Southern Oscillation Index (SOI)
The Southern Oscillation Index (SOI) is a standardized index based on the observed sea level pressure differences between Tahiti and Darwin, Australia. The SOI is one measure of the large-scale fluctuations in air pressure occurring between the western and eastern tropical Pacific (i.e., the state of the Southern Oscillation) during El Niño and La Niña episodes. In general, smoothed time series of the SOI correspond very well with changes in ocean temperatures across the eastern tropical Pacific. The negative phase of the SOI represents below-normal air pressure at Tahiti and above-normal air pressure at Darwin. Prolonged periods of negative (positive) SOI values coincide with abnormally warm (cold) ocean waters across the eastern tropical Pacific typical of El Niño (La Niña) episodes. The methodology used to calculate SOI is available below. More information can be found at the Climate Prediction Center SOI page.
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Source: http://www.cpc.ncep.noaa.gov/data/indices/soi
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Expand Data Table
| Date | SOI |
|---|---|
| 195101 | +1.5 |
| 195102 | +0.9 |
| 195103 | -0.1 |
| 195104 | -0.3 |
| 195105 | -0.7 |
| 195106 | +0.2 |
| 195107 | -1.0 |
| 195108 | -0.2 |
| 195109 | -1.1 |
| 195110 | -1.0 |
| 195111 | -0.8 |
| 195112 | -0.7 |
| 195201 | -0.9 |
| 195202 | -0.6 |
| 195203 | +0.5 |
| 195204 | -0.2 |
| 195205 | +0.8 |
| 195206 | +0.7 |
| 195207 | +0.5 |
| 195208 | +0.1 |
| 195209 | -0.2 |
| 195210 | +0.4 |
| 195211 | 0.0 |
| 195212 | -1.2 |
| 195301 | +0.3 |
| 195302 | -0.5 |
| 195303 | -0.2 |
| 195304 | +0.2 |
| 195305 | -1.7 |
| 195306 | +0.1 |
| 195307 | 0.0 |
| 195308 | -1.2 |
| 195309 | -1.2 |
| 195310 | +0.1 |
| 195311 | -0.3 |
| 195312 | -0.5 |
| 195401 | +0.7 |
| 195402 | -0.3 |
| 195403 | +0.3 |
| 195404 | +0.6 |
| 195405 | +0.5 |
| 195406 | +0.1 |
| 195407 | +0.4 |
| 195408 | +1.1 |
| 195409 | +0.2 |
| 195410 | +0.3 |
| 195411 | +0.1 |
| 195412 | +1.4 |
| 195501 | -0.5 |
| 195502 | +1.9 |
| 195503 | +0.6 |
| 195504 | -0.1 |
| 195505 | +1.0 |
| 195506 | +1.3 |
| 195507 | +1.6 |
| 195508 | +1.5 |
| 195509 | +1.3 |
| 195510 | +1.5 |
| 195511 | +1.2 |
| 195512 | +1.0 |
