scholarly journals Stationarity of the tropical pacific teleconnection to North America in CMIP5/PMIP3 model simulations

2013 ◽  
Vol 40 (18) ◽  
pp. 4927-4932 ◽  
Author(s):  
Sloan Coats ◽  
Jason E. Smerdon ◽  
Benjamin I. Cook ◽  
Richard Seager
Keyword(s):  
North America ◽  
Tropical Pacific ◽  
Model Simulations ◽  
The Tropical Pacific

scholarly journals A Link between the Hiatus in Global Warming and North American Drought

2015 ◽  
Vol 28 (9) ◽  
pp. 3834-3845 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng ◽  
Anthony Rosati ◽  
Gabriel A. Vecchi ◽  
Andrew T. Wittenberg
Keyword(s):  
Global Warming ◽  
North America ◽  
Surface Temperature ◽  
North American ◽  
Radiative Forcing ◽  
Tropical Pacific ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
The Impact ◽  
The Tropical Pacific

Abstract Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus—a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.

scholarly journals Distorted Pacific–North American teleconnection at the Last Glacial Maximum

2020 ◽  
Vol 16 (1) ◽  
pp. 199-209 ◽  
Author(s):  
Yongyun Hu ◽  
Yan Xia ◽  
Zhengyu Liu ◽  
Yuchen Wang ◽  
Zhengyao Lu ◽  
...  
Keyword(s):  
North America ◽  
Last Glacial Maximum ◽  
North American ◽  
Tropical Pacific ◽  
Glacial Maximum ◽  
Jet Stream ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Tropical Pacific ◽  
The Last Glacial

Abstract. The Pacific–North American (PNA) teleconnection is one of the most important climate modes in the present climate condition, and it enables climate variations in the tropical Pacific to exert a significant influence on North America. Here, we show climate simulations in which the PNA teleconnection was largely distorted or broken at the Last Glacial Maximum (LGM). The distorted PNA is caused by a split in the westerly jet stream, which is ultimately forced by the large, thick Laurentide ice sheet that was present at the LGM. Changes in the jet stream greatly alter the extratropical waveguide, distorting wave propagation from the North Pacific to North America. The distorted PNA suggests that climate variability in the tropical Pacific, notably El Niño–Southern Oscillation (ENSO), would have little direct impact on North American climate at the LGM.

scholarly journals Solar forcing of the tropical Pacific climate and impacts over North America for the last millennium

PAGES news ◽  
2006 ◽  
Vol 14 (2) ◽  
pp. 12-14
Author(s):  
Amy C Clement ◽  
Julien Emile-Geay ◽  
Richard Seager ◽  
Mark Cane ◽  
Michael N Evans
Keyword(s):  
North America ◽  
Tropical Pacific ◽  
Last Millennium ◽  
Solar Forcing ◽  
The Tropical Pacific

scholarly journals The Turn of the Century North American Drought: Global Context, Dynamics, and Past Analogs*

2007 ◽  
Vol 20 (22) ◽  
pp. 5527-5552 ◽  
Author(s):  
Richard Seager
Keyword(s):  
North America ◽  
North American ◽  
Tropical Pacific ◽  
Turn Of The Century ◽  
La Niña ◽  
Global Pattern ◽  
Model Simulations ◽  
Global Context ◽  
The North ◽  
La Nina

Abstract The causes and global context of the North American drought between 1998 and 2004 are examined using atmospheric reanalyses and ensembles of atmosphere model simulations variously forced by global SSTs or tropical Pacific SSTs alone. The drought divides into two distinct time intervals. Between 1998 and 2002 it coincided with a persistent La Niña–like state in the tropical Pacific, a cool tropical troposphere, poleward-shifted jet streams, and, in the zonal mean, eddy-driven descent in midlatitudes. During the winters reduced precipitation over North America in the climate models was sustained by anomalous subsidence and reductions of moisture convergence by the stationary flow and transient eddies. During the summers reductions of evaporation and mean flow moisture convergence drove the precipitation reduction, while transient eddies acted diffusively to oppose this. During these years the North American drought fitted into a global pattern of circulation and hydroclimate anomalies with noticeable zonal and hemispheric symmetry. During the later period of the drought, from 2002 to 2004, weak El Niño conditions prevailed and, while the global climate adjusted accordingly, western North America remained, uniquely among midlatitude regions, in drought. The ensemble mean of the climate model simulations did not simulate the continuation of the drought in these years, suggesting that the termination of the drought was largely unpredictable in terms of global ocean conditions. The global context of the most recent, turn of the century, drought is compared to the five prior persistent North American droughts in the instrumental record from the mid-nineteenth century on. A classic La Niña pattern of ocean temperature in the Pacific is common to all. A cold Indian Ocean, also typical of La Niña, is common to all five prior droughts, but not the most recent one. Except in southern South America the global pattern of precipitation anomalies of the turn of the century drought is similar to that during the five prior droughts. These comparisons suggest that the earlier period of this most recent drought is the latest in a series of multiyear droughts forced by persistent changes in tropical Pacific Ocean temperatures. Warm tropical North Atlantic Ocean temperatures may play a secondary role.

