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&S The data are much sparse.

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 Reference: Lumpkin, R. and Z. Garraffo, 2005: Evaluating the Decomposition of Tropical Atlantic Drifter Observations. J. Atmos. Oceanic Techn. I 22, Lumpkin, R. and S. L. Garzoli, 2005: Near-surface Circulation in the Tropical Atlantic Ocean. Deep-Sea Res. I 52(3), , /j.dsr

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

Annual Mean Surface Current Pacific Ocean, 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 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) where (3) (4) are total zonal and meridional transport of mass sum of geostrophic and ageostropic transports

Differentiating, we have DefineWe 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 35 o N,  -4 s -1,  2  m -1 s -1, assume  x  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) =10 6 m 3 /s

A More General Form of Sverdrup Equation Surface stress curl Bottom stress curl Bottom topography effect Vanish if the bottom is flat Or flow follows topographic contour