| 195601 | +1.3 |
| 195602 | +1.6 |
| 195603 | +1.3 |
| 195604 | +0.9 |
| 195605 | +1.4 |
| 195606 | +1.1 |
| 195607 | +1.1 |
| 195608 | +1.2 |
| 195609 | +0.1 |
| 195610 | +1.8 |
| 195611 | +0.2 |
| 195612 | +1.1 |
| 195701 | +0.6 |
| 195702 | -0.1 |
| 195703 | +0.2 |
| 195704 | +0.2 |
| 195705 | -0.7 |
| 195706 | +0.2 |
| 195707 | +0.2 |
| 195708 | -0.5 |
| 195709 | -0.9 |
| 195710 | 0.0 |
| 195711 | -1.0 |
| 195712 | -0.3 |
| 195801 | -1.9 |
| 195802 | -0.5 |
| 195803 | +0.3 |
| 195804 | +0.4 |
| 195805 | -0.5 |
| 195806 | +0.3 |
| 195807 | +0.4 |
| 195808 | +0.9 |
| 195809 | -0.3 |
| 195810 | +0.1 |
| 195811 | -0.4 |
| 195812 | -0.6 |
| 195901 | -0.9 |
| 195902 | -1.4 |
| 195903 | +1.3 |
| 195904 | +0.4 |
| 195905 | +0.5 |
| 195906 | -0.1 |
| 195907 | -0.3 |
| 195908 | -0.1 |
| 195909 | 0.0 |
| 195910 | +0.5 |
| 195911 | +0.9 |
| 195912 | +0.9 |
| 196001 | +0.1 |
| 196002 | +0.1 |
| 196003 | +1.0 |
| 196004 | +0.8 |
| 196005 | +0.5 |
| 196006 | +0.1 |
| 196007 | +0.5 |
| 196008 | +0.8 |
| 196009 | +0.7 |
| 196010 | +0.1 |
| 196011 | +0.5 |
| 196012 | +0.8 |
| 196101 | -0.3 |
| 196102 | +0.9 |
| 196103 | -1.8 |
| 196104 | +0.8 |
| 196105 | +0.3 |
| 196106 | +0.1 |
| 196107 | +0.2 |
| 196108 | +0.2 |
| 196109 | +0.1 |
| 196110 | -0.3 |
| 196111 | +0.5 |
| 196112 | +1.5 |
| 196201 | +2.0 |
| 196202 | -0.3 |
| 196203 | +0.1 |
| 196204 | +0.2 |
| 196205 | +1.1 |
| 196206 | +0.7 |
| 196207 | +0.1 |
| 196208 | +0.6 |
| 196209 | +0.4 |
| 196210 | +1.0 |
| 196211 | +0.3 |
| 196212 | +0.2 |
| 196301 | +1.0 |
| 196302 | +0.6 |
| 196303 | +1.1 |
| 196304 | +0.8 |
| 196305 | +0.4 |
| 196306 | -0.5 |
| 196307 | -0.1 |
| 196308 | 0.0 |
| 196309 | -0.6 |
| 196310 | -1.2 |
| 196311 | -0.8 |
| 196312 | -1.2 |
| 196401 | -0.4 |
| 196402 | 0.0 |
| 196403 | +1.1 |
| 196404 | +1.1 |
| 196405 | +0.2 |
| 196406 | +0.8 |
| 196407 | +0.6 |
| 196408 | +1.5 |
| 196409 | +1.3 |
| 196410 | +1.3 |
| 196411 | +0.2 |
| 196412 | -0.3 |
| 196501 | -0.4 |
| 196502 | +0.4 |
| 196503 | +0.8 |
| 196504 | -0.5 |
| 196505 | +0.2 |
| 196506 | -0.6 |
| 196507 | -1.8 |
| 196508 | -0.7 |
| 196509 | -1.3 |
| 196510 | -0.9 |
| 196511 | -1.5 |
| 196512 | +0.2 |
| 196601 | -1.3 |
| 196602 | -0.2 |
| 196603 | -0.9 |
| 196604 | -0.2 |
| 196605 | -0.4 |
| 196606 | +0.3 |
