IMU Raw data - "ACC" coordinate frame

Hello all.

Recently, I logged the raw data from the accelerometers (“ACC” tab in the log screen). While going through the graphs, I noticed that the Acc_Z was centered about -9.8 m/s/s (note that the value is negative), however, if the sensors are oriented to give values in terms of NED (which I assumed was true), shouldn’t Acc_Z be centered around +9.8 m/s/s (positive)? Why is it negative, then?
Also, since it is negative, then what should I assume my accelerometer’s coordinate frame to be? Is it giving data in ENU?

The FC I am using is Cube Orange. Also, I had mounted the FC in the default orientation (all rotations 0, i.e., front of FC is front of vehicle, top of FC is top of vehicle).