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- Title
Balancing Volume, Temperature, and Salinity Budgets During 2014–2018 in the Tropical Pacific Ocean State Estimate.
- Authors
Verdy, Ariane; Mazloff, Matthew R.; Cornuelle, Bruce D.; Subramanian, Aneesh C.
- Abstract
A state estimate of the tropical Pacific Ocean is used to analyze regional volume, temperature, and salinity budgets during 2014–2018. The simulated ocean state is constrained by both model dynamics and assimilated observations. Comparisons with independent mooring data show that the state estimate is consistent with the observed variability in temperature and velocity. Budgets are analyzed between 5°S and 5°N in the upper 300 m, inside a box defined to represent the central and eastern equatorial Pacific. Transports through the faces of this box are quantified to understand the processes responsible for variability in box‐mean properties. Vertical mixing across 300 m is negligible; temperature and salinity tendencies are balanced by surface fluxes and advective divergence, which is decomposed into geostrophic and ageostrophic components. The onset and recovery of the 2015/2016 El Niño event is found to be dominated by anomalous surface fluxes and horizontal advection. During the onset phase, weaker trade winds cause the shallow meridional overturning circulation to slow down, which reduces the poleward transport of heat and leads to upper ocean warming. Anomalous precipitation and advection of fresh water from the western Pacific drive the net freshening of the region. Relaxation from El Niño conditions is dominated by wind‐driven meridional advection at 5°N. As the meridional advection regains strength, Ekman advection efficiently exports the warm, fresh surface water out of the equatorial region. Quantifying the heat and salt transport changes in response to wind variability strengthens our understanding of global ocean heat transport. Plain Language Summary: We have combined observations and an ocean model to produce an estimate of the tropical Pacific Ocean properties. Of particular interest are changes to the upper‐ocean temperature and salinity over the period 2014–2018. The largest changes occur in the central and eastern equatorial Pacific, and to diagnose the causes we define an analysis box representative of that region. Transports through five faces of this box (the sixth face is a land boundary) are diagnosed to understand the processes responsible for variability in box‐average properties. We examine the cooling and freshening that occurs during the El Niño event of 2015/2016. The region is typically characterized by a near surface poleward flow away from the equator and a compensating flow toward the equator from below. This circulation is wind driven and slows down due to changing winds associated with the El Niño. When the winds return to their average state, currents are re‐invigorated, leading to the dissipation of El Niño conditions. This paper focuses on determining the size and timing of these processes. Key Points: A data‐assimilating model of tropical Pacific Ocean state is validated against independent mooring observationsTemperature, salinity, and volume budgets are quantified during the onset and recovery of the 2015/2016 El NiñoSurface fluxes and horizontal advection are the main drivers of regional property changes
- Subjects
EL Nino; MERIDIONAL overturning circulation; OCEAN; SALINITY; FRESH water; SEAWATER salinity; GEOSTROPHIC currents
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 7, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC019576