 NCL Home > Documentation > Functions > Climatology

# clmMonTLL

Calculates long term monthly means (monthly climatology) from monthly data: (time,lat,lon) version

## 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 clmMonTLL (
x [*][*][*] : float or double
)

return_val [*][*] :  numeric
```

## Arguments

x

A three-dimensional array of type float or numeric. Dimensions must be time, lat, lon. The time dimension must be a multiple of 12. The dimensions must be named.

## Return value

An array of the same size and type as x except that the leftmost dimension will be of size 12.

## Description

Calculate long term monthly means (monthly climatology) from monthly data. The "temporal" dimension will be of size 12 and will be named "month".

## Examples

The following require that contributed.ncl be loaded prior to invoking the function.

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

Example 1

Calculate the monthly climatology of T2m(time,lat,lon) where

```[time | 528] x [lat | 128] x [lon | 256]
```
This represent 44 years [44*12=528] of monthly data. Consider the following code snippet:
```      f    = addfile("T2m.1958-2001.nc, "r")
t    = f->T2m
tClm = clmMonTLL( t )
printVarSummary(tClm)
```
The result is:
```variable: tClm
Type: float
Total Size: 36175872 bytes
9043968 values
Number of Dimensions: 3
Dimensions and sizes:   [month | 12] x [lat | 128] x [lon | 256]
Coordinates:
month: [0..11]
lat: [-88.92773..88.92773]
lon: [ 0..358.53]
Number Of Attributes: 7
time_op_ncl : Climatology: 44 years
cell_method : time: mean
standard_name :       eastward_wind
units :       m/s
long_name :   U velocity
_FillValue :  -999
```