scholarly journals Origins of Coupled Model Biases in the Arabian Sea Climatological State

2018 ◽  
Vol 31 (5) ◽  
pp. 2005-2029 ◽  
Author(s):  
Motoki Nagura ◽  
J. P. McCreary ◽  
H. Annamalai
Keyword(s):  
Mixed Layer ◽  
Persian Gulf ◽  
Arabian Sea ◽  
Coupled Model ◽  
Sea Surface Salinity ◽  
Western Boundary ◽  
Coastal Current ◽  
Surface Cooling ◽  
Surface Salinity ◽  
High Salinity Water

This study investigates biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean–atmosphere models. The focus is to understand the cause of the large biases in the depth of the 20°C isotherm [Formula: see text] that occur in many of them. Other prominent biases are the depth [Formula: see text] and temperature [Formula: see text] of Persian Gulf water (PGW) and the wintertime mixed-layer thickness (MLT) along the northern boundary. For models that lack a Persian Gulf (group 1), [Formula: see text] is determined by the wintertime MLT bias [Formula: see text] through the formation of an Arabian Sea high-salinity water mass (ASHSW) that is too deep. For models with a Persian Gulf (group 2), if [Formula: see text] > MLT (group 2B), PGW remains mostly trapped to the western boundary and, again, [Formula: see text] directly controls [Formula: see text]. If [Formula: see text] MLT (group 2A), PGW spreads into the NAS and impacts [Formula: see text] because [Formula: see text] > 20°C; nevertheless [Formula: see text] still influences [Formula: see text] indirectly through its impact on [Formula: see text]. The thick wintertime mixed layer is driven primarily by surface cooling [Formula: see text] during the fall. Nevertheless, variations in ΔMLT among the models are more strongly linked to biases in the density stratification (jump) across the bottom of the mixed layer than to [Formula: see text] biases. The jump is in turn determined primarily by sea surface salinity biases (ΔSSS) advected into the NAS by the West India Coastal Current, and the source of ΔSSS is the rainfall deficit associated with the models’ weak summer monsoon. Ultimately, then, ΔD20 is linked to this deficit.

scholarly journals Mesoscale eddies and submesoscale structures of Persian Gulf Water off the Omani coast in spring 2011

Ocean Science ◽  
2016 ◽  
Vol 12 (3) ◽  
pp. 687-701 ◽  
Author(s):  
Pierre L'Hégaret ◽  
Xavier Carton ◽  
Stephanie Louazel ◽  
Guillaume Boutin
Keyword(s):  
Persian Gulf ◽  
Arabian Sea ◽  
Cold Water ◽  
Mesoscale Eddies ◽  
High Salinity Water ◽  
Strait Of Hormuz ◽  
Persian Gulf Water ◽  
Salinity Water ◽  
The Persian Gulf ◽  
Sea Of Oman

Abstract. The Persian Gulf produces high-salinity water (Persian Gulf Water, PGW hereafter), which flows into the Sea of Oman via the Strait of Hormuz. Beyond the Strait of Hormuz, the PGW cascades down the continental slope and spreads in the Sea of Oman under the influence of the energetic mesoscale eddies. The PGW outflow has different thermohaline characteristics and pathways, depending on the season. In spring 2011, the Phys-Indien experiment was carried out in the Arabian Sea and in the Sea of Oman. The Phys-Indien 2011 measurements, as well as satellite observations, are used here to characterize the circulation induced by the eddy field and its impact on the PGW pathway and evolution. During the spring intermonsoon, an anticyclonic eddy is often observed at the mouth of the Sea of Oman. It creates a front between the eastern and western parts of the basin. This structure was observed in 2011 during the Phys-Indien experiment. Two energetic eddies were also present along the southern Omani coast in the Arabian Sea. At their peripheries, ribbons of freshwater and cold water were found due to the stirring created by the eddies. The PGW characteristics are strongly influenced by these eddies. In the western Sea of Oman, in 2011, the PGW was fragmented into filaments and submesoscale eddies. It also recirculated locally, thus creating salty layers with different densities. In the Arabian Sea, a highly saline submesoscale lens was recorded offshore. Its characteristics are analyzed here and possible origins are proposed. The recurrence of such lenses in the Arabian Sea is also briefly examined.

