Code covered by the BSD License  

Highlights from
Get El Niño Southern Oscillation Index values

Be the first to rate this file! 13 Downloads (last 30 days) File Size: 15.1 KB File ID: #38629
image thumbnail

Get El Niño Southern Oscillation Index values

by

 

15 Oct 2012 (Updated )

Get SOI (or ENSO) values as a time series from the year 1866 to present.

| Watch this File

File Information
Description

get_soi(start_date,end_date) retrieves monthly standardized values of the Southern Oscillation Index (SOI) computed by UCAR using the standardization approach outlined by Trenberth (1984) to maximize the signal. Note that SOI values prior to 1935 should be used with caution. There are questions regarding the consistency and quality of the Tahiti pressure values prior to 1935.

SOI or El Niño Southern Oscillation (ENSO) is a climatological pattern measured by pressure anomalies in the western Pacific Ocean. High positive values indicate a La Niña year, and low negative values indicate an El Niño year.

INPUT ARGUMENTS: (optional)
start_date = beginning date of range in Matlab's datenum format
             (e.g. datenum(1936,4,1) for April 1, 1936). Valid for
             Jan. 1866 or after, however values before 1935 are
             questionable. start_date is an optional input and can be
             used without declaring an end_date.

end_date = ending date of investigation period in Matlab's datenum
           format. end_date is an optional input.

OUTPUTS:
soi_ind = Standardized southern oscillation index time series.
soi_dates = corresponding date vector in Matlab's datenum format.

VALID SYNTAX INCLUDES:
soi_ind = get_soi; % (indices only, full historical range)
[soi_ind,soi_dates] = get_soi; % (indices & dates, full historical range)
[soi_ind,soi_dates] = get_soi(datenum(1936,4,1)); % Apr. 1936 to present
[soi_ind,soi_dates] = get_soi(datenum(1936,4,1),datenum('March 28, 2010'));

EXAMPLE 1:
[soi_ind,soi_dates] = get_soi;
figure
plot([soi_dates(1) soi_dates(end)],[0 0],'k'); hold on
plot(soi_dates,soi_ind,'b')
datetick
xlim([soi_dates(1) soi_dates(end)])
box off
text(0,.9,' La Nina years','units','normalized')
text(0,.1,' El Nino years','units','normalized')
ylabel('Standardized Southern Oscillation Index')

EXAMPLE 2:
(This example requires Signal Processing Toolbox, but the get_soi function does not.)

[soi_ind,soi_dates] = get_soi(datenum(1936,4,1));
figure
subplot(2,1,1)
plot([soi_dates(1) soi_dates(end)],[0 0],'k'); hold on
plot(soi_dates,soi_ind,'b')
datetick
xlim([soi_dates(1) soi_dates(end)])
box off
text(0,.9,' La Nina years','units','normalized')
text(0,.1,' El Nino years','units','normalized')
ylabel('Standardized SOI')
xlabel('year')

[Px_soi,f_soi] = pwelch(soi_ind(isfinite(soi_ind)),2^9,2^8,[],12);
subplot(2,1,2)
semilogx(f_soi,10*log10(abs(Px_soi)))
xlim([f_soi(1) f_soi(end)])
set(gca,'xtick',1./[10 7 5 4 3 2 1],'xticklabel',[10 7 5 4 3 2 1])
xlabel('oscillation period (years)')
ylabel('power spectrum (dB)')
box off

References:
Trenberth (1984), "Signal versus Noise in the Southern Oscillation"
Monthly Weather Review 112:326-332.

UCAR website http://www.cgd.ucar.edu/cas/catalog/climind/soi.html

Acknowledgements

Get Global Mean Sea Levels inspired this file.

This file inspired Get Land Surface Temperatures.

Required Products MATLAB
MATLAB release MATLAB 7.11 (R2010b)
Other requirements Requires an internet connection.
Tags for This File   Please login to tag files.
Please login to add a comment or rating.
Updates
16 Oct 2012

Clarified script documentation.

17 Oct 2012

Fixed a glitch related to the declaration of date ranges.

Contact us