Evidence for the Jumping Jet Hypothesis of abrupt climateChange

Evidence of Abrupt Climate Change- DO Events from GISP 2At least 20 DO (Dansgaard-Oeschger) events recorded in the last 120 Kyears (Rahmstorf, 2003) Rapid warming followed by slow cooling then rapid cooling

(Stuiver and Grooves, 2000)(Stuiver and Grooves, 2001)TIMEWarmer

Dust In Greenland During AbruptClimate ChangeMoreDustWarmerTimeCold times in Greenland are dustier (order of magnitude) Courtesy of Stephen Barker

High resolution abrupt warmingTemperatureDustTimeWarmColdMoreDustLessDust50 yearsDust changes are more abrupt and precede temperature changesFuhrer, 1999

Scatter Plot of ice core oxygen isotope and calcium concentrationStadial (Cold)Data PointsInterstadial (Warm) DataTemperature (oxygen isotopes) overlap between regimes but calcium does notCLIMATE REGIME IS BEST CHARACTERIZED BY ATMOSPHERC DUST LOAD FACTOR OF 10 change[Fuhrer,1999]WarmerMoreDust

Ideas that do NOT explain dust changesStrength of Deposition- Wet deposition is dominant [Steffenson, 1997]Change in source area- all dust is from Asia [Svenson, 2000]Change in size of source area- Greenland change is too quick [Fuhrer, 1999]Stronger winds- sea salts in core change moderately [Mogenson, 2002]

Could the Laurentide Ice Sheet Cause the Jet Stream to Jump?Jet flows to the south of the topography- similar to the Modern day circulationJet flows to the north ofthe topography

Force A General Circulation Model with glacial conditions and two different ice sheetsCourtesy Camille Li

How does the atmospheric circulation change- Stationary waves

How does the Atlantic JetAnd storm track change?Small IceBig IceK m/sContours =Jet speed (m/s)At 300 hPa

Colors =Storm activity(VT at 700 hPa)

Back Trajectories from GreenlandSmall IceBig IceBackTrajectoriesFrom SummitOrigin(15 daysAt 500 hPa)

How sensitive is the transitionin atmospheric circulation to theice sheet topography?Courtesy Joe Barsugli

ConclusionsThe dust changes in Greenland during abrupt climate change are more rapid and precede the temperature changesWe speculate these changes indicate a change in the atmospheric circulation regimeA general circulation model shows that the Jet Stream may jump during the glacial in a way which may be consistent with the change in dust loading

Courtesy Stephen Barker