scholarly journals Salinity-induced mixed and barrier layers in the southwestern tropical Atlantic Ocean off the northeast of Brazil

Ocean Science ◽  
2011 ◽  
Vol 7 (1) ◽  
pp. 63-73 ◽  
Author(s):  
M. Araujo ◽  
C. Limongi ◽  
J. Servain ◽  
M. Silva ◽  
F. S. Leite ◽  
...  
Keyword(s):  
Barrier Layer ◽  
Austral Summer ◽  
Late Winter ◽  
Brazilian Coast ◽  
Tropical Atlantic ◽  
Austral Winter ◽  
Surface Salinity ◽  
Barrier Layer Thickness ◽  
Near Surface ◽  
Mixed Layers

Abstract. High-resolution hydrographic observations of temperature and salinity are used to analyze the formation and distribution of isothermal depth (ZT), mixed depth (ZM) and barrier layer thickness (BLT) in a section of the southwestern Atlantic (0°30´ N–14°00´ S; 31°24´–41°48´ W), adjacent to the northeastern Brazilian coast. Analyzed data consists of 279 CTD casts acquired during two cruises under the Brazilian REVIZEE Program. One occurred in late austral winter (August–October 1995) and another in austral summer (January–April 1997). Oceanic observations are compared to numerical modeling results obtained from the French Mercator-Coriolis Program. Results indicate that the intrusion of subtropical Salinity Maximum Waters (SMW) is the major process contributing to the seasonal barrier layer formation. These waters are brought by the South Equatorial Current (SEC), from the subtropical region, into the western tropical Atlantic boundary. During late austral winter southeastern trade winds are more intense and ITCZ precipitations induce lower surface salinity values near the equator. During this period a 5–90 m thick BLT (median = 15 m) is observed and BLT > 30 m is restricted to latitudes higher than 8° S, where the intrusion of salty waters between 8°–12.3° S creates shallow mixed layers over deep (ZT ≥ 90 m) isothermal layers. During austral summer, shallow isothermal and mixed layers prevail, when northeasterly winds are predominant and evaporation overcomes precipitation, causing saltier waters at the surface/subsurface layers. During that period observed BLT varies from 5 to 70 m and presents thicker median value of 35 m, when comparing to the winter. Furthermore, BLT ≥ 30 m is observed not only in the southernmost part of the study area, as verified during late winter, but in the latitude range 2°–14° S, where near-surface salty waters are transported westward by the SEC flow. These results indicate that the inclusion of salinity dynamics and its variability are necessary for studying mixed and barrier layer behaviors in the tropical Atlantic, where ocean-atmosphere coupling is known to be stronger.

scholarly journals Salinity-induced mixed and barrier layers in the southwestern tropical Atlantic Ocean off the northeast of Brazil

2009 ◽  
Vol 6 (1) ◽  
pp. 557-579
Author(s):  
M. Araujo ◽  
C. Limongi ◽  
J. Servain ◽  
M. Silva ◽  
C. A. D. Lentini
Keyword(s):  
Austral Summer ◽  
Late Winter ◽  
Brazilian Coast ◽  
Tropical Atlantic ◽  
Austral Winter ◽  
Near Surface ◽  
Barrier Layers ◽  
Latitude Range ◽  
Equatorial Current ◽  
Mixed Layers

