Seasonal to interannual variability of the Pacific water boundary current in the Beaufort Sea

Pacific water contributes significantly to the Arctic Ocean freshwater budget. Recent increases in Arctic freshwater flux, also affected by the Pacific-derived Arctic water, impact the Atlantic overturning circulation with implications for global climate. The interannual variability of the Pacific water outflow remains poorly understood, partly due to different branches of the Pacific water flow in the Arctic Ocean. The shelfbreak current over the Beaufort Sea continental slope transports ~50% of the Pacific-derived water eastward along the Beaufort Sea continental slope towards the Canadian Archipelago. The oceanographic mooring deployed over the eastern Beaufort Sea continental slope in October 2003 recorded current velocities through depths of 28–108 m until September 2005. Data analysis revealed that these highly energetic currents have two different modes of depth-dependent behaviour. The downwelling-favourable wind associated with cyclones passing north of the Beaufort Sea continental slope toward the Canadian Archipelago generates depth-intensified shelfbreak currents with along-slope northeastward flow. A surface Ekman on-shore transport and associated increase of the sea surface heights over the shelf produce a cross-slope pressure gradient that drives an along-slope northeastward barotropic flow, in the same direction as the wind. In contrast, the upwelling-favourable wind associated with deep Aleutian Low cyclones over the Alaskan Peninsula and/or Aleutian Island Arc leads to surface-intensified currents with along-slope westward flow. This northeasterly wind generates a surface Ekman transport that moves surface waters offshore. The associated cross-slope pressure gradient drives an along-slope southwestward barotropic flow. The wind-driven barotropic flow generated by upwelling and downwelling is superimposed on the background bottom-intensified shelfbreak current. For downwelling, this flow amplifies the depth-intensified background baroclinic circulation with enhanced Pacific water transport towards the Canadian Archipelago. For upwelling, the shelfbreak current is reversed, which results in surface-intensified flow in the opposite direction. These results are supported by numerical simulations.

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A Climatology of 500-hPa Closed Lows in the Northeastern Pacific Ocean, 1948–2011

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-13-0223.1 ◽

2014 ◽

Vol 53 (6) ◽

pp. 1578-1592 ◽

Cited By ~ 19

Author(s):

Nina S. Oakley ◽

Kelly T. Redmond

Keyword(s):

United States ◽

Pacific Ocean ◽

Interannual Variability ◽

West Coast ◽

The United States ◽

Western United States ◽

The West ◽

Reanalysis Dataset ◽

The Pacific ◽

Northeastern Pacific

AbstractThe northeastern Pacific Ocean is a preferential location for the formation of closed low pressure systems. These slow-moving, quasi-barotropic systems influence vertical stability and sustain a moist environment, giving them the potential to produce or affect sustained precipitation episodes along the west coast of the United States. They can remain motionless or change direction and speed more than once and thus often pose difficult forecast challenges. This study creates an objective climatological description of 500-hPa closed lows to assess their impacts on precipitation in the western United States and to explore interannual variability and preferred tracks. Geopotential height at 500 hPa from the NCEP–NCAR global reanalysis dataset was used at 6-h and 2.5° × 2.5° resolution for the period 1948–2011. Closed lows displayed seasonality and preferential durations. Time series for seasonal and annual event counts were found to exhibit strong interannual variability. Composites of the tracks of landfalling closed lows revealed preferential tracks as the features move inland over the western United States. Correlations of seasonal event totals for closed lows with ENSO indices, the Pacific decadal oscillation (PDO), and the Pacific–North American (PNA) pattern suggested an above-average number of events during the warm phase of ENSO and positive PDO and PNA phases. Precipitation at 30 U.S. Cooperative Observer stations was attributed to closed-low events, suggesting 20%–60% of annual precipitation along the West Coast may be associated with closed lows.