| 196607 | +0.1 |
| 196608 | +0.6 |
| 196609 | -0.2 |
| 196610 | -0.1 |
| 196611 | 0.0 |
| 196612 | -0.3 |
| 196701 | +1.7 |
| 196702 | +1.7 |
| 196703 | +1.2 |
| 196704 | 0.0 |
| 196705 | 0.0 |
| 196706 | +0.6 |
| 196707 | +0.2 |
| 196708 | +0.7 |
| 196709 | +0.5 |
| 196710 | +0.1 |
| 196711 | -0.4 |
| 196712 | -0.6 |
| 196801 | +0.5 |
| 196802 | +1.3 |
| 196803 | +0.1 |
| 196804 | 0.0 |
| 196805 | +1.2 |
| 196806 | +1.1 |
| 196807 | +0.7 |
| 196808 | +0.3 |
| 196809 | -0.3 |
| 196810 | -0.1 |
| 196811 | -0.3 |
| 196812 | +0.2 |
| 196901 | -1.5 |
| 196902 | -0.5 |
| 196903 | +0.4 |
| 196904 | -0.4 |
| 196905 | -0.2 |
| 196906 | +0.2 |
| 196907 | -0.5 |
| 196908 | -0.1 |
| 196909 | -1.0 |
| 196910 | -0.9 |
| 196911 | -0.1 |
| 196912 | +0.4 |
| 197001 | -1.1 |
| 197002 | -1.0 |
| 197003 | +0.6 |
| 197004 | -0.1 |
| 197005 | +0.4 |
| 197006 | +1.0 |
| 197007 | -0.4 |
| 197008 | +0.6 |
| 197009 | +1.2 |
| 197010 | +1.0 |
| 197011 | +1.6 |
| 197012 | +1.9 |
| 197101 | +0.4 |
| 197102 | +2.0 |
| 197103 | +2.3 |
| 197104 | +1.7 |
| 197105 | +0.9 |
| 197106 | +0.4 |
| 197107 | +0.2 |
| 197108 | +1.5 |
| 197109 | +1.4 |
| 197110 | +1.7 |
| 197111 | +0.5 |
| 197112 | +0.3 |
| 197201 | +0.5 |
| 197202 | +1.1 |
| 197203 | +0.6 |
| 197204 | -0.1 |
| 197205 | -1.6 |
| 197206 | -0.5 |
| 197207 | -1.4 |
| 197208 | -0.5 |
| 197209 | -1.4 |
| 197210 | -0.9 |
| 197211 | -0.3 |
| 197212 | -1.3 |
| 197301 | -0.3 |
| 197302 | -1.4 |
| 197303 | +0.7 |
| 197304 | +0.1 |
| 197305 | +0.4 |
| 197306 | +1.1 |
| 197307 | +0.6 |
| 197308 | +1.3 |
| 197309 | +1.2 |
| 197310 | +0.8 |
| 197311 | +2.6 |
| 197312 | +1.8 |
| 197401 | +2.4 |
| 197402 | +2.1 |
| 197403 | +2.4 |
| 197404 | +0.9 |
| 197405 | +1.0 |
| 197406 | +0.4 |
| 197407 | +1.1 |
| 197408 | +0.8 |
| 197409 | +1.1 |
| 197410 | +0.9 |
| 197411 | -0.1 |
| 197412 | +0.2 |
| 197501 | -0.5 |
| 197502 | +0.8 |
| 197503 | +1.6 |
| 197504 | +1.2 |
| 197505 | +0.6 |
| 197506 | +1.3 |
| 197507 | +1.9 |
| 197508 | +2.0 |
| 197509 | +2.1 |
| 197510 | +1.7 |
| 197511 | +1.2 |
| 197512 | +2.1 |
| 197601 | +1.4 |
| 197602 | +1.7 |
| 197603 | +1.7 |
| 197604 | +0.3 |
| 197605 | +0.4 |
| 197606 | +0.3 |
| 197607 | -0.9 |
| 197608 | -0.8 |
| 197609 | -1.1 |
| 197610 | +0.4 |
| 197611 | +0.7 |
