scholarly journals Near-Surface Shear Flow in the Tropical Pacific Cold Tongue Front*

2009 ◽  
Vol 39 (5) ◽  
pp. 1200-1215 ◽  
Author(s):  
Meghan F. Cronin ◽  
William S. Kessler
Keyword(s):  
Turbulent Viscosity ◽  
Instability Wave ◽  
Surface Currents ◽  
Cold Tongue ◽  
Surface Shear ◽  
Near Surface ◽  
The Pacific ◽  
Geostrophic Shear ◽  
Moored Current Meters ◽  
The Tropical Pacific

Abstract Near-surface shear in the Pacific cold tongue front at 2°N, 140°W was measured using a set of five moored current meters between 5 and 25 m for nine months during 2004–05. Mean near-surface currents were strongly westward and only weakly northward (∼3 cm s−1). Mean near-surface shear was primarily westward and, thus, oriented to the left of the southeasterly trades. When the southwestward geostrophic shear was subtracted from the observed shear, the residual ageostrophic currents relative to 25 m were northward and had an Ekman-like spiral, in qualitative agreement with an Ekman model modified for regions with a vertically uniform front. According to this “frontal Ekman” model, the ageostrophic Ekman spiral is forced by the portion of the wind stress that is not balanced by the surface geostrophic shear. Analysis of a composite tropical instability wave (TIW) confirms that ageostrophic shear is minimized when winds blow along the front, and strengthens when winds blow oblique to the front. Furthermore, the magnitude of the near-surface shear, both in the TIW and diurnal composites, was sensitive to near-surface stratification and mixing. A diurnal jet was observed that was on average 12 cm s−1 stronger at 5 m than at 25 m, even though daytime stratification was weak. The resulting Richardson number indicates that turbulent viscosity is larger at night than daytime and decreases with depth. A “generalized Ekman” model is also developed that assumes that viscosity becomes zero below a defined frictional layer. The generalized model reproduces many of the features of the observed mean shear and is valid both in frontal regions and at the equator.

scholarly journals Diurnal cycles of near‐surface currents across the tropical Pacific

2021 ◽  
Author(s):  
Jessica Masich ◽  
William S. Kessler ◽  
Meghan F. Cronin ◽  
Karen R. Grissom
Keyword(s):  
Tropical Pacific ◽  
Surface Currents ◽  
Near Surface ◽  
Diurnal Cycles ◽  
The Tropical Pacific

scholarly journals Measurement Characteristics of Near-Surface Currents from Ultra-Thin Drifters, Drogued Drifters, and HF Radar

2018 ◽  
Vol 10 (10) ◽  
pp. 1633 ◽  
Author(s):  
Steven Morey ◽  
Nicolas Wienders ◽  
Dmitry Dukhovskoy ◽  
Mark Bourassa
Keyword(s):  
High Frequency ◽  
Measurement Techniques ◽  
Hf Radar ◽  
Stokes Drift ◽  
Surface Velocity ◽  
Surface Currents ◽  
Material Transport ◽  
Surface Shear ◽  
Near Surface ◽  
Radar Velocity

Concurrent measurements by satellite tracked drifters of different hull and drogue configurations and coastal high-frequency radar reveal substantial differences in estimates of the near-surface velocity. These measurements are important for understanding and predicting material transport on the ocean surface as well as the vertical structure of the near-surface currents. These near-surface current observations were obtained during a field experiment in the northern Gulf of Mexico intended to test a new ultra-thin drifter design. During the experiment, thirty small cylindrical drifters with 5 cm height, twenty-eight similar drifters with 10 cm hull height, and fourteen drifters with 91 cm tall drogues centered at 100 cm depth were deployed within the footprint of coastal High-Frequency (HF) radar. Comparison of collocated velocity measurements reveals systematic differences in surface velocity estimates obtained from the different measurement techniques, as well as provides information on properties of the drifter behavior and near-surface shear. Results show that the HF radar velocity estimates had magnitudes significantly lower than the 5 cm and 10 cm drifter velocity of approximately 45% and 35%, respectively. The HF radar velocity magnitudes were similar to the drogued drifter velocity. Analysis of wave directional spectra measurements reveals that surface Stokes drift accounts for much of the velocity difference between the drogued drifters and the thin surface drifters except during times of wave breaking.

