Arctic Oscillation (AO)

The Arctic Oscillation (AO) is a large scale mode of climate variability, also referred to as the Northern Hemisphere annular mode. The AO is a climate pattern characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. When the AO is in its positive phase, a ring of strong winds circulating around the North Pole acts to confine colder air across polar regions. This belt of winds becomes weaker and more distorted in the negative phase of the AO, which allows an easier southward penetration of colder, arctic airmasses and increased storminess into the mid-latitudes.

AO index is obtained by projecting the AO loading pattern to the daily anomaly 1000 millibar height field over 20°N-90°N latitude. The AO loading pattern has been chosen as the first mode of EOF analysis using monthly mean 1000 millibar height anomaly data from 1979 to 2000 over 20°N-90°N. For more information on the AO, please see CPC's AO page.

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Download: xml csv json
DateAO
195001-0.060
1950020.627
195003-0.008
1950040.555
1950050.072
1950060.539
195007-0.802
195008-0.851
1950090.358
195010-0.379
195011-0.515
195012-1.928
195101-0.085
195102-0.400
195103-1.934
195104-0.776
195105-0.863
195106-0.918
1951070.090
195108-0.377
195109-0.818
195110-0.213
195111-0.069
1951121.987
1952010.368
195202-1.747
195203-1.859
1952040.539
195205-0.774
195206-0.441
1952070.383
195208-0.030
195209-0.383
195210-0.437
195211-1.891
195212-1.827
195301-1.036
195302-0.249
1953031.068
195304-1.256
195305-0.562
1953060.023
1953070.333
1953080.085
1953090.662
195310-0.194
1953110.354
1953120.575
195401-0.148
195402-0.181
1954030.476
1954040.512
195405-1.656
195406-0.268
1954070.341
195408-0.122
1954090.301
1954100.513
195411-0.328
1954120.553
195501-1.163
195502-1.542
195503-1.568
1955040.194
1955050.242
195506-0.266
1955070.332
1955080.760
1955090.357
1955100.099
195511-1.342
195512-0.444
195601-1.204
195602-2.029
1956030.470
195604-0.868
1956051.391
1956060.280
195607-0.215
195608-0.652
195609-0.202
1956101.139
195611-0.066
1956120.001
1957012.062
195702-1.513
195703-2.013
1957040.238
195705-0.966
195706-0.760
195707-0.646
1957080.097
195709-0.956
1957100.903
195711-1.380
1957120.828
195801-1.438
195802-2.228
195803-2.522
195804-0.360
195805-0.336
195806-1.149
195807-0.684
195808-0.755
195809-0.012
1958100.770
195811-0.011
195812-1.687
195901-2.013
1959022.544
1959031.432
1959040.119
195905-0.341
195906-0.033
1959070.105
195908-0.745
195909-0.281
195910-0.249
195911-1.411
195912-0.042
196001-2.484
196002-2.212
196003-1.625
196004-0.297
196005-0.857
1960060.055
196007-0.619
196008-1.008
196009-0.382
196010-1.187
196011-0.553
196012-0.343
196101-1.506
1961020.621
1961030.341
196104-0.237
1961050.157
1961060.837
196107-0.108
1961080.013
1961090.815
1961100.203
196111-0.010
196112-1.668
1962011.645
196202-0.358
196203-2.848
1962041.169
1962050.068
1962060.287
196207-0.927
1962080.152
196209-0.056
196210-0.016
196211-1.112
196212-0.711
196301-3.311
196302-1.721
1963030.724
196304-0.348
1963050.771
196306-0.585
196307-0.303
196308-0.625
1963090.083
1963101.069
196311-0.419
196312-1.178
1964010.385
196402-0.575
196403-0.558
1964040.663
1964051.174
1964060.142
1964070.734
196408-1.207
196409-0.227
1964100.342
196411-0.344
196412-0.246
196501-1.046
196502-2.084
196503-0.905
1965040.568
196505-0.153
1965060.038
196507-0.510
196508-0.255
196509-0.698
1965100.394
196511-1.341
1965120.163
196601-3.232
196602-1.438
196603-0.911
196604-1.837
1966051.124
1966060.408
1966070.011
196608-0.945
1966090.011
196610-1.077
1966110.111
