Why can't i get the thunderstorm skull in halo 3 by myself?

[kyle]

I had previously got the campaign beaten with my friend on normal and we were getting the skulls but he left so i decided to do the the thunder storm skull. I started from the very beginning and the skull didn't appear in its proper location whats wrong? Do i have to beat the campaign by myself to hunt the skulls by myself?

 

[Darth Sega]

If you can't get it retry the level from the beginning where you get off the pelican disable the first tower and then get down to the beach and get in the hornet. Then you will se a green phantom leaving from the second citadel. Go and land by on the citadel then walk up the ramp to get the skull. If you are wondering about the other skull there are 7 rings 1 is the closest to truth jump through the rings in order 4564534 before or after killing truth if it doesn't work retry it from 1. This is how to get the skulls on this level I think it has to be on normal or harder, but I'm not sure.