term dominates:

Mass Transport

Since

Let ,

,

where is stream function.

Problem: only one boundary condition can be satisfied.

1 Sverdrup (Sv) =106 m3/s

A More General Form of Sverdrup Equation

Surface stress curl

Bottom stress curl

Bottom topography effectVanish if the bottom is flatOr flow follows topographic contour