Abstract. High resolution hydrographic observations of temperature and salinity were used to analyze the formation and distribution of isothermal (ZT), mixed (ZM) and barrier layers (BL) in a section of the southwestern Atlantic (0°30' N–14°00' S; 31°24'–41°48' W), adjacent to the northeastern Brazilian coast. Analyzed data consisted of 279 CTD casts acquired during two cruises under the Brazilian REVIZEE Program, one in late austral winter (August–October 1995) and another in austral summer (January–April 1997). Results indicated that the intrusion of subtropical Salinity Maximum Waters (SMW) brought by the South Equatorial Current (SEC) from the subtropical region into the western tropical Atlantic boundary is the major process contributing to the seasonal BL formation. During late austral winter, BL 5–90 m thickness (BLT) (median=15 m) was observed, but BLT>30 m was restricted to latitudes higher than 8° S as a result of a combination of deep isothermal layers (ZT≥90 m) and shallow mixed layers, where the latter was created by the intrusion of salty waters between 8–12.3° S. During austral summer, shallow isothermal and mixed layers prevailed and the BL formation was clearly driven by establishing a salt-induced pycnocline inside an isothermal layer. Observed BLT was less variable (5–70 m) and thicker (median=35 m). BLT≥30 m was observed not only in the southernmost part of the study area, as verified during late winter, but in the latitude range 2° S–14° S, where near surface salty waters were transported westward by the SEC flow.

scholarly journals Response of the Salinity-Stratified Bay of Bengal to Cyclone Phailin

2019 ◽  
Vol 49 (5) ◽  
pp. 1121-1140 ◽  
Author(s):  
Dipanjan Chaudhuri ◽  
Debasis Sengupta ◽  
Eric D’Asaro ◽  
R. Venkatesan ◽  
M. Ravichandran
Keyword(s):  
Barrier Layer ◽  
Bay Of Bengal ◽  
Sea Surface ◽  
Density Stratification ◽  
Upper Ocean ◽  
Dimensional Model ◽  
Cyclone Track ◽  
Surface Salinity ◽  
Near Surface ◽  
One Dimensional

AbstractCyclone Phailin, which developed over the Bay of Bengal in October 2013, was one of the strongest tropical cyclones to make landfall in India. We study the response of the salinity-stratified north Bay of Bengal to Cyclone Phailin with the help of hourly observations from three open-ocean moorings 200 km from the cyclone track, a mooring close to the cyclone track, daily sea surface salinity (SSS) from Aquarius, and a one-dimensional model. Before the arrival of Phailin, moored observations showed a shallow layer of low-salinity water lying above a deep, warm “barrier” layer. As the winds strengthened, upper-ocean mixing due to enhanced vertical shear of storm-generated currents led to a rapid increase of near-surface salinity. Sea surface temperature (SST) cooled very little, however, because the prestorm subsurface ocean was warm. Aquarius SSS increased by 1.5–3 psu over an area of nearly one million square kilometers in the north Bay of Bengal. A one-dimensional model, with initial conditions and surface forcing based on moored observations, shows that cyclone winds rapidly eroded the shallow, salinity-dominated density stratification and mixed the upper ocean to 40–50-m depth, consistent with observations. Model sensitivity experiments indicate that changes in ocean mixed layer temperature in response to Cyclone Phailin are small. A nearly isothermal, salinity-stratified barrier layer in the prestorm upper ocean has two effects. First, near-surface density stratification reduces the depth of vertical mixing. Second, mixing is confined to the nearly isothermal layer, resulting in little or no SST cooling.

scholarly journals Observation, Preconditioning and Recurrence of Exceptionally High Salinities in the Adriatic Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Hrvoje Mihanović ◽  
Ivica Vilibić ◽  
Jadranka Šepić ◽  
Frano Matić ◽  
Zrinka Ljubešić ◽  
...  
Keyword(s):  
High Salinity ◽  
Eastern Mediterranean ◽  
Heat Fluxes ◽  
Late Winter ◽  
Intermediate Water ◽  
Surface Salinity ◽  
Near Surface ◽  
Winter Convection ◽  
Dry Conditions ◽  
Forecasting System

