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snindex_yrmo

Calculates the Southern Oscillation Index and the noise index given two series of year-month values.

Prototype

	function snindex_yrmo (
		slpt      [*][*] : numeric,  
		slpd      [*][*] : numeric,  
		iprnt        [1] : integer,  
		soi_noise [*][*] : float     ; or double
	)

	return_val [dimsizes(slpt)] :  float or double

Arguments

slpt

A two-dimensional array of monthly data from station/grid point 1. Dimensions must be number of years by number of months.

slpd

A two-dimensional array of monthly data from station/grid point 2 (must have same dimensions as slpt).

iprnt

A scalar indicating whether to print information (0 means do not print).

soi_noise

(output)
A two-dimensional array of noise index (same dimension as slpt, slpd). Space for this variable must be explicitly allocated by the user (see example 1 below).

Return value

This function returns a two-dimensional array with the same dimensions as slpt and slpd. The output array will be double if slpt or slptd are double, and float otherwise.

The attributes long_name, short_name, and units are returned as well.

Description

Given two series of year-month values (e.g slp), this function calculates an "index" (e.g. Southern Oscillation Index). The overall anomaly standard deviation is used to normalize the anomalies.

Examples

Note: these code snippets contain examples of both functions sindex_yrmo and snindex_yrmo.

Example 1

begin
  nmos    = 12                         ; number of months
  nyrstrt = 1880                       ; first year of data
  nyrlast = 1997                       ; last year with data
  nyrs    = (nyrlast-nyrstrt+1)        ; total number of years
  xmsg    = -999.9                     ; missing value
  ncol    = nmos+1                     ; number of columns
  iprnt   = 1                          ; print soi out

; ================================>  ; READ THE ASCII FILES
  filet = asciiread ("tahiti.slp",(/nyrs,ncol/), "float")
  filed = asciiread ("darwin.slp",(/nyrs,ncol/), "float")
                                     ; create vector/arrays
  yr   = filet(:,0 )                   ; vector containing the years
  slpt = filet(:,1:)                   ; tahiti slp
  slpd = filed(:,1:)                   ; darwin slp
  slpt@_FillValue = xmsg
  slpd@_FillValue = xmsg

  soi = sindex_yrmo (slpt,slpd,iprnt)
  print("soi@_FillValue=" + soi@_FillValue)
  print(soi@long_name)
  print(soi@short_name)
  print(soi@units)

  xoi_noise = new ( (/nyrs,nmos/), float  )
  xoi = snindex_yrmo(slpt,slpd,iprnt,xoi_noise)
  print(xoi@long_name)
  print(xoi@short_name)
  print(xoi@units)
end

Example 2

Assume slp is dimensioned time x lat x lon and that the "time" dimension spans full years (i.e. for 50 years there are 12*50=600 time steps). Further assume the two grid points be at (lat1,lon1) and (lat2,lon2). Then:

   ntim = dimsizes(time)
   nyrs = ntim/12
   nmos = 12

   index = sindex_yrmo( onedtond(slp(:,{lat1},{lon1}), (/nyrs,nmos/))   \
                      , onedtond(slp(:,{lat2},{lon2}), (/nyrs,nmos/)), 0) 
   index@long_name = "my favorite index"
   index!0    = "time"
   index&time = time

Example 3

Same as example 2, but calculate signal and noise: