Assessing the observational requirements to capture and quantify key ocean processes in the tropical Pacific through focused modeling studies

The Tropical Pacific Observing System 2020 (TPOS 2020) effort has at its core the goal to enhance and redesign observations of the tropical Pacific. As part of the design strategy a number of process studies have been identified that will help in the design of the TPOS Backbone, which will monitor the state of the Pacific system, as well as aid understanding and model improvement related to sub-seasonal to interannual variability of the system and its prediction (e.g. MJO, ENSO). The two process studies given highest priority are “Air-sea interaction at the eastern edge of the warm pool” and “Pacific Upwelling and Mixing Physics (PUMP)”. This proposal is directed towards providing modeling support in the pre-field phase of both of these studies.
The use of models to assess observational strategies requires the model to capture the relevant processes. A major focus of our studies will be the effect of vertical resolution on observational estimates and model physics, an often overlooked aspect in studies. We have demonstrated the need for high vertical resolution in both observations and models to capture important physics in the tropics, in not only the surface layer but throughout the thermocline. Our approach is to utilize an existing model setup that allows downscaling through a series of nested grids. The model is demonstrated to have a high fidelity in capturing a number of important aspects of the tropical Pacific.
Our modeling strategy will provide insights into the role of upper-ocean stratification and fine-scale shear in impacting the SST. SST is an important property in the tropical Pacific. It influences the life-cycle of the MJO and ENSO. Its amplitude and spatial distribution impacts various interactive processes determining precipitation and atmospheric diabatic heating on sub-seasonal to seasonal (S2S), and interannual timescales.
We will apply the model system to both the eastern edge of the western warm pool and the eastern upwelling region (PUMP). Model experiments will be used to address a number of the guiding questions of the TPOS process studies that include: what aspects need to be observed, what sampling strategies best provide quantitative estimates of processes, how representative are the time and space restricted studies, and how best to provide guidance on improving models.
The model runs and analysis are designed to help in the assessment of the design of the observational component of the process studies. We propose a number of assessments using the model, but note that specific assessment studies will be done in strong collaboration with observational and other modeling groups.