Inhibition of mixed-layer deepening during winter in the northeastern Arabian Sea by the West India Coastal Current

2015 ◽  
Vol 47 (3-4) ◽  
pp. 1049-1072 ◽  
Author(s):  
D. Shankar ◽  
R. Remya ◽  
P. N. Vinayachandran ◽  
Abhisek Chatterjee ◽  
Ambica Behera
Keyword(s):  
Mixed Layer ◽  
Arabian Sea ◽  
Coastal Current ◽  
The West

scholarly journals Climatology of the Eastern Arabian Sea during the last glacial Cycle reconstructed from paired measurement of foraminiferal δ18O and Mg/Ca

2010 ◽  
Vol 73 (3) ◽  
pp. 535-540 ◽  
Author(s):  
V.K. Banakar ◽  
B.S. Mahesh ◽  
G. Burr ◽  
A.R. Chodankar
Keyword(s):  
Time Series ◽  
Arabian Sea ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Glacial Cycle ◽  
Surface Salinity ◽  
Last Glacial ◽  
Sst Cooling ◽  
Eastern Arabian Sea ◽  
The Last Glacial

Paired measurements of Mg/Ca and δ18O of Globigerenoides sacculifer from an Eastern Arabian Sea (EAS) sediment core indicate that sea-surface temperature (SST) varied within 2°C and sea-surface salinity within 2 psu during the last 100 ka. SST was coldest (∽ 27°C) during Marine Isotope Stage (MIS) 4 and 2. Sea-surface salinity was highest (∽ 37.5 psu) during most of the last glacial period (∽ 60–18 ka), concurrent with increased δ18O G.sacculifer and C/N ratios of organic matter and indicative of sustained intense winter monsoons. SST time series are influenced by both Greenland and Antarctic climates. However, the sea-surface salinity time series and the deglacial warming in the SST record (beginning at ∽18 ka) compare well with the LR04 benthic δ18O-stack and Antarctic temperatures. This suggests a teleconnection between the climate in the Southern Hemisphere and the EAS. Therefore, the last 100-ka variability in EAS climatology appears to have evolved in response to a combination of global climatic forcings and regional monsoons. The most intense summer monsoons within the Holocene occurred at ∽8 ka and are marked by SST cooling of ∽ 1°C, sea-surface salinity decrease of 0.5 psu, and δ18O G.sacculifer decrease of 0.2‰.

Indian Ocean sea surface salinity variations in a coupled model

2009 ◽  
Vol 33 (2-3) ◽  
pp. 245-263 ◽  
Author(s):  
P. N. Vinayachandran ◽  
Ravi S. Nanjundiah
Keyword(s):  
Indian Ocean ◽  
Coupled Model ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Salinity Variations

scholarly journals Oxygen isotopic analyses of individual planktic foraminifera species: implications for seasonality in the western Arabian Sea

2014 ◽  
Vol 10 (5) ◽  
pp. 3661-3688 ◽  
Author(s):  
P. D. Naidu ◽  
N. Niitsuma ◽  
S. Naik
Keyword(s):  
Arabian Sea ◽  
High Standard ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Ocean Drilling Program ◽  
Surface Salinity ◽  
Planktic Foraminifera ◽  
Isotopic Analyses ◽  
Forcing Mechanisms ◽  
The Individual

Abstract. The variation of stable isotopes between individual shells of planktic foraminifera of a given species and size may provide short-term seasonal insight on Paleoceanography. In this context, oxygen isotope analyses of individual Globigerinoides sacculifer and Neogloboquadrina dutertrei were carried out from the Ocean Drilling Program Site 723A in the western Arabian Sea to unravel the seasonal changes for the last 22 kyr. δ18O values of single shells of G. sacculifer range from of 0.54 to 2.09‰ at various depths in the core which cover a time span of the last 22 kyr. Maximum inter-shell δ18O variability and high standard deviation is noticed from 20 to 10 kyr, whereas from 10 kyr onwards the inter shell δ18O variability decreased. The individual contribution of sea surface temperature (SST) and sea surface salinity (SSS) on the inter shell δ18O values of G. sacculifer were quantified. Maximum seasonal SST between 20 and 14 ka was caused due to weak summer monsoon upwelling and strong cold winter arid continental winds. Maximum SSS differences between 18 and 10 ka is attributed to the increase of net evaporation minus precipitation due to the shift of ITCZ further south. Overall, winter dominated SST signal in Greenland would be responsible to make a teleconnection between Indian monsoon and Greenland temperature. Thus the present study has wider implications in understanding wether the forcing mechanisms of tropical monsoon climate lies in high latitudes or in the tropics.

scholarly journals On the porosity of barrier layers

Ocean Science ◽  
2009 ◽  
Vol 5 (3) ◽  
pp. 379-387 ◽  
Author(s):  
J. Mignot ◽  
C. de Boyer Montégut ◽  
M. Tomczak
Keyword(s):  
Large Scale ◽  
Sea Surface Salinity ◽  
Computation Method ◽  
Western Boundary ◽  
Climatic Impact ◽  
Surface Salinity ◽  
Data Set ◽  
Salinity Stratification ◽  
Boundary Currents ◽  
Barrier Layers

