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month_to_season

Computes a user-specified three-month seasonal mean (DJF, JFM, FMA, MAM, AMJ, MJJ, JJA, JAS, ASO, SON, OND, NDJ).

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function month_to_season (
		xMon    : numeric,  
		season  : string    
	)

	return_val  :  typeof(x)

Arguments

xMon

A one-, three-, or four-dimensional array [xMon(time) or xMon(time,lat,lon) or xMon(time,lev,lat,lon)] of any numeric type.

xMon must have named dimensions and the time (leftmost) dimension must be divisible by 12. The data are assumed to be monthly mean data and the first record is assumed to be January.

season

A string representing the season to calculate: e.g., "JFM", "JJA".

Return value

The return value will be of the same type and dimensionality as xMon, except the leftmost dimension will have been divided by 12.

If the input data contains metadata (e.g., coordinate variables and attributes), these will be retained. There is no output time dimension. The output contains only the season requested.

The attribute "NMO" is returned (for possible use in subscripting.)

Description

This function computes a user-specified three-month seasonal mean (DJF, JFM, FMA, MAM, AMJ, MJJ, JJA, JAS, ASO, SON, OND, NDJ). The first average (DJF=JF) and the last average (NDJ=ND) are actually two-month averages.

The following table shows how the output variable is dimensioned with respect to the input variable:

Input	Output
xMon(time)	xSea(time/12)
xMon(time,lat,lon)	xSea(time/12,lat,lon)
xMon(time,lev,lat,lon)	xSea(time/12,lev,lat,lon)

Examples

Example 1: Consider a three-dimensional array xMon(time,lat,lon). The "time" dimension must be divisible be 12. For example:

     Dimensions and sizes:   [time | 216] x [lat | 64] x [lon | 128]

Here 216/12=18 JJA seasons.

     xJJA = month_to_season (xMon, "JJA")

     printVarSummary(xJJA)

     print(xJJA&time+"   "+xJJA(:,n,m) )

The output would look like:

Variable: xJJA
 [snip]
Number of Dimensions: 3
Dimensions and sizes:   [time | 18] x [lat | 64] x [lon | 128]
Coordinates: 
            time: [197907..199607]
            lat: [-87.8638..87.8638]
            lon: [ 0..357.1875]
 [snip]

The output for one specific grid point is: