Format description of the json file
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The JSON format contains the objects metadata, datetime, the selected index (e.g. Kp) and, if available, status.

The object metadata contains the license CC BY 4.0 and the data source GFZ Potsdam.

In datetime the start time of the time interval of the index is given. It has a format according to the ISO 8601 standard.
For example, the time interval starting on at UTC 03 hours on January 1st, 2022 has the time stamp "2022-01-01T03:00:00Z".

The object containing the index data is named like the selected index. 
The format depends on the selected index according to the following table (index, minimum value, second smallest value, arbitrary example value, maximum value):
Kp 0 0.333 3 9
ap 0 2 3 400
Ap 0 2 3 400
Cp 0 0.1 0.2 2.5
C9 0 1 2 9
For the Hpo indices (index, minimum value, second smallest value, arbitrary example value, arbitrary example value):
Hp30 0 0.333 1 11.333
Hp60 0 0.333 1 11.333

The status, if available, can have the values "def" for definitive and "pre" for preliminary.
Status is available for Kp, ap, Ap, Cp, and C9. Status is not available for Hp30 and Hp60.