Abstract. Barrier layers are defined as the layer between the pycnocline and the thermocline when the latter are different as a result of salinity stratification. We present a revisited 2-degree resolution global climatology of monthly mean oceanic Barrier Layer (BL) thickness first proposed by de Boyer Montégut et al. (2007). In addition to using an extended data set, we present a modified computation method that addresses the observed porosity of BLs. We name porosity the fact that barrier layers distribution can, in some areas, be very uneven regarding the space and time scales that are considered. This implies an intermittent alteration of air-sea exchanges by the BL. Therefore, it may have important consequences for the climatic impact of BLs. Differences between the two computation methods are small for robust BLs that are formed by large-scale processes. However, the former approach can significantly underestimate the thickness of short and/or localized barrier layers. This is especially the case for barrier layers formed by mesoscale mechanisms (under the intertropical convergence zone for example and along western boundary currents) and equatorward of the sea surface salinity subtropical maxima. Complete characterisation of regional BL dynamics therefore requires a description of the robustness of BL distribution to assess the overall impact of BLs on the process of heat exchange between the ocean interior and the atmosphere.

scholarly journals Mindanao Current and Undercurrent: Thermohaline Structure and Transport from Repeat Glider Observations

2017 ◽  
Vol 47 (8) ◽  
pp. 2055-2075 ◽  
Author(s):  
Martha C. Schönau ◽  
Daniel L. Rudnick
Keyword(s):  
North Pacific Ocean ◽  
Maximum Velocity ◽  
Sea Surface Salinity ◽  
North Equatorial Current ◽  
Western Boundary ◽  
Thermocline Depth ◽  
Boundary Current ◽  
Surface Salinity ◽  
The North ◽  
Mindanao Current

AbstractAutonomous underwater Spray gliders made repeat transects of the Mindanao Current (MC), a low-latitude western boundary current in the western tropical North Pacific Ocean, from September 2009 to October 2013. In the thermocline (<26 kg m−3), the MC has a maximum velocity core of −0.95 m s−1, weakening with distance offshore until it intersects with the intermittent Mindanao Eddy (ME) at 129.25°E. In the subthermocline (>26 kg m−3), a persistent Mindanao Undercurrent (MUC), with a velocity core of 0.2 m s−1 and mean net transport, flows poleward. Mean transport and standard deviation integrated from the coast to 130°E is −19 ± 3.1 Sv (1 Sv ≡ 106 m3 s−1) in the thermocline and −3 ± 12 Sv in the subthermocline. Subthermocline transport has an inverse linear relationship with the Niño-3.4 index and is the primary influence of total transport variability. Interannual anomalies during El Niño are greater than the annual cycle for sea surface salinity and thermocline depth. Water masses transported by the MC/MUC are identified by subsurface salinity extrema and are on isopycnals that have increased finescale salinity variance (spice variance) from eddy stirring. The MC/MUC spice variance is smaller in the thermocline and greater in the subthermocline when compared to the North Equatorial Current and its undercurrents.

scholarly journals On Sea Surface Salinity Skin Effect Induced by Evaporation and Implications for Remote Sensing of Ocean Salinity

2010 ◽  
Vol 40 (1) ◽  
pp. 85-102 ◽  
Author(s):  
Lisan Yu
Keyword(s):  
Remote Sensing ◽  
Skin Effect ◽  
Skin Layer ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Slight Reduction ◽  
Surface Cooling ◽  
Surface Salinity ◽  
Ocean Salinity ◽  
Salt Component

Abstract The existence of a cool and salty sea surface skin under evaporation was first proposed by Saunders in 1967, but few efforts have since been made to perceive the salt component of the skin layer. With two salinity missions scheduled to launch in the coming years, this study attempted to revisit the Saunders concept and to utilize presently available air–sea forcing datasets to analyze, understand, and interpret the effect of the salty skin and its implication for remote sensing of ocean salinity. Similar to surface cooling, the skin salinification would occur primarily at low and midlatitudes in regions that are characterized by low winds or high evaporation. On average, the skin is saltier than the interior water by 0.05–0.15 psu and cooler by 0.2°–0.5°C. The cooler and saltier skin at the top is always statically unstable, and the tendency to overturn is controlled by cooling. Once the skin layer overturns, the time to reestablish the full increase of skin salinity was reported to be on the order of 15 min, which is approximately 90 times slower than that for skin temperature. Because the radiation received from a footprint is averaged over an area to give a single pixel value, the slow recovery by the salt diffusion process might cause a slight reduction in area-averaged skin salinity and thus obscure the salty skin effect on radiometer retrievals. In the presence of many geophysical error sources in remote sensing of ocean salinity, the salt enrichment at the surface skin does not appear to be a concern.

Sign in / Sign up

Export Citation Format

Share Document