UNSW@ADFA Oceanography Seminars

A link to the 2006/07 program of Oceanography Seminars is placed here for those interested in looking at previous activities.

Wednesday 21 May , 11.00-12.00, LT9

Speaker: Assoc. Prof. Adam Sobel, Columbia University

Title: Dynamics of tropical intraseasonal variability

Abstract: The tropical atmosphere varies strongly and coherently on the intraseasonal (30-60 day) time scale. The most prominent mode of intraseasonal variability is the Madden-Julian Oscillation (MJO). The MJO controls the active and break periods of the monsoon in northern Australia and Indonesia as well as regulating convection over the equatorial Indian and western Pacific oceans. The MJO influences extratropical weather through teleconnections, and plays a role in the dynamics of ENSO by generating westerly wind bursts over the equator.

Despite several decades of intense research, there is no agreement on the mechanisms involved in the initiation and maintenance of the MJO. I will argue for the hypothesis that interactive feedbacks involving surface enthalpy fluxes are important to the dynamics of all coherent intraseasonal variability, including the MJO as well as a somewhat distinct mode that modulates the Asian monsoon. The relevant feedbacks include those involving surface turbulent fluxes as well as cloud-radiative effects. Evidence in favor of this hypothesis includes the observed spatial distribution of intraseasonal variance in precipitation and outgoing longwave radiation, the observed local relationship between intraseasonal latent heat flux and precipitation anomalies in regions where intraseasonal variability is strong, and sensitivity experiments performed with a small number of general circulation and idealized models.