The paper aims to describe the preconditioning and observations of exceptionally high salinity values that were observed in summer and autumn of 2017 in the Adriatic. The observations encompassed CTD measurements carried out along the well-surveyed climatological transect in the Middle Adriatic (the Palagruža Sill, 1961–2020), Argo profiling floats and several glider missions, accompanied with satellite altimetry and operational ocean numerical model (Mediterranean Forecasting System) products. Typically, subsurface salinity maximum, with values lower than 39.0, is observed in the Southern Adriatic (usually between 200 and 400 m), related to ingressions of saltier and warmer waters originating in the eastern Mediterranean (Levantine Intermediate Water—LIW). However, seasonally strong inflow of warm and high salinity waters (S > 38.8) has been observed much closer to the surface since spring 2015. The main LIW core deepened at the same time (to 400–700 m). Such double-maxima vertical pattern was eventually disturbed by winter convection at the beginning of 2017, increasing salinities throughout the water column. A new episode of very strong inflow of high salinity waters from the Northern Ionian was observed in late winter and spring of 2017, this time restricted almost to the surface. As most of 2017 was characterized by extremely dry conditions, low riverine inputs and warmer than usual summer over the Adriatic and Northern Ionian, salinity values above the sharp and shallow (15–40 m) thermocline significantly increased. The maximum recorded salinity was 39.26, as measured by the Argo float in the Southern Adriatic. Surface salinity maximum events, but with much lower intensity, have been documented in the past. Both past events and the 2017 event were characterized by (i) concurrence with overall high salinity conditions and cyclonic or transitional phase of the Adriatic-Ionian Bimodal Oscillating System, (ii) very low river discharges preconditioning the events for a year or more, (iii) higher-than-average heat fluxes during most of the summer and early autumn periods, forming a stable warm layer above the thermocline, and (iv) higher-than-average E-P (evaporation minus precipitation) acting on this warm surface layer. Importantly, the 2017 event was also preceded by strong near-surface inflow of very saline waters from the Northern Ionian in early 2017.

scholarly journals The seasonal and interannual variabilities of the barrier layer thickness in the tropical Indian Ocean

2019 ◽  
Author(s):  
Xu Yuan ◽  
Zhongbo Su
Keyword(s):  
Indian Ocean ◽  
Layer Thickness ◽  
Barrier Layer ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Barrier Layer Thickness ◽  
Enso Events

Abstract. The seasonal and interannual variations of the barrier layer thickness (BLT) in the tropical Indian Ocean (TIO) is investigated in this study using the Simple Ocean Data Assimilation (SODA) version 3 reanalysis dataset from 1980 to 2015. BLT presents a significant seasonal variation in the TIO, mainly attributed to the variations of the sea surface salinity (SSS) and the thermocline. In particular, BLT anomalies are negatively correlated to SSS anomalies in the western TIO, except in summer. In the eastern TIO, the thermocline anomalies positively impact BLT anomalies in all seasons. However, the dependency of BLT anomalies on thermocline in the western TIO is only observed during winter. Furthermore, It is found that BLT could feedback on SSS, as BLT of the spring-time can negatively affect the SSS of the summer-time in the western TIO. In terms of the interannual BLT variation, we found that both the Indian Ocean Dipole (IOD)and El Niño South Oscillation (ENSO) events could impact the variation of BLT by affecting the thermocline, especially in the eastern TIO. In addition, BLT in the western TIO presents remarkable seasonal phase locking feature during the El Niño years. During the developing and mature phases of El Niño, thicker BLT is due to the change of thermocline, while during the decaying phase of El Niño BLT opposing to the weakened thermocline change becomes more significant because of the change of SSS.

scholarly journals Tropical Atlantic Contributions to Strong Rainfall Variability Along the Northeast Brazilian Coast

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
G. A. Hounsou-gbo ◽  
M. Araujo ◽  
B. Bourlès ◽  
D. Veleda ◽  
J. Servain
Keyword(s):  
Rainy Season ◽  
Rainfall Variability ◽  
Mixed Layer Depth ◽  
Warm Pool ◽  
Brazilian Coast ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Barrier Layer Thickness ◽  
June July ◽  
Predictive Effect

