Acoustic Detection of Rainfall using Ocean Gliders in the Tropical Indian Ocean

Rainfall is of fundamental importance to people's livelihoods and is a critical part of our climate system. Nowhere is this more true than in the Maritime Continent region of southeast Asia, the engine room of the global atmosphere. But rainfall is notoriously difficult to measure at sea, and we know little about the interplay of weather systems and ocean-atmosphere interactions that occur there. TerraMaris will combine air-, sea- and land-based measurements from Java, Christmas Island, and the tropical Indian Ocean, to improve our understanding of rainfall in this critical region. You will join the international TerraMaris field campaign from November 2019 to March 2020, deploying autonomous underwater vehicles, known as ocean gliders, to measure sound deep in the ocean. From these novel measurements, you will determine rainfall and wind speed from the noise these processes make at the sea surface, but which can be heard even in the ocean's interior. Specific questions are: How deep in the ocean can you 'hear' rain and wind? How do you distinguish the sound of rain and wind from other ocean noise? How do these acoustic measurements compare with other observations? You will also take part in the land campaign, launching radiosondes (weather balloons), from Christmas Island. You will receive training in glider and radiosonde operations before your fieldwork. You will analyse your observations, in combination with satellite and other global data sets, to better understand the processes that drive weather systems over the Maritime Continent. In particular, you will quantify the development of the daily cycle of atmospheric convection, with clouds and rain over the islands during the day and offshore overnight. Your work will pin down the importance of the ocean in this process.

Due to the integral nature of the MC and the Madden-Julian Oscillation (MJO) within the global weather and climate system, this work will significantly impact forecasting on scales ranging from the short-range process-level understanding to climate prediction. Weather forecasters, including the UK Met Office and Indonesian BMKG (project partners), will benefit from TerraMaris through scientific advances in understanding and modelling the interactions of convection with atmospheric dynamics and ocean thermodynamics and the impact of these processes on severe and hazardous weather, including UK weather. This will feed into improved measures of uncertainty in weather forecasts, and into the process of developing the next generation of convective parameterisation schemes through the ParaCon project.

The MC provides a unique test bed for the new convective parameterisation schemes being developed in ParaCon, within which no new field measurements could be funded. The performance of parametrisations over the MC is critical to global modelling. Improved convection schemes will lead directly to improved rainfall forecasts, not only over the MC, but by improving the MC convection, across the world. The MC mosaic of steep, high, mountainous islands set among shallow warm seas, will provide a challenging and distinct regime in which to evaluate these schemes compared with, e.g., convection over open ocean or over continental regions (e.g., Great Plains of North America, Sahel region of Africa). TerraMaris will deliver a comprehensive, state-of-the-art set of case studies and statistical observations, a hierarchy of model simulations and detailed understanding of convective processes within this regime to validate convective paradigms developed in ParaCon, and to benchmark quantitatively ParaCon numerical simulations of convection and its interaction with atmospheric dynamics. TerraMaris will develop these products in close consultation with ParaCon, through Co-I's Woolnough, Marsham and Birch.

An improved understanding of the MJO and its propagation through the MC will lead to better constraints on the confidence of global medium-range forecasts (up to 15 days) at the UK Met Office, the European Centre for Medium Range Weather Forecasts, and other national meteorological agencies. The MC is a critical region for the El Nino-Southern Oscillation (ENSO), the major source of climate predictability on seasonal to inter-annual time scales; hence improved understanding of MC processes will feed into ENSO prediction and analysis of biases in ENSO forecasts. These will improve sub-seasonal and seasonal forecasts. On climate time scales (decadal and longer), the identification of the causes of regional model errors over the MC will lead to better constraints on regional climate projections, benefitting the IPCC and end users of climate projections, such as national and regional governments, and stakeholders in agriculture and water supply sectors.

Indonesian researchers in climate science, meteorology and oceanography will benefit from the advances described above, as well as the new techniques that TerraMaris will develop and apply (e.g., coordination of aircraft, radiosonde, land and ocean based measurements to measure the diurnal cycle of convection and land-sea breezes and gravity waves). The ocean observations will also include elements of biogeochemistry, so our results will benefit those working on fisheries management, carbon sequestration and ecosystem modelling. TerraMaris will benefit the International Indian Ocean Expedition 2 (IIOE-2), by improving understanding of ocean-atmosphere coupling in the Indian Ocean region. Scientists in the developing countries of the MC region will benefit by learning how to operate radiosondes and take surface flux measurements, and how to deploy, operate and pilot Seagliders and Wavegliders.