The Evolution of the MJO as Revealed by Multivariate Principal Oscillation Analysis

We have applied Principal Oscillation Pattern (POP) analysis to minimally filtered gridded analyses of several variables which can be used as markers of Madden-Julian Oscillation (MJO) initiation. One of the resulting modes is MJO-like, with an 11-pentad period and a 3-pentad decay time. We have separately used a variety of criteria to identify several MJO events during boreal winters 1998-2012 for individual examination. Here we explore how the MJO-like mode evolves during these cases in multiple ways. We track the contributions to that mode by upper- and lower-level zonal winds and latent heating (as proxied by Outgoing Longwave Radiation, OLR), as well as the contributions made by mid-tropospheric temperature (T400) and sea-level pressure (SLP) in the pre-cursor and early stages of the events. We also examine the stochastic forcing of these cases using diagnostics based on fluctuation-dissipation theory, and compare the characteristics of this forcing during the early stages of several MJO events.