The eastern equatorial Indian Ocean and seas of the maritime continent are at the heart of the tropical warm pool. They are a region of high sea surface temperatures (SSTs) that support deep atmospheric convection in the region. Hence, ocean-atmosphere interactions will likely be important for the generation and development of the atmospheric convectively coupled equatorial Kelvin waves (CCKWs) that are the main focus of this project. These atmospheric processes play a critical role in determining the magnitude and variability of harmful algal blooms and deoxygenation
The surface conditions and mixed layer structure of the ocean will have a strong control over these ocean-atmosphere interactions. We propose detailed (high vertical resolution and high temporal resolution) measurements of the ocean surface and mixed layer before, during and after the passage of CCKWs, on an equatorial transect of the CCKW propagation path along 1°N. The diurnal cycle, particularly the development of the surface diurnal warm layer, has recently been identified as an important component driving productivity in shelf seas and linked to the intensity of harmful algal blooms.
The sea between Sumatra and Borneo is very shallow (order 100 m) and is unsuitable for ocean gliders, due to the strong currents and lack of vertical distance to manoeuvre. However, a waveglider is an ideal platform to deploy in these conditions. A waveglider is an autonomous surface vehicle driven using solar and wave power. It is equipped with instruments to measure surface meteorological conditions (automatic weather station: air temperature, humidity, wind speed and direction, precipitation, radiation fluxes) and near surface oceanographic conditions (profile of temperature and salinity over top few metres). Hence, it is an excellent platform to measure ocean-atmosphere interaction and biological productivity in shallow seas. We will deploy a waveglider at approximately 108°E, 1°N, to measure the oceanic and atmospheric conditions related to the passage of CCKWs between Sumatra and Borneo.
The waveglider would be deployed alongside deploy two ocean gliders in the equatorial eastern Indian Ocean to the west of Sumatra, one at 94°E, 1°N, and one on the continental shelf at 96.5°E, 1°N. These two ocean gliders will measure ocean-atmosphere in the Indian Ocean, particularly that related to the eastward propagation of CCKWs that have developed over the Indian Ocean and are approaching Sumatra. Finally, an ocean glider will be deployed in the Celebes Sea at approximately 122°E. Due to the island of Sulawesi along 1°N, this deployment will be further north, at approximately 2°N. The Celebes Sea is over 1000 m deep, highly suitable for ocean glider deployment.
The ocean gliders and wave gliders have long durability and battery life, and can be deployed for up to 4 months, enabling long, continuous time series to be measured, and many CCKW events to be sampled.
All biogeochemical measurements, including dissolved oxygen and chlorophyll fluorescence, will be made available for the dead zone project and will be valuable measurements for the wider IIOE2 and YMC campaigns, in a data-sparse region.
The two ocean gliders in the Indian Ocean west of Sumatra would be deployed from the island of Pulau Nias (97.5°E, 1°N). The gliders would be freighted to Gunungsitoli (the main town on Pulau Nias) on the eastern side of the island. Road transport would then be needed to reach the western side of the island, then a small boat to take gliders a few miles offshore into deeper water, where they can be launched. Similar logistics would be needed from a base to deploy the wave glider, and the third ocean glider in the Celebes Sea. Power and internet would be needed on land. Similar logistics would be needed for retrieval. Funding would be needed to prepare the gliders (battery replacement, ballasting etc.) and to cover Iridium satellite communications costs during deployment, and for travel and subsistence for personnel to deploy and retrieve the gliders. UEA (Matthews, Queste, and the UEA ocean glider team) have considerable practical and science experience in operating ocean gliders and scientific analysis of glider measurements.
This project would have interactions with other related projected in the region, including BoBBLE during 2016 in the Bay of Bengal, and the wider YMC programme.
Dr Bastien Queste, University of East Anglia, UK. Physical oceanography and ocean biogeochemistry; ocean glider operations.
Prof. Adrian Matthews, University of East Anglia, UK. Ocean-atmosphere interactions; tropical dynamics; intraseasonal variability; observations; modelling; ocean gliders.
UEA Ocean Glider Team (led by Prof. Karen Heywood). Ocean glider operations.
Dr Dariusz Baranowski. Convectively coupled Kelvin waves; ocean-atmosphere interactions; glider operations.
Dr Kyla Drushka, Applied Physics Laboratory, University of Washington, US. Physical oceanography