Observed triggering of tropical convection by a cold surge: implications for MJO initiation

Abstract

The extratropical influence is an important mechanism in the initiation of the Madden-Julian Oscillation (MJO). Based on analyses of several datasets, this article demonstrates that the MJO case initiated in late January 2008 was strengthened by a preceding cold surge over West Asia when the MJO was at its initiation phase. The cold surge-related northerlies propagated southward along the east coast of Africa. The associated convergence on the edge of the surge enhanced ascending motion in the tropical western Indian Ocean and led to the onset of deep convection to the north of Madagascar. This process helped to amplify the MJO convection rapidly, as shown in the development of the moist static energy anomalies. In this way, the cold surge affected the behaviour of the MJO and modified the timing of its initiation to some extent. These results support previous studies that extratropical factors are important for the initiation of the MJO, and suggest that the subtropical cold surges are likely to strengthen and accelerate the build-up of deep MJO convection at the MJO initiation phase.

Precursor Environmental Conditions Associated with the Termination of Madden–Julian Oscillation Events

“…A number of theories regarding MJO initiation have been developed including boundary layer frictional convergence (Wang and Rui 1990), surface wind-evaporation feedbacks (Emanuel 1987;Neelin et al 1987), stochastic linearized convection and deep convective heating (e.g., Salby et al 1994), and influences from higher latitudes such as Rossby wave trains and cold-air outbreaks (Hsu et al 1990;Matthews and Kiladis 1999;Ray and Zhang 2010;Wang et al 2012). Topographic effects may be important for MJO initiation (e.g., Hsu and Lee 2005) and mean sea level pressure (MSLP) anomalies associated with dry Kelvin waves from previous MJO disturbances may help initiate a successive event (Matthews 2000).…”

Moistening Processes before the Convective Initiation of Madden–Julian Oscillation Events during the CINDY2011/DYNAMO Period

“…Regarding the origin of MJO initiation, there are two categories of hypotheses: those stressing tropical internal dynamics [e.g., a circumnavigating signal of the previous episode: Lau and Peng (1987); Wang and Li (1994); Kikuchi and Takayabu (2003); Matthews (2008); or local processes in the tropics: Hu and Randall (1994); Jiang and Li (2005); Straub (2013)] and those emphasizing extratropical forcing (e.g., Hsu et al 1990;Bladé and Hartmann 1993;Matthews and Kiladis 1999;Pan and Li 2007;Lin et al 2007;Ray and Zhang 2010;Wang et al 2012). Ray and Li (2013) evaluated the relative importance of circumnavigating signals and extratropical forcing by performing sensitivity experiments using a general circulation model and concluded that extratropical forcing was more important than were circumnavigating signals in association with mean moisture convergence.…”

Predicting the Real-Time Multivariate Madden–Julian Oscillation Index through a Low-Order Nonlinear Stochastic Model

“…These two PC time series are defined as the RMM index (Wheeler and Hendon 2004). Since the publication of the work (Wheeler and Hendon 2004), the RMM index has become the leading method for identifying the state of the MJO in observations (Jiang et al 2011;Riley et al 2011;Wang et al 2012;Straub 2013) and model analyses (Kim et al 2009;Gottschalck et al 2010).…”