Re: [ferret_users] making a continuous timesaxis with JJAS values

To: ferret_users@xxxxxxxx

Subject: Re: [ferret_users] making a continuous timesaxis with JJAS values

From: "Ansley C. Manke" <ansley.b.manke@xxxxxxxx>

Date: Mon, 23 Jul 2018 10:23:22 -0700

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Hi Chinnu,

If you have defined the monthly axis so that it really lines up with your JJAS time axis, then the values won't be changed with a linear interpolation. "Monthly" time is a bit ambiguous, so if the time coordinates aren't exactly the same on the axis you define, then Ferret will do some interpolating between the axes.

Look at the details for a few months of your axes:

yes? ! the axis of your original data yes? show axis/t=1-jun-1948:30-sep-1949 `var,return=taxis`

yes? ! the axis you are defining yes? show axis/t=1-jun-1948:30-sep-1949 tax_mon
Do the coordinates have the same dates and times for the months that are present on the original data axis? Are they both regularly spaced? The two axes do NOT need to have the same units. Ferret converts between different time units so if your original data has units of days or hours, that's fine. But if the coordinates don't agree, then the data will be interpolated.

You could try to define your monthly time axis so that the coordinates for JJAS match on both axes, or look at using a different regridding transformation.

Ansley

On 7/23/2018 5:17 AM, chinnu sachi wrote:

Dear Ferret users,

I have time series which had only four month( ie JJAS ) values.

1948 jun 1.370

1948 jul 1.636

1948 aug 1.542

1948 sep 1.832

1949 jun 0.523

1949 jul 0.220

1949 aug 0.532

1949 sep 1.313

1950 jun 0.275

1950 jul 1.068

1950 aug 1.100

1950 sep 1.347

etc till

2015 jun -1.662

2015 jul -3.908

2015 aug -3.032

2015 sep -2.286

I would like to make above time axis into a continuous one from january to december for the entire data period without having any change in the JJAS values. I tried to define a grid with

DEFINE AXIS/t=15-jun-1948:15-sep-2015:1/UNITS=months tax_mon

LET var_new = var[Gt=tax_mon@lin]
save/file=out.nc/clobber var_new

I am getting continuous time axis from january to december for 1948 to 2015, but the values of JJAS of each year has been changed.

Thanks in advance.

--

Regards,
Chinnu Sachidanandan