scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Irregular structure of the mid-latitude sporadic-E caused by neutral turbulence
Kyzyurov Yurij
Main Astronomcal Observatory NASU
The neutral air turbulence plays an important role in the dynamics of the ionospheric D and E
regions. Above an altitude of 80 km a source of the turbulence may be destruction of the
atmospheric gravity waves and tides propagating from the lower atmospheric layers and also
the nonlinear interaction of planetary waves and tides. These large-scale atmospheric motions
are responsible for a vertical shear in the neutral wind that is necessary for the production of
mid-latitude sporadic-E. The sporadic-E is an example of the ionosphere-atmosphere
interaction. The neutral turbulence exerts an essential influence on sporadic-E parameters and
generates its irregular structure. Intensification of the turbulence may decrease the peak
amplitude of the layer and increase the sporadic-E thickness. Main steps needed to derive
analytic expressions for the spatial spectrum of sporadic-E plasma irregularities caused by the
neutral turbulence and for evaluation of the RMS fluctuation level of irregularities are
described in the present report. The derived formulae are used to analyze the dependence of
sporadic-E irregular structure on the ion composition of the layer under unchanged intensity
of the turbulence. The dependence of the irregular structure on intensification of the
turbulence under the fixed ion composition is analyzed too. Changes in the ion composition is
taken into account through changes in the mean ion mass, mi, whereas intensification of the
turbulence through increase in the mean rate of turbulent energy dissipation (TED).
Calculations were made for the mid-latitude sporadic-E (magnetic dip angle about 44°) near
height of 100 km. An increase in mi caused by heavy metallic ions that are known to exist in
the night-time sporadic-E results in the reduction in the RMS fluctuation level of the irregular
structure and in decrease of the slope of irregularity spectrum that can be measured during
rocket flights. The change in mi from 31 to 51 AMU results in the fluctuation level decrease
from 7.7 to 4.1% and change in the power index from -3.0 to -2.6 under the TED rate 10
mW/kg. It is also shown that enhancement of the turbulence (the TED rate changes from 5 to
20 mW/kg) results in the reduction in the fluctuation level form 6.9 to 4.4% and change in the
power index from -2.7 to -2.3 for the sporadic-E composition with mi=41 AMU. Results of
this report can be tested in rocket experiments that include measurements of parameters of the
sporadic-E and the turbulent neutral wind.