netCDF specificities

%matplotlib inline
# for figures in notebook

# import & initialize epygram
import epygram
epygram.init_env()

import os
INPUTS_DIR = os.path.join('..', 'inputs')

r = epygram.formats.resource(os.path.join(INPUTS_DIR, 'aladin.197901.nc'), 'r')

# Equivalent of `ncdump -h`
r.what()

### FORMAT: netCDF

NetCDF Global Attributes:
        name: 'test_phys'
        description: 'Created by xios'
        title: 'Created by xios'
        Conventions: 'CF-1.5'
        production: 'An IPSL model'
        timeStamp: '2016-Apr-15 13:09:53 CEST'
NetCDF dimension information:
        Name: axis_nbounds
                size: 2
        Name: x
                size: 49
        Name: y
                size: 39
        Name: time_counter
                size: 12
NetCDF variable information:
        Name: nav_lat
                dimensions: ('y', 'x')
                size: 1911
                type: dtype('float32')
                standard_name: 'latitude'
                long_name: 'Latitude'
                units: 'degrees_north'
                nav_model: 'FULL'
        Name: nav_lon
                dimensions: ('y', 'x')
                size: 1911
                type: dtype('float32')
                standard_name: 'longitude'
                long_name: 'Longitude'
                units: 'degrees_east'
                nav_model: 'FULL'
        Name: psl
                dimensions: ('time_counter', 'y', 'x')
                size: 22932
                type: dtype('float32')
                long_name: 'air_pressure_at_sea_level (Pa)'
                units: 'Pa'
                online_operation: 'instant'
                interval_operation: '1 h'
                interval_write: '2 h'
                cell_methods: 'time: point (interval: 1 h)'
                _FillValue: 1e+20
                missing_value: 1e+20
                coordinates: 'time_instant nav_lat nav_lon'
        Name: time_instant
                dimensions: ('time_counter',)
                size: 12
                type: dtype('float64')
                standard_name: 'time'
                long_name: 'Time axis'
                calendar: 'gregorian'
                units: 'seconds since 1979-01-01 00:00:00'
                time_origin: '1979-01-01 00:00:00'
                bounds: 'time_instant_bounds'
        Name: time_instant_bounds
                dimensions: ('time_counter', 'axis_nbounds')
                size: 24
                type: dtype('float64')
        Name: time_counter
                dimensions: ('time_counter',)
                size: 12
                type: dtype('float64')
                axis: 'T'
                standard_name: 'time'
                long_name: 'Time axis'
                calendar: 'gregorian'
                units: 'seconds since 1979-01-01 00:00:00'
                time_origin: '1979-01-01 00:00:00'
                bounds: 'time_counter_bounds'
        Name: time_counter_bounds
                dimensions: ('time_counter', 'axis_nbounds')
                size: 24
                type: dtype('float64')

Specify non-trivial variables for grid

Genuinely, this line:

r.readfield('psl')

would result in the following error:

# [2021/01/19-18:59:55][epygram.formats.netCDF][find_grid_in_variables:0459][ERROR]: unable to find X_grid in variables. Please specify with readfield() argument adhoc_behaviour={'X_grid':'name_of_the_variable'} for instance or my_resource.behave(X_grid='name_of_the_variable')

# Hence we need to specify grids
# just for this read
f = r.readfield('psl', adhoc_behaviour={'X_grid':'nav_lon', 'Y_grid':'nav_lat'})
# or for the whole runtime
r.behave(X_grid='nav_lon', Y_grid='nav_lat')
f = r.readfield('psl')

print(f.validity)

<List of FieldValidity which date/time are:
1979-01-01 01:00:00
1979-01-01 03:00:00
1979-01-01 05:00:00
1979-01-01 07:00:00
1979-01-01 09:00:00
1979-01-01 11:00:00
1979-01-01 13:00:00
1979-01-01 15:00:00
1979-01-01 17:00:00
1979-01-01 19:00:00
1979-01-01 21:00:00
1979-01-01 23:00:00
>

Read only a single index of the data

f = r.readfield('psl', only={'time_counter':0})

print(f.validity)

<List of FieldValidity which date/time are:
1979-01-01 01:00:00
>