Influence of Assimilation of Subsurface Temperature Measurements on Simulations of Equatorial Undercurrent and South Equatorial Current along the Pacific Equator

1998 ◽  
Vol 15 (6) ◽  
pp. 1471-1477 ◽  
Author(s):  
David Halpern ◽  
Ming Ji ◽  
Ants Leetmaa ◽  
Richard W. Reynolds
Keyword(s):  
Temperature Measurements ◽  
Subsurface Temperature ◽  
South Equatorial Current ◽  
Equatorial Undercurrent ◽  
The Pacific ◽  
Equatorial Current

scholarly journals Surface Circulation and Vertical Structure of Upper Ocean Variability Around Fernando de Noronha Archipelago and Rocas Atoll During Spring 2015 and Fall 2017

2021 ◽  
Vol 8 ◽  
Author(s):  
Alex Costa da Silva ◽  
Alexis Chaigneau ◽  
Alina N. Dossa ◽  
Gerard Eldin ◽  
Moacyr Araujo ◽  
...  
Keyword(s):  
Mixed Layer ◽  
The South ◽  
South Equatorial Current ◽  
Equatorial Undercurrent ◽  
Study Region ◽  
Near Surface ◽  
North Brazil ◽  
Fernando De Noronha ◽  
Equatorial Current ◽  
Central South

Using current, hydrographic and satellite observations collected off Northeast Brazil around the Fernando de Noronha Archipelago and Rocas Atoll during two oceanographic cruises (spring 2015 and fall 2017), we investigated the general oceanic circulation and its modifications induced by the islands. In spring 2015, the area was characterized by lower SST (26.6°C) and deep mixed-layer (∼90 m). At this depth, a strong current shear was observed between the central branch of the eastward flowing near-surface South Equatorial Current and the westward flowing South Equatorial Undercurrent. In contrast, in fall 2017, SST was higher (∼28.8°C) and the mixed-layer shallower (∼50 m). The shear between the central South Equatorial Current and the South Equatorial Undercurrent was weaker during this period. Interestingly, no oxygen-rich water from the south (retroflection of the North Brazil undercurrent) was observed in the region in fall 2017. In contrast, we revealed the presence of an oxygen-rich water entrained by the South Equatorial Undercurrent reaching Rocas Atoll in spring 2015. Beside these global patterns, island wake effects were noted. The presence of islands, in particular Fernando de Noronha, strongly perturbs central South Equatorial Current and South Equatorial Undercurrent features, with an upstream core splitting and a reorganization of single current core structures downstream of the islands. Near islands, flow disturbances impact the thermohaline structure and biogeochemistry, with a negative anomaly in temperature (−1.3°C) and salinity (−0.15) between 200 and 400 m depth in the southeast side of Fernando Noronha (station 5), where the fluorescence peak (>1.0 mg m–3) was shallower than at other stations located around Fernando de Noronha, reinforcing the influence of flow-topography. Satellite maps of sea-surface temperature and chlorophyll-a confirmed the presence of several submesoscale features in the study region. Altimetry data suggested the presence of a cyclonic mesoscale eddy around Rocas Atoll in spring 2015. A cyclonic vortex (radius of 28 km) was actually observed in subsurface (150–350 m depth) southeast of Rocas Atoll. This vortex was associated with topographically induced South Equatorial Undercurrent flow separation. These features are likely key processes providing an enrichment from the subsurface to the euphotic layer near islands, supplying local productivity.

scholarly journals Origin of Sustained Continuous Measurements of Surface Wind and Upper-Ocean Current and Temperature on the Pacific Equator: EQUA Project

2021 ◽  
pp. 1-47
Author(s):  
David Halpern
Keyword(s):  
Time Series ◽  
Surface Wind ◽  
Temperature Measurements ◽  
Ocean Current ◽  
Upper Ocean ◽  
Kelvin Wave ◽  
Equatorial Undercurrent ◽  
Pilot Experiment ◽  
The Pacific

AbstractIn 1976, a pilot experiment, called first Equatorial Mooring (EQUA-1), tested an innovative technique for anchoring a taut-line surface mooring at 0°, 150°W where the water depth is 4.5 km. The 36-day deployment contained a wind recorder and fixed-level current meters at 50 and 100 m in the Equatorial Undercurrent (EUC). The following year, in a second pilot experiment, named EQUA-2, a similar mooring was deployed at 0°, 125°W for 99 days. EQUA-2, with current meters at 10, 50, 100, 150 and 200 m, recorded a surge in EUC transport during April 1977 when 3-day averaged eastward current speeds at 50-m depth reached 2 m s‒1. The associated eastward transport per unit meridional width over the 50- to 200-m layer was 190 m2 s‒1. Based on observations recorded in April 1980, the EQUA-2 pulse would correspond to a total EUC transport surge of about 38 Sverdrups and would represent an equatorially trapped first-mode baroclinic Kelvin wave. This paper describes EQUA Project observations and why and how I created the high risk-of-failure opportunity to record pioneering time series measurements at the equator. The enduring legacy of the EQUA Project is the sustained maintenance of in-situ surface wind and upper-ocean current and temperature measurements at numerous sites in the equatorial oceans, starting in the Pacific to improve forecasts of the El Niño and La Niña phenomenon. For example, the 40-year records of surface wind and upper-ocean current and temperature measurements at 0°, 110°W and 0°, 140°W are some of oceanography’s longest time series recorded far from land.

scholarly journals Observing the Galápagos–EUC Interaction: Insights and Challenges

