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Re: [ferret_users] Monthly variation of diurnal cycle



Hi Pratik

On Mon, Jul 27, 2020 at 10:53 AM Pratik Kad <pratikkad17@xxxxxxxxx> wrote:



I'm plotting the monthly variation on the diurnal scale, Please have a look at the attachment.

currently SET data sets:

     1> ./temperature.nc  (default)

 name         title                     I        J        K       L

 temp_h     6-hourly temperature       1:1      1:1      ...     1:1460

 temp_m     monthly temperature        1:1      1:1      ...     1:12 

By default, I have a monthly time axis. Here, I tried to define a 2nd-time axis (for an hourly scale) using an auxiliary coordinate regridding;

If I understand correctly, you want to regrid your 6-hourly temperature timesearies temp_h(t) into a two dimensional variable with its horizontal axis spans a day and vertical axis representing days.

To do so, the RESHAPE function

https://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/XPRESSIONS#_VPINDEXENTRY_336

is what you need.  Define a fake "x" axis, which actually represents hours within a day:

let lmax = `temp_h,return=lmax`
define axis/x=0:24:6/edges/units=hours axis_hour  ! data defined at 03:00, 09:00, 15:00, 21:00. 
define axis/t=0:`lmax/6`:1/units=days axis_day
let grid_var = x[gx=axis_hour] + t[gt=axis_day]
let temp2d = RESHAPE(temp_h, grid_var)
shade temp2d

The code isn't tested.  Likely to include error.

[ This solution is less than perfect because the periodicity of the day isn't exploited.  I mean, before 03:00 of "today", there is the data at the 21:00 of "yesterday" and after the 21:00 of today, there is the 03:00 of "tomorrow".  The fake "x" axis above doesn't represent this continuity.  Perhaps you can use three different "x" axes, one spanning [-3, 15], one [3, 21], and the other [9, 27], and merge the three regridded fields . . .  I don't know . . . ]

Ryo

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