dired-ls-sorting-switches is a variable defined in `dired.el'.
Its value is

String of `ls' switches (single letters) except "t" that influence sorting.

This indicates to Dired which option switches to watch out for because they
will change the sorting order behavior of `ls'.

To change the default sorting order (e.g. add a `-v' option), see the
variable `dired-listing-switches'. To temporarily override the listing
format, use `C-u C-x d'.