Multi-timescale near-surface salinity variability at the eastern edge of the warm pool: A Modeling and an OSSE study in support of TPOS 2020

As part of the Tropical Pacific Observing System 2020 (TPOS 2020) first report, several process studies were identified that would guide development of the observing system and lead to improved understanding and predictability of the Pacific climate system. Here we focus on prefield phase needs of the process study “Air-sea interaction at the eastern edge of the western Pacific warm pool (WPWP)”. This study builds upon previous studies in the WPWP (e.g., TOGA COARE) by focusing on the interactions at the front at the eastern edge of the WPWP.
Towards the implementation of the process study to understand air-sea interaction at the eastern edge of the WPWP, this proposal is primarily a model-based study to provide some necessary insights for the design of the field phase of the experiment. Our objectives are to (a) explore the multi-timescale near-surface salinity variations at the Warm Pool eastern edge (WPEE), and (b) To identify possible sampling requirements (and strategies) that may be essential to capture this variability. To achieve the objectives, the following tasks are proposed:
1) A coupled simulation using the modified Coupled Forecast System version 2 (CFSv2) with 1-m vertical resolution in the upper ocean will be conducted. Diagnostics related to the sea surface salinity (SSS) front at the WPEE and multi-timescale SSS variability will be made to enhance our understanding of air-sea interaction in the presence of barrier layer over this region;
2) Mimicking a realistic combination of sampling variables, sampling locations/frequencies and sampling technologies that may be viable for observing the variability associated WPEE, a set of “synthetic observations” will be constructed based on the above coupled model simulation; and
3) Observing system simulation experiments (OSSEs) will be performed by assimilating the “synthetic observations” into an ocean data assimilation to obtain an ocean analysis. Comparisons with the original coupled simulation will be made to ascertain if the proposed observational strategies will be adequate to capture essential features of WPEE.
We anticipate that the proposed research will enhance our understanding of processes associated with multi-timescale near-surface salinity at the warm pool eastern edge and identify possible sampling requirements (and strategies) essential to capture them. The outcomes from the project will not only improve our understanding of air-sea interaction at the eastern edge of the warm pool, but will also help guide the pre-cruise planning and field campaign development for TPOS 2020, and further, in the design of the sustained observing system.