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I am using temperature information from ERA5 reanalysis hourly data on a single level, and I am confused about time reference.

If I download global temperature data for a specific day and time (for example, 2000-08-08 07:00) is this UTC or is it adjusted to the local time of each point of the grid? In other words, will I be looking for 07:00 in the US and also for 07:00 in Germany? Or they are referred to UTC, and in the US I will be looking for nighttime temperature while in Germany it will already be morning?

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UTC (Coordinated Universal Time) is the only way that makes sense for a global dataset. Using local timezones would be an absolute nightmare for exactly this reason.

I found several references to UTC in the ERA5 data documentation.

  • 'time' in analyses Each analysis has a validity time, i.e. the time the data values refer to (not the time when the analysis was computed). All validity times are in hours UTC. source

  • 'time' in forecasts Each forecast starts with the atmospheric conditions at a specific 'initialization time'. In ERA5 a new forecast is computed twice a day, with initialization times of 06:00 and 18:00 UTC. In the ERA5 data archive, for forecasts, 'time' (and date) refers to the initialization time.

I didn't anything that explicitly says they used UTC throughout, but the documentation is hundreds of pages long and I didn't read it word-for-word. If anyone manages to find specific confirmation whether all the times in this dataset are in UTC, please provide a direct link.

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