Potential Vorticity of the Madden–Julian Oscillation

Abstract

This study explores the extent to which the dynamical structure of the Madden-Julian oscillation (MJO), its evolution, and its connection to diabatic heating can be described in terms of potential vorticity (PV). The signature PV structure of the MJO is an equatorial quadrupole of cyclonic and anticyclonic PV that tilts westward and poleward. This PV quadrupole is closely related to positive and negative anomalies in precipitation that are in a swallowtail pattern extending eastward along the equator and splitting into offequatorial branches westward. Two processes dominate the generation of MJO PV. One is linear, involving MJO diabatic heating alone. The other is nonlinear, involving diabatic heating and relative vorticity of perturbations spectrally outside the MJO domain but spatially constrained to the MJO convective envelope. The MJO is thus partially a self-sustaining system and partially a consequence of scale interaction of MJOconstrained stochastic processes. Convective initiation of the MJO over the Indian Ocean features a swallowtail pattern of negative anomalous precipitation and associated anticyclonic PV anomalies at the early stage, and increasing cyclonic PV generation straddling the equator in the midtroposphere due to increasing positive anomalies in precipitation. These lead to the swallowtail pattern in positive anomalous precipitation and the associated PV quadrupole that signifies the fully developed MJO. The equatorial Kelvin and Rossby waves bear PV structures distinct from that of the MJO. They contribute insignificantly to the structure and generation of MJO PV. Solely based on the PV analysis, a hypothesis is proposed that the fundamental dynamics of the MJO depends on neither Kelvin nor Rossby waves.

A general theoretical framework for understanding essential dynamics of Madden–Julian oscillation

“…The current model result suggests it is important to identify new mechanism that causes moisture increase in the lower troposphere. Also note that the BL convergence pattern may be a possible explanation of the swallowtail precipitation pattern as described by Zhang and Ling (2012).…”

Regression Analysis of Zonally Narrow Components of the MJO

“…When assessed over a long climatology, the spectra of these signals are not easily distinguished from red noise except that signals characterized by phase speeds between 2 and 8 m s 21 appear to be favored (Roundy 2012a). Following a 40-yr tradition, the Madden-Julian oscillation (MJO; Madden andJulian 1972, 1994;Zhang 2005) is frequently described as a distinct signal projecting most strongly onto planetary scales and the 30-60-or 40-50-day band. Hereafter, I label these 30-60-day signals as the traditionally defined MJO.…”

“…As further motivation to study such zonally narrow signals, they might feed back onto patterns at larger scales because the response to the release of latent heat within the smaller-scale convective elements remains in the environment for longer than the periods of the elements themselves (MacRitchie and Roundy 2012; Zhang and Ling 2012). The MJO can also modulate the activity and propagation characteristics of the shorter time-scale signals (e.g., Straub and Kiladis 2003).…”

“…The MJO can also modulate the activity and propagation characteristics of the shorter time-scale signals (e.g., Straub and Kiladis 2003). In other words, planetary-scale events are associated with enhanced activity in smaller-scale signals, and the response to the release of latent heat in smaller-scale signals propagating near the equator generates background circulation signals that become part of planetary-scale events (MacRitchie and Roundy 2012; Zhang and Ling 2012). These conclusions taken together with the wavelet analysis of Roundy (2012a) suggest that it is unlikely that many of these zonally narrow, slow, eastward-moving signals will be found to be completely independent from longer time-scale planetary-scale signals of the traditionally defined MJO, thus complicating their analysis.…”

Subseasonal intensity variation of the South Asian high in relationship to diabatic heating: observation and CMIP5 models

“…A similar pattern of ⟨Q 1 ⟩ and ⟨Q 2 ⟩ over summer monsoon region indicates that condensational heating induced by precipitation is the major component of diabatic heating (Yanai and Tomita 1998;Jin et al 2013). A variable is decomposed into its time mean (denoted with an overbar) and subseasonal (denoted with a prime), and non-subseasonal components (Zhang and Ling 2012;Ren et al 2015). The horizontal advection of relative vorticity and the two vorticity generation terms in Eq.…”