Potential Roles of the ITCZ and Maritime Continent in MJO Initiation

This proposed research plans to address two issues that emerged from the DYNAMO field campaign: possible roles of the ITCZ and the Maritime Continent in MJO initiation. The pre-onset phases of the two MJO events (in October and November 2011) during the field campaign were characterized by active ITCZ south of the equator. The convective onset or initiation of each MJO event was marked by a shift of the ITCZ toward the equator. Preliminary diagnostics indicate that the ITCZ and its northward movement were present during about 50% of convective initiation events of the MJO over the Indian Ocean since 1998. It is unknown whether the processes of MJO initiation with and without the ITCZ would be very different or the ITCZ is simply an extraneous feature during convective initiation of the MJO. Possible roles of the ITCZ in MJO initiation have never been studied and were not considered in DYNAMO science documents. They are relevant to DYNAMO Hypothesis II, because it would make a huge difference in evolution of cloud population statistics with or without the ITCZ during the pre-initiation phases of the MJO.

Another intriguing phenomenon observed during the DYNAMO field campaign is westward moisture advection into the tropical Indian Ocean from the Maritime Continent (MC) by low-level easterlies during the initiation of the two MJO events. The MC may act as a moisture source because of its almost perpetual precipitating convective clouds. The westward advection of moisture from the MC and its convergence over the equatorial Indian Ocean appear also in composites of past MJO events. This mechanism would be complementary to possible moistening by shallow convection that has been commonly assumed. The possible moistening by westward advection is relevant to DYNAMO Hypothesis I.

In this proposed research, the possible roles of the ITCZ and MC in MJO initiation will be investigated through diagnostics of long-term time series of satellite and reanalysis data, DYNAMO field observations, and ensemble forecast during the DYNAMO field campaign. In addition, numerical experiments will be performed to help explore the role of the MC in MJO initiation.

This proposal enters the 2013 competition of the NOAA Earth System Science (ESS) Program. It targets the ESS 2013 research priority of “Understanding and Improving Prediction of Tropical Convection using Results from the DYNAMO (Dynamics of the Madden-Julian Oscillation) Field Campaign”. The MJO is an important component of the tropical climate system. It affects many weather and climate phenomena globally, including their extreme events. By improving our understanding of the MJO and its initiation, this proposed research helps NOAA to achieve its longterm objective of “Improved scientific understanding of the changing climate system and its impacts”.