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Interdecadal changes in the interannual variability of the summer temperature over Northeast Asia

Journal of Climate ◽

10.1175/jcli-d-21-0115.1 ◽

2021 ◽

pp. 1-50

Author(s):

Ruidan Chen ◽

Zhiping Wen ◽

Riyu Lu ◽

Wenjun Liu

Keyword(s):

Interannual Variability ◽

Northeast Asia ◽

Tropical Indian Ocean ◽

Summer Temperature ◽

Atmospheric Variability ◽

The Pacific ◽

The Mean ◽

Southeastern Tropical Indian Ocean ◽

Interdecadal Changes ◽

Mean State

AbstractThis study reveals the interdecadal changes in the interannual variability of the summer temperature over Northeast Asia (NEA), which presents an enhancement around the early 1990s and a reduction after the mid-2000s. The stronger NEA temperature variability after the early 1990s is favored by the enhanced influence of the Pacific–Japan (PJ) teleconnection, which is remotely modulated by the southeastern tropical Indian Ocean (SETIO). After the early 1990s, the mean state over the SETIO presents relatively warmer SST and ascending motion, favoring a good relationship between the local SST and convection. Therefore, the SETIO SST could prominently influence the local convection and subsequently modulate the convection over the western North Pacific (WNP) via a cross-equatorial overturning circulation. The abnormal convection over the WNP further triggers the PJ teleconnection to influence NEA. However, these ocean–atmosphere processes disappear before the early 1990s. In this period, the mean state over the SETIO features relatively colder SST and subsiding motion, accompanied by a poor relationship between the local SST and convection. Therefore, the variability of convection over the SETIO is weak, thus the atmospheric variability over the WNP is also weakened and the PJ teleconnection presents a different distribution that could not influence NEA. The reduced variability of NEA temperature after the mid-2000s is related to the feeble influence of the PJ teleconnection and the reduced variability of the SETIO SST, which is modulated by the SST over the tropical central–eastern Pacific during the preceding winter to spring.

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Intraseasonal-to-Interannual Variability of South Indian Ocean Sea Level and Thermocline: Remote versus Local Forcing

Journal of Physical Oceanography ◽

10.1175/jpo-d-11-084.1 ◽

2012 ◽

Vol 42 (4) ◽

pp. 602-627 ◽

Cited By ~ 42

Author(s):

Laurie L. Trenary ◽

Weiqing Han

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

Sea Level ◽

Time Scales ◽

Ekman Pumping ◽

Remote Forcing ◽

South Indian ◽

The Pacific ◽

The Indian Ocean ◽

Thermocline Variability

Abstract The relative importance of local versus remote forcing on intraseasonal-to-interannual sea level and thermocline variability of the tropical south Indian Ocean (SIO) is systematically examined by performing a suite of controlled experiments using an ocean general circulation model and a linear ocean model. Particular emphasis is placed on the thermocline ridge of the Indian Ocean (TRIO; 5°–12°S, 50°–80°E). On interannual and seasonal time scales, sea level and thermocline variability within the TRIO region is primarily forced by winds over the Indian Ocean. Interannual variability is largely caused by westward propagating Rossby waves forced by Ekman pumping velocities east of the region. Seasonally, thermocline variability over the TRIO region is induced by a combination of local Ekman pumping and Rossby waves generated by winds from the east. Adjustment of the tropical SIO at both time scales generally follows linear theory and is captured by the first two baroclinic modes. Remote forcing from the Pacific via the oceanic bridge has significant influence on seasonal and interannual thermocline variability in the east basin of the SIO and weak impact on the TRIO region. On intraseasonal time scales, strong sea level and thermocline variability is found in the southeast tropical Indian Ocean, and it primarily arises from oceanic instabilities. In the TRIO region, intraseasonal sea level is relatively weak and results from Indian Ocean wind forcing. Forcing over the Pacific is the major cause for interannual variability of the Indonesian Throughflow (ITF) transport, whereas forcing over the Indian Ocean plays a larger role in determining seasonal and intraseasonal ITF variability.

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

Journal of Climate ◽

10.1175/jcli-d-14-00351.1 ◽

2015 ◽

Vol 28 (9) ◽

pp. 3441-3452 ◽

Cited By ~ 2

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.