196612-1.401
196701-0.576
1967021.180
1967031.967
1967041.700
1967050.127
1967060.647
1967070.259
196708-0.293
1967090.133
1967101.299
1967110.334
196712-0.347
196801-0.409
196802-2.154
1968031.741
1968040.328
196805-0.241
1968060.420
196807-0.836
196808-0.671
196809-1.009
196810-1.013
196811-2.183
196812-0.783
196901-2.967
196902-3.114
196903-1.582
1969040.438
196905-0.720
196906-0.348
1969070.410
196908-0.782
196909-0.083
1969100.098
1969110.326
196912-1.856
197001-2.412
197002-1.325
197003-2.084
1970040.302
1970050.531
1970060.875
1970070.139
197008-0.263
1970090.030
1970100.098
1970110.378
197012-0.399
197101-0.163
197102-0.922
197103-1.091
197104-0.583
1971050.679
197106-0.668
197107-0.578
1971080.818
1971090.153
1971101.185
1971110.419
1971120.824
1972010.166
197202-0.195
197203-0.141
1972041.007
1972050.140
197206-0.049
197207-0.553
197208-0.082
197209-0.920
1972100.392
197211-0.380
1972121.238
1973011.232
1973020.786
1973030.537
197304-1.126
1973050.073
1973060.531
1973070.270
1973080.313
1973090.114
1973100.337
1973110.002
197312-0.181
1974010.232
197402-0.489
197403-0.746
1974040.309
197405-0.507
197406-0.048
1974070.390
197408-0.533
197409-0.136
197410-1.024
197411-0.435
1974120.556
1975011.595
1975020.194
1975030.151
1975040.409
197505-0.614
197506-0.323
1975070.345
1975080.130
1975091.278
1975100.138
1975110.619
1975121.290
1976010.034
1976021.656
1976030.587
1976040.440
1976050.060
1976060.328
197607-0.325
1976080.559
197609-0.743
197610-0.804
197611-0.087
197612-2.074
197701-3.767
197702-2.010
1977030.344
1977041.329
1977050.104
197706-0.226
197707-0.492
197708-1.412
1977090.586
197710-0.009
1977110.605
197712-0.240
197801-0.347
197802-3.014
1978030.502
197804-0.967
1978050.059
1978060.635
197807-0.604
197808-0.354
197809-0.099
1978100.895
1978112.470
197812-0.980
197901-2.233
197902-0.697
197903-0.814
197904-1.157
197905-0.250
1979060.933
1979070.039
197908-0.684
197909-0.046
197910-1.243
1979110.475
1979121.295
198001-2.066
198002-0.934
198003-1.433
198004-0.419
198005-1.155
1980060.721
198007-0.622
198008-0.185
1980090.313
198010-0.521
198011-1.361
198012-0.057
198101-0.116
198102-0.332
198103-1.645
1981040.430
1981050.180
198106-0.438
1981070.561
198108-0.244
198109-1.040
198110-1.167
198111-0.188
198112-1.216
198201-0.883
1982020.974
1982031.074
1982041.454
198205-0.209
198206-1.180
1982070.005
1982080.362
1982090.558
198210-0.211
1982110.661
1982120.967
1983011.359
198302-1.806
198303-0.567
198304-0.738
198305-0.441
1983060.313
1983070.131
1983081.098
1983090.167
1983101.369
198311-0.688
1983120.186
1984010.905
198402-0.303
198403-2.386
198404-0.284
1984050.479
1984060.007
1984070.019
1984080.466
198409-0.413
198410-0.270
198411-0.966
1984120.446
198501-2.806
198502-1.440
1985030.551
1985040.652
198505-0.432
198506-0.347
198507-0.390
198508-0.001
1985090.114
1985101.035
198511-1.218
198512-1.948
198601-0.568
198602-2.904
1986031.931
1986040.103
1986050.367
1986060.535
198607-0.008
198608-0.826
198609-0.023
1986101.425
1986110.926
1986120.060
198701-1.148
198702-1.473
198703-1.746
1987040.387
1987050.325
198706-0.710
198707-0.466
198708-0.836
1987090.287
198710-0.080
198711-0.536
198712-0.534
1988010.265
198802-1.066
198803-0.197
198804-0.561
198805-0.846
1988060.061
198807-0.143
1988080.255
1988091.039
1988100.032
198811-0.035
1988121.679
1989013.106
1989023.279
1989031.530
198904-0.250
1989050.889
1989060.345
1989070.866
1989080.551
1989090.703
1989100.991
1989110.034
198912-0.644
1990011.001
1990023.402
1990032.990
1990041.879
1990050.943
1990060.304
199007-0.296
199008-0.180
199009-0.210
1990100.660
1990110.521
