Question on time-steps of tracks

[Paolo De Luca]

Hello,

I have downloaded the file IBTrACS.ALL.v04r00.nc and I am wondering if there is a way to obtain the real time-steps (date and time) of when the tropical cyclones actually occurred?

I need the real date and time because I would like to complement the tracks with atmospheric variables, such as precipitation and sea-level pressure.

Best regards

Paolo

[Paolo De Luca]

maybe the iso_time variable is what I am looking for?

if yes, how can I extract the variable from the netcdf? I tried with CDO but it does not work.

paolo

[Ken Knapp - NOAA Federal]

Hi Paolo

You can use the coordinate variable 'time' to calculate the time of the observation.

        double time(storm, date_time) ;
                time:long_name = "time" ;
                time:standard_name = "time" ;
                time:units = "days since 1858-11-17 00:00:00" ;
                time:_FillValue = -9999000. ;
                time:description = "Nominally, time steps are 3 hourly, but can be more often since some agencies include extra position (e.g., times near landfall, maximum intensity, etc.)" ;
                time:Note = "Variable:time can be missing since the tracks are stored in a fixed 2-D grid where tracks have varying lengths" ;
                time:calendar = "standard" ;
                time:coverage_content_type = "physicalMeasurement" ;

Depending on the language that you're using to read the file, you can calculate the new date. In pseudo code, it would look something like this:

## Put the reference date into some coordinate system like Julian Day
reference_date = julday(11,17,1858,0,0,0) 
##Use a value of time to calculate ... time has units of days so this works if using Julian Date as your reference
start_date = reference_date + time(0,0)
##Convert from coordinate system to some calendar entry ... or whatever you need.
caldate = julian_to_calendar(start_date)

Hope this helps.

-Ken

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