| 197612 | -0.3 |
| 197701 | -0.4 |
| 197702 | +1.2 |
| 197703 | -0.5 |
| 197704 | -0.4 |
| 197705 | -0.5 |
| 197706 | -0.9 |
| 197707 | -1.1 |
| 197708 | -0.8 |
| 197709 | -0.8 |
| 197710 | -1.0 |
| 197711 | -1.3 |
| 197712 | -1.1 |
| 197801 | -0.3 |
| 197802 | -2.7 |
| 197803 | -0.2 |
| 197804 | -0.3 |
| 197805 | +1.4 |
| 197806 | +0.7 |
| 197807 | +0.6 |
| 197808 | +0.4 |
| 197809 | +0.1 |
| 197810 | -0.4 |
| 197811 | 0.0 |
| 197812 | -0.1 |
| 197901 | -0.4 |
| 197902 | +1.0 |
| 197903 | +0.1 |
| 197904 | -0.1 |
| 197905 | +0.5 |
| 197906 | +0.6 |
| 197907 | +1.3 |
| 197908 | -0.2 |
| 197909 | +0.1 |
| 197910 | -0.1 |
| 197911 | -0.4 |
| 197912 | -0.7 |
| 198001 | +0.4 |
| 198002 | +0.3 |
| 198003 | -0.4 |
| 198004 | -0.6 |
| 198005 | 0.0 |
| 198006 | 0.0 |
| 198007 | 0.0 |
| 198008 | +0.4 |
| 198009 | -0.5 |
| 198010 | 0.0 |
| 198011 | -0.3 |
| 198012 | -0.1 |
| 198101 | +0.4 |
| 198102 | -0.2 |
| 198103 | -1.3 |
| 198104 | -0.1 |
| 198105 | +0.8 |
| 198106 | +1.2 |
| 198107 | +0.8 |
| 198108 | +0.7 |
| 198109 | +0.3 |
| 198110 | -0.4 |
| 198111 | +0.2 |
| 198112 | +0.5 |
| 198201 | +1.2 |
| 198202 | +0.3 |
| 198203 | +0.6 |
| 198204 | +0.1 |
| 198205 | -0.3 |
| 198206 | -1.0 |
| 198207 | -1.5 |
| 198208 | -1.7 |
| 198209 | -1.7 |
| 198210 | -1.7 |
| 198211 | -2.6 |
| 198212 | -2.2 |
| 198301 | -3.5 |
| 198302 | -3.6 |
| 198303 | -2.4 |
| 198304 | -0.9 |
| 198305 | +0.6 |
| 198306 | 0.0 |
| 198307 | -0.6 |
| 198308 | +0.1 |
| 198309 | +0.9 |
| 198310 | +0.4 |
| 198311 | -0.1 |
| 198312 | 0.0 |
| 198401 | +0.2 |
| 198402 | +0.9 |
| 198403 | -0.2 |
| 198404 | +0.3 |
| 198405 | +0.2 |
| 198406 | -0.3 |
| 198407 | +0.2 |
| 198408 | +0.4 |
| 198409 | +0.1 |
| 198410 | -0.3 |
| 198411 | +0.3 |
| 198412 | -0.1 |
| 198501 | -0.3 |
| 198502 | +1.2 |
| 198503 | +0.8 |
| 198504 | +1.2 |
| 198505 | +0.4 |
| 198506 | -0.4 |
| 198507 | -0.1 |
| 198508 | +1.0 |
| 198509 | 0.0 |
| 198510 | -0.4 |
| 198511 | -0.2 |
| 198512 | +0.2 |
| 198601 | +1.0 |
| 198602 | -1.0 |
| 198603 | +0.5 |
| 198604 | +0.3 |
| 198605 | -0.2 |
| 198606 | +1.0 |
| 198607 | +0.3 |
| 198608 | -0.4 |
| 198609 | -0.5 |
| 198610 | +0.6 |
| 198611 | -1.2 |
| 198612 | -1.4 |
| 198701 | -0.7 |
| 198702 | -1.2 |
| 198703 | -1.3 |
| 198704 | -1.4 |
