NSFGEO-NERC: Equatorial Line Observations (ELO) Field Campaign during the International Years of Maritime Continent Program: Oceanography and Atmospheric Perspective

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The warm shallow seas and mountainous islands of the Maritime Continent (MC, the region between the Indian Ocean and the western Pacific) pose a challenge for atmospheric disturbances propagating through the area. The larges of these disturbances is the Madden-Julian Oscillation (MJO), a broad envelope of clouds and precipitation that forms in the Indian Ocean and moves slowly eastward as far as the central equatorial Pacific. The MJO affects weather and climate over much of the globe, with US impacts including hurricane formation in the Gulf of Mexico and flooding in California due to atmospheric rivers. The slow evolution and widespread impacts of the MJO have spurred interest in MJO prediction, and the MC presents a challenge to forecasting as models have difficulty predicting which events will transit the region and which will dissipate within it. The desirability of long-range forecasts of MJO impacts has thus lead to an interest in understanding the mechanisms through which the MC interacts with the MJO and serves as a gatekeeper for their entry into the equatorial Pacific.This project is one component of the Equatorial Line Observations (ELO) field campaign, which seeks to understand the local MC processes that influence MJO propagation. The campaign is a joint project between researchers in the US, Great Britain, and Indonesia in which oceanic observations are taken along the equator using sea gliders off the west coast of Sumatra and moorings in the Karimata Strait between Sumatra and Borneo. The oceanic observations are complemented by land-based observations in eastern Sumatra and on the west coast of Borneo, with deployment scheduled between November 2018 and February 2019. ELO is part of a larger international effort known as the Years of the Maritime Continent, organized under the auspices of the World Meteorological Organization.The campaign targets three factors which are hypothesized to influence MJO propagation through the MC. The first is interactions between atmospheric disturbances and the underlying ocean. Abundant rainfall over the internal seas of the MC produces a shallow surface layer of fresh water which can be warmed and cooled rapidly by variations in sunlight reaching the surface, wind-driven evaporation, and other factors. Variations in sea surface temperature can in turn influence cloudiness and precipitation, and the campaign seeks to understand how this air-sea coupling affects eastward propagating atmospheric disturbance.The second is the interaction of the MJO with convectively coupled Kelvin waves (CCKWs), which are smaller equatorial weather disturbances which propagate eastward at a faster rate than the MJO and are regarded as its "building blocks". The PIs hypothesize that the problems with the representation of MJO propagation through the MC seen in forecast models are related to poor simulation of CCKW activity in the region.The third is the interaction of CCKWs with the diurnal cycle of precipitation in the MC, as intense precipitation generally occurs after noon over Sumatra and Borneo but in the morning over the Karimata Strait separating them. The distance between the islands is such that a CCKW passing over Sumatra during the rainy part of the day is likely to arrive at Borneo in time for the precipitation maximum on the following day. The PI hypothesizes that the extra condensational heating received by CCKWs which are synchronized with the island diurnal cycles could favor their growth and further interaction with the MJO.The work has societal as well as scientific value given the worldwide impacts of the MJO and the potential for improvement of MJO-related forecasts. The work also promotes international capacity building in atmospheric science and operational forecasting, as it is conducted in collaboration with Indonesian partners. The campaign involves PhD students from the US, Great Britain, and Indonesia, thus providing future workforce development in this research area.