Interesting question. I thought it was just part of the structure design, but we'll see if someone else knows differently. It's not the TCAS antenna since airplanes were not equipped with TCAS at the time that photo was taken. Best guess is it's just the way the structure was designed.
Roseflyer From United States of America, joined Feb 2004, 9132 posts, RR: 52 Reply 3, posted (7 months 3 weeks 2 days 6 hours ago) and read 4323 times:
The only humps or auxiliary equipment on top of a fuselage that I know of is satellite communication systems, however the first satellite communication system for airplanes wasn't developed until 1987.
[Edited 2013-04-15 15:37:49]
If you have never designed an airplane part before, let the real designers do the work!