First in situ observations of neutral and
plasma density fluctuations within a PMSE layer
The NLC-91 rocket and radar campaign provided the first opportunity
for high resolution neutral and plasma turbulence measurements with
simultaneous observations of PMSE (polar mesospheric summer echoes).
During the flight of the TURBO payload on August 1, 1991, CUPRI and
EISCAT observed double PMSE layers located at 86 and 88 km altitude,
repectively. Strong neutral density fluctuations were observed in the
upper layer but not in the lower layer. The fluctuation spectra of
the ions and neutrals within the uper layer are consistent with
standard turbulence theories. However, we show that there is no
neutral turbulence present in the lower layer and that something else
must have been operating here to create the plasma fluctuations and
hence the radar echoes. Although the in situ measurements of the
electron density fluctuations are much stronger in the lower layer,
the higher absolute electron density of the upper layer more than
compensated for weaker fluctuations yielding comparable radar echo
powers.
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