| 198705 | -1.3 |
| 198706 | -1.1 |
| 198707 | -1.4 |
| 198708 | -0.9 |
| 198709 | -1.0 |
| 198710 | -0.4 |
| 198711 | 0.0 |
| 198712 | -0.5 |
| 198801 | -0.1 |
| 198802 | -0.4 |
| 198803 | +0.6 |
| 198804 | +0.1 |
| 198805 | +0.9 |
| 198806 | +0.1 |
| 198807 | +1.0 |
| 198808 | +1.5 |
| 198809 | +1.8 |
| 198810 | +1.4 |
| 198811 | +1.7 |
| 198812 | +1.2 |
| 198901 | +1.5 |
| 198902 | +1.2 |
| 198903 | +1.1 |
| 198904 | +1.6 |
| 198905 | +1.2 |
| 198906 | +0.7 |
| 198907 | +0.9 |
| 198908 | -0.3 |
| 198909 | +0.5 |
| 198910 | +0.8 |
| 198911 | -0.2 |
| 198912 | -0.5 |
| 199001 | -0.1 |
| 199002 | -1.8 |
| 199003 | -0.4 |
| 199004 | +0.2 |
| 199005 | +1.2 |
| 199006 | +0.3 |
| 199007 | +0.5 |
| 199008 | -0.2 |
| 199009 | -0.7 |
| 199010 | +0.3 |
| 199011 | -0.5 |
| 199012 | -0.2 |
| 199101 | +0.6 |
| 199102 | +0.3 |
| 199103 | -0.7 |
| 199104 | -0.6 |
| 199105 | -1.0 |
| 199106 | -0.1 |
| 199107 | 0.0 |
| 199108 | -0.4 |
| 199109 | -1.5 |
| 199110 | -1.0 |
| 199111 | -0.7 |
| 199112 | -1.8 |
| 199201 | -2.9 |
| 199202 | -0.9 |
| 199203 | -2.0 |
| 199204 | -1.0 |
| 199205 | +0.3 |
| 199206 | -0.6 |
| 199207 | -0.6 |
| 199208 | +0.4 |
| 199209 | +0.1 |
| 199210 | -1.4 |
| 199211 | -0.7 |
| 199212 | -0.6 |
| 199301 | -0.9 |
| 199302 | -0.7 |
| 199303 | -0.5 |
| 199304 | -1.2 |
| 199305 | -0.3 |
| 199306 | -0.8 |
| 199307 | -0.8 |
| 199308 | -0.9 |
| 199309 | -0.7 |
| 199310 | -1.1 |
| 199311 | -0.1 |
| 199312 | +0.2 |
| 199401 | -0.1 |
| 199402 | +0.3 |
| 199403 | -0.7 |
| 199404 | -1.3 |
| 199405 | -0.7 |
| 199406 | -0.4 |
| 199407 | -1.3 |
| 199408 | -1.2 |
| 199409 | -1.6 |
| 199410 | -1.1 |
| 199411 | -0.6 |
| 199412 | -1.2 |
| 199501 | -0.4 |
| 199502 | -0.1 |
| 199503 | +0.8 |
| 199504 | -0.7 |
| 199505 | -0.4 |
| 199506 | +0.1 |
| 199507 | +0.4 |
| 199508 | +0.3 |
| 199509 | +0.3 |
| 199510 | 0.0 |
| 199511 | 0.0 |
| 199512 | -0.5 |
| 199601 | +1.0 |
| 199602 | +0.3 |
| 199603 | +1.1 |
| 199604 | +0.8 |
| 199605 | +0.3 |
| 199606 | +1.2 |
| 199607 | +0.7 |
| 199608 | +0.7 |
| 199609 | +0.6 |
| 199610 | +0.6 |
| 199611 | -0.1 |
| 199612 | +0.9 |
| 199701 | +0.5 |
| 199702 | +1.7 |
| 199703 | -0.4 |
| 199704 | -0.6 |
| 199705 | -1.3 |
| 199706 | -1.4 |
| 199707 | -0.8 |
| 199708 | -1.4 |
| 199709 | -1.4 |
| 199710 | -1.5 |
