Utilizing a Lagrangian View of Moisture Dynamics to Study the MJO

Friday, 19 December 2014
Walter Hannah, University of Miami, Miami, FL, United States and Brian E Mapes, RSMAS, University of Miami, Atmospheric Sciences, Miami, FL, United States
Tropical precipitation has a strongly non-linear dependence on column moisture, such that it increases rapidly above a critical threshold of column moisture. Thus, the enhanced phase of the Madden Julian Oscillation (MJO) can be thought of as a large contiguous area, in which most air columns have crossed over this moisture threshold. What processes dictate how this threshold is crossed at intraseasonal timescales?

To begin answering this, we introduce a Lagrangian perspective on the column moisture budget of the MJO. As opposed to conventional Eulerian metrics, a Lagrangian perspective allows us to consider moistening processes with respect to air columns that are being advected by the flow. Techniques are introduced for estimating the column moisture tendencies using analysis and satellite observations, and estimates are compared for validation. We then examine how the critical column moisture threshold can influence how we think about MJO dynamics. Implications for MJO compositing methods will also be discussed.