Uncrewed Surface Vehicles as a Research Platform for Tropical Pacific Observing Platform (TPOS) Field Campaigns

As part of the plan to address uncertainties in processes regulating sea surface temperatures (SSTs) that lead to biases in the eastern tropical Pacific and reduced skill in El Niño / Southern Oscillation (ENSO) predictions, the Tropical Pacific Observing System First Report recommends implementation of two air-sea interaction process studies: The Pacific Upwelling and Mixing Physics (PUMP) and the Eastern Edge of the Warm Pool (EEWP). The two regions are also identified by the Precipitation Prediction Grand Challenge Strategic Plan as “sources of precipitation predictability”. An aim of these process studies is to determine the minimum observations needed, and on what time and space scales they are needed, for monitoring ocean variability and related climate and weather modes, as well as for constraining models. However, process studies require intensive field observations to resolve ALL critical processes. New uncrewed surface vehicles (USVs) offer great promise for intensive observations of phenomena like the EEWP that can migrate zonally tens of thousands of kilometers, and for upwelling studies that require potentially four surface-to-depth current profilers to be able to estimate the current divergence at a central point. The current proposed work uses recent USV observations and model output to test the capabilities of these platforms in PUMP and EEWP process studies.
In particular, the objects of the current study are:
1) An analysis of historical USV data from past Tropical Pacific Observing System (TPOS)
missions, including exploring approaches to calculate vertical velocity from the surface to
60-100 m in the PUMP domain;
2) The development of a “USV Sampler” that generates synthetic USV tracks within
gridded reanalysis and forecast model fields based upon desired way points and the
model’s winds and currents;
3) An evaluation of the synthetic USV data in models (existing high-resolution simulations)
to assess the representation of the air-sea interface and upper ocean in the model products
and to validate the USV Sampler; and,
4) Informed by the results of the assessments in 3), test a range of adaptive sampling
strategies for capturing air-sea interaction processes within the PUMP and EEWP regions
to aid future field studies.
This project will contribute to a process level understanding of the PUMP and EEWP regions that is critical for advancing long standing biases in global forecasting and climate models and improving subseasonal-to-seasonal and ENSO prediction skill, a priority for the CVP program. This project also raises the technological readiness level of USVs for use in TPOS process studies by evaluating and demonstrating their capabilities within the equatorial Pacific environment. A higher technical readiness level is also an important step for being able to include USVs in the Global Ocean Observing System (GOOS).