IS THIS AN AIR FORCE 737?WHATS THAT THING ON TOP?

This aircraft is based on a Boeing BBJ airframe, with extended range. The thing on top AKA as the surfboard here in OZ, is a MESA or Multi-Role Electronically Scanned Array. This radar antennae is fixed as opposed to the Boeing E3 Sentry, which has a rotating saucer shaped radar on top of its fuselage. The MESA is much lighter and more capable than the older technology found on the E3 Sentry.

Interesting addition of aft ventral strakes. Frank does this compensate for some instability from the antenna? Nice pic BTW!

Thanks Dave! I honestly don't know the answer to your question, but your, "stability" explanation sounds credible, especially with a strong cross wind landing or take off. I must credit Google with making me sound like I knew what I was talking about in the first place and to which I will now turn too, in the hope of finding an answer!

Beautifully photographed, with a pin sharp lens.
Hardly any fuselage surface remaining without an antenna disturbing the free stream flow of air!