NCL Home > Documentation > Functions > Climatology

smthClmDayTLL

Calculates a smooth mean daily annual cycle for an array nominally dimensioned (Time,Lat,Lon).

Prototype

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

	function smthClmDayTLL (
		clmDay [366][*][*] : float or double,  
		nHarm          [1] : integer           
	)

	return_val [366][*][*] :  typeof(clmDay)

Arguments

clmDay

A three-dimensional array (366, lat, lon) output by clmDayTLL.

nHarm

The number of harmonics that will be used to construct the smoothed mean annual cycle. Usually, nHarm is 1 to 3 with 2 being most common. A value of 2 means to use the annual and semi-annual harmonics only.

Return value

A climatological time series where the leftmost dimension refers to the sequential day of the year.

Description

Calculate a smooth annual cycle using the output from clmDayTLL. A Fourier analysis is performed via an FFT. Next, all harmonics greater than nHarm are set to zero and a backward transform is performed.

In 6.2.1, this function was updated to work on daily SST data which have _FillValue over land.

Examples

Example 1

Compute the smooth long term daily means. The input is daily 500 hPa heights spanning 1990-1999. The values are packed as type short and the time is in units "hours since 1-1-1 00:00:0".

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl" 
   :
   :
   diri    = "./"                             ; input directory   
   fili    = "HGT.nc"                         ; input file       
   f       = addfile (diri+fili , "r")                          
;***********************************************************
; Read time and create required yyyyddd                    
;***********************************************************
   time    = f->time                          ; time:units = "hours since 1-1-1 00:00:0.0"                               
   TIME    = cd_calendar(time, 0)          ; type float 
   year    = toint( TIME(:,0) )
   month   = toint( TIME(:,1) )
   day     = toint( TIME(:,2) ) 
   ddd     = day_of_year(year, month, day) 
   yyyyddd = year*1000 + ddd                                  ; needed for input
;***********************************************************
; Read data: short2flt                                     
;*********************************************************** 
   hgt     = short2flt( f->hgt(:,0,:,:) )    ; convert to float 
;***********************************************************
; Compute raw daily climatology  
;***********************************************************
   hClmDay    = clmDayTLL(hgt, yyyyddd)     ; daily climatology at each grid point                                      
;***********************************************************
; Compute smoothed daily climatology using 2 harmonics  
;***********************************************************
   hClmDay_sm = smthClmDayTLL(hClmDay, 2)  
   printVarSummary(hClmDay_sm)

The (edited) output yields