scholarly journals Decadal and Interdecadal Variations of the Aleutian Low Activity and Their Relation to Upper Oceanic Variations over the North Pacific

2009 ◽  
Vol 87 (4) ◽  
pp. 601-614 ◽  
Author(s):  
Shusaku SUGIMOTO ◽  
Kimio HANAWA
Keyword(s):  
North Pacific ◽  
Aleutian Low ◽  
The North ◽  
The North Pacific ◽  
Low Activity

scholarly journals Impact of Remote Reemergence of the Subtropical Mode Water on Winter SST Variation in the Central North Pacific

2007 ◽  
Vol 20 (2) ◽  
pp. 173-186 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Heat Content ◽  
Aleutian Low ◽  
Mode Water ◽  
The North ◽  
Winter Mixed Layer ◽  
The North Pacific ◽  
Low Activity ◽  
Central North Pacific

Abstract Using long-term datasets of sea surface temperature (SST), core-layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW), and the North Pacific index, an impact of remote reemergence of NPSTMW on winter SST variation in the central North Pacific is quantitatively investigated. A running correlation analysis between CLT and winter SST in the remote reemergence area clearly shows that an occurrence of remote reemergence of NPSTMW strongly depends on the specific time period: occurrence period and nonoccurrence period. It is found that background conditions, such as formation rate of NPSTMW, winter mixed layer depth, ocean heat content, and buoyancy flux, play a crucial role in the period-dependent remote reemergence. In the occurrence (nonoccurrence) periods, since a large positive (negative) upper-ocean heat content anomaly is located around the central North Pacific, a deeper (shallower) winter mixed layer is formed in both the formation area and the reemergence area of NPSTMW. Therefore, a large (small) amount of NPSTMW is formed, and consequently the advective part of NPSTMW is preserved (dissipated) from (because of) a vigorous mixing due to salt-finger-type convection. In addition, larger (less) oceanic buoyancy loss contributes to an occurrence of reemergence. These are favorable (unfavorable) conditions for persistence of thermal anomalies and occurrence of reemergence in the central North Pacific. Using a multiple regression analysis, it is shown that remote reemergence gives a significant impact to an equivalent degree to the surface thermal forcing related with the Aleutian low activity on winter SST variation during the occurrence periods, while there is no significant contribution to SST variation during the nonoccurrence periods. It is also shown that the period-dependent reemergence closely connects with the Aleutian low activity with a lag of 6 to 8 yr, that is, the spinup/spindown of the subtropical gyre.

scholarly journals Seasonal Evolution of Aleutian Low Pressure Systems: Implications for the North Pacific Subpolar Circulation*

2009 ◽  
Vol 39 (6) ◽  
pp. 1317-1339 ◽  
Author(s):  
Robert S. Pickart ◽  
Alison M. Macdonald ◽  
G. W. K. Moore ◽  
Ian A. Renfrew ◽  
John E. Walsh ◽  
...  
Keyword(s):  
North Pacific ◽  
Lower Troposphere ◽  
Gulf Of Alaska ◽  
Low Pressure ◽  
Aleutian Low ◽  
The North ◽  
Early Fall ◽  
The Impact ◽  
The North Pacific ◽  
Low Pressure Systems

Abstract The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres.

A Synoptic Analysis of the Interannual Variability of Winter Cyclone Activity in the Aleutian Low Region

2007 ◽  
Vol 20 (8) ◽  
pp. 1523-1538 ◽  
Author(s):  
Xiaojie Zhu ◽  
Jilin Sun ◽  
Zhengyu Liu ◽  
Qinyu Liu ◽  
Jonathan E. Martin
Keyword(s):  
North Pacific ◽  
Aleutian Low ◽  
Cyclone Activity ◽  
Cyclone Intensity ◽  
Low Intensity ◽  
Interannual Change ◽  
The North ◽  
Relative Change ◽  
Cyclone Frequency ◽  
The North Pacific

