From 29 June to July 6, 2003, the ROMA-Svalrak (Rocketborne Observations of the Middle Atmosphere at the Svalrak facilities) sounding rocket campaign took place at Ny-Ålesund (Spitsbergen, geographical coord. 79N, 12E, geomagnetic coord. 76N, 110E). Three sounding rockets were launched to study neutral air turbulence and small scale plasma dynamics around polar mesosphere summer echoes (PMSE). During all three flights both PMSE and plasma instability events were observed. It is known that small-scale field aligned structures in the E-region plasma density can be created by unstable electromagnetic waves. The mechanism responsible for creating the structures causing radar echoes (PMSE) is believed to be neutral air turbulence in the presence of heavy charged particles. E-region plasma irregularities recorded during the last rocket flight (labeled RO-MI-03) were observed only during the upleg of the trajectory but not during the downleg. Also, on the upleg there was no clear spatial separation between PMSE and the plasma instability regions. In the current paper we consider this transition region in detail. ; This paper was published as Journal of Atmospheric and Solar-Terrestrial Physics, 2009, 71 (1), pp. 143-157. It is available from http://www.sciencedirect.com/science/journal/13646826. Doi: 10.1016/j.jastp.2008.10.003 ; Metadata only entry