NCL Home > Documentation > Functions > Climatology

# clmMonLLT

Calculates long term monthly means (monthly climatology) from monthly data (lat,lon,time 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 clmMonLLT (
x [*][*][*] : numeric
)

return_val [*][*][12] :  numeric
```

## Arguments

x

A three-dimensional array of any numeric type. Dimensions must be lat, lon, time. 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 rightmost dimension will be of size 12.

## Description

Calculate long term monthly means (monthly climatology) from monthly data.

## 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 u(lev,lat,lon,time) where

```[lat | 128] x [lon | 256] x [time | 528]
```
This represent 44 years [44*12=528] of monthly data. Consider the following code snippet:
```      f    = addfile("x.1958-2001.nc, "r")
t    = f->T2m
tClm = clmMonLLT( t )
printVarSummary(tClm)
```
The result is:
```variable: tClm
Type: float
Total Size: 36175872 bytes
9043968 values
Number of Dimensions: 3
Dimensions and sizes:  [lat | 128] x [lon | 256] x [month | 12]
Coordinates:
lat: [-88.92773..88.92773]
lon: [ 0..358.53]
month: [0..11]
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
```