easyclimate.field.teleconnection.index_pna

Pacific/North American (PNA) Index

The Pacific/North American teleconnection pattern (PNA) is one of the most prominent modes of low-frequency variability in the Northern Hemisphere extratropics. The positive phase of the PNA pattern features above-average heights in the vicinity of Hawaii and over the intermountain region of North America, and below-average heights located south of the Aleutian Islands and over the southeastern United States. The PNA pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. The positive phase is associated with an enhanced East Asian jet stream and with an eastward shift in the jet exit region toward the western United States. The negative phase is associated with a westward retraction of that jet stream toward eastern Asia, blocking activity over the high latitudes of the North pacific, and a strong split-flow configuration over the central North Pacific.

The positive phase of the PNA pattern is associated with above-average temperatures over western Canada and the extreme western United States, and below-average temperatures across the south-central and southeastern U.S. The PNA tends to have little impact on surface temperature variability over North America during summer. The associated precipitation anomalies include above-average totals in the Gulf of Alaska extending into the Pacific Northwestern United States, and below-average totals over the upper Midwestern United States.

Although the PNA pattern is a natural internal mode of climate variability, it is also strongly influenced by the El Niño/ Southern Oscillation (ENSO) phenomenon. The positive phase of the PNA pattern tends to be associated with Pacific warm episodes (El Niño), and the negative phase tends to be associated with Pacific cold episodes (La Niña).

https://www.cpc.ncep.noaa.gov/data/teledoc/pna.shtml

Functions

calc_index_PNA_modified_pointwise(, lon_dim, lat_dim, ...)	The calculation of monthly mean PNA index is constructed by following modified pointwise method:
calc_index_PNA_Wallace_Gutzler_1981(, lon_dim, ...)	The calculation of monthly mean PNA index using Pointwise method following Wallace and Gutzler (1981):
calc_index_PNA_NH_REOF(, lon_dim, lat_dim, lat_range, ...)	The calculation of monthly mean PNA index using rotated empirical orthogonal functions (REOFs) method over the entire Northern Hemisphere:

Module Contents

easyclimate.field.teleconnection.index_pna.calc_index_PNA_modified_pointwise(z_monthly_data: xarray.DataArray, time_range: slice = slice(None, None), lon_dim: str = 'lon', lat_dim: str = 'lat', time_dim: str = 'time', normalized: bool = True) → xarray.DataArray

The calculation of monthly mean PNA index is constructed by following modified pointwise method:

\[\mathrm{PNA = Z^*(15^{\circ}N-25^{\circ}N,180-140^{\circ}W)-Z^*(40^{\circ}N-50^{\circ}N,180-140^{\circ}W)+Z^*(45^{\circ}N-60^{\circ}N,125^{\circ}W-105^{\circ}W)-Z^*(25^{\circ}N-35^{\circ}N,90^{\circ}W-70^{\circ}W)}\]

where \(Z^*\) denotes monthly mean 500 hPa height anomaly.

Parameters

z_monthly_data: xarray.DataArray.

The monthly geopotential height. The 500hPa layer is recommended.

time_range: slice, default: slice(None, None).

The time range of seasonal cycle means to be calculated. The default value is the entire time range.

lon_dim: str, default: lon.

Longitude coordinate dimension name. By default extracting is applied over the lon dimension.

lat_dim: str, default: lat.

Latitude coordinate dimension name. By default extracting is applied over the lat dimension.

time_dim: str, default: time.

The time coordinate dimension name.

normalized: bool, default True, optional.

Whether to standardize the index based on standard deviation over time_range.

Returns

The monthly mean PNA index (xarray.DataArray).

Reference

• https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/month_pna_index2.shtml

easyclimate.field.teleconnection.index_pna.calc_index_PNA_Wallace_Gutzler_1981(z_monthly_data: xarray.DataArray, time_range: slice = slice(None, None), lon_dim: str = 'lon', lat_dim: str = 'lat', time_dim: str = 'time', normalized: bool = True) → xarray.DataArray

The calculation of monthly mean PNA index using Pointwise method following Wallace and Gutzler (1981):

\[\mathrm{PNA = Z^*(20^{\circ}N,160^{\circ}W)-Z^*(45^{\circ}N,165^{\circ}W)+Z^*(55^{\circ}N,115^{\circ}W)-Z^*(30^{\circ}N,85^{\circ}W)}\]

where \(Z^*\) denotes monthly mean 500 hPa height anomaly.

Parameters

z_monthly_data: xarray.DataArray.

The monthly geopotential height. The 500hPa layer is recommended.

time_range: slice, default: slice(None, None).

The time range of seasonal cycle means to be calculated. The default value is the entire time range.

lon_dim: str, default: lon.

Longitude coordinate dimension name. By default extracting is applied over the lon dimension.

lat_dim: str, default: lat.

Latitude coordinate dimension name. By default extracting is applied over the lat dimension.

time_dim: str, default: time.

The time coordinate dimension name.

normalized: bool, default True, optional.

Whether to standardize the index based on standard deviation over time_range.

Returns

The monthly mean PNA index (xarray.DataArray).

Reference

• Wallace, J. M., & Gutzler, D. S. (1981). Teleconnections in the Geopotential Height Field during the Northern Hemisphere Winter. Monthly Weather Review, 109(4), 784-812.

• https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/month_pna_index2.shtml

easyclimate.field.teleconnection.index_pna.calc_index_PNA_NH_REOF(z_monthly_data: xarray.DataArray, time_range: slice = slice(None, None), lon_dim: str = 'lon', lat_dim: str = 'lat', lat_range: slice = slice(20, 85), time_dim: str = 'time', random_state=None, solver: Literal['auto', 'full', 'randomized'] = 'auto', solver_kwargs: dict = {}, normalized: bool = True) → xarray.DataArray

The calculation of monthly mean PNA index using rotated empirical orthogonal functions (REOFs) method over the entire Northern Hemisphere:

Parameters

z_monthly_data: xarray.DataArray.

The monthly geopotential height. The 500hPa layer is recommended.

time_range: slice, default: slice(None, None).

The time range of seasonal cycle means to be calculated. The default value is the entire time range.

lon_dim: str, default: lon.

Longitude coordinate dimension name. By default extracting is applied over the lon dimension.

lat_dim: str, default: lat.

Latitude coordinate dimension name. By default extracting is applied over the lat dimension.

lat_range: slice, default: slice(20, 85).

The latitude range of computation using REOFs over the Northern Hemisphere. The default value is from \(\mathrm{20^{\circ}N}\) to \(\mathrm{85^{\circ}N}\).

time_dim: str, default: time.

The time coordinate dimension name.

random_state: int, default None.

Seed for the random number generator.

solver: {“auto”, “full”, “randomized”}, default: “auto”.

Solver to use for the REOFs computation.

solver_kwargs: dict, default {}.

Additional keyword arguments to be passed to the REOFs solver.

normalized: bool, default True, optional.

Whether to standardize the index based on standard deviation over time_range.

Returns

The monthly mean PNA index (xarray.DataArray).

Reference

• Rodionov, S., & Assel, R. (2001). A new look at the Pacific/North American index. Geophysical Research Letters, 28(8), 1519-1522.

• Soulard, N., Lin, H. The spring relationship between the Pacific-North American pattern and the North Atlantic Oscillation. Clim Dyn 48, 619–629 (2017).

• https://www.ncei.noaa.gov/access/monitoring/pna/

• https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/history/method.shtml

See also

get_REOF_model