ao: AO - Arctic Oscillation

In pbs-assess/PACea: An R package of Pacific ecosystem information to help facilitate an ecosystem approach to fisheries management

AO - Arctic Oscillation

Description

The Arctic Oscillation (AO) is a back-and-forth shifting of atmospheric pressure between the Arctic and the mid-latitudes of the North Pacific and North Atlantic.

Usage

ao

Format

A tibble also of class 'pacea_index' with columns:

year:

year of value

month:

month (1 to 12) of value

anomaly:

The AO index is defined using the daily or monthly 1000 hPa geopotential height anomalies from latitudes 20 deg N to 90 deg N. The anomalies are projected onto the AO loading pattern, which is defined as the first empirical orthogonal function of monthly mean 1000 hPa geopotential height during the 1979-2000 period. The time series is then normalized with the monthly mean index's standard deviation. Such normalised monthly anomalies are given here.

Details

The most obvious reflection of the phase of the AO is the north-to-south location of the storm-steering, mid-latitude jet stream. Thus, the AO can have a strong influence on weather and climate in major population centers in North America, Europe, and Asia, especially during winter. A strongly positive AO is characterized by lower-than-average air pressure over the Arctic paired with higher-than-average pressure over the northern Pacific and Atlantic Oceans. The jet stream is farther north than average under these conditions, and storms can be shifted northward of their usual paths. Thus, the mid-latitudes of North America, Europe, Siberia, and East Asia generally see fewer cold air outbreaks than usual during the positive phase of the AO.

Conversely, AO's negative phase has higher-than-average air pressure over the Arctic region and lower-than-average pressure over the northern Pacific and Atlantic Oceans. The jet stream shifts toward the equator under these conditions, so the globe-encircling river of air is south of its average position. Consequently, locations in the mid-latitudes are more likely to experience outbreaks of frigid, polar air during winters when the AO is negative. In New England, for example, higher frequencies of coastal storms known as "Nor'easters" are linked to AO's negative phase.

Above adapted from https://www.climate.gov/news-features/understanding-climate/climate-variability-arctic-oscillation

Also see https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/history/method.shtml https://en.wikipedia.org/wiki/Arctic_oscillation

For reference see Thompson, D.W.J., and J.M. Wallace, 2001: Regional Climate Impacts of the Northern Hemisphere Annular Mode. Science, 293, 85-89. and other references on the above websites.

Associated code adapted from code generously shared by Chris Rooper.

Author(s)

Andrew Edwards

Source

Generated from running 'data-raw/coastwide-indices/coastwide-indices.R'.

Examples

## Not run: 
ao
plot(ao)
plot(ao, smooth_over_year=TRUE)

## End(Not run)

pbs-assess/PACea documentation built on April 17, 2025, 11:36 p.m.