Abstract
A Madden–Jillian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) are important climate variabilities, which affect a forecast of weather and climate. In this study, the MJO and the BSISO hindcasts from the Global Seasonal Forecast System, version 5 (GS5) were diagnosed using dynamic-oriented theories. We additionally analyzed the GS5 climatological run to identify whether the weakness of the GS5 hindcast results from the model physics or initialization processes. The GS5 hindcast captures three-dimensional dynamics and thermodynamics structure of MJO eastward propagation well in the Indian Ocean. The model produces the boundary layer (BL) moisture convergence anomalies to the east of the MJO deep precipitation with easterly anomalies associated with the Kelvin wave. The enhanced BL moisture convergence increases upward transport of moisture from the surface to the lower troposphere, inducing the moist lower troposphere and the positive convective instability by destabilization of the lower atmosphere and, thus, generating the next convection to the east of MJO deep convection and promoting MJO eastward propagation. However, the signal for eastward propagation is relatively weak in the Maritime Continent (MC) and the Western Pacific (WP). To improve the MJO eastward propagation in the MC and WP, improved heating induced by shallow (or congestus) clouds interacting with enhanced BL dynamics may be required. On the other hand, the GS5 hindcast reproduces the BSISO northward propagation reasonably well in the Indian Ocean, which is attributed to positive vorticity anomalies induced by strong vertical shear.
Highlights
The Madden–Julian oscillation (MJO) shows a convective system propagating eastward with a 20–70-day period over 15◦ S and 15◦ N
Another study [23] demonstrated that the interaction among wave dynamics, vorticity anomalies, and vertical wind shear is the dominant process for boreal summer intraseasonal oscillation (BSISO) northward propagation in the Indian Ocean
This study describes the analysis of the MJO and BSISO simulation using dynamicoriented diagnostics
Summary
The Madden–Julian oscillation (MJO) shows a convective system propagating eastward with a 20–70-day period over 15◦ S and 15◦ N. The heating and moisture that are induced by boundary layer convergence precede the MJO major precipitation, which leads to the MJO-scale coupled Kelvin–Rossby wave structure with eastward propagation. Many processes have been proposed to understand the BSISO northward propagation in the Indian Ocean, including air-sea interaction, moisture advection in the boundary layer, and vorticity anomalies generated by vertical shear. A study suggested that the northward propagation of ISO convection may be generated by inducing a boundary layer moisture convergence to the north of the BSISO convection center [23]. Another study [23] demonstrated that the interaction among wave dynamics, vorticity anomalies, and vertical wind shear is the dominant process for BSISO northward propagation in the Indian Ocean.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