East Australian current adjacent to the Great Barrier Reef

1987 ◽  
Vol 38 (6) ◽  
pp. 671 ◽  
Author(s):  
JA Church
Keyword(s):  
Great Barrier Reef ◽  
Bifurcation Point ◽  
Monsoon Season ◽  
Surface Flow ◽  
Barrier Reef ◽  
Surface Shear ◽  
Near Surface ◽  
Indonesian Archipelago ◽  
The Pacific ◽  
The Indian Ocean

Hydrographic data from a series of cruises during 1980-1981 are used to determine the circulation in the western Coral Sea region immediately adjacent to the Great Barrier Reef. The data show flow westward towards the Great Barrier Reef, bifurcating just north of 18�S. During the monsoon season (December to February), the bifurcation point moves north to at least 14�s. The geostrophic westward flow has a subsurface maximum at a depth of about 150 m. South of the bifurcation point, the flow is south-eastward on the upper continental slope and north-eastward offshore. North of the bifurcation point, the surface flow and transport (relative to 900 dbar) are northward. However, there is sometimes a south-eastwards near-surface shear. Near the bifurcation point, the surface currents are weak and variable. All of these features of the surface flow are reflected in the paths followed by satellite-tracked drifters. Although the drifters were fixed infrequently, the drifter data indicate the possible presence of small cyclonic eddies in the region of the bifurcation. All of the satellite-tracked drifters went aground in the Great Barrier Reef within 30 days of entering the region offshore from the Reef. The data are consistent with recent models of the wind-driven circulation in the South Pacific that propose that the westward flow bifurcates at about 20�S., with 17 x 106 m3 s-1 flowing through the Indonesian Archipelago from the Pacific Ocean to the Indian Ocean.

Growing Coconut Palms in the Pacific Islands: Colliding Knowledge and Values

2020 ◽  
Author(s):  
Judith A. Bennett
Keyword(s):  
Pacific Islands ◽  
Social Values ◽  
Coconut Oil ◽  
Tropical Pacific ◽  
Experiential Knowledge ◽  
The West ◽  
Passive Resistance ◽  
The People ◽  
The Pacific ◽  
The Tropical Pacific

Coconuts provided commodities for the West in the form of coconut oil and copra. Once colonial governments established control of the tropical Pacific Islands, they needed revenue so urged European settlers to establish coconut plantations. For some decades most copra came from Indigenous growers. Administrations constantly urged the people to thin old groves and plant new ones like plantations, in grid patterns, regularly spaced and weeded. Local growers were instructed to collect all fallen coconuts for copra from their groves. For half a century, the administrations’ requirements met with Indigenous passive resistance. This paper examines the underlying reasons for this, elucidating Indigenous ecological and social values, based on experiential knowledge, knowledge that clashed with Western scientific values.

scholarly journals The evolving response of mesopelagic fishes to declining midwater oxygen concentrations in the southern and central California Current

2018 ◽  
Vol 76 (3) ◽  
pp. 626-638 ◽  
Author(s):  
J Anthony Koslow ◽  
Pete Davison ◽  
Erica Ferrer ◽  
S Patricia A Jiménez Rosenberg ◽  
Gerardo Aceves-Medina ◽  
...  
Keyword(s):  
Baja California ◽  
Southern Oscillation ◽  
Global Climate ◽  
California Current ◽  
Deep Ocean ◽  
Near Surface ◽  
Oxygen Minimum Zones ◽  
The North ◽  
The Pacific ◽  
Oxygen Concentrations

