Enhancements to NCSS related to TDS 5

[lesserwhirls]

In TDS v5, the NCSS API has been extended with parameters related to 2D time datasets and ensemble dataset.

2D time datasets

For example:

https://thredds-test.unidata.ucar.edu/thredds/catalog/grib/NCEP/HRRR/CONUS_2p5km/catalog.html?dataset=grib/NCEP/HRRR/CONUS_2p5km/TwoD

As an example here, the variable Temperature_isobaric looks like

Temperature_isobaric[reftime=85][time1=19][isobaric=5][y=1377][x=2145]

where reftime is the model run time dimension, and time1 is the forecast valid time dimension.

Specifying a time range on the NCSS query (resulting in an NCSS query with time_start and time_end) will not give you what you'd expect (whatever your expectation is...not sure what it should be). For example:

https://thredds-test.unidata.ucar.edu/thredds/ncss/grid/grib/NCEP/HRRR/CONUS_2p5km/TwoD?var=Temperature_isobaric&north=52.818&west=-130.123&east=-60.866&south=20.179&time_start=2019-07-16T00:00:00Z&time_end=2019-07-17T12:00:00Z

will give you one reftime and one time1, so:

Temperature_isobaric[reftime=1][time1=1][isobaric=5][y=1377][x=2145]

Enter TDS v5 parameters runtime and offsetTime. If I add a runtime to the previous query:

https://thredds-test.unidata.ucar.edu/thredds/ncss/grid/grib/NCEP/HRRR/CONUS_2p5km/TwoD?var=Temperature_isobaric&north=52.818&west=-130.123&east=-60.866&south=20.179&time_start=2019-07-16T00:00:00Z&time_end=2019-07-17T12:00:00Z&runtime=2019-07-15T12:00:00Z

we get

Temperature_isobaric[reftime=1][time1=7][isobaric=5][y=1377][x=2145]

That is, the seven forecast times between 2019-07-16 0Z and 2019-07-17 12Z from the 2019-07-15 12Z run of the HRRR CONUS 2.5km collection. Why seven? Each run of the HRRR has 18 hours of hourly output, so the 12Z run on the 15th should only have data from 2019-07-15 12Z through 2019-07-16 6Z, thus only 7 forecast times are available between the times requested.

A second new parameter, timeOffset, can be used as well, but only in combination with runtime. So, if we request:

https://thredds-test.unidata.ucar.edu/thredds/ncss/grid/grib/NCEP/HRRR/CONUS_2p5km/TwoD?var=Temperature_isobaric&north=52.818&west=-130.123&east=-60.866&south=20.179&&runtime=2019-07-15T12:00:00Z&timeOffset=2

we get

Temperature_isobaric[reftime=1][time1=1][isobaric=5][y=1377][x=2145]

In this case, we have the forecast valid at "valid forecast time" coordinate 2 from the 2019-07-15 12z run of the HRRR (in this case, 2 hours into the run).

In theory, runtime can be "all", but that's not working. In the query above, that would give us all of the 2 hour old forecasts from all of the model runs.

More generally, the rules for the time, runtime, and timeoffset parameters should follow those outlined here under 2D Time subsetting

Ensemble datasets

In addition to the new 2D time parameters, we also have ensCoord, which allows you to select a single ensemble coordinate (index) for a dataset with an ensemble dimension. So, if we add ensCoord=3 to a request query for a dataset with an ensemble dimension, we should get the data back from the third ensemble member only.

[lesserwhirls]

Here is a visual depiction of the 2D time datasets: https://www.unidata.ucar.edu/software/thredds/current/tds/tutorial/files/FmrcPoster.pdf