[NARCCAP-discuss] time discrepancy

[Shane Brennan]

Hi Seth,

I notice "time" data skips a day near the end of the year in some
cases. For example, in a few files I have looked at, the "time"
variable goes from 1093 to 1095, as well as 2918 to 2920, etc. This
does not happen in NCEP files which are Gregorian. Is this a
consequence of the no leap year calendar? I had assumed that "time"
counted up from 0 (from 1968) and that day 59 would be a leap day in
Gregorian and March 1st in the no leap year calendar.

Basically, I would like to compare NCEP data with modeled data on a
monthly basis, so making sure I have my calendars straight is
important. Does anyone have any suggestions on the best way to go
about this? Currently I am creating two "days from" fields in Excel
which have the time variable, and in one field I increment the value
(and subsequent values) at leap years, all the way down, so that the
final product is a field with the correct days offset depending on the
number of preceding leap days. However, the skipped day I am running
in to is causing me to put this method into question.

Thanks, and sorry if I am missing something obvious...

Shane


On Sun, Aug 26, 2012 at 12:10 PM, Seth McGinnis <mcginnis at ucar.edu> wrote:
> Hi Shane,
>
> Information about time in the NARCCAP data can be found here:
> http://narccap.ucar.edu/about/time-periods.html
>
> Cheers,
>
> --Seth
>
> On Sat, 25 Aug 2012 16:09:54 -0400
>  Shane Brennan <sbren006 at odu.edu> wrote:
>>OK, thanks, Seth. Is the same calendar used for all models? Is there
>>documentation on the timesteps used?
>>
>>Shane
>>
>>On Sat, Aug 25, 2012 at 11:25 AM, Seth McGinnis <mcginnis at ucar.edu> wrote:
>>> Hi Shane,
>>>
>>> It's the calendar.  CCSM uses a 365-day or "noleap" calendar, in which every
>>> year has 365 days and there are no leap years ever.  The date calculation
>>> functions in Excel use the standard Gregorian calendar, which does have leap
>>> years.
>>>
>>> If you count up the leap days between the base time (1968/01/01) and the
>>start
>>> of your file (1996/01/01), there are seven of them, which is the difference
>>> between your expected start date and the start date you're seeing in the
>>Excel
>>> calculations.  (And then there's another one in 1996, so the discrepancy for
>>> the end dates is 8 days.)
>>>
>>> Cheers,
>>>
>>> --Seth
>>>
>>> On Fri, 24 Aug 2012 11:13:44 -0400
>>>  Shane Brennan <sbren006 at odu.edu> wrote:
>>>>Hi,
>>>>
>>>>I am writing a C# program to parse and manipulate NARCCAP data. I
>>>>wanted to verify the missing data values to make sure I was handling
>>>>them correctly so I checked out:
>>>>
>>>>http://www.narccap.ucar.edu/data/missing/CRCM_ccsm-current_table3_missing.txt
>>>>
>>>>to find where I could look for missing values. In the URL above, it
>>>>states that evps in the file evps_CRCM_ccsm_1996010103.nc has missing
>>>>values for 1999-12-01 03:00 through 2000-01-01 00:00.
>>>>
>>>>I would expect the time series for the entire file to run from
>>>>1996-01-01 03:00 to 2000-01-01 00:00. However, when I parse this file
>>>>with my program and then use excel to calculate the times from
>>>>1/1/1968 (the start date returned from ncdump for this file), I get a
>>>>time series that runs from 12/25/1995 03:00 to 12/24/1999 00:00. In
>>>>this file, my missing values run from 11/23/1999 03:00 to 12/24/1999
>>>>00:00.
>>>>
>>>>Naturally, I became concerned that I had a bug in my program. However,
>>>>when I use nc2text.exe using the instructions detailed in the ASCII
>>>>HowTo, I get the same results.
>>>>
>>>>In Excel I calculate the offset date by entering 1/1/1968 into a cell,
>>>>and calculating a new field as that cell value added to each time
>>>>value (for example, if the cell for 1/1/1968 is G1, then my formula
>>>>for the first cell is "=$G$1 + a1". I then copy this formula all the
>>>>way down).
>>>>
>>>>Does anyone know what is going on? Perhaps there is some issue with
>>>>leap years or DST?
>>>>
>>>>Shane
>>>>_______________________________________________
>>>>narccap-discuss mailing list
>>>>narccap-discuss at mailman.ucar.edu
>>>>http://mailman.ucar.edu/mailman/listinfo/narccap-discuss
>>>
>>> _______________________________________________
>>> narccap-discuss mailing list
>>> narccap-discuss at mailman.ucar.edu
>>> http://mailman.ucar.edu/mailman/listinfo/narccap-discuss
>>>
>>>
>>> --
>>>
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