| 199711 | -1.2 |
| 199712 | -1.0 |
| 199801 | -2.7 |
| 199802 | -2.0 |
| 199803 | -2.4 |
| 199804 | -1.4 |
| 199805 | +0.3 |
| 199806 | +1.0 |
| 199807 | +1.2 |
| 199808 | +1.2 |
| 199809 | +1.0 |
| 199810 | +1.1 |
| 199811 | +1.0 |
| 199812 | +1.4 |
| 199901 | +1.8 |
| 199902 | +1.0 |
| 199903 | +1.3 |
| 199904 | +1.4 |
| 199905 | +0.2 |
| 199906 | +0.3 |
| 199907 | +0.5 |
| 199908 | +0.4 |
| 199909 | -0.1 |
| 199910 | +1.0 |
| 199911 | +1.0 |
| 199912 | +1.4 |
| 200001 | +0.7 |
| 200002 | +1.7 |
| 200003 | +1.3 |
| 200004 | +1.2 |
| 200005 | +0.4 |
| 200006 | -0.2 |
| 200007 | -0.2 |
| 200008 | +0.7 |
| 200009 | +0.9 |
| 200010 | +1.1 |
| 200011 | +1.8 |
| 200012 | +0.8 |
| 200101 | +1.0 |
| 200102 | +1.7 |
| 200103 | +0.9 |
| 200104 | +0.2 |
| 200105 | -0.5 |
| 200106 | +0.3 |
| 200107 | -0.2 |
| 200108 | -0.4 |
| 200109 | +0.2 |
| 200110 | 0.0 |
| 200111 | +0.7 |
| 200112 | -0.8 |
| 200201 | +0.4 |
| 200202 | +1.1 |
| 200203 | -0.2 |
| 200204 | -0.1 |
| 200205 | -0.8 |
| 200206 | -0.2 |
| 200207 | -0.5 |
| 200208 | -1.0 |
| 200209 | -0.6 |
| 200210 | -0.4 |
| 200211 | -0.5 |
| 200212 | -1.1 |
| 200301 | -0.2 |
| 200302 | -0.7 |
| 200303 | -0.3 |
| 200304 | -0.1 |
| 200305 | -0.3 |
| 200306 | -0.6 |
| 200307 | +0.3 |
| 200308 | +0.1 |
| 200309 | -0.1 |
| 200310 | 0.0 |
| 200311 | -0.3 |
| 200312 | +1.1 |
| 200401 | -1.3 |
| 200402 | +1.2 |
| 200403 | +0.4 |
| 200404 | -0.9 |
| 200405 | +1.0 |
| 200406 | -0.8 |
| 200407 | -0.5 |
| 200408 | -0.3 |
| 200409 | -0.3 |
| 200410 | -0.1 |
| 200411 | -0.7 |
| 200412 | -0.8 |
| 200501 | +0.3 |
| 200502 | -3.1 |
| 200503 | +0.3 |
| 200504 | -0.6 |
| 200505 | -0.8 |
| 200506 | +0.4 |
| 200507 | +0.2 |
| 200508 | -0.3 |
| 200509 | +0.4 |
| 200510 | +1.2 |
| 200511 | -0.2 |
| 200512 | 0.0 |
| 200601 | +1.7 |
| 200602 | +0.1 |
| 200603 | +1.8 |
| 200604 | +1.1 |
| 200605 | -0.5 |
| 200606 | -0.2 |
| 200607 | -0.6 |
| 200608 | -1.0 |
| 200609 | -0.6 |
| 200610 | -1.3 |
| 200611 | +0.1 |
| 200612 | -0.3 |
| 200701 | -0.8 |
| 200702 | -0.1 |
| 200703 | +0.2 |
| 200704 | -0.1 |
| 200705 | -0.1 |
| 200706 | +0.5 |
| 200707 | -0.3 |
| 200708 | +0.4 |
| 200709 | +0.2 |
| 200710 | +0.7 |
| 200711 | +0.9 |
| 200712 | +1.7 |
| 200801 | +1.8 |
| 200802 | +2.6 |
| 200803 | +1.4 |
