Examining the Subtropical Mode Water in the Southwestern Atlantic From in Situ Observations

Ferreira, Márcio Borges; Sato, O. T.; Polito, P. S.; Bernardo, P. S.

doi:10.1029/2018jc014762

Cited by 5 publications

(6 citation statements)

References 18 publications

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“…We used the ERA‐5 surface heat flux data distributed by the European Center for Medium‐Range Weather Forecasts (Hersbach et al, ). Previous studies (Ferreira et al, ; Sato & Polito, ) showed a phase delay between the heat flux and the formation cycles. This is a reflection to the fact that it takes time for the ocean to adjust to the heat flux forcing which will precondition it before the mode water formation.…”

Section: Sastmw Interannual Variabilitymentioning

confidence: 84%

“…The outcropping is a result of vigorous exchange of heat between the ocean and the atmosphere (Talley & McCartney, ; Worthington, ) when both boundary layers experience convective mixing due to that interaction (Marshall et al, ). On the ocean side, the typical winter mixed layer deepens as the surface water sinks due to cooling when the ocean loses heat to the atmosphere (Ferreira et al, ). The amount of water formed is related to the strength and duration of the thermodynamical forcing.…”

Section: Introductionmentioning

confidence: 99%

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Volumetric Characterization of the South Atlantic Subtropical Mode Water Types

Bernardo

Sato

2020

Geophysical Research Letters

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Time series (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) of a global monthly objectively analyzed fields of temperature and salinity were used to investigate the South Atlantic subtropical mode water (SASTMW). It is characterized as homogeneous layers in the temperature range of 13 to 16 • C and with low potential vorticity. Three different types of SASTMW were distinguished allowing us to evaluate their temporal volumetric variation. Each type has its distinct spatial and temporal distribution patterns and consequently dissimilar volumetric variation. This variability is seen in the volume anomaly and turnover time of each type. To examine these differences we compared two rates: the water formation in a given temperature range due to heat flux and the mode water formation. The first (13.1±2.4 Sv) is higher than the second (10.2±2.0 Sv), showing that although heat flux is essential for the formation of SASTMW, there are other factors that influence each type differently. Plain Language SummaryThis article aimed to investigate the South Atlantic subtropical mode water (SASTMW) to better understand how the volume of this mode water varies over the years (from 2002 to 2018) and in space (the South Atlantic basin). It is defined as a layer with very low vertical temperature, in a specific range (13 to 16 • C), and density variation. Three different types of SASTMW can been seen. This allowed us to independently assess the volume and its modifications over time for each one and we saw that each type has specific temperature/density characteristics and changes of its volume over time. It is understood that the formation of mode water is directly related to the processes that occur between the atmosphere and the ocean. Thus, we investigate whether the different volume variations of each type are related to these interactions. As a first approach, we investigated two rates: the rate of the amount of water that is cooled or heated to the 13-16 • C range per month and the SASTMW formation rate. By the difference between these rates, we understand that despite the importance of heat flux for the existence of SASTMW, other factors influence each type in a different way.

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Section: Sastmw Interannual Variabilitymentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Volumetric Characterization of the South Atlantic Subtropical Mode Water Types

Bernardo

Sato

2020

Geophysical Research Letters

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“…The influence of mesoscale fluctuations in the region is apparent from Figure 6a, where along 39°S, near 39°W and 36°W, there are two cold (SST ≤ 14.1°C) meanders of the South Atlantic Current. To illustrate the effectiveness of the air-sea exchanges to promote a small scale response, Ferreira et al (2019) used TS profiles in the same region, obtained from two customized Argo profilers for a 5-day cycle sampling, and showed a formation event that occurred during one single Argo cycle. In Figure 4a, the area between those limiting contours already has a layer of low PV whose density is such that even a small change in buoyancy flux would be enough to trigger a convective SASTMW formation event (Figure 4d).…”

