IONOSPHERE
Set to 2 different clues across 2 published puzzles, most often “Where the Northern Lights occur” — The New York Times, Monday, 1 August 2011.
10 letters
Every clue on record, most used first
- Where the Northern Lights occuronce
The New York Times — Monday, 1 August 2011
- Radio wave reflectoronce
The New York Times — Friday, 3 January 2003