Assessing trends in atmospheric circulation patterns across North America

2020 ◽  
Author(s):  
Erik T. Smith ◽  
Omon Obarein ◽  
Scott C. Sheridan ◽  
Cameron C. Lee
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns

scholarly journals Characteristics of Observed Atmospheric Circulation Patterns Associated with Temperature Extremes over North America

2012 ◽  
Vol 25 (20) ◽  
pp. 7266-7281 ◽  
Author(s):  
Paul C. Loikith ◽  
Anthony J. Broccoli
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Extreme Temperature ◽  
Future Climate Change ◽  
Temperature Extremes ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Patterns And Processes

Abstract Motivated by a desire to understand the physical mechanisms involved in future anthropogenic changes in extreme temperature events, the key atmospheric circulation patterns associated with extreme daily temperatures over North America in the current climate are identified. The findings show that warm extremes at most locations are associated with positive 500-hPa geopotential height and sea level pressure anomalies just downstream with negative anomalies farther upstream. The orientation, physical characteristics, and spatial scale of these circulation patterns vary based on latitude, season, and proximity to important geographic features (i.e., mountains, coastlines). The anomaly patterns associated with extreme cold events tend to be similar to, but opposite in sign of, those associated with extreme warm events, especially within the westerlies, and tend to scale with temperature in the same locations. Circulation patterns aloft are more coherent across the continent than those at the surface where local surface features influence the occurrence of and patterns associated with extreme temperature days. Temperature extremes may be more sensitive to small shifts in circulation at locations where temperature is strongly influenced by mountains or large water bodies, or at the margins of important large-scale circulation patterns making such locations more susceptible to nonlinear responses to future climate change. The identification of these patterns and processes will allow for a thorough evaluation of the ability of climate models to realistically simulate extreme temperatures and their future trends.

scholarly journals Dominant Modes of Moisture Flux Anomalies over North America

2005 ◽  
Vol 6 (2) ◽  
pp. 194-209 ◽  
Author(s):  
Francina Dominguez ◽  
Praveen Kumar
Keyword(s):  
United States ◽  
North America ◽  
Atmospheric Circulation ◽  
Moisture Flux ◽  
Eof Analysis ◽  
Anomaly Field ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Complex Eof ◽  
Precipitation Events

Abstract This study investigates the principal modes of seasonal moisture flux transport over North America, analyzing their possible dependence on large-scale atmospheric circulation patterns. It uses 23 yr (1979–2001) of 6-hourly data from the NCEP–NCAR reanalysis I project. Complex empirical orthogonal function (complex-EOF) analysis is implemented on the vertically integrated and seasonally averaged moisture flux, to identify the dominant modes. For every season, the characteristic spatial pattern of the two most dominant modes is compared to the geopotential height anomaly field and precipitation anomaly field using correlation analysis. The two dominant winter modes capture the variability in the moisture flux field associated with extreme precipitation events over the western coast of the United States. The first winter mode captures 52% of the variability of the season and is related to the strong ENSO events of 1982/83 and 1997/98 (El Niño) and 1989 (La Niña). The second winter mode captures anomalous high moisture flux over the southwest related to the east Pacific teleconnection pattern. The intense moisture transport associated with high-precipitation events in the central United States (including the 1993 flood) is captured by summer mode 1, while the second mode of the summer season captures the moisture flux variability related to the 1983 and 1988 droughts. The results show that these summer flood and drought events are characterized by very different moisture flux anomalies and are not the positive and negative phases of a given mode. The use of complex-EOF analysis captures extreme hydrologic events as characteristic modes of interannual variability and allows a better understanding of the atmospheric circulation patterns associated with these events.

scholarly journals Comparison between Observed and Model-Simulated Atmospheric Circulation Patterns Associated with Extreme Temperature Days over North America Using CMIP5 Historical Simulations

2015 ◽  
Vol 28 (5) ◽  
pp. 2063-2079 ◽  
Author(s):  
Paul C. Loikith ◽  
Anthony J. Broccoli
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Climate Models ◽  
Extreme Temperature ◽  
Coupled Model ◽  
General Circulation Models ◽  
Multimodel Ensemble ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns

Abstract Circulation patterns associated with extreme temperature days over North America, as simulated by a suite of climate models, are compared with those obtained from observations. The authors analyze 17 coupled atmosphere–ocean general circulation models contributing to the fifth phase of the Coupled Model Intercomparison Project. Circulation patterns are defined as composites of anomalies in sea level pressure and 500-hPa geopotential height concurrent with days in the tails of temperature distribution. Several metrics used to systematically describe circulation patterns associated with extreme temperature days are applied to both the observed and model-simulated data. Additionally, self-organizing maps are employed as a means of comparing observed and model-simulated circulation patterns across the North American domain. In general, the multimodel ensemble resembles the observed patterns well, especially in areas removed from complex geographic features (e.g., mountains and coastlines). Individual model results vary; however, the majority of models capture the major features observed. The multimodel ensemble captures several key features, including regional variations in the strength and orientation of atmospheric circulation patterns associated with extreme temperatures, both near the surface and aloft, as well as variations with latitude and season. The results from this work suggest that these models can be used to comprehensively examine the role that changes in atmospheric circulation will play in projected changes in temperature extremes because of future anthropogenic climate warming.

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