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Arctic Dipole Anomaly (DA) Drove the Record Lows in the Arctic Sea Ice Extent. Jia Wang ( [email protected]) NOAA Great Lakes Environmental Research Lab, Ann Arbor, Michigan Jinlun Zhang (1) , Eiji Watanabe (2), Kohei Mizobata (3), John Walsh (2), and, Xuezhi Bai (4), and Moto Ikeda (5)
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seaice-monitor.cgi?lang=j1. Introduction: Sea ice minimums in the western Arctic Ocean off the Coast of Alaska: 2002-2005, and 2007 (record low)!
1) Is the AO/NAO the only dominant mode driving the Arctic ice-ocean system?
2) Are both Arctic sea ice circulation and sea ice export (sea ice thinning) only related to the AO (in a sense of cyclonic or anti-cyclonic anomaly)?
3) During neutral/negative AO phase (after year 2000), why sea ice set record lows one after one in the western Arctic, leading to a record minimum in September 2007!?
max. ice export
in coupled climate
History of DA:1) Skeie (2000): BO; 2) Holland (2003); 3) Goose et al. 2003; 4) Semenov and Bengttson (2003)0) Wang et al. (1995)—Internal report of CCGCR of McGill
EOF2 of Wang et al. (1995)
Ice export regresses to SLP in CCM2, Holland (2003)
BO: EOF2, Skeie (2000)
1) Japan CCSR/NIES/FRCGC global GCM: 1900-2010
2) Regional Coupled Ice-Ocean Model (CIOM) in the pan Arctic and North Atlantic Ocean (Wang et al. 2002, 2005), and Bering/Beaufort/Chukchi seas (Wang et al. 2008)
EOF 1st mode
- Annular structure
- In the positive AO phase
high : Arctic region
low : Mid-latitude
Each mode is independent
by test of North et al. (1982)
EOF 2nd mode
- Dipole structure
- In the positive DA phase
high : Greenland Sea
low : Laptev SeaRegression maps of AO and DA using GCM (K1) and NCEP
Regressed winter mean SLP anomalies to each EOF mode (NCEP) [hPa]
Difference of sea ice thickness (cm) and velocity (cm/s)
between the positive and negative phases
(AO +) – (AO -)
(DA +) – (DA -)
Circulation shows cyclonic anomaly.
Thickness difference is not significant.
Circulation shows meridional anomaly.
Thickness difference is significant.
to EOF1 (AO, upper) and EOF2
Sea ice volume flux
2008 (not record low,
but 2nd lowest ever!)
Summer 2007 falls in state: -AO/+DA
SLP anomaly was a DA-dominated two-center structure, and the wind anomaly was meridional, blowing from the western to the eastern Arctic This DA-induced wind anomaly was responsible for the 2007 summer minimum
Since 1995, AO was near neutral and negative, while the DA was active.
Record low years: 1995, 2002, 2007 and 2008) in first quadrant with +DA persistent from winter-spring to summer. In 1999 and 2005, strong summer +DA contributed to the ice minimum.
Scatter plot with summer DA as x-axis and winter-spring DA as y-axis
Heat Flux was calculated using in situ observation and Satellite SST
Summer DA Index
Relation between Bering strait heat flux and summer DA index
The +DA strengthened inflow of the warm Pacific water since 2000s
Wind Anomaly in m/s
SLP and wind anomalies in Aug 2007 (Left) and 2008 (right)
National Snow and Ice Data Center
Zhang Simulated the sea ice and circulation for 1978-2008 under daily forcing.
Ice advection = ice mass convergence:
One of every 36 ice velocity vectors plotted.
Min ice cover ever on Sep 24, 2007
Simulated compares well against the obs. The correlation is 0.93 in Sep. and 0.92 in Jan-Sep mean. The model reproduces summer ice minima in 1995, 2002, 2005, 2007 and 2008 as well, not for 1999
+DAWind anomaly blows from Pacific Arctic to Atlantic Arctic, enhancing TDS, sucking more Pacific Water inflow, driving away and melting more sea ice in Pacific Arctic (Woodgate et al. 2005; Shimada et al. 2006)
-DAWind anomaly blows from Atlantic Arctic to Pacific Arctic, weakening TDS, blocking Pacific Water inflow, detaining more ice in the Pacific Arctic
-- Direct (short-term, seasonal): driving sea ice and enhancing TDS, +SAT/SST, local ice/ocean albedo feedback (Wang et al. 2005)
-- Indirect (long-term, interannual): sucking in more warm Pacific Water inflow, +SAT/SST, melting more sea ice, enhancing local ice/ocean albedo feedback