Abstract An analysis of cyclone activity in winter associated with years of strong and weak Aleutian low in the North Pacific is presented. From 1958 to 2004, 10 winters with a strong Aleutian low are defined as the strong years, while 8 winters with a weak Aleutian low are defined as the weak years. Employing a system-centered Lagrangian method, some characteristics of the cyclone activity in both sets of years are revealed. The cyclone frequency, duration, and intensity are nearly the same in both strong and weak years. The cyclone tracks in the strong years are more zonal than those in the weak years. More intense cyclone events and more large cyclone cases occur in strong years than in weak years and the deepening of cyclones in strong years is stronger than that in weak years. The analyses of geopotential height, wind, stationary Rossby wavenumber, and Eady growth rate index at 500 or 300 hPa reveal that conditions are favorable for more zonal tracks and greater cyclone growth in strong years than in weak years. An estimation of the relative change of cyclone intensity and the relative change of Aleutian low intensity is made, which shows that the interannual change of cyclone intensity is about 73% of the interannual change of Aleutian low intensity. This result suggests that the evolution of individual cyclones may be a significant driver of changes in the Aleutian low.

scholarly journals Coupled impacts of sea ice variability and North Pacific atmospheric circulation on Holocene hydroclimate in Arctic Alaska

2020 ◽  
Vol 117 (52) ◽  
pp. 33034-33042
Author(s):  
Ellie Broadman ◽  
Darrell S. Kaufman ◽  
Andrew C. G. Henderson ◽  
Irene Malmierca-Vallet ◽  
Melanie J. Leng ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Pacific ◽  
Regional Climate ◽  
Coupled Model ◽  
The Arctic ◽  
Bering Strait ◽  
Aleutian Low ◽  
The North ◽  
Arctic Alaska ◽  
The North Pacific

Arctic Alaska lies at a climatological crossroads between the Arctic and North Pacific Oceans. The modern hydroclimate of the region is responding to rapidly diminishing sea ice, driven in part by changes in heat flux from the North Pacific. Paleoclimate reconstructions have improved our knowledge of Alaska’s hydroclimate, but no studies have examined Holocene sea ice, moisture, and ocean−atmosphere circulation in Arctic Alaska, limiting our understanding of the relationship between these phenomena in the past. Here we present a sedimentary diatom assemblage and diatom isotope dataset from Schrader Pond, located ∼80 km from the Arctic Ocean, which we interpret alongside synthesized regional records of Holocene hydroclimate and sea ice reduction scenarios modeled by the Hadley Centre Coupled Model Version 3 (HadCM3). The paleodata synthesis and model simulations suggest the Early and Middle Holocene in Arctic Alaska were characterized by less sea ice, a greater contribution of isotopically heavy Arctic-derived moisture, and wetter climate. In the Late Holocene, sea ice expanded and regional climate became drier. This climatic transition is coincident with a documented shift in North Pacific circulation involving the Aleutian Low at ∼4 ka, suggesting a Holocene teleconnection between the North Pacific and Arctic. The HadCM3 simulations reveal that reduced sea ice leads to a strengthened Aleutian Low shifted west, potentially increasing transport of warm North Pacific water to the Arctic through the Bering Strait. Our findings demonstrate the interconnectedness of the Arctic and North Pacific on multimillennial timescales, and are consistent with future projections of less sea ice and more precipitation in Arctic Alaska.

scholarly journals The Aleutian Low and Winter Climatic Conditions in the Bering Sea. Part I: Classification*

2005 ◽  
Vol 18 (1) ◽  
pp. 160-177 ◽  
Author(s):  
S. N. Rodionov ◽  
J. E. Overland ◽  
N. A. Bond
Keyword(s):  
Atmospheric Circulation ◽  
Time Scales ◽  
Bering Sea ◽  
North Pacific ◽  
Cyclonic Activity ◽  
Aleutian Low ◽  
The North ◽  
Type Pattern ◽  
The North Pacific ◽  
The Bering Sea

