For various reasons you may need to change the location of the temporary directory that ImageMagick uses. I common one is that ephemeral disk can easily run out space due to large *.pam files like magick-14446qjlotf0hZnw8.pam
The ImageMagick temporary folder on Acquia Cloud will default to using /tmp. Fortunately ImageMagick has environment variables and the one that interests us here called MAGICK_TEMPORARY_PATH which controls the path of the ImageMagick temporary directory.
On Acquia Cloud Enterprise you can follow creating custom environment variables to set your own custom Environment variables.
By following the above guide on creating custom environment variables, create one named MAGICK_TEMPORARY_PATH and set the value to /mnt/tmp/[docroot].[env]/ making sure to replace [docroot] and [env] with the appropriate values for the application and environment you wish to modify the location of the temporary folder for ImageMagick.