Differences between population lifetime and dipole moment lifetime

the_wizard

Reading a book about atomic transitions i really don't understand physically what the book means when it talks about differences between the population lifetime and the dipole lifetime that appear in the coerence part of the density matrix of a 2 or a 3 level system.
I imagine that the population lifetime refers to how many atoms of the system pass from the upper state to the lower one, but i can't visualize the meaning of the dipole lifetime.
How can be possible that the lifetime of the population is much longer than the dipole lifetime? Can anyone give me an example of what happens in systems like these?