Abstract The Aleutian low is examined as a primary determinant of surface air temperature (SAT) variability in the Bering Sea during the winter [December–January–February–March (DJFM)] months. The Classification and Regression Tree (CART) method is used to classify five types of atmospheric circulation for anomalously warm months (W1–W5) and cold months (C1–C5). For the Bering Sea, changes in the position of the Aleutian low are shown to be more important than changes in its central pressure. The first two types, W1 and C1, account for 51% of the “warm” and 37% of the “cold” months. The W1-type pattern is characterized by the anomalously deep Aleutian low shifted west and north of its mean position. In this situation, an increased cyclonic activity occurs in the western Bering Sea. The C1-type pattern represents a split Aleutian low with one center in the northwestern Pacific and the other in the Gulf of Alaska. The relative frequency of the W1 to C1 types of atmospheric circulation varies on decadal time scales, which helps to explain the predominance of fluctuations on these time scales in the weather of the Bering Sea. Previous work has noted the prominence of multidecadal variability in the North Pacific. The present study finds multidecadal variations in frequencies of the W3 and C3 patterns, both of which are characterized by increased cyclonic activity south of 51°N. In general, the CART method is found to be a suitable means for characterizing the wintertime atmospheric circulation of the North Pacific in terms of its impact on the Bering Sea. The results show that similar pressure anomaly patterns for the North Pacific as a whole can actually result in different conditions for the Bering Sea, and that similar weather conditions in the Bering Sea can arise from decidedly different large-scale pressure patterns.

Simulation of the 1976/77 Climate Transition over the North Pacific: Sensitivity to Tropical Forcing

2006 ◽  
Vol 19 (23) ◽  
pp. 6170-6180 ◽  
Author(s):  
Clara Deser ◽  
Adam S. Phillips
Keyword(s):  
Indian Ocean ◽  
North Pacific ◽  
Equatorial Pacific ◽  
Ensemble Average ◽  
Aleutian Low ◽  
The North ◽  
Tropical Ssts ◽  
Climate Transition ◽  
Western Half ◽  
The North Pacific

Abstract This study examines the contribution of tropical sea surface temperature (SST) forcing to the 1976/77 climate transition of the winter atmospheric circulation over the North Pacific using a combined observational and modeling approach. The National Center for Atmospheric Research (NCAR) Community Atmospheric Model version 3 (CAM3) simulates approximately 75% of the observed 4-hPa deepening of the wintertime Aleutian low from 1950–76 to 1977–2000 when forced with the observed evolution of tropical SSTs in a 10-member ensemble average. This response is driven by precipitation increases over the western half of the equatorial Pacific Ocean. In contrast, the NCAR Community Climate Model version 3 (CCM3), the predecessor to CAM3, simulates no significant change in the strength of the Aleutian low when forced with the same tropical SSTs in a 12-member ensemble average. The lack of response in CCM3 is traced to an erroneously large precipitation increase over the tropical Indian Ocean whose dynamical impact is to weaken the Aleutian low; this, when combined with the response to rainfall increases over the western and central equatorial Pacific, results in near-zero net change in the strength of the Aleutian low. The observed distribution of tropical precipitation anomalies associated with the 1976/77 transition, estimated from a combination of direct measurements at land stations and indirect information from surface marine cloudiness and wind divergence fields, supports the models’ simulated rainfall increases over the western half of the Pacific but not the magnitude of CCM3’s rainfall increase over the Indian Ocean.

scholarly journals Seasonal evolution of Aleutian low-pressure systems: Implications for the North Pacific sub-polar circulation

2008 ◽  
Vol preprint (2008) ◽  
pp. 1 ◽  
Author(s):  
Robert S. Pickart ◽  
G.W.K. Moore ◽  
Alison M. Macdonald ◽  
Ian A. Renfrew ◽  
John E. Walsh ◽  
...  
Keyword(s):  
North Pacific ◽  
Low Pressure ◽  
Aleutian Low ◽  
Seasonal Evolution ◽  
The North ◽  
The North Pacific ◽  
Low Pressure Systems

scholarly journals The Atmospheric Response to Positive IPV, Positive AMV, and Their Combination in Boreal Winter

