It's not Ominous Latin Chanting, it's not the Cherubic Choir, but somewhere in between, close to the Ethereal Choir. A solitary, usually wordless wail (possibly to simulate wind or grieving), usually done by either a woman or, for extra poignancy points, a child (usually a boy soprano). The best time to include this trope is during the aftermath of something really dramatic -- a battle, natural disaster, etc. Basically, any event where Ominous Latin Chanting would just fall short in the sadness department. Beware, though, for overuse of this trope can send you on a Narmtastic voyage...