scholarly journals North American Droughts of the Last Millennium from a Gridded Network of Tree-Ring Data

2007 ◽  
Vol 20 (7) ◽  
pp. 1353-1376 ◽  
Author(s):  
Celine Herweijer ◽  
Richard Seager ◽  
Edward R. Cook ◽  
Julien Emile-Geay
Keyword(s):  
North America ◽  
Tree Ring ◽  
North American ◽  
Tropical Pacific ◽  
La Niña ◽  
Last Millennium ◽  
Spatial Mode ◽  
Drought Variability ◽  
La Nina ◽  
The Tropical Pacific

Abstract Drought is the most economically expensive recurring natural disaster to strike North America in modern times. Recently available gridded drought reconstructions have been developed for most of North America from a network of drought-sensitive tree-ring chronologies, many of which span the last 1000 yr. These reconstructions enable the authors to put the famous droughts of the instrumental record (i.e., the 1930s Dust Bowl and the 1950s Southwest droughts) into the context of 1000 yr of natural drought variability on the continent. We can now, with this remarkable new record, examine the severity, persistence, spatial signatures, and frequencies of drought variability over the past milllennium, and how these have changed with time. The gridded drought reconstructions reveal the existence of successive “megadroughts,” unprecedented in persistence (20–40 yr), yet similar in year-to-year severity and spatial distribution to the major droughts experienced in today’s North America. These megadroughts occurred during a 400-yr-long period in the early to middle second millennium a.d., with a climate varying as today’s, but around a drier mean. The implication is that the mechanism forcing persistent drought in the West and the Plains in the instrumental era is analagous to that underlying the megadroughts of the medieval period. The leading spatial mode of drought variability in the recontructions resembles the North American ENSO pattern: widespread drought across the United States, centered on the Southwest, with a hint of the opposite phase in the Pacific Northwest. Recently, climate models forced by the observed history of tropical Pacific SSTs have been able to successfully simulate all of the major North American droughts of the last 150 yr. In each case, cool “La Niña–like” conditions in the tropical Pacific are consistent with North American drought. With ENSO showing a pronounced signal in the gridded drought recontructions of the last millennium, both in terms of its link to the leading spatial mode, and the leading time scales of drought variability (revealed by multitaper spectral analysis and wavelet analysis), it is postulated that, as for the modern day, the medieval megadroughts were forced by protracted La Niña–like tropical Pacific SSTs. Further evidence for this comes from the global hydroclimatic “footprint” of the medieval era revealed by existing paleoclimatic archives from the tropical Pacific and ENSO-sensitive tropical and extratropical land regions. In general, this global pattern matches that observed for modern-day persistent North American drought, whereby a La Niña–like tropical Pacific is accompanied by hemispheric, and in the midlatitudes, zonal, symmetry of hydroclimatic anomalies.

scholarly journals Simulating Global and North American Climate Using the Global Environmental Multiscale Model with a Variable-Resolution Modeling Approach

2010 ◽  
Vol 138 (10) ◽  
pp. 3967-3987 ◽  
Author(s):  
Marko Markovic ◽  
Hai Lin ◽  
Katja Winger
Keyword(s):  
North America ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Tropical Pacific ◽  
Eastern Indian Ocean ◽  
Variable Resolution ◽  
Modeling Approach ◽  
Global Environmental ◽  
Global Environmental Multiscale ◽  
The Tropical Pacific

Abstract Results from two simulations using the Global Environmental Multiscale (GEM) model in a variable-resolution modeling approach are evaluated. Simulations with a highly resolved domain positioned over North America and over the tropical Pacific–eastern Indian Ocean are assessed against the GEM uniform grid control run, 40-yr ECMWF Re-Analysis (ERA-40), and available observations in terms of regional and global climate and interannual variability. It is found that the variable-resolution configurations realistically simulate global and regional climate over North America with seasonal means and variability generally closer to ERA-40 or observations than the control run. Systematic errors of the control run are still present within the variable-resolution simulations but alleviated to some extent over their respective highly resolved domains. Additionally, there is some evidence of performance deterioration due to the increased resolution. There is little evidence that an increased resolution over the tropical Pacific–eastern Indian Ocean, with better-resolved local processes (e.g., convection and equatorial waves), has a significant impact on the extratropical time mean fields. However, in terms of simulating the Northern Hemisphere atmospheric flow anomaly associated with the dominant mode of sea surface temperature interannual variability in the equatorial eastern Pacific (i.e., El Niño), both stretched configurations have more realistic teleconnection patterns than the control run.

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