Tropical Atlantic (TA) Ocean-atmosphere interactions and their contributions to strong variability of rainfall along the Northeast Brazilian (NEB) coast were investigated for the years 1974–2008. The core rainy seasons of March-April and June-July were identified for Fortaleza (northern NEB; NNEB) and Recife (eastern NEB; ENEB), respectively. Lagged linear regressions between sea surface temperature (SST) and pseudo wind stress (PWS) anomalies over the entire TA and strong rainfall anomalies at Fortaleza and Recife show that the rainfall variability of these regions is differentially influenced by the dynamics of the TA. When the Intertropical Convergence Zone is abnormally displaced southward a few months prior to the NNEB rainy season, the associated meridional mode increases humidity and precipitation during the rainy season. Additionally, this study shows predictive effect of SST, meridional PWS, and barrier layer thickness, in the Northwestern equatorial Atlantic, on the NNEB rainfall. The dynamical influence of the TA on the June-July ENEB rainfall variability shows a northwestward-propagating area of strong, positively correlated SST from the southeastern TA to the southwestern Atlantic warm pool (SAWP) offshore of Brazil. Our results also show predictive effect of SST, zonal PWS, and mixed layer depth, in the SAWP, on the ENEB rainfall.

scholarly journals Barrier Layer Development Local to Tropical Cyclones based on Argo Float Observations

2018 ◽  
Vol 48 (9) ◽  
pp. 1951-1968 ◽  
Author(s):  
John Steffen ◽  
Mark Bourassa
Keyword(s):  
Barrier Layer ◽  
Radial Distance ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Translation Speed ◽  
Layer Potential ◽  
Barrier Layer Thickness ◽  
Near Surface ◽  
Argo Float ◽  
Layer Development

AbstractThe objective of this study is to quantify barrier layer development due to tropical cyclone (TC) passage using Argo float observations of temperature and salinity. To accomplish this objective, a climatology of Argo float measurements is developed from 2001 to 2014 for the Atlantic, eastern Pacific, and central Pacific basins. Each Argo float sample consists of a prestorm and poststorm temperature and salinity profile pair. In addition, a no-TC Argo pair dataset is derived for comparison to account for natural ocean state variability and instrument sensitivity. The Atlantic basin shows a statistically significant increase in barrier layer thickness (BLT) and barrier layer potential energy (BLPE) that is largely attributable to an increase of 2.6 m in the post-TC isothermal layer depth (ITLD). The eastern Pacific basin shows no significant changes to any barrier layer characteristic, likely due to a shallow and highly stratified pycnocline. However, the near-surface layer freshens in the upper 30 m after TC passage, which increases static stability. Finally, the central Pacific has a statistically significant freshening in the upper 20–30 m that increases upper-ocean stratification by ~35%. The mechanisms responsible for increases in BLPE vary between the Atlantic and both Pacific basins; the Atlantic is sensitive to ITLD deepening, while the Pacific basins show near-surface freshening to be more important in barrier layer development. In addition, Argo data subsets are used to investigate the physical relationships between the barrier layer and TC intensity, TC translation speed, radial distance from TC center, and time after TC passage.

scholarly journals An Assessment of ERA5 Reanalysis for Antarctic Near-Surface Air Temperature

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 217
Author(s):  
Jiangping Zhu ◽  
Aihong Xie ◽  
Xiang Qin ◽  
Yetang Wang ◽  
Bing Xu ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Antarctic Peninsula ◽  
Austral Summer ◽  
Correlation Coefficients ◽  
East Antarctica ◽  
West Antarctica ◽  
Austral Spring ◽  
Reanalysis Dataset ◽  
Near Surface ◽  
The Antarctic

