Judges’ Queries and Presenter’s Replies

  • May 20, 2013 | 07:15 p.m.

    How does your work represent an advance over previous research?

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 20, 2013 | 09:46 p.m.

    Dr. Hirschberg,

    Thanks for your question. The major advance is theoretical in nature. One of the goals of oceanography is to map-out the pathways and speeds of the ocean’s circulation (surprisingly little is known for sure). Previous studies have inferred aspects of the circulation using the time-lagged correlation of oceanic time series data (e.g. Sutton and Allen, Nature, 1997, who analyze sea surface temperatures propagating across the Atlantic and infer a mean current speed of 1.7 cm/s in the Gulf Stream). However these studies invite skepticism because they lack a theoretical framework for connecting correlation functions to fluid dynamics equations (correlation doesn’t imply causation). Our major advance has been to provide that framework. This was accomplished using the Green’s function solution of the fluid transport equations. Also, in developing the theory, we realized that a properly done time-lagged correlation could contain more information about the physical transport process than previous thought. We’re now applying the theory to reveal new aspects of the circulation in the North Atlantic.

  • May 21, 2013 | 10:40 p.m.

    Are you the first researchers to apply the Green’s function solution of the fluid transport equations on as large a scale as ocean circulation? How does your work differ from that of others who have used Green’s function in fluid transport?

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 22, 2013 | 09:39 p.m.

    Dr. Cowles,

    Great question.  My advisor and his colleagues (as far as we know) were the first to use Green’s functions to interpret large scale oceanic circulation (e.g. Haine and Hall, Generalized Transport, 2002).  Its has also been applied to transport in lakes, ground water flows, and the atmosphere (see publications by Darryn Waugh).

    Many of the applications above interpret the spread of passive tracers (such as CFC molecules) in the flow.  My work builds on and expands this work by including the correlation of propagating temperature and salinity anomalies as a source of oceanic data which can be interpreted by the Green’s function framework.

  • May 21, 2013 | 10:48 p.m.

    Are there other applications that can benefit from your Green’s function mathematical model other than the characterization of dense water currents? And what are the practical benefits of developing a better understanding of how the global overturning circulation will respond to climate change?

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 22, 2013 | 09:43 p.m.

    Dr. Bassiouni,

    I hope so!  An interesting and related application is the Green’s function retrieval in the field of seismology.  Here they characterize waves propagating through the Earth’s crust by correlating small fluctuations in seismic activity (Sneider, Retrieving the Green’s function, 2006).   In a wider sense, the theory of relating correlation functions to Green’s functions can be applied to any system of stochastically forced linear partial differential equations.

    If global warming alters the overturning circulation in a significant way, we could see drastic changes in temperature and precipitation patterns in Europe.  This is because the overturning circulation drives the Gulf stream which heats Europe’s atmosphere.  The main practical implication is the impact on crop production.  However that in turn could lead to more serious economic and political consequences.

  • Further posting is closed as the competition has ended.

Poster Discussion

  • Icon for: Adam Hinkle

    Adam Hinkle

    Trainee
    May 20, 2013 | 06:01 p.m.

    Excellent work! Your animations are really impressive. Good luck. -Adam

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 21, 2013 | 10:49 a.m.

    Thanks Adam! Many of the animations were produced by the data visualization studio at the NASA Goddard Space Flight facility.

  • Icon for: Tanya Waith

    Tanya Waith

    Coordinator
    May 21, 2013 | 10:10 a.m.

    Stephen,

    I’m wowed by any and all technical information that I can “understand.” You did fantastic work on your video and poster – never expected anything less than perfection from you. You’re my #1 choice!!!

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 21, 2013 | 10:50 a.m.

    Thanks Tanya! Sorry I didn’t include the ducks :)

  • Icon for: Ellen Chenoweth

    Ellen Chenoweth

    Trainee
    May 21, 2013 | 04:36 p.m.

    I love the Earthrise picture. I have a huge print in my room. Nice tie-in.

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 21, 2013 | 09:06 p.m.

    Me too! Thank you.

  • Icon for: Thomas Haine

    Thomas Haine

    Faculty
    May 22, 2013 | 03:52 p.m.

    Great job Stephen! Good luck!

  • Icon for: Edinah Gnang

    Edinah Gnang

    Trainee
    May 23, 2013 | 05:47 p.m.

    Great Job !!! Do you think your model can be used to describe fluid currents in the upper atmosphere as well ?

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 28, 2013 | 11:12 a.m.

    Edinah, good idea. A professor in my department also suggested atmospheric applications. Something I’m excited to look into!

  • Icon for: Ashley Richter

    Ashley Richter

    Trainee
    May 23, 2013 | 07:07 p.m.

    Beautifully choreographed video! I love that you used the importance of the earth image as a reference to human understanding of the global habitat as your jumping off point.

  • Icon for: Stephen Jeffress

    Stephen Jeffress

    Presenter
    May 28, 2013 | 11:14 a.m.

    Thanks Ashley! I was going for multiple meanings of a “climate of curiosity.”

  • Further posting is closed as the competition has ended.

Icon for: Stephen Jeffress

STEPHEN JEFFRESS

Presenter’s IGERT
Johns Hopkins
Years in Grad School: 4

Judges’
Choice

A Climate of Curiosity

The famous Earthrise photograph inspired an awareness of the complexity and vulnerability of Earth’s climate. Today scientists are studying the interconnected dynamics between the ocean and atmosphere. One way of characterizing chaotic ocean currents is by correlating small scale fluctuations in observations. However since correlation does not imply causation, it was previously unclear how to relate correlation functions to the underlying physics of fluid transport. We have made this relationship clear using an advanced mathematical technique known as a Green’s function. We are now applying correlation functions to estimate transit times in the Denmark Strait Overflow. Improving our characterization of transport in this region may help us understand how the global overturning circulation will respond to climate change.