2010 ◽  
Vol 40 (12) ◽  
pp. 2768-2777 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Raghu Murtugudde ◽  
Antonio J. Busalacchi
Keyword(s):  
Climate Models ◽  
Current System ◽  
Critical Role ◽  
Equatorial Undercurrent ◽  
Eastern Equatorial Pacific ◽  
The Pacific ◽  
Adcp Measurements ◽  
Equatorial Current ◽  
Coupled Variability ◽  
Striking Effect

Abstract Although sustained observations yield a description of the mean equatorial current system from the western Pacific to the eastern terminus of the Tropical Atmosphere Ocean (TAO) array, a comprehensive observational dataset suitable for describing the structure and pathways of the Equatorial Undercurrent (EUC) east of 95°W does not exist and therefore climate models are unconstrained in a region that plays a critical role in ocean–atmosphere coupling. Furthermore, ocean models suggest that the interaction between the EUC and the Galápagos Islands (∼92°W) has a striking effect on the basic state and coupled variability of the tropical Pacific. To this end, the authors interpret historical measurements beginning with those made in conjunction with the discovery of the Pacific EUC in the 1950s, analyze velocity measurements from an equatorial TAO mooring at 85°W, and analyze a new dataset from archived shipboard ADCP measurements. Together, the observations yield a possible composite description of the EUC structure and pathways in the eastern equatorial Pacific that may be useful for model validation and guiding future observation.

scholarly journals From the western boundary currents to the Pacific Equatorial Undercurrent: Modeled pathways and water mass evolutions

2011 ◽  
Vol 116 (C12) ◽  
Author(s):  
Mélanie Grenier ◽  
Sophie Cravatte ◽  
Bruno Blanke ◽  
Christophe Menkes ◽  
Ariane Koch-Larrouy ◽  
...  
Keyword(s):  
Water Mass ◽  
Western Boundary ◽  
Western Boundary Currents ◽  
Equatorial Undercurrent ◽  
Boundary Currents ◽  
The Pacific

scholarly journals Iron sources and pathways into the Pacific Equatorial Undercurrent

2016 ◽  
Vol 43 (18) ◽  
pp. 9843-9851 ◽  
Author(s):  
Xuerong Qin ◽  
Laurie Menviel ◽  
Alex Sen Gupta ◽  
Erik van Sebille
Keyword(s):  
Equatorial Undercurrent ◽  
The Pacific

Interannual Modality of Upper-Ocean Temperature: 4D Structure Revealed by Argo Data

2015 ◽  
Vol 28 (9) ◽  
pp. 3441-3452 ◽  
Author(s):  
Ge Chen ◽  
Hanou Chen
Keyword(s):  
Interannual Variability ◽  
Southern Oscillation ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Upper Ocean ◽  
Kelvin Wave ◽  
Argo Data ◽  
Sea Temperature ◽  
Equatorial Undercurrent ◽  
The Pacific

Abstract Using the newly available decade-long Argo data for the period 2004–13, a detailed study is carried out on deriving four-dimensional (4D) modality of sea temperature in the upper ocean with emphasis on its interannual variability in terms of amplitude, phase, and periodicity. Three principal modes with central periodicities at 19.2, 33.8, and 50.3 months have been identified, and their relationship with El Niño–Southern Oscillation (ENSO) is investigated, yielding a number of useful results and conclusions: 1) A striking tick-shaped pipe-like feature of interannual variability maxima, which is named the “Niño pipe” in this paper, has been revealed within the 10°S–10°N upper Pacific Ocean. 2) The pipe core extends downward from ~50 m at 130°E to ~250 m near the date line before tilting upward to the sea surface at about 275°E, coinciding nicely with the pathway of the Pacific equatorial undercurrent (EUC). 3) The double-peak zonal modality pattern of the Niño pipe in the upper Pacific is echoed in the subsurface Atlantic and Indian Oceans through Walker circulation, while its single-peak meridional modality pattern is mirrored in the subsurface North and South Pacific through Hadley circulation. 4) A coherent three-peak modal structure implies a strong coupling between sea level variability at the surface and sea temperature variability around the thermocline. Accumulating evidence suggests that Rossby/Kelvin wave dynamics in tandem with EUC-based thermocline dynamics are the main mechanisms of the three-mode Niño pipe in ENSO cycles.

scholarly journals A Climatological Interpretation of the Circulation in the Western South Pacific*

2002 ◽  
Vol 32 (9) ◽  
pp. 2492-2508 ◽  
Author(s):  
Tangdong Qu ◽  
Eric J. Lindstrom
Keyword(s):  
Papua New Guinea ◽  
New Guinea ◽  
Western Boundary ◽  
Guinea Coast ◽  
Boundary Currents ◽  
The North ◽  
Intermediate Layers ◽  
Water Property ◽  
The Pacific ◽  
Equatorial Current

Abstract Time-averaged circulation is examined using historical hydrographic data near the Australia and Papua New Guinea coast in the Pacific. By averaging the data along isopycnal surfaces in a 0.5° × 0.5° grid, the authors are able to show many detailed phenomena associated with the narrow western boundary currents, including the vertical structure of the bifurcation latitude of the South Equatorial Current (SEC) and the connection between the Solomon and Coral Seas. The bifurcation latitude of the SEC is found to move southward from about 15°S near the surface to south of 22°S in the intermediate layers. The origin of the Great Barrier Reef Undercurrent (GBRUC) is identified to be at about 22°S. Farther to the north, the GBRUC intensifies underlying the surface East Australian Current, and merges with the North Queensland Current (NQC) at about 15°S. The NQC turns eastward to flow along the Papua New Guinea coast and feeds into the New Guinea Coastal Undercurrent (NGCUC) through the Louisiade Archipelago. Further analysis shows that there is a strong water property connection between the Coral and Solomon Seas, confirming the earlier speculation on the water mass origins of the NGCUC.

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