Hi,
for ERA5 hourly data on single level the suggestion is to retrieve one month at time. If you need data for grid points the suggestions is to download the data from the ERA5 single-levels dataset available in analysis-ready, cloud-optimised (ARCO) Zarr stores: ERA5 hourly time-series data on single levels from 1940 to present
If the variable is not available in the list, it is anyway better to ask for the whole globe and after cut the area/grid point needed on your local machine.
For ERA5 data on model levels as the data are store on tapes, to retrieve data efficiently (and get your data quicker!) you should retrieve all the data you need from one tape, then from the next tape, and so on.
As a rule of thumb everything shown on one page at parameter level in the MARS ERA5 catalogue is grouped together on one tape
- For analysis fields this is one month of data with respect to one particular level type (e.g. surface).
- For forecast fields on model levels this is limited to one single day.
A general suggestion is to send requests sequentially, wait for the first to finish and then send the next one.
Thanks