ELECTRIC-FIELD MEASUREMENTS IN THE VICINITY OF NOCTILUCENT CLOUDS ANDPMSE

We report mesospheric electric field structure in the vicinity of noct ilucent clouds (NLC) and polar mesospheric summer echoes (PMSEs) measu red on the DECIMALS-B rocket payload launched during the international rocket-radar campaign NLC-91 from Esrange, Sweden on August 10, 1991. Unusually large vertical E- fields, E(Z), about 100-300 mV/m on ascen t and greater than 1 V/m on descent were detected at 82.5-84.5- km. Th e region of the large E(z) was clearly limited by the NLC layer on the bottom and by the distinctly separated PMSE layer on the top. A narro w negative peak in the E(z) height profile observed on ascent in the l ower part of the NLC layer was apparently caused by the interaction of the field mill with impacting NLC particles possibly carrying negativ e charge. If the impact signature is due to single particles, their si ze is estimated to at least 0.5 mum and their concentration about 10(- 4) cm-3 locally. Based on the fight-scattering properties of NLC such massive particles can only be a minor part of the NLC population.