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 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 Characteristics of Subsurface Ocean Response to ENSO Assessed from Simulations with the NCEP Climate Forecast System

2013 ◽  
Vol 26 (20) ◽  
pp. 8065-8083 ◽  
Author(s):  
Hui Wang ◽  
Arun Kumar ◽  
Wanqiu Wang
Keyword(s):  
Indian Ocean ◽  
North Pacific ◽  
Temperature Response ◽  
Tropical Indian Ocean ◽  
Tropical Atlantic ◽  
Subsurface Temperature ◽  
The North ◽  
Subsurface Ocean ◽  
The North Pacific ◽  
The Tropical Pacific

Abstract The subsurface ocean temperature response to El Niño–Southern Oscillation (ENSO) is examined based on 31-yr (1981–2011) simulations with the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) coupled model. The model sea surface temperature (SST) in the tropical Pacific is relaxed to observations to ensure realistic ENSO variability in the simulations. In the tropical Pacific, the subsurface temperature response to the ENSO SST is closely related to the variability of thermocline. The subsurface response is stronger and deeper in the tropical Indian Ocean than in the tropical Atlantic. The analysis at three selected locations reveals that the peak response of the subsurface temperature to ENSO lags the Niño-3.4 SST by 3, 6, and 6 months, respectively, in the southern tropical Indian Ocean, the northern tropical Atlantic, and the North Pacific, where SSTs are also known to be strongly influenced by ENSO. The ENSO-forced temperature anomalies gradually penetrate to the deeper ocean with time in the North Pacific and the tropical Atlantic, but not in the tropical Indian Ocean where the subsurface response at different depths peaks almost at the same time (i.e., at about 3–4 months following ENSO). It is demonstrated that the ENSO-induced surface wind stress plays an important role in determining the time scale and strength of the subsurface temperature response to ENSO in the North Pacific and the northern tropical Atlantic. Additionally, the ENSO-related local surface latent heat flux also contributes to the subsurface response to ENSO in these two regions.

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.

scholarly journals On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean

2021 ◽  
Author(s):  
Zvi Steiner ◽  
Amit Sarkar ◽  
Xuewu Liu ◽  
William M. Berelson ◽  
Jess F. Adkins ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
Red Sea ◽  
North Pacific ◽  
The North ◽  
The North Pacific

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

The North Pacific Climate Transitions of the Winters of 1976/77 and 1988/89

2011 ◽  
Vol 24 (4) ◽  
pp. 1170-1183 ◽  
Author(s):  
Sang-Wook Yeh ◽  
Yune-Jung Kang ◽  
Yign Noh ◽  
Arthur J. Miller
Keyword(s):  
Sea Level ◽  
North Pacific ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
Sst Variability ◽  
Transition Project ◽  
Climate Transition ◽  
The Tropics ◽  
The North Pacific

Abstract This paper examines characteristic changes in North Pacific sea surface temperature (SST) variability during the boreal winter (December–February) for two subperiods (1956–88 and 1977–2009) during which the 1976/77 and the 1988/89 climate transitions occurred. It is found that the Pacific decadal oscillation (PDO)-like SST variability plays a dominant role in the 1976/77 climate transition, while both the North Pacific Gyre Oscillation (NPGO)-like and PDO-like SST variability contribute to the 1988/89 climate transition. Furthermore, the leading mode changes from PDO-like SST variability during the period 1956–88 to NPGO-like SST variability during the period 1977–2009, indicative of an enhancement of NPGO-like SST variability since 1988. Changes in sea level pressure across the 1976/77 climate transition project strongly onto the Aleutian low pressure system. But sea level pressure changes across the 1988/89 climate transition project primarily onto the North Pacific Oscillation, which is associated with remote changes in the Arctic Oscillation over the polar region as well. This contributes to enhancing the NPGO-like SST variability after 1988. The authors also analyze the output from an ensemble of Tropical Ocean and Global Atmosphere (TOGA) experiments in which the observed SSTs are inserted only at grid points in the tropics between 20°S and 20°N. The results indicate that the changes in the North Pacific atmosphere in the 1976/77 climate transition are mostly due to the tropics, whereas those in the 1988/89 climate transition are not.

scholarly journals Contributions of the North Pacific Meridional Mode to Ensemble Spread of ENSO Prediction

2017 ◽  
Vol 30 (22) ◽  
pp. 9167-9181 ◽  
Author(s):  
Jing Ma ◽  
Shang-Ping Xie ◽  
Haiming Xu
Keyword(s):  
Rapid Growth ◽  
North Pacific ◽  
Equatorial Pacific ◽  
Ensemble Spread ◽  
Enso Prediction ◽  
The North ◽  
Northeastern Pacific ◽  
Meridional Mode ◽  
The North Pacific ◽  
Pacific Meridional Mode

Abstract Seasonal prediction of El Niño–Southern Oscillation (ENSO) employs the ensemble method, which samples the uncertainty in initial conditions. While much attention has been given to the ensemble mean, the ensemble spread limits the reliability of the forecast. Spatiotemporal coevolution of intermember anomalies of sea surface temperature (SST) and low-level winds over the Pacific is examined in ensemble hindcasts. Two types of evolution of intermember SST anomalies in the equatorial Pacific are identified. The first features an apparent southwestward propagation of the SST spread from the subtropical northeastern Pacific southeast of Hawaii to the central equatorial Pacific in boreal winter–spring, indicative of the precursor effect of the North Pacific meridional mode (NPMM) on ENSO variability. Extratropical atmospheric variability generates ensemble spread in ENSO through wind–evaporation–SST (WES) in the subtropical northeastern Pacific and then Bjerknes feedback on the equator. In the second type, ensemble spread grows in the equatorial Pacific with a weak contribution from the subtropical southeastern Pacific in summer. Thus, the extratropical influence on ENSO evolution is much stronger in the Northern Hemisphere than in the Southern Hemisphere. The growth of Niño-4 SST ensemble spread shows a strong seasonality. In hindcasts initialized in September–March, the Niño-4 SST spread grows rapidly in January–April, stabilizes in May–June, and grows again in July–September. The rapid growth of the Niño-4 SST spread in January–April is due to the arrival of NPMM, while the slowdown in May–June and rapid growth in July–September are attributable primarily to the seasonality of equatorial ocean–atmosphere interaction. NPMM contributes to the ensemble spread in equatorial Pacific SST, limiting the reliability of ENSO prediction.

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