Atmospheric Science Seminar: "Madden-Julian Oscillation Predictability and Global Impacts over the past 100 Years"

Presented by: Eric C. J. Oliver, Physical Oceanography, Department of Oceanography, Dalhousie University

Abstract
:

The most widely accepted characterization of the Madden–Julian oscillation (MJO) is the bivariate index developed by Wheeler and Hendon (Monthly Weather Review, 2004). A damped harmonic oscillator model for the Wheeler and Hendon MJO index was developed in order to gain new insights into the predictability of the MJO. Building on a tradition of idealized models, the model for the MJO state consists of a bivariate autoregressive process, equivalent to a finite difference approximation to a dynamical underdamped harmonic oscillator. The statistical properties of the model (the ensemble mean, ensemble variance, and within-ensemble correlation) are used to develop predictability time scales for canonical MJO events. It is shown that the predictability time scales, and thus MJO predictability, vary as a function of MJO phase and season. The result has relevance for the interpretation of the Maritime Continent prediction barrier.

This MJO index relies in part on satellite-based observations of outgoing longwave radiation and thus is not defined for the presatellite era. The MJO is known to have a strong signature in surface pressure, and daily measurements of this variable are available as far back as the late nineteenth century. We present a statistical reconstruction of the Wheeler and Hendon MJO index from 1905 to 2014 based on tropical surface pressures estimated by the twentieth-century reanalysis project, with errors quantified using an ensemble of indices. The temporal and spectral properties of the reconstructed index are shown to be consistent with the Wheeler and Hendon index over the common period (1979–2008), as are known links with a number of atmospheric and oceanic variables. The long reconstructed index has been used to examine historical links between the MJO and surface winds and cloud cover over the ocean (1952-2008), extreme precipitation in Australia (1905-2011), Pacific sea levels (1905-2008), global and North Atlantic tropical cyclone activity (1905-2011), wintertime air temperature in Alaska (1906-2010), snowfall and storm tracks over New England (1936-2011), heatwaves in Patagonia (1957-2010), and the mid-summer drought in Costa Rica (1956-2014). The joint-modulation of these MJO responses by lower-frequency modes (ENSO, AMO) is also explored.

Category

Atmospheric Science Seminars

Time

Location

Dunn 304