Check what process is spiking the average load with atop

In trying to find the culprit of a high load average on a system during night (which does not seem to be related to logrotate) I installed atop to write a raw file with a specific interval. While reading the file, it seems the processlist stands still, can I somehow go back and forth between the samples to see what sticks out, and further sort by any column (like cpu usage)?