Distinctive Roles of Air–Sea Coupling on Different MJO Events: A New Perspective Revealed from the DYNAMO/CINDY Field Campaign*

Abstract

Previous observational analysis and modeling studies indicate that air–sea coupling plays an essential role in improving MJO simulations and extending MJO forecasting skills. However, whether the SST feedback plays an indispensable role for the existence of the MJO remains controversial, and the precise physical processes through which the SST feedback may lead to better MJO simulations and forecasts remain elusive. The DYNAMO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY) field campaign recently completed over the Indian Ocean reveals a new perspective and provides better data to improve understanding of the MJO. It is found that among the five MJO events that occurred during the DYNAMO/CINDY field campaign, only two MJO events (the November and March ones) have robust SST anomalies associated with them. For the other three MJO events (the October, December, and January ones), no coherent SST anomalies are observed. This observational scenario suggests that the roles of air–sea coupling on the MJO vary greatly from event to event. To elucidate the varying roles of air–sea coupling on different MJO events, a suite of hindcast experiments was conducted with a particular focus on the October and November MJO events. The numerical results confirm that the October MJO is largely controlled by atmospheric internal dynamics, while the November MJO is strongly coupled with underlying ocean. For the November MJO event, the positive SST anomalies significantly improve MJO forecasting by enhancing the response of a Kelvin–Rossby wave couplet, which prolongs the feedback between convection and large-scale circulations, and thus favors the development of stratiform rainfall, in turn, facilitating the production of eddy available potential energy and significantly amplifying the intensity of the model November MJO.

An Ensemble Hindcast of the Madden-Julian Oscillation during the CINDY2011/DYNAMO Field Campaign and Influence of Seasonal Variation of Sea Surface Temperature

“…Convection in the Indian Ocean weakens in early December when the region of active convection is in the MC. The lack of the strong convection of MJO1 approximately on 6 November in the MC region is similar to the simulation initialized on 7 October of Fu et al (2015) and the earlier initiation of MJO2 by approximately 5 days is also common with their simulation initialized on 4 November. These defects are readily detectable in Fig.…”

“…These defects are readily detectable in Fig. 3 of Fu et al (2015), although they did not point these explicitly. In contrast, the 76 day simulation of Wang et al (2015) appears to successfully reproduce the strong convection approximately on 6 November.…”

“…Fu et al (2015) and Wang et al (2015) have already reported successful simulations of MJO2 by coupled/ atmosphere-only global models and a regional atmospheric model, respectively. They showed that MJO2 representation was improved significantly by using daily SST values instead of a constant SST value throughout the simulation as the bottom boundary condition.…”

Evaluation of the Near Real-Time Forecasts Using a Global Nonhydrostatic Model during the CINDY2011/DYNAMO

“…Modeling studies have also been undertaken with operational forecasts Fu et al 2013;Ling et al 2014;Kerns and Chen 2014a) and global/regional model simulations (Fu et al 2015;Hannah and Maloney 2014;Miyakawa et al 2014;Nasuno 2013;Subramanian and Zhang 2014;Chen et al 2015;Hagos et al 2014a, b;Seo et al 2014;Wang et al 2015). With regard to the moistening process of the MJO, a special focus has been given on multi-scale processes (Chen et al 2015;Hagos et al 2014b;Kerns and Chen 2014a).…”

“…The significant impact of the diurnal sea surface temperature (SST) variation on moisture buildup prior to the active phase of the MJO was demonstrated; Chen et al (2015) addressed that the diurnal SST variation contributed to the moisture resurgence in the suppressed period of the MJO event through enhancement of moisture transport associated with the atmospheric mixed Rossby-gravity waves, and Seo et al (2014) reported the impacts of the collocation of the diurnal peaks of SST and latent heat fluxes. Fu et al (2013Fu et al ( , 2015, who evaluated the forecast skill of operational and research models, concluded that the air-sea coupling enabled a better prediction skill of MJO events.…”