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The scikits.hydroclimpy.enso module provides two functions to create some standard ENSOIndicator objects from online data repository. For convenience, online data are downloaded the first time they are accessed, and then a local copy is used instead.

Indicators based on the data of the Japanese Meteorological Association (JMA) can be accessed with the load_jma function. The data is based on the Sea Surface Temperature (SST) anomalies recorded in the Niño-3 region of the Pacific Ocean (5N-5S, 150W-90W). Three different data sets can be used:

  • the COAPS dataset uses a slightly narrower area than Niño-3 (4N-4S instead of 5N-5S). Monthly mean SSTs were computed on boxes of 2-deg latitude x 2-deg longitude over the given area. Normal mean SSTs were computed using 1961-1990 as a reference period and are reported in Table. The SST anomalies correspond therefore to the deviation of the monthly average SSTs from the normal SSTs. A 5-month running mean filter was then applied on the data. From January 1949 to present, the anomalies are based on the actual data. Before 1949, the anomalies are based on reconstructed monthly mean SST fields, computed using orthogonal projection technique, and using the same normal SSTs.
  • The Standard dataset is based on the data recorded over region Niño-3 by the JMA. Anomalies are computed using a fixed reference period of 1971-2000.
  • The Sliding dataset is similar to the Standard dataset, except that anomalies are computed as the deviations from a sliding 30 year average.

The Oceanic Nino Index (ONI) used by the Climate Prediction Center (CPC) for its previsions can be accessed with the load_oni function. The ONI is based on the 3-m running mean of ERSST.v3 SST anomalies in the Niño-3.4 region (5N-5S, 120W-170W), using the period 1971-2000 as a reference for the calculation of monthly normal SSTs.

load_jma(mode='COAPS', **options)

Load the JMA 5-month running mean monthly SST anomalies over the Nino-3 zone (5N-5S, 150W-90W) and returns a ENSOIndicator object. Three different modes are available:

coaps
The data is downloaded from the COAPS website.
standard
The data is downloaded from the JMA site and corresponds to the SST anomalies computed using a fixed reference period (1971-2000).
sliding
The data is also downloaded from the JMA site, but corresponds this time to anomalies computed using a sliding 30-year rule.

By default, the configuration options are read from the configuration file. These options can be overwritten by the optional input parameters.

Parameters:

mode : {‘coaps’,’standard’,’sliding’}, optional

Mode describing the data to download.

options : dictionary

Optional parameters to parse to the ENSOIndicator for the definition of ENSO indices.

thresholds : tuple

Low and high temperature thresholds for the definition of El Niño or La Niña conditions. By default, the JMA uses -0.5oC and +0.5oC.

minimum_size : int

Minimum number of consecutive months in El Niño/La Niña conditions required for the definition of an episode. By default, the JMA use 6 consecutive months.

reference_season : string, tuple

Months that must be in an episode for it to be valid. By default, the original JMA COAPS index uses 'OND' (October to December included), while the newer COAPS index uses 'NDJ' (November to January included).

full_year : boolean

Whether episodes are defined from Oct. 1st to the following Sep. 30th, or last only until the SST anomalies conditions are no longer met. The original JMA COAPS index uses full_year=True, while the newer index uses full_year=False.

load_oni(mode='standard', **options)

Loads the ONI 3-m averaged monthly SST anomalies over the Niño-3.4 region and returns a ENSOIndicator object.

Two modes are accepted as arguments:

  • in the standard mode, the SSTs are retrieved from the original CPC website. Data are available from Jan. 1950 to present.
  • in the backup mode, the SSTs are retrieved from the CPC ftp site. Data are available from Jan. 1900 to present.
Parameters:

mode : {‘standard’,’backup’}, optional

Mode describing the data to download.

options : dictionary

Optional parameters to parse to the ENSOIndicator for the definition of ENSO indices.

thresholds : tuple of floats, optional

Low and high temperature thresholds for the definition of El Niño and La Niña conditions. By default, the CPC uses -0.5oC and +0.5oC.

minimum_size : int, optional

Minimum number of consecutive months in El Niño / La Niña conditions required for the definition of an episode. By default, the CPC use 5 consecutive months.

reference_season : string or tuple, optional

Months that must be in an episode for it to be valid. By default, the CPC uses None (no restriction on the months).

full_year : boolean, optional

The CPC uses full_year=False.

References

Xue, Y., T. M. Smith, and R. W. Reynolds, 2003: Interdecadal changes of 30-yr SST normals during 1871-2000. J. Climate, 16, 1601-1612.