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Re: [ferret_users] difference in trend computation from CDO and from ferret



Thanks to Pratik,
My problem is solved after upgrading from pyferret 7.4 to 7.5.

Cheers, Saurabh

On Wed, Jun 19, 2019 at 4:02 PM saurabh rathore <rohitsrb2020@xxxxxxxxx> wrote:
Hi Pratik,
That was one thing in my mind but was lazy to do. I will update my pyferret also then let you know.

thanks for your help

Cheers, Saurabh

On Wed, Jun 19, 2019 at 3:55 PM Pratik Kad <pratikkad17@xxxxxxxxx> wrote:
Hi Saurabh,

After doing the exact similar thing in the ferret, I got the same figure which you got from CDO.
It seems you need to update your PyFerret.
test-ferret_1.png

Regards, 
Pratik

On Wed, Jun 19, 2019 at 2:35 PM saurabh rathore <rohitsrb2020@xxxxxxxxx> wrote:
Hi Pratik,

Thank for your reply. I checked the calendar and time steps of my data that is why I am multiplying my slope with 12 to convert it into per year. But the pattern of the slope is wrong, look the pattern of the slope that I plotted from the trend calculation of cdo with the same data, it is not matching with the pattern of the slope computed using ferret. I checked it with NCL also and its pattern is same as cdo but not like ferret.

One thing I can guess that ferret is doing something else with the time index but I am not able to understand it.

Cheers, Saurabh

On Wed, Jun 19, 2019 at 3:34 PM saurabh rathore <rohitsrb2020@xxxxxxxxx> wrote:
Hi Pratik,

Thank for your reply. I checked the calendar and time steps of my data that is why I am multiplying my slope with 12 to convert it into per year. But the pattern of the slope is wrong, look the pattern of the slope that I plotted from the trend calculation of cdo with the same data, it is not matching with the pattern of the slope computed using ferret. I checked it with NCL also and its pattern is same as cdo but not like ferret.

One thing I can guess that ferret is doing something else with the time index but I am not able to understand it.

Cheers, Saurabh

On Wed, Jun 19, 2019 at 2:32 PM Pratik Kad <pratikkad17@xxxxxxxxx> wrote:
Hi Saurabh,

As we know ferret is sensitive to the time axis. by default, it takes the unit of a given parameter, So you need to the checkout time unit of netCDF file. Then multiply by that factor as per your interest.
Here your file has time unit in months ( which gives trend per month); Hence you need to multiply by 12 then you will get trend per year.  

Regards
Pratik


On Wed, Jun 19, 2019 at 12:09 PM saurabh rathore <rohitsrb2020@xxxxxxxxx> wrote:
Dear Ferreters,
G'day

I am having very strange problem in computation of trend (slope). I am replotting my data after 1 year or so and I want to compute trend from it. I am having my data from 2005-2015.

Here is the attached data.

from ferret I used this script
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
let p=t[gt=ohcg1]
let q=ohcg1
go regresst
fill/lev=(-inf)(-20,20,4)(inf)/pal=blue_orange slope*10^-7*12
frame/file=test-ferret.png
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

from CDO i used this command


here b.nc is the slope, then I plotted this slope.

use b.nc
fill/lev=(-inf)(-20,20,4)(inf)/pal=blue_orange ohcg1*10^-7*12
frame/file=test-cdo.nc

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Now you can see the difference in both the plots. I don't understand why it is happening. Then I checked with NCL also and it is matching with the plot from CDO. Computation of slope from ferret is messing up my calculation and I dont understand why it is so because it never happened before. I am simply modifying my previous plots but it is showing wrong results now with the same old data and scripts.

Any suggestions that what is I am doing wrong with ferret ?
Cheers, Saurabh


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434

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