SOUnding SYstem for atmospheric structure and dymanics
At present one of the most intruiging topics of research is the so-called
"dirty plasma" in the mesosphere. It consists of charged and
neutral gas molecules as well as dust and small ice particles. At mesospheric
heights the dusty plasma results in extremely strong radar
echoes. They are called Polar Mesospheric Summer Echoes (PMSE).
The figure presents as an example a colour intensity plot of the
echo intensity ( upper part) and the velocity (lower part) as a
function of height and time, received in the vertically pointing radar beam.
The very thin layer observed at about 86 km is modulated
by a gravity wave with a period of 9 min. The vertical velocity
clearly reveals the periodic structure of up- and downward motions.