The European Center for Medium-Range Weather Forecasts (ECMWF) released its latest reanalysis dataset named ERA5 in 2017. To assess the performance of ERA5 in Antarctica, we compare the near-surface temperature data from ERA5 and ERA-Interim with the measured data from 41 weather stations. ERA5 has a strong linear relationship with monthly observations, and the statistical significant correlation coefficients (p < 0.05) are higher than 0.95 at all stations selected. The performance of ERA5 shows regional differences, and the correlations are high in West Antarctica and low in East Antarctica. Compared with ERA5, ERA-Interim has a slightly higher linear relationship with observations in the Antarctic Peninsula. ERA5 agrees well with the temperature observations in austral spring, with significant correlation coefficients higher than 0.90 and bias lower than 0.70 °C. The temperature trend from ERA5 is consistent with that from observations, in which a cooling trend dominates East Antarctica and West Antarctica, while a warming trend exists in the Antarctic Peninsula except during austral summer. Generally, ERA5 can effectively represent the temperature changes in Antarctica and its three subregions. Although ERA5 has bias, ERA5 can play an important role as a powerful tool to explore the climate change in Antarctica with sparse in situ observations.

Impact of mesoscale eddies on salinity and CO2 ocean parameters in the western tropical Atlantic in February 2020

2021 ◽  
Author(s):  
Léa Olivier ◽  
Jacqueline Boutin ◽  
Nathalie Lefèvre ◽  
Gilles Reverdin ◽  
Peter Landschützer ◽  
...  
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Salinity Gradient ◽  
Sea Surface Salinity ◽  
Amazon River ◽  
Tropical Atlantic ◽  
Surface Salinity ◽  
The North ◽  
Brazil Current ◽  
North Brazil

&lt;p&gt;Large oceanic eddies are formed by the retroflection of the North Brazil Current (NBC) near 8&amp;#176;N in the western tropical Atlantic. The EUREC&lt;sup&gt;4&lt;/sup&gt;A-OA/Atomic cruise took place in January - February 2020, and extensively documented two NBC rings. The NBC flows northward across the Equator and pass the mouth of the Amazon River, entraining fresh and nutrient-rich water along its nearshore edge. From December to March, the Amazon river discharge is low but a freshwater filament stirred by a NBC ring was nevertheless observed. The strong salinity gradient can be used to delineate the NBC ring during its initial phase and its westward propagation. Using satellite sea surface salinity and ocean color associated to in-situ measurements of salinity, temperature, dissolved inorganic carbon, alkalinity and fugacity of CO&lt;sub&gt;2&lt;/sub&gt; we characterize the salinity and biogeochemical signature of NBC rings.&lt;/p&gt;

Ocean Salinity Aspects of the Ningaloo Niño

2021 ◽  
pp. 1
Author(s):  
Yaru Guo ◽  
Yuanlong Li ◽  
Fan Wang ◽  
Yuntao Wei
Keyword(s):  
Fresh Water ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Climate ◽  
Ocean Model ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Near Surface ◽  
Ocean Salinity

AbstractNingaloo Niño – the interannually occurring warming episode in the southeast Indian Ocean (SEIO) – has strong signatures in ocean temperature and circulation and exerts profound impacts on regional climate and marine biosystems. Analysis of observational data and eddy-resolving regional ocean model simulations reveals that the Ningaloo Niño/Niña can also induce pronounced variability in ocean salinity, causing large-scale sea surface salinity (SSS) freshening of 0.15–0.20 psu in the SEIO during its warm phase. Model experiments are performed to understand the underlying processes. This SSS freshening is mutually caused by the increased local precipitation (~68%) and enhanced fresh-water transport of the Indonesian Throughflow (ITF; ~28%) during Ningaloo Niño events. The effects of other processes, such as local winds and evaporation, are secondary (~18%). The ITF enhances the southward fresh-water advection near the eastern boundary, which is critical in causing the strong freshening (> 0.20 psu) near the Western Australian coast. Owing to the strong modulation effect of the ITF, SSS near the coast bears a higher correlation with the El Niño-Southern Oscillation (0.57, 0.77, and 0.70 with Niño-3, Niño-4, and Niño-3.4 indices, respectively) than sea surface temperature (-0.27, -0.42, and -0.35) during 1993-2016. Yet, an idealized model experiment with artificial damping for salinity anomaly indicates that ocean salinity has limited impact on ocean near-surface stratification and thus minimal feedback effect on the warming of Ningaloo Niño.

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