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Intraseasonal and Interannual Variability in North American Storm Tracks and Its Relationship to Equatorial Pacific Variability

Monthly Weather Review ◽

10.1175/mwr-d-12-00322.1 ◽

2013 ◽

Vol 141 (10) ◽

pp. 3610-3625 ◽

Cited By ~ 42

Author(s):

Kevin M. Grise ◽

Seok-Woo Son ◽

John R. Gyakum

Keyword(s):

North America ◽

Interannual Variability ◽

North American ◽

Southern Oscillation ◽

Extratropical Cyclones ◽

The North ◽

The Pacific ◽

Cyclone Tracks ◽

Lagrangian Tracking ◽

The North Atlantic Oscillation

Abstract Extratropical cyclones play a principal role in wintertime precipitation and severe weather over North America. On average, the greatest number of cyclones track 1) from the lee of the Rocky Mountains eastward across the Great Lakes and 2) over the Gulf Stream along the eastern coastline of North America. However, the cyclone tracks are highly variable within individual winters and between winter seasons. In this study, the authors apply a Lagrangian tracking algorithm to examine variability in extratropical cyclone tracks over North America during winter. A series of methodological criteria is used to isolate cyclone development and decay regions and to account for the elevated topography over western North America. The results confirm the signatures of four climate phenomena in the intraseasonal and interannual variability in North American cyclone tracks: the North Atlantic Oscillation (NAO), the El Niño–Southern Oscillation (ENSO), the Pacific–North American pattern (PNA), and the Madden–Julian oscillation (MJO). Similar signatures are found using Eulerian bandpass-filtered eddy variances. Variability in the number of extratropical cyclones at most locations in North America is linked to fluctuations in Rossby wave trains extending from the central tropical Pacific Ocean. Only over the far northeastern United States and northeastern Canada is cyclone variability strongly linked to the NAO. The results suggest that Pacific sector variability (ENSO, PNA, and MJO) is a key contributor to intraseasonal and interannual variability in the frequency of extratropical cyclones at most locations across North America.

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Dynamical connections between large marine ecosystems of austral South America based on numerical simulations

Ocean Science ◽

10.5194/os-16-271-2020 ◽

2020 ◽

Vol 16 (2) ◽

pp. 271-290 ◽

Cited By ~ 2

Author(s):

Karen Guihou ◽

Alberto R. Piola ◽

Elbio D. Palma ◽

Maria Paz Chidichimo

Keyword(s):

South America ◽

Interannual Variability ◽

Large Scale ◽

Marine Ecosystem ◽

Outer Part ◽

Marine Ecosystems ◽

Seasonal And Interannual Variability ◽

Magellan Strait ◽

The Pacific ◽

Large Marine Ecosystem

Abstract. The Humboldt Large Marine Ecosystem (HLME) and Patagonian Large Marine Ecosystem (PLME) are the two largest marine ecosystems in the Southern Hemisphere and are respectively located along the Pacific and Atlantic coasts of southern South America. This work investigates the exchange between these two LMEs and its seasonal and interannual variability by employing numerical model results and offline particle-tracking algorithms. Our analysis suggests a general poleward transport on the southern region of the HLME, a well-defined flux from the Pacific to the Atlantic, and equatorward transport on the PLME. Lagrangian simulations show that the majority of the southern PS waters originate from the upper layer in the southeast South Pacific (<200 m), mainly from the southern Chile and Cape Horn shelves. The exchange takes place through the Le Maire Strait, Magellan Strait, and the shelf break. These inflows amount to a net northeastward transport of 0.88 Sv at 51∘ S in the southern PLME. The transport across the Magellan Strait is small (0.1 Sv), but due to its relatively low salinity it greatly impacts the density and surface circulation of the coastal waters of the southern PLME. The water masses flowing into the Malvinas Embayment eventually reach the PLME through the Malvinas Shelf and occupy the outer part of the shelf. The seasonal and interannual variability of the transport are also addressed. On the southern PLME, the interannual variability of the shelf exchange is partly explained by the large-scale wind variability, which in turn is partly associated with the Southern Annular Mode (SAM) index (r=0.52).

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