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month_to_annual

Converts monthly values to annual values.

Available in version 4.2.0.a033 or later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

	function month_to_annual (
		x       : numeric,  
		opt [1] : integer   
	)

Arguments

An array containing monthly values. The "time" dimension must be the leftmost dimension if there are multiple dimensions. Ideally, the size of the "time" dimension is evenly divisable by 12.

opt

option

      opt=0 compute the unweighted sum of 12 values. 
      opt=1 divide the unweighted sum by 12 to get the annual mean value(s)..

Return value

Returns an array with the "time" dimension is decimated by a factor of 12.

Description

Typical usage is that an array of monthly precipitation totals (eg, mm) or monthly mean temperatures are input. For precipitation, generally opt=0, and the sum of the 12 values is returned. For temperature, generally opt=1, and the (unweighted) annual average is returned.

Examples

Example 1

A one dimensional array of monthly precipitation totals [mm] is to be converted to annual total. If prc(time) and the size of time is 240 monthly values then 20 (=240/12) values (years) will be returned.

        prc_annual_total = month_to_annual(prc, 0)  ; prc_annual_total(20)

If the array contains, say, monthly mean temperatures (tmp), then

        tmp_annual_mean = month_to_annual(tmp, 1)   ; tmp_annual_mean(20)

Example 2

A multi-dimensional array of monthly precipitation totals [mm] is to be converted to annual total. If prc(time,lat,lon) and the size of time is 1200 monthly values then 100 (=120/12) values (years) will be returned.

        PRC = month_to_annual(prc, 0)  ; PRC(100,nlat,mlon)

If the array contains, say, monthly mean temperatures [tmp(time,lev,lat,lon)], then