2019 ◽  
Vol 32 (14) ◽  
pp. 4193-4213 ◽  
Author(s):  
Dillon Elsbury ◽  
Yannick Peings ◽  
David Saint-Martin ◽  
Hervé Douville ◽  
Gudrun Magnusdottir
Keyword(s):  
Surface Temperature ◽  
Extreme Events ◽  
North Pacific ◽  
Climate Models ◽  
Wave Activity ◽  
Atmospheric Response ◽  
Aleutian Low ◽  
The North ◽  
The North Pacific ◽  
Wave Activity Flux

AbstractThe interdecadal Pacific oscillation (hereafter termed IPV, using “variability” in lieu of “oscillation”) and the Atlantic multidecadal oscillation (hereafter AMV, similar to IPV) are regulators of global mean temperature, large-scale atmospheric circulation, regional temperature and precipitation, and related extreme events. Despite a growing recognition of their importance, the combined influence of these modes of low-frequency sea surface temperature (SST) variability remains elusive given the short instrumental record and the difficulty of coupled climate models to simulate them satisfactorily. In this study, idealized simulations with two atmospheric global climate models (AGCMs) are used to show a partial cancellation of the North Pacific atmospheric response to positive IPV (i.e., deeper Aleutian low) by the concurrent positive phase of the AMV. This effect arises from a modulation of the interbasin Walker circulation that weakens deep convection in the western Pacific and the associated Rossby wave train into the northern extratropics. The weaker Aleutian low response is associated with less upward wave activity flux in the North Pacific; however, the associated stratospheric jet weakening is similar to when the +IPV alone forces the vortex, as additional upward wave activity flux over Siberia makes up the difference. While comparable warming of the polar stratosphere is found when the positive AMV is included with the positive IPV, the downward propagation of the stratospheric response is significantly reduced, which has implications for the associated surface temperature extremes. The robust anticorrelation between the positive IPV and positive AMV signals over the North Pacific and their lack of additivity highlight the need to consider the IPV–AMV interplay for anticipating decadal changes in mean climate and extreme events in the Northern Hemisphere.

scholarly journals A Multivariate Estimate of the Cold Season Atmospheric Response to North Pacific SST Variability

2018 ◽  
Vol 31 (7) ◽  
pp. 2771-2796 ◽  
Author(s):  
Adèle Révelard ◽  
Claude Frankignoul ◽  
Young-Oh Kwon
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Late Winter ◽  
Aleutian Low ◽  
Central Pacific ◽  
The North ◽  
Sst Variability ◽  
The North Pacific ◽  
Robust Response

The Generalized Equilibrium Feedback Analysis (GEFA) is used to distinguish the influence of the Oyashio Extension (OE) and the Kuroshio Extension (KE) variability on the atmosphere from 1979 to 2014 from that of the main SST variability modes, using seasonal mean anomalies. Remote SST anomalies are associated with each single oceanic regressor, but the multivariate approach efficiently confines their SST footprints. In autumn [October–December (OND)], the OE meridional shifts are followed by a North Pacific Oscillation (NPO)-like signal. The OE influence is not investigated in winter [December–February (DJF)] because of multicollinearity, but a robust response with a strong signal over the Bering Sea is found in late winter/early spring [February–April (FMA)], a northeastward strengthening of the Aleutian low following a northward OE shift. A robust response to the KE variability is found in autumn, but not in winter and late winter when the KE SST footprint becomes increasingly small and noisy as regressors are added in GEFA. In autumn, a positive PDO is followed by a northward strengthening of the Aleutian low and a southward shift of the storm track in the central Pacific, reflecting the surface heat flux footprint in the central Pacific. In winter, the PDO shifts the maximum baroclinicity and storm track southward, the response strongly tilts westward with height in the North Pacific, and there is a negative NAO-like teleconnection. In late winter, the North Pacific NPO-like response to the PDO interferes negatively with the response to the OE and is only detected when the OE is represented in GEFA. A different PDO influence on the atmospheric circulation is found from 1958 to 1977.

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