Multi-scale variability in North American summer maximum temperatures and modulations from the North Atlantic simulated by an AGCM

Multi-scale variability in North American summer maximum temperatures and modulations from the... AbstractSix recurrent thermal regimes are identified over continental North America from June to September through a k – means clustering applied to daily maximum temperature simulated by ECHAM5 forced by historical SSTs for 1930-2013 and validated using NCEP-DOE II reanalysis over the 1980-2009 period. Four regimes are related to a synoptic wave pattern propagating eastwards in the midlatitudes with embedded ridging anomalies that translate into maximum warming transiting along. Two other regimes, associated with broad continental warming and above average temperatures in the northeast US, respectively, are characterized by ridging anomalies over America, Europe and Asia that suggest correlated heat waves occurrences in these regions. Their frequencies are both mainly related to La Niña and warm conditions in the North Atlantic. Removing all variability beyond the seasonal cycle in the North Atlantic in ECHAM5 leads to a significant drop in the occurrences of the regime associated with warming in the northeast US. Superimposing positive (negative) anomalies mimicking the AMV in the North Atlantic translates into more (less) warming over the US across all regimes, and does alter regime frequencies but less significantly. Regime frequency changes are thus primarily controlled by Atlantic SST variability on all time-scales beyond the seasonal cycle, rather than mean SST changes, whereas the intensity of temperature anomalies are impacted by AMV SST forcing, due to upper-tropospheric warming and enhanced stability suppressing rising motion during positive phase of the AMV. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

Multi-scale variability in North American summer maximum temperatures and modulations from the North Atlantic simulated by an AGCM

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0442
D.O.I.
10.1175/JCLI-D-17-0392.1
Publisher site
See Article on Publisher Site

Abstract

AbstractSix recurrent thermal regimes are identified over continental North America from June to September through a k – means clustering applied to daily maximum temperature simulated by ECHAM5 forced by historical SSTs for 1930-2013 and validated using NCEP-DOE II reanalysis over the 1980-2009 period. Four regimes are related to a synoptic wave pattern propagating eastwards in the midlatitudes with embedded ridging anomalies that translate into maximum warming transiting along. Two other regimes, associated with broad continental warming and above average temperatures in the northeast US, respectively, are characterized by ridging anomalies over America, Europe and Asia that suggest correlated heat waves occurrences in these regions. Their frequencies are both mainly related to La Niña and warm conditions in the North Atlantic. Removing all variability beyond the seasonal cycle in the North Atlantic in ECHAM5 leads to a significant drop in the occurrences of the regime associated with warming in the northeast US. Superimposing positive (negative) anomalies mimicking the AMV in the North Atlantic translates into more (less) warming over the US across all regimes, and does alter regime frequencies but less significantly. Regime frequency changes are thus primarily controlled by Atlantic SST variability on all time-scales beyond the seasonal cycle, rather than mean SST changes, whereas the intensity of temperature anomalies are impacted by AMV SST forcing, due to upper-tropospheric warming and enhanced stability suppressing rising motion during positive phase of the AMV.

Journal

Journal of ClimateAmerican Meteorological Society

Published: Jan 8, 2018

References

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