Section: Changes In the Decorrelation Scalesmentioning

confidence: 99%

“…There are three types of subtropical mode waters identified in that basin. On the western side, the mode water occupies a region between the Brazil Current Recirculation gyre to the north and the Brazil‐Malvinas confluence region to the south (Ferreira et al., 2019). That is the site where the deepest layers of the SASTMWs are formed (Bernardo & Sato, 2020; Santos et al., 2024).…”

Section: Introductionmentioning

confidence: 99%

On the Spatio‐Temporal Scales of the Subtropical Mode Water Formation in the South Atlantic

Sato,

Polito,

Dottori

2024

JGR Oceans

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We examined the changes in the ocean’s upper layer structure involved in the formation of the subtropical mode water in the South Atlantic. Here we present the results from a survey done in the region of formation between 37°W and 32°W and 34°S and 37°S from July–October 2018, using high‐resolution measurements obtained from an underwater glider. From its records, the mode water development was observed for the first time in the South Atlantic as localized chimney‐like patterns in the temperature, salinity, and potential vorticity (PV) measurements with a horizontal scale of (7 ± 2) km, associated with wintertime oceanic convective processes. Over time, these submesoscale structures tend to expand and dominate the region as a large volume of mode water. These vertical structures present highly homogeneous temperature and salinity values. The observed PV was on the order of 5.0 × 10−11 m−1 s−1, which is one order of magnitude smaller than the pre‐existent mode water at the lower layers; negative values were observed, indicating active convection. A 1‐D vertical model was used to predict the depth of the mixed layer conditioned by the surface fluxes and triggered by its changes in winter to late spring. Comparisons of the sea surface temperature measured from satellite collocated with the glider’s measurements showed a very good agreement. From this analysis, we were able to establish the decorrelation scales that characterize mode water formation. Further inspection of the glider data yielded temporal decorrelation scales indicative of convection modified by planetary rotation.

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“…Thus, it is considered one of the most energetic regions among the oceans (Pezzi et al, 2005). Consequently, we can identify intense gradients of energy and momentum flux, which vertically influence the atmosphere and oceanic thermodynamics, generating deep convective processes leading to vigorous mixing (Ferreira et al, 2019). For these reasons, BMC can be considered an important source of thermostats (Gordon, 1981).…”

Section: Introductionmentioning

confidence: 99%

Simulated response of South Atlantic Subtropical Mode Water to air-sea processes

Bernardo

Sato

Taschetto

2021

Preprint

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Subtropical mode water is formed in winter-time deep mixed layer due to variations in air-sea processes. In the South Atlantic, three formation cores are identified between 30oS and 40oS: in the west, in the east, and north of the Subtropical Front. Each one of these three types presents typical mean thickness and horizontal distribution patterns, mainly because of local dynamic and thermodynamic characteristics of each part of the basin. In this study we assess the effects of momentum, freshwater and radiative fluxes on the variation in volume and composition of the South Atlantic Subtropical Mode Water (SASTMW). Sensitivity experiments were designed using the National Center for Atmospheric Research Community Earth System Model. Multiple one-year simulations are forced with varying intensity of wind, precipitation and shortwave radiation. By comparing to a control run, we were able to determine that the water volume variations in the east (SASTMW type 1) and south (SASTMW type 3) are significantly affected by precipitation and shortwave radiation, and thus are more sensitive to thermodynamic processes. On the other hand, SASTMW type 2 has a greater relationship with dynamic processes and is influenced by the Indian-Atlantic interbasin exchanges.

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Examining the Subtropical Mode Water in the Southwestern Atlantic From in Situ Observations

Cited by 5 publications

References 18 publications

Volumetric Characterization of the South Atlantic Subtropical Mode Water Types

Volumetric Characterization of the South Atlantic Subtropical Mode Water Types

On the Spatio‐Temporal Scales of the Subtropical Mode Water Formation in the South Atlantic

Simulated response of South Atlantic Subtropical Mode Water to air-sea processes

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