Methodology behind ERA5 Data Downscaling in CDSAPI: Request for Details

Hello everyone,

I've been working with the ERA5 single level data through the CDSAPI and have come across an option to adjust the grid size to obtain data at finer horizontal resolutions than the original 0.25-degree resolution. As an example, I recently requested data with a 0.1-degree resolution grid. This got me wondering about the downscaling technique that's employed for such resolutions.

Could someone provide insights into the methodology used for this downscaling? If there's specific documentation or references detailing this process, I'd greatly appreciate being pointed in that direction.

Thanks in advance for your guidance!