Understanding Coupled Ocean-Atmosphere Processes at the Eastern Edge of the Warm Pool in Support of TPOS 2020
PI: Shuyi S. Chen, Co-PIs: Dongxiao Zhang and Meghan Cronin
The eastern edge of the warm pool marks the boundary between the western Pacific warm pool, where large-scale winds converge to form deep convection, and the equatorial cold tongue water to the east, where trade winds prevail. During El Niño, the eastern edge of the warm pool migrates eastward, shifting the location of the deep convection with it. This project uses a high resolution coupled ocean-atmosphere model to 1) understand the ocean-atmosphere interactions that play a role in both affecting the sharpness of the front and causing it to migrate eastward during onset of the El Niño; and 2) investigate the observational needs that would help model development and improve prediction of El Niño onset. This project uses the high-resolution Unified Wave Interface-Coupled Model (UWIN-CM) to investigate the coupled ocean-atmosphere and upper-ocean processes at the edge of the warm/fresh pool. UWIN-CM is a fully coupled ocean-atmosphere model, which consists of the Hybrid Coordinate Ocean Model (HYCOM) and the Weather Research and Forecasting (WRF) model. Specifically, this project will examine (1) Linkages among WWE (Westerly Wind Events), MJO propagation and eastward migration of WPWP at the eastern edge; (2) Characteristics of the diurnal cycle in the upper ocean and atmospheric convection; (3) Air-sea interactions at different temporal (diurnal to intraseasonal) and spatial scales during the active-WWE events and non-WWE conditions. Results from this project would provide a better understanding and quantitative assessment on possible sources of the ENSO prediction barrier problem in numerical models. This would guide the strategy of TPOS 2020 observations in general, and help fulfill NOAA’s long-term climate goal of improved scientific understanding of the changing climate system and its impacts, and address challenges in weather and climate extremes.
The success of coupled WRF-HYCOM modeling of the MJO and onset of El Nino over the tropical Pacific will have a significant impact on coupled model predictive capability on multiscale phenomena from diurnal, subseasonal to seasonal and possibly beyond.
During the first year of this project, we have made a significant progress in three main areas:
1. We have compiled a detailed analysis of the Madden-Julian Oscillations in relation to the El Nino onset over the last 20 years using satellite and in situ observations.
2. We have added a new feature to the coupled WRF-HYCOM model by including charge of salinity due to freshwater from rainfall.
3. We conducted three months long coupled WRF-HYCOM model simulation to investigate the effects of the MJO on the upper ocean through strong surface westerly winds and rain.
During the second year of this project, we have made a significant progress in four main areas:
1. We developed and implemented a rainfall induced freshwater-salinity coupling method the coupled atmosphere-ocean model (WRF-HYCOM). Salinity is input directly from the atmosphere model without relaxation to climatology. This allows the upper ocean to respond and feed back to the atmosphere in a manner that is more physically tied to the MJO than the commonly used method of salinity relaxation to climatology. The results will be reported by Kerns, Jauregui, and Chen at the 2020 AGU Fall Meeting.
2. We have completed a five-month long coupled WRF-HYCOM model simulation of three MJO events leading up to the onset of El Nino from January-May 2018, in which the precipitation from the MJO events can have a direct impact on the salinity.
3. We conducted detailed analysis using both the coupled model simulation and observational data from satellite and moorings to investigate the effects of the MJO on the upper ocean through strong surface westerly winds and rain (Jauregui and Chen, 2020a)
4. We have submitted an manuscript on a detailed analysis of the Madden-Julian Oscillations in relation to the El Nino onset over the last 20 years using satellite and in situ observations (Jauregui and Chen, 2020b)
We will focus on the following objectives during the next year:
1) Complete an manuscript on freshwater-salinity coupling and their impact on upper ocean stratification during the MJO events leading up to El Nino for publication (Kerns and Chen, 2021).
2) Analysis of the upper ocean heat budget to quantify how various physical processes (dynamical and thermodynamic) contribute to the eastward extension of the warm pool during the MJO events leading to onset of El Nino.
3) Summarize the results in a manuscript for publication.
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None at this time.