I found something. "ata" seems to mean "atmosphere absolute" and describes the total pressure:

"The ata unit is used in place of atm to indicate the total pressure of the system, compared to a vacuum. For example, underwater pressure of 3 ata would mean that this pressure includes 1 atm of air pressure and thus 2 atm due to the water.", from https://en.wikipedia.org/wiki/Standard_atmosphere_(unit)#Pre...