NCL Home > Documentation > Functions > Climatology

calcDayAnomTLL

Calculates daily anomalies from a daily data climatology.

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 calcDayAnomTLL (
		x        [*][*][*] : float or double,  
		yyyyddd        [*] : integer,          
		clmDay [366][*][*] : float or double   
	)

	return_val  :  dimsizes(x)

Arguments

A three-dimensional array (time, lat, lon) containing the raw daily data. The dimensions must be named.

yyyyddd

A one-dimensional array (same size as the "time" dimension of x) containing values of the form yyyy*1000 + Day_of_Year where yyyy is a year [eg: 1993] and ddd is the sequential day of the current year [eg: Jan01=>1, Jan31=>31, etc.

clmDay

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

Return value

A daily time series containing anomalies.

Description

Subtract the mean daily annual cycle from the raw daily data.


       x(time,lat,lon)  <==== input dimension order
       x!0 = "time"     <==== time is in days
       x!1 = "lat"
       x!2 = "lon"

non-Leap  yyyyddd
       1905001 =>  Jan  1, 1905
       1905032 =>  Feb  1, 1905
       1905059 =>  Feb 28, 1905
       1905060 =>  Mar  1, 1905
       1905365 =>  Dec 31, 1905

Leap      yyyyddd
       1908001 =>  Jan  1, 1908
       1908032 =>  Feb  1, 1908
       1908059 =>  Feb 28, 1908
       1908060 =>  Feb 29, 1908
       1908061 =>  Mar  1, 1908
       1908366 =>  Dec 31, 1908

Examples

Example 1

Compute daily anomalies using a climatology created by clmDayTLL or smthClmDayTLL. 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 
   printVarSummary( hgt ) 
;***********************************************************
; Compute daily climatology: raw and then 'smoothed'  
;***********************************************************
   hClmDay    = clmDayTLL(hgt, yyyyddd)     ; daily climatology at each grid point                                      
   printVarSummary(hClmDay)                                                                                              
;***********************************************************
; Compute smoothed daily climatology using 2 harmonics
;***********************************************************
   hClmDay_sm = smthClmDayTLL(hClmDay, 2)
   printVarSummary(hClmDay_sm)

;***********************************************************
; Compute daily anomalies using raw and smoothed daily climatologies
;***********************************************************
    hAnom      = calcDayAnomTLL (hgt, yyyyddd, hClmDay)     
    printVarSummary(hAnom_sm)
    printMinMax(hAnom, 0)

    hAnom_sm   = calcDayAnomTLL (hgt, yyyyddd, hClmDay_sm)     

    hAnom_sm@long_name = "Anomalies from Smooth Daily Climatology"
    printVarSummary(hAnom_sm)
    printMinMax(hAnom_sm, 0)

The (edited) output yields

Variable: hgt
Type: float
imensions and sizes:   [time | 3652] x [lat | 73] x [lon | 144]
Coordinates: 
            time: [17435256..17522880]
            lat: [90..-90]
            lon: [ 0..357.5]
Number Of Attributes: 16
  _FillValue :  1e+20
  level :       500
  long_name :   mean Daily Geopotential height

The raw daily climatology

Variable: hClmDay
Type: float
Total Size: 15389568 bytes
            3847392 values
Number of Dimensions: 3
Dimensions and sizes:   [year_day | 366] x [lat | 73] x [lon | 144]
Coordinates: 
            year_day: [1..366]
            lat: [90..-90]
            lon: [ 0..357.5]
Number Of Attributes: 4
  long_name :   Daily Climatology: mean Daily Geopotential height
  units :       m
  information : Raw daily averages across all years
  smoothing :   None

The smoothed daily climatology

Variable: hClmDay_sm
Type: float
Number of Dimensions: 3
Dimensions and sizes:   [year_day | 366] x [lat | 73] x [lon | 144]
Coordinates:
            year_day: [1..366]
            lat: [90..-90]
            lon: [ 0..357.5]
Number Of Attributes: 4
  smoothing :   FFT: 2 harmonics were retained.
  information : Smoothed daily climatological averages
  units :       m
  long_name :   Daily Climatology: mean Daily Geopotential height

The daily anomalies from the unsmoothed daily climatology.

Variable: hAnom
Dimensions and sizes:   [time | 3652] x [lat | 73] x [lon | 144]
Coordinates: 
            time: [17435256..17522880]
            lat: [90..-90]
            lon: [ 0..357.5]
Number Of Attributes: 3
  _FillValue :  1e+20
  long_name :   Anomalies: mean Daily Geopotential height
  units :       m
(0)      
(0)     Anomalies: mean Daily Geopotential height: min=-563.6   max=608

The daily anomalies from the smoothed daily climatology.