Jennifer Francis Institute of Marine and Coastal Sciences Rutgers University In collaboration with Steve Vavrus, U. of Wisconsin Arctic Linkages Workshop National Academies of Sciences 12-13 September 2013, U. of MD
Chain of Events Linking Arctic Amplification (AA) with Increased Extreme Weather in Mid-Latitudes AA: Arctic warming 2-3 times faster than N. hemisphere Poleward temperature gradient weakening More persistent weather patterns, extremes more likely Large-scale waves progress more slowly eastward 500 mb zonal winds decreasing where gradient weakens Amplitude of Rossby waves increasing, blocking more likely Upper-level flow becoming more meridional
The Evidence AA: Arctic warming 2-3 times faster than N. hemisphere Winter JFM Spring AMJ Summer JAS Fall OND T 1000mb 90-70 o N 70-30 o N OND JAS 1000-500mb Thickness 2000 to 2012
The Evidence Poleward temperature gradient weakening OND JAS Trends in poleward thickness gradient (1000-500 hpa) from 1979 to 2012
The Evidence 500 mb zonal winds decreasing where gradient weakens 20 JFM OND OND JAS Zonal-mean zonal winds at 500 hpa, 40-60 o N, N. Hem. Anomalies in zonal winds at 500 hpa from 2000 to 2012 % change in 500 mb AMJ 10 zonal winds in 4 x CO 2 run of CCSM4 JAS 0 Fall -10 Winter Spring from Barnes (2013) Summer -20 30 o N 45 o N 60 o N Trends in U500
The Evidence Upper-level flow becoming more meridional OND JAS CCSM4 4 x CO 2 Change in Meridional Wind Fraction @45 o N Trends in meridional component Winter of the +33% 500 Spring hpa wind (1979 +21% to 2011) Summer +21% Fall +19% Less wavy More wavy
Amplitude of Rossby waves increasing, blocking more likely The Evidence OND JAS Northern Hemisphere Ridge peaks Trends in Amplitude deg/dec Trend in ridges Trough bottoms Trends in Amplitude from Barnes (2013) from Barnes (2013) 500mb heights JAS 2000-2012 Amplitude from Screen and Simmonds (2013)
The Evidence Amplitude of Rossby waves increasing, blocking more likely Ridge peaks OND NH Blocking (days/year) U500 r = -0.68
An Artifact of the Methodology? 1980-1995 1996-2011 500 mb height with maximum waviness 500 mb height contour used in FV12 Wave amplitude (deg. latitude) from Barnes (2013)
An Artifact of the Methodology? Typical 500 hpa pattern in Nov 1980-1995 1996-2011 Wave amplitude (deg. latitude) from Barnes (2013) Contour with max waviness has different shape from FV12 s contour in max gradient
An Artifact of the Methodology? Contour with max waviness has is 15 o different farther north, shape not from in max FV12 s wind zone, contour not representative in max gradient of jet stream trajectory.
The Evidence Large-scale waves progress more slowly eastward From Barnes (2013) We find a robust decrease in wave phase speeds in OND, which is consistent with the u500 reductions. More work is needed to assess changes in speed of large wave progression.
The Evidence More persistent weather patterns, extremes more likely NOAA/NCDC Climate Extremes Index US, annual
The Evidence SON More persistent weather patterns, extremes more likely Tmax Mean day-to-day temperature differences in Beaver City, NE before and after 1995. Tmin Small day-to-day temperature changes becoming more common.
Upper-air Circulation Anomalies during Extreme Weather in Chicago from S. Vavrus High-Amplitude Wave Patterns 10 Coldest Days 10 Hottest Days X X 10 Wettest Days 10 Driest Summers X X
The Evidence More persistent weather patterns, extremes more likely Projected increased ridging over continents associated with higher SATs. Ridging over N. Atlantic cools western Europe
Mean Frequency Surface Air Temp. The Evidence More persistent weather patterns, extremes more likely Mean TAS JJA JJA CCSM4 Mean TAS @ vs. 40U500 o N, percentiles 100 o W 1950s JJA CCSM4 (40N, 100W) 28 vs 2090s (RCP 8.5) 27 26 25 24 23 22 21 20 JJA U500 for 20 th century run 5 15 25 35 45 55 65 75 85 95 Percentiles 500 hpa zonal wind 500 hpa zonal U500 JJA wind percentile speed In recent decades, higher summer SATs occur when 500 hpa zonal winds are weak or easterly, i.e., under dome of ridge. Projection for 2090s suggests that light and easterly winds will become more common at the expense of west winds» higher SATs, extremes more likely.
The Evidence More persistent weather patterns, extremes more likely Regression of detrended fall anomalies (left) and in spring winter snow (right) cover sea-ice and summer anomalies sea-ice on extreme extent on cold extreme events in summer winter. heat waves. Tang, Zhang, Yang, and Francis, ERL (2013) Tang, Zhang, and Francis, submitted Winter Even though ice anomalies snow have anomalies stronger are twice association large, sea with ice has extreme a larger influence. cold events over the US.
Summary Evidence for Arctic linkages to changes in midlatitude weather patterns is piling up Many links in the chain are solid Connections strongest in fall, but AA is emerging in other seasons, response should strengthen More work needed to assess: Changing propagation of large-scale waves (speed and cause) Changing persistence of weather patterns Changing frequency of extremes Interactions among AA and other large-scale influences (ENSO, PDO, etc.)
Extras
Change in JJA Snow Cover Fraction 2090s Late 21 st C (CCSM4 RCP8.5)
JJA Band of increased MCI across U.S. and Asia through N. Pacific, decreases over Canada and Alaska, suggesting wavier flow
Anomalies in zonal-mean heights and zonal winds for OND 2007-2012
Conditions leading up to Sandy Time/latitude evolution during Oct. 2012 of heights (1000 hpa and 500 hpa) and zonal wind anomalies at 500 hpa in the N. Atlantic (0 to 90 o W). Blocking high begins ~Oct 20th with positive anomalies at 1000 hpa across the Arctic related to surface temperatures. 500 hpa ridge causes weakening zonal winds between 38 o N-50 o N. 10/1 10/5 10/10 10/15 10/20 10/25 1000 hpa 500 hpa U500 10/30 Latitude
from Barnes et al (2013) Zonal wind anoms 700 hpa Oct 1980-1992 Oct 2000-2012
ASO (2076-2099) (1980-2004) ASO anomalies in 500 hpa heights ASO anomalies 2007-2012 in 850 hpa zonal winds 2007-2012 Change in Oct zonal wind -- CCSM4 -- 4 x CO 2 Contours = average easterlies during Oct. 27-29, 5 m s -1 from Barnes et al (2013) Stronger easterlies in recent years of low ice extent Zonal in wind region anomaly where strong m s -1 easterlies existed during Sandy. from S. Vavrus