Originally Posted by
Propduffer
I don't know what the circle represents, but we can see the 'MH370' track before and after the circle on a (gustimated) 295 degree heading. So the circle isn't where the track was lost. If you look closely at the MH370 track you'll see a series of dots that presumably indicate the sweeps of a search radar.
If you notice the top of that image, it claims that the radar track is from Pulau Perak. I'm not familiar with that part of the world, so I looked it up on Wikipedia. Pulau Perak is a very small island at 5° 40′ 50″ N, 98° 56′ 27″ E (5.680556, 98.940833). It does not even appear (at least to me) on Google Maps satellite view. I was able to see a rough image of it on Yahoo Maps. Pulau Perak appears to be very close to the flight path that was tracked from Butterworth. In other words, the aircraft transited above the highest beam angle of the military radar there. That is likely why there are no returns. It is possible that the white circle represents an internal limit which the radar there cannot see unless the return is from something quite low in altitude (when that close).