On the role of charged aerosols in polar
mesosphere summer echoes
Submicron aerosols, as evidenced by the occurrence of polar
mesospheric and noctilucent clouds, exist at heights from which polar
mesosphere summer echoes (PMSE) are observed. We investigate the role
of positively and negatively charged aerosols in the scattering
processes proposed in the literature. These aerosols, if charged
substantially, can account for the remarkably high radar reflectivity
at both VHF and UHF by raising the electron Schmidt number through the
ambipolar effect. A positively charged component may be responsible
for enhanced UHF radar scatter by increasing the incoherent scatter
power through a dressed dust effect, although such a process is not
realistic as an explanation for VHF scatter during PMSE. Such an
enhanced UHF scatter will be associated with extremely narrow
backscatter spectra. We propose a model in which both negatively and
positively charged aerosols are present to explain both the radar
properties and the rocket probe observations of charged particle
depletions. Finally, we point out that the Poker Flat 50-MHz long-term
data, which contrary to accepted dynamical theory show average
downward velocities in the summertime upper mesosphere, can be
attributed to the fall speed of the aerosols responsible for PMSE.
Send e-mail to
j y n c @ m i t . e d u for a copy of
the complete article.
Return to publications list.