| 200804 | +0.7 |
| 200805 | -0.1 |
| 200806 | +0.6 |
| 200807 | +0.3 |
| 200808 | +1.0 |
| 200809 | +1.2 |
| 200810 | +1.3 |
| 200811 | +1.3 |
| 200812 | +1.4 |
| 200901 | +1.1 |
| 200902 | +1.9 |
| 200903 | +0.4 |
| 200904 | +0.8 |
| 200905 | -0.1 |
| 200906 | +0.1 |
| 200907 | +0.2 |
| 200908 | -0.2 |
| 200909 | +0.3 |
| 200910 | -1.2 |
| 200911 | -0.6 |
| 200912 | -0.7 |
| 201001 | -1.1 |
| 201002 | -1.5 |
| 201003 | -0.7 |
| 201004 | +1.2 |
| 201005 | +0.9 |
| 201006 | +0.4 |
| 201007 | +1.8 |
| 201008 | +1.8 |
| 201009 | +2.2 |
| 201010 | +1.7 |
| 201011 | +1.3 |
| 201012 | +2.9 |
| 201101 | +2.3 |
| 201102 | +2.7 |
| 201103 | +2.5 |
| 201104 | +1.9 |
| 201105 | +0.4 |
| 201106 | +0.2 |
| 201107 | +1.0 |
| 201108 | +0.4 |
| 201109 | +1.0 |
| 201110 | +0.8 |
| 201111 | +1.1 |
| 201112 | +2.5 |
| 201201 | +1.1 |
| 201202 | +0.5 |
| 201203 | +0.7 |
| 201204 | -0.3 |
| 201205 | 0.0 |
| 201206 | -0.4 |
| 201207 | 0.0 |
| 201208 | -0.2 |
| 201209 | +0.2 |
| 201210 | +0.3 |
| 201211 | +0.3 |
| 201212 | -0.6 |
| 201301 | -0.1 |
| 201302 | -0.2 |
| 201303 | +1.5 |
| 201304 | +0.2 |
| 201305 | +0.8 |
| 201306 | +1.2 |
| 201307 | +0.8 |
| 201308 | +0.2 |
| 201309 | +0.3 |
| 201310 | -0.1 |
| 201311 | +0.7 |
| 201312 | +0.1 |
| 201401 | +1.4 |
| 201402 | +0.1 |
| 201403 | -0.9 |
| 201404 | +0.8 |
| 201405 | +0.5 |
| 201406 | +0.2 |
| 201407 | -0.2 |
| 201408 | -0.7 |
| 201409 | -0.7 |
| 201410 | -0.6 |
| 201411 | -0.9 |
| 201412 | -0.6 |
| 201501 | -0.8 |
| 201502 | +0.2 |
| 201503 | -0.7 |
| 201504 | 0.0 |
| 201505 | -0.7 |
| 201506 | -0.6 |
| 201507 | -1.1 |
| 201508 | -1.4 |
| 201509 | -1.6 |
| 201510 | -1.7 |
| 201511 | -0.5 |
Calculation of SOI
Note the anomalies are departures from the 1951-1980 base period.
| SOI | = | (Standardized Tahiti - Standardized Darwin) |
|---|---|---|
| MSD |
where
| Standardized Tahiti | = | (Actual Tahiti SLP - Mean Tahiti SLP) |
|---|---|---|
| Standard Deviation Tahiti |
where
Standard Deviation Tahiti =
where
N = number of months
and
| Standardized Darwin | = | (Actual Darwin SLP - Mean Darwin SLP) |
|---|---|---|
| Standard Deviation Darwin |
where
Standard Deviation Darwin =
where
N = number of months
and
MSD = Monthly Standard Deviation =
where
N = number of summed months