Abstract Declining oxygen concentrations in the deep ocean, particularly in areas with pronounced oxygen minimum zones (OMZs), are a growing global concern related to global climate change. Its potential impacts on marine life remain poorly understood. A previous study suggested that the abundance of a diverse suite of mesopelagic fishes off southern California was closely linked to trends in midwater oxygen concentration. This study expands the spatial and temporal scale of that analysis to examine how mesopelagic fishes are responding to declining oxygen levels in the California Current (CC) off central, southern, and Baja California. Several warm-water mesopelagic species, apparently adapted to the shallower, more intense OMZ off Baja California, are shown to be increasing despite declining midwater oxygen concentrations and becoming increasingly dominant, initially off Baja California and subsequently in the CC region to the north. Their increased abundance is associated with warming near-surface ocean temperature, the warm phase of the Pacific Decadal oscillation and Multivariate El Niño-Southern Oscillation Index, and the increased flux of Pacific Equatorial Water into the southern CC.

scholarly journals A warm jet in a cold ocean

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jennifer A. MacKinnon ◽  
Harper L. Simmons ◽  
John Hargrove ◽  
Jim Thomson ◽  
Thomas Peacock ◽  
...  
Keyword(s):  
The Arctic ◽  
Bering Strait ◽  
Near Surface ◽  
Ice Melt ◽  
Beaufort Gyre ◽  
The Pacific ◽  
Climate Simulations ◽  
Initial Evolution ◽  
Forecast Models

AbstractUnprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

Rattus exulans (Pacific rat).

2021 ◽  
Author(s):  
Aaron Shiels
Keyword(s):  
Southeast Asia ◽  
Bird Species ◽  
Tropical Pacific ◽  
Pacific Basin ◽  
The Past ◽  
The Pacific ◽  
Ground Nesting ◽  
The Tropical Pacific

Abstract The Pacific rat, R. exulans, is an major agricultural and environmental pest in parts of Southeast Asia and the Pacific. Thought to have spread with Polynesian colonists over the past several thousand years, it is now found through much of the Pacific basin, and is extensively distributed in the tropical Pacific. It poses a significant threat to indigenous wildlife, particularly ground-nesting birds, and has been linked to the extinction of several bird species. R. exulans may also transmit diseases to humans.

Reconstructing an Interdecadal Pacific Oscillation Index from a Pacific Basin–Wide Collection of Ice Core Records

2021 ◽  
Vol 34 (10) ◽  
pp. 3839-3852
Author(s):  
Stacy E. Porter ◽  
Ellen Mosley-Thompson ◽  
Lonnie G. Thompson ◽  
Aaron B. Wilson
Keyword(s):  
Ice Core ◽  
Ice Cores ◽  
Tropical Pacific ◽  
Ice Age ◽  
Pacific Basin ◽  
Interdecadal Pacific Oscillation ◽  
The Pacific ◽  
Instrumental Period ◽  
The Tropical Pacific ◽  
Ice Core Records

AbstractUsing an assemblage of four ice cores collected around the Pacific basin, one of the first basinwide histories of Pacific climate variability has been created. This ice core–derived index of the interdecadal Pacific oscillation (IPO) incorporates ice core records from South America, the Himalayas, the Antarctic Peninsula, and northwestern North America. The reconstructed IPO is annually resolved and dates to 1450 CE. The IPO index compares well with observations during the instrumental period and with paleo-proxy assimilated datasets throughout the entire record, which indicates a robust and temporally stationary IPO signal for the last ~550 years. Paleoclimate reconstructions from the tropical Pacific region vary greatly during the Little Ice Age (LIA), although the reconstructed IPO index in this study suggests that the LIA was primarily defined by a weak, negative IPO phase and hence more La Niña–like conditions. Although the mean state of the tropical Pacific Ocean during the LIA remains uncertain, the reconstructed IPO reveals some interesting dynamical relationships with the intertropical convergence zone (ITCZ). In the current warm period, a positive (negative) IPO coincides with an expansion (contraction) of the seasonal latitudinal range of the ITCZ. This relationship is not stationary, however, and is virtually absent throughout the LIA, suggesting that external forcing, such as that from volcanoes and/or reduced solar irradiance, could be driving either the ITCZ shifts or the climate dominating the ice core sites used in the IPO reconstruction.

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