Consistency of rocket and radar
electron density observations: Implication about the anisotropy of
mesospheric turbulence
We report about a quantitative comparison of rocket observations of
electron density fluctuations and simultaneous 53.5-MHz radar
measurements that were obtained during the MAC/SINE campaign in
northern Norway in summer 1987. Out of three rockets launched during
the Turbulence/Gravity Wave salvo on 14 July 1987, two were flown
during conditions that allowed a detailed investigation. For a large
part of the data from these rocket flights it is found that the radar
reflectivity is about 10 dB enhanced over what would be expected from
the rocket observations in the case of isotropic electron density
fluctuations. The observations can be reconciled under the assumption
of an anisotropic turbulence. Assuming a simple model spectrum for
electron density fluctuations, we derive a relation between the rocket
and radar observations that covers the whole range from isotropic
turbulent scatter to Fresnel scatter at horizontal density
stratifications. For the observed data set, an anisotropy which
typically corresponds to a ratio of horizontal to the vertical
coherence length of about 10 is consistent with the comparison of
rocket and radar observations. A similar anisotropy is found also
from the observed aspect sensitivity of the radar echoes. The
variation of the anisotropy with height and time shows an
anticorreltaion with the turbulence level of the mesosphere deduced
from the spectral width of the radar echoes. The anisotropy is found
to maximize in heights where the electron density displays deep
"bite-outs." These depletions in the electon desnity were
independently observed by a Langmuir and an admittance probe on board
two of the rockets.
Send e-mail to inhester@Linax1.mpae.gwdg.de for a
copy of the complete article.
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