1 Descriptive Section

1.1 Indicator category

Habitat-Physical

1.2 Indicator name

Southern Oscillation Index

Includes variable(s): ALL

1.3 Indicator brief description

The Southern Oscillation Index (SOI) measures differences over time in sea level air pressure between the central (Tahiti) and western (Darwin, Australia) tropical Pacific.

1.4 Indicator visualization

The SOI oscillates between negative (pressure higher at Darwin Australia, often associated with warmer ocean water El Niño conditions) and positive (pressure higher over Tahiti, often associated with cooler ocean water La Niña conditions) phases every 2-7 years, and was in a positive phase as of late 2025.

2 SMART Attribute Section

2.1 Indicator documentation

2.1.1 Are indicators available for others to use (data downloadable)?

Yes

2.1.1.1 Where can indicators be found?

All marea indicators are here: https://github.com/MarEcosystemApproaches/marea

2.1.1.2 How often are they updated? Are future updates likely?

Unknown

2.1.1.3 Who is the contact?

Jamie C. Tam jamie.tam@dfo-mpo.gc.ca

2.1.2 Gather indicator statistics

2.1.2.1 Units

Indicator	Units
Southern Oscillation Index

2.1.2.2 Length of time series, start and end date, periodicity

General overview: Annual and Monthly

Indicator specifics:

Indicator	EPU	StartYear	EndYear
Southern Oscillation Index	Equatorial Pacific	1951	2025

2.1.2.3 Spatial location, scale and extent

General overview: Tahiti-Darwin (SLP diff)

Indicator specifics:

Indicator	EPU
Southern Oscillation Index	Equatorial Pacific

2.1.2.4 Management scale: all species, FMP level, species level, can it be aggregated or separated to different scales?

Basinwide scale applying to the entire Pacific with potential teleconnections to the Atlantic; cannot be aggregated or separated.

2.1.2.5 Uncertainty metrics

Uncertainty is captured in these variables:

character(0)

2.1.3 Are methods clearly documented to obtain source data and calculate indicators?

No methods documentation is provided

2.1.3.1 Can the indicator be calculated from current documentation?

No. No methods documentation is provided

2.1.3.2 Is code publicly available? up to date?

No. No link to code in metadata

2.1.4.2 How/by whom are source data updated? Are future updates likely?

No. No source data steward information

2.1.4.3 How often are they updated?

Monthly (https://www.cpc.ncep.noaa.gov/data/indices/Readme.index.shtml ) Current data lag by 1 month from present.

2.2 Indicator analysis/testing or history of use

2.2.1 What decision or advice processes are the indicators currently used in?

None known in the Mid-Atlantic.

2.2.2 What implications of the indicators are currently listed?

This is one indicator of the El Niño/Southern Oscillation (ENSO) pattern that affects atmospheric patterns and weather conditions globally. To declare El Niño or La Niña conditions, the SIO and ENSO sea surface temperature indicators need to be synchronized. See https://www.climate.gov/news-features/understanding-climate/climate-variability-southern-oscillation-index. Different regions can experience unusual flooding or droughts as a result of the ENSO conditions and their effects on winds, upwelling, water temperature, and changes in atmospheric pressure affecting precipitation. While drought or flooding could occur anytime, regional events may be more predictable during one phase or the other of SIO and ENSO. See https://www.ncei.noaa.gov/access/monitoring/enso/ and https://iri.columbia.edu/our-expertise/climate/enso/why-do-we-care-about-el-nino-and-la-nina/

2.2.3 Do target, limit, or threshold values already exist for the indicator?

Yes, criteria for this indicator (in combination with ENSO sea surface temperature indicators) are established to establish the current phase of ENSO conditions.

2.2.4 Have the indicators been tested to ensure they respond proportionally to a change in the underlying process?

Yes, but generally other ENSO indicators are compared against the SOI for predicting El Niño, La Niña, or neutral conditions. See https://journals.ametsoc.org/view/journals/clim/16/8/1520-0442_2003_16_1249_aqeoei_2.0.co_2.xml

2.2.5 Are the indicators sensitive to a small change in the process, or what is the threshold of change that is detectable?

Unknown, may depend on how data are aggregated into the index

2.2.6 Is there a time lag between the process change and the indicator change? How long?