npi_monthly: NPI - North Pacific Index monthly values

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

NPI – North Pacific Index monthly values

Description

The North Pacific index measures interannual to decadal variations in atmospheric circulation across the North Pacific.

Usage

npi_monthly

Format

A tibble also of class 'pacea_index' with columns:

year:

year of value

month:

month (1 to 12) of value

val:

absolute monthly value (average?), hPa, with an 'NA' for December 1944

Details

The North Pacific Index (NPI) is the area-weighted sea level pressure over the region 30 deg N to 65 deg N, 160 deg E to 140 deg W. The dominant atmosphere-ocean relation in the North Pacific is one where atmospheric changes lead changes in sea surface temperatures (SST) by one to two months. However, strong ties exist with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Taken from ##' https://climatedataguide.ucar.edu/climate-data/north-pacific-np-index-trenberth-and-hurrell-monthly-and-winter

Key reference is Trenberth and Hurrell (1994): Decadal atmosphere-ocean variations in the Pacific, Climate Dynamics 9:303-319. Above website suggest to reference the data as: North Pacifi Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA, Trenberth and Hurrell (1994). Updated Regularly. Accessed DD Month YYYY (you can check the date that 'npi_annual.rda' or 'npi_monthly.rda' was last saved in pacea at https://github.com/pbs-assess/pacea/tree/main/data).

'npi_monthly' contains monthly absolute values. Annual average winter values and anomalies are in 'npi_annual'.

Ross and Robert (2022; see '?oni' for reference): The NPI is a useful indicator of the intensity and real extent of the Aleutian Low Pressure system. The NPI was generally positive from 1950 to 1976, and generally negative (red) from 1977 to 2008; a change than can be attributed to the strengthening of the Aleutian Low Pressure system after 1977. From 2008 to present [2021], the NPI was mostly positive, due to weaker Aleutian Lows. The NPI anomaly, plotted in Figure 7-2 [of Ross and Robert (2022)], was calculated from the NPI by removing the 1950-2018 mean.

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: 
npi_monthly
plot(npi_annual)
plot(npi_monthly,
  value = "value",    # plot the absolute value as no anomaly defined
  style = "plain",    # plot a plain line, not the red-blue style
  ylab = "North Pacific Index (absolute, hPa)") # Refine label

## End(Not run)

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