Linked from
The 14 pages that link to Southern Hemisphere, each with the reason it gives.
EquatorBroader topic: The Equator forms its northern boundary.
SeasonsBroader topic: Its seasons are roughly opposite those of the Northern Hemisphere.
HemisphereBroader topic: It is the other half of Earth divided by the equator.
Hemispheres of EarthBroader topic: It is the equator's counterpart to the Northern Hemisphere.