10 North Atlantic Oscillation Index

Data Type: Tabular Data

Spatial Scope: North Atlantic

Duration 1951-2024

Source: NOAA NCEP via azmpdata; https://www.ncei.noaa.gov/access/monitoring/nao/

10.1 Introduction to Indicator

The North Atlantic Oscillation (NAO) index is defined as the winter (December, January, February, March) 500 mb pressure Principal Component Analysis which is representative of the difference between the Icelandic low and Azores high.

The NAO in linked to several weather and climate phenomena in the North Atlantic, including speed and direction of westerly winds, storm activity, and precipitation patterns from the North American Eastern Seaboard to Europe and Siberia (Hurrell et al. 2003).

In Canada, high NAO values are typically associated with cold air and sea temperatures off the Eastern coast, northwest wind patterns, and ice in the Laborador and Newfoundland shelves, whereas low NAO values are associated with the opposite (Layton et al. 2025).

10.2 View Data

library(plotly)
plotly_df <- data@data %>%
  mutate(smooth_10yr = zoo::rollapply(anomaly_value, mean, width = 10, partial = TRUE),
         overall_mean = mean(anomaly_value))

p <- plot_ly(plotly_df, x = ~year) %>%
  add_lines(y = ~anomaly_value,
            name = "Yearly Anomaly",
            line = list(color = "lightgrey"),
            hovertemplate = "Monthly anomaly: %{y:.2f}<extra></extra>"
           ) %>%
  add_lines(y = ~smooth_10yr,
            name = "10-yr Smooth",
            line = list(color = "red", width = 2),
            hovertemplate = "10-yr smoothed: %{y:.2f}<extra></extra>",
           ) %>%
    add_lines(y = ~overall_mean,
            name = "Overall Mean",
            line = list(color = "black", width = 2, dash = "dash"),
            hovertemplate = "Overall Mean: %{y:.2f}<extra></extra>",
           ) %>%
  layout(
    title = "North Atlantic Oscillation Index for North Atlantic",
    xaxis = list(title = "Date"),
    yaxis = list(title = "NAO Index",
                 fixedrange = TRUE),
    hovermode = "x unified",
    margin = list( t = 80)
    
  ) %>%
  config(displayModeBar = FALSE) 

p

Figure 10.1: NAO Index Value; 1951-2024

10.3 Summary and Trends

Trend and summary values are automatically generated; data were last updated on marea package install on 2026-02-10

As of the most recent data entry in 2024, the NAO value is 1.21, which is high among values in the timeseries. The NAO is currently in a positive phase, and has been since 2011. The NAO value has shown an decreasing trend in recent years.

10.3.1 Summary Table

Summary values for the North Atlantic Oscillation Index are found in the table below (Table 10.1)

Table 10.1: Summary table of NAO values through time.

Metric	Value	Description
Most Recent Value (2024)	1.21	The most recent value is high within the timeseries, in the 83.78 percentile of all values.
Timeseries Record High	2.05	The highest value in the timeseries was recorded on 2015, and was 1.47 higher than the overall timeseries mean.
Timeseries Record Low	-1.03	The lowest value in the timeseries was recorded on 2010, and was 1.61 lower than the overall timeseries mean.

10.4 Relevance to Research and Stock Assessments

The NAO is closely linked to ecosystem and fisheries dynamics in the North Altantic, with variable impacts on the Northeast and Northwest.

In Canada, negative NAO values are associated with favorable conditions for important fisheries such as cod and other groundfish, whereas positive NAO values are associated with unfavorable conditions. Positiove NAO values drive stronger northwesterly winds off Eastern Canada, as well as colder sea temperatures, which are negatively associated with cod recruitment (Mann and Drinkwater 1994). Positive NAO values in the 1980s and 1990s are hypothesized to have contributed (along with overfishing) to the decline in cod in Eastern Canada during that time (Parsons and Lear 2001).

Conversely, cold conditions during positive NAO phases are favorable for recruitment of snow crabs on the Newfoundland and Labrador shelves. Following favorable early-life conditions, NAO values are correlated with exploitable biomass of snow crabs on a 6-8 year lag (Fisheries and Oceans Canada (DFO) 2022).

10.5 Variable Definitions

Table 10.2: Column names and definitions in the NAO dataset.

variable	description	unit
year	year of modeled value
anomaly_value	NAO anomaly

10.6 Additional Data

No additional data for NAO.

10.7 Get the Data

library(marea)
data('nao')
plot(nao)