DART retrieves several basin-scale indices from the NOAA Physical Sciences Laboratory and reproduces one index (Johnstone and Mantua 2014) using sea surface temperature data from NOAA NCEI. These basin-scale indices are updated on DART monthly and as data are made available from their sources. Each basin-scale index is described in more detail below.

MEI v2

“The bi-monthly Multivariate El Niño/Southern Oscillation (ENSO) index (MEI.v2) is the time series of the leading combined Empirical Orthogonal Function (EOF) of five different variables (sea level pressure (SLP), sea surface temperature (SST), zonal and meridional components of the surface wind, and outgoing longwave radiation (OLR)) over the tropical Pacific basin (30°S-30°N and 100°E-70°W). The EOFs are calculated for 12 overlapping bi-monthly 'seasons' (Dec-Jan, Jan-Feb, Feb-Mar,..., Nov-Dec) in order to take into account ENSO's seasonality, and reduce effects of higher frequency intraseasonal variability.” (MEI.v2: NOAA Physical Sciences Laboratory) The values of the MEI.v2 are available at a monthly timestep from 1979 to present.

Niño 3.4

The values of the Nino 3.4 index are “SST anomalies averaged over the NINO34 region 5°North-5°South;170-120°West … calculated from the Monthly NOAA ERSST V5 (at NOAA/CPC).” (Neutral ENSO Index Dashboard: NOAA Physical Sciences Laboratory) Niño 3.4 values are available at a monthly timestep from 1950 to present. More information can be found at Climate Prediction Center - Monitoring & Data: Current Monthly Atmospheric and Sea Surface Temperatures Index Values FAQ's and Niño 3.4 SST Index from the NOAA ERSST V5: NOAA Physical Sciences Laboratory.

NOI

The Northern Oscillation Index (NOI) “is an index of climate variability based on the difference in SLP anomalies at the North Pacific High and near Darwin Australia." (Neutral ENSO Index Dashboard: NOAA Physical Sciences Laboratory; Schwing et al, 2002) “NOI… [is] computed from NCEP sea level pressure anomalies (SLPA) (monthly sea level pressure minus climatology) of the North Pacific High (NPH) [35N,130W], … [and] Darwin [10S,130E].” (Extratropical-based Northern Oscillation Index, ERD, NOAA) In particular, NOI = SLPA_NPH - SLPDA_DARWIN. The values of the NOI are available at a monthly timestep from 1948 to present, as made available.

NPGO

“The North Pacific Gyre Oscillation [NPGO] ... is used as an index to measure changes in ocean currents and circulation patterns... It is significantly correlated with previously unexplained fluctuations of salinity, nutrients and chlorophyll-a… Fluctuations in the NPGO are driven by regional and basin-scale variations in wind-driven upwelling and horizontal advection.” (Ocean-Atmosphere Climate Indices, NOAA Fisheries) The values of the NPGO index are available at monthly granularity from 1950 to present. More information can be found at North Pacific Gyre Oscillation, Georgia Institute of Technology and North Pacific Gyre Oscillation (NPGO): NOAA Physical Sciences Laboratory.

ONI

The Oceanic Niño Index (ONI) is the “3 month running mean of ERSST.v5 SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW) … based on centered 30-year base periods updated every 5 years.” (NOAA, NWS, Climate Prediction Center, ONI) The values of the ONI are available at a monthly timestep from 1948 to present.

PDO

“The Pacific Decadal Oscillation (PDO) is defined by the leading pattern (EOF) of sea surface temperature (SST) anomalies in the North Pacific basin (typically, polewards of 20°N). The SST anomalies are obtained by removing both the climatological annual cycle and the global-mean SST anomaly from the data at each gridpoint.” (Pacific Decadal Oscillation (PDO): Definition and Indices | Climate Data Guide, NSF NCAR) The values of the PDO index are available at a monthly timestep from 1854 to present. More information can be found at https://www.ncei.noaa.gov/access/monitoring/pdo/.

PNA

“The [Pacific North American Index (PNA)] is one of the most prominent modes of extratropical variability in the northern Hemisphere. This version is calculated at NOAA/CPC. It is based on EOF's calculated from monthly anomalies of 500mb height from the NCEP Reanalysis.” (Neutral ENSO Index Dashboard: NOAA Physical Sciences Laboratory) The values of the PNA index are available at a monthly timestep from 1950 to present. More information can be found at NOAA, NWS, Climate Prediction Center - Teleconnections: Pacific North American Pattern.

SSTarc

This sea surface temperature index is a monthly mean of the ERSST (extended reconstructed sea surface temperature) anomaly summarized across the NE Pacific Arc, which “corresponds closely to the eastern pole of the PDO, stretching around the North American coast from Alaska to California and offshore toward Hawaii” (Johnstone and Mantua 2014). The values of the SSTarc index are available at a monthly timestep from 1900 to present. DART recalculates the SSTarc index using the gridded sea surface temperature data from ERRST v5. More information about ERSST is available at Extended Reconstructed Sea Surface Temperature (ERSST) | National Centers for Environmental Information (NCEI).