1990121.277
1991010.723
199102-0.876
199103-0.527
1991040.530
1991050.486
199106-0.115
199107-0.188
1991080.797
199109-0.112
199110-0.252
1991110.285
1991121.613
1992010.550
1992021.122
1992030.984
199204-0.521
1992051.341
199206-0.302
1992070.191
1992080.535
199209-0.640
199210-0.366
1992110.717
1992121.627
1993013.495
1993020.184
1993030.764
199304-0.435
199305-1.607
199306-0.520
199307-0.511
199308-0.393
199309-0.361
199310-0.565
1993111.002
199312-0.104
199401-0.288
199402-0.862
1994031.881
1994040.225
199405-0.115
1994061.606
1994070.351
1994080.828
199409-0.084
1994100.174
1994111.779
1994120.894
199501-0.154
1995021.429
1995030.393
199504-0.963
199505-0.891
199506-0.112
199507-0.217
1995080.544
199509-0.549
1995100.075
199511-0.723
199512-2.127
199601-1.200
1996020.163
199603-1.483
199604-1.525
199605-0.226
1996060.497
1996070.715
1996080.125
199609-1.140
1996100.183
1996110.136
199612-1.721
199701-0.457
1997021.889
1997031.091
1997040.324
199705-0.961
199706-0.815
199707-0.431
1997080.121
1997090.195
199710-0.700
199711-0.661
199712-0.071
199801-2.081
199802-0.183
199803-0.254
199804-0.038
1998050.429
199806-0.711
199807-0.212
1998080.650
199809-1.050
1998100.294
199811-1.449
1998121.353
1999010.110
1999020.482
199903-1.492
1999040.284
1999050.226
1999060.707
199907-0.002
199908-0.672
1999090.059
199910-0.006
1999110.611
1999121.043
2000011.270
2000021.076
200003-0.451
200004-0.279
2000050.969
2000060.586
200007-0.649
2000080.144
2000090.395
2000100.317
200011-1.581
200012-2.354
200101-0.959
200102-0.622
200103-1.687
2001040.906
2001050.452
200106-0.015
200107-0.031
2001080.521
200109-0.707
2001100.707
2001110.819
200112-1.322
2002011.381
2002021.304
2002030.902
2002040.748
2002050.401
2002060.573
2002070.328
200208-0.229
200209-0.043
200210-1.489
200211-1.425
200212-1.592
200301-0.472
2003020.128
2003030.933
200304-0.178
2003051.017
200306-0.102
2003070.075
200308-0.280
2003090.467
200310-0.670
2003110.642
2003120.265
200401-1.686
200402-1.528
2004030.318
200404-0.409
200405-0.094
200406-0.236
200407-0.201
200408-0.720
2004090.855
200410-0.515
2004110.678
2004121.230
2005010.356
200502-1.271
200503-1.348
200504-0.046
200505-0.763
200506-0.383
200507-0.030
2005080.026
2005090.802
2005100.030
2005110.228
200512-2.104
200601-0.170
200602-0.156
200603-1.604
2006040.138
2006050.156
2006061.071
2006070.103
200608-0.265
2006090.606
200610-1.029
2006110.521
2006122.282
2007012.034
200702-1.307
2007031.182
2007040.544
2007050.894
200706-0.555
200707-0.397
200708-0.034
2007090.179
2007100.383
200711-0.519
2007120.821
2008010.819
2008020.938
2008030.586
200804-0.455
200805-1.205
200806-0.090
200807-0.480
200808-0.080
200809-0.327
2008101.676
2008110.092
2008120.648
2009010.800
200902-0.672
2009030.121
2009040.973
2009051.194
200906-1.351
200907-1.356
200908-0.054
2009090.875
200910-1.540
2009110.459
200912-3.413
201001-2.587
201002-4.266
201003-0.432
201004-0.275
201005-0.919
201006-0.013
2010070.435
201008-0.117
201009-0.865
201010-0.467
201011-0.376
201012-2.631
201101-1.683
2011021.575
2011031.424
2011042.275
201105-0.035
201106-0.858
201107-0.472
201108-1.063
2011090.665
2011100.800
2011111.459
2011122.221
201201-0.220
201202-0.036
2012031.037
201204-0.035
2012050.168
201206-0.672
2012070.168
2012080.014
2012090.772
201210-1.514
201211-0.111
201212-1.749
201301-0.610
201302-1.007
201303-3.185
2013040.322
2013050.494
2013060.549
201307-0.011
2013080.154
201309-0.461
2013100.263
2013112.029
2013121.475
201401-0.969
2014020.044
2014031.206
2014040.972
2014050.464
201406-0.507
201407-0.489
201408-0.372
2014090.102
201410-1.134