Abstract 209

Abstract ID: 209

Some indications of key components for the MJO and relevant phenomena over the Maritime Continent from the recent field observations

Lead Author: Kunio Yoneyama

Keywords: MJO, YMC, air-sea interaction, field observations, Maritime Continent

Abstract: As part of the international field program “Years of the Maritime Continent (YMC)”, we at JAMSTEC conducted two field campaigns in the vicinity of the west coast of Sumatra Island, Indonesia in 2015 and 2017. In addition to in-situ measurements, we study weather and climate characteristics over the Maritime Continent using satellite and mooring data as well. In this presentation, we will briefly review the recent works that provide several key knowledge obtained through analyses of those observations, which may improve the prediction skill of subseasonal-to-seasonal time scale phenomena. We will emphasize the importance of in-situ measurements in the coastal region for several phenomena.
One of the main specific research themes of the YMC is to know the interaction between local circulation (especially diurnal cycle) and the Madden-Julian Oscillation (MJO). Since the diurnal cycle of rain dominates along the coast, we conducted field observations on and off the west coast of Sumatra using research vessel, mooring, unmanned automated surface vehicle and land-based site. Based on intensive analyses of these data sets, we can summarize some key knowledge obtained so far. They are; 1) A numerical model, which suffers from simulating offshore propagation of diurnal cycle of rain developed over the coast, has been much improved by incorporating in situ sea surface temperature (SST) data into their numerical model initial condition instead of reanalysis product alone owing to the reduction of biases. 2) Although there are many global SST products, validation with in situ measurements demonstrates significant biases over the eastern Indian Ocean for some products. 3) Convections associated with the MJO were well simulated when high-frequency (3-hourly or better) air-sea coupling was adopted. 4) Gravity waves caused by afternoon precipitation over the land act as precursor causing unstable condition over the sea and inducing offshore propagation. 5) Since the behavior of lower troposphere, where gravity waves were observed, is a key for favorable condition of convection development, background wind such as monsoonal flow and the MJO and their interaction with local wind should be well monitored.
Above knowledge related to diurnal cycle of rain can be used to improve simulation of the MJO over the Maritime Continent. In addition to those results which indicate important role of air-sea interaction near the coast for the interaction between local circulation and the MJO, a recent study, which analyzed satellite-derived sea surface chlorophyll-a data, demonstrated the cold waters due to the coastal upwelling off south of Java Island spread westward and cause the positive Indian Ocean Dipole phenomena. It also indicated that westward spread was accompanied the winds associated with the MJO. This implies that local air-sea interaction in the Maritime Continent has potential to connect large-scale phenomena through the MJO. Thus, again, observation in the coastal region is a key to understand S2S and larger timescale phenomena.

Satoru Yokoi (JAMSTEC)
Ning Zhao (JAMSTEC)
Peiming Wu (JAMSTEC)
Qoosaku Moteki (JAMSTEC)
Takanori Horii (JAMSTEC)