# [ncl-talk] calcMonAnomTLL

Setareh Rahimi setareh.rahimi at gmail.com
Thu May 27 01:23:59 MDT 2021

```Dear all NCL users,

https://www.ncl.ucar.edu/Document/Functions/Contributed/calcMonAnomTLL.shtml ,
which is about monthly anomalies. But I could not understand the way it
calculates the anomalies.

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Example 1

air  = *short2flt*
<https://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml>(
fa->air)                           ; air temp
nobs = *short2flt*
<https://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml>(
fb->air)                           ; # obs for air
; filter out geographic locations that have < nMin observations
nMin   = 2                                           ; min # obs

;---Compute the climatology using a function in contributed.ncl
yrStrt = 1950
yrLast = 1979
moStrt = (yrStrt-1800)*12              ; start subscript
moLast = (yrLast-1800)*12 + 11         ; last  subscript
clm = *clmMonTLL*
<https://www.ncl.ucar.edu/Document/Functions/Contributed/clmMonTLL.shtml>
(air(moStrt:moLast,:,:)) ; monthly climatology

;---Compute the anomalies from the climatology just computed
xAnom = *calcMonAnomTLL* (air,clm)

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May I ask you please explain subscript method? Why using 1800 and then
multiply 12?

what do moStrt and moLast show?