|
|
 |
|
|
Ann. Geophys., 24, 2959-2979, 2006
www.ann-geophys.net/24/2959/2006/
© European Geosciences Union 2006
Low-frequency electrostatic waves in the ionospheric E-region: a comparison of rocket observations and numerical simulations
L. Dyrud1,2, B. Krane3, M. Oppenheim4, H. L. Pécseli2,5, K. Schlegel6, J. Trulsen2,7, and A. W. Wernik2,8
1Center for Remote Sensing, 3702 Pender Dr., Fairfax, VA 22030, USA
2Centre for Advanced Study, Drammensveien 78, N-0271 Oslo, Norway
3Norwegian Defense Research Establishment (NDRE), Box 25, N-2027 Kjeller, Norway
4Center for Space Physics, Boston University, 725 Commonwealth Ave., Boston MA 02215, USA
5University of Oslo, Physics Department, P.O. Boks 1048 Blindern, N-0316 Oslo, Norway
6Max Planck Institute für Sonnensystemforschung, D-37191 Katlenburg-Lindau, Germany
7University of Oslo, Institute of Theoretical Astrophysics, P.O. Boks 1029 Blindern, N-0315 Oslo, Norway
8Space Research Center, Polish Academy of Sciences, ul. Bartycka 18a, 00-716 Warsaw, Poland
Abstract. Low frequency electrostatic waves in the lower parts of the ionosphere are
studied by a
comparison of observations by instrumented rockets and of results from
numerical
simulations. Particular attention is given to the spectral properties of
the waves. On the basis of a good agreement between the
observations and the simulations, it can be argued that the most important
nonlinear dynamics can be accounted for in a 2-D numerical model,
referring to a plane perpendicular to a locally homogeneous magnetic
field. It does not seem necessary to take into account turbulent
fluctuations or motions in the neutral gas component. The numerical
simulations explain the observed strongly intermittent nature of the
fluctuations: secondary instabilities develop on the large scale
gradients of the largest amplitude waves, and the small scale dynamics is
strongly influenced by these secondary instabilities. We compare
potential variations obtained at a single position in the numerical
simulations with two point potential-difference signals, where the latter
is the adequate representation for the data obtained by instrumented
rockets. We can demonstrate a significant reduction in the amount of
information concerning the plasma turbulence when the latter signal is used for
analysis. In particular we show that the bicoherence estimate is
strongly affected. The conclusions have implications for studies of
low frequency ionospheric fluctuations in the E and F regions by
instrumented rockets, and also for other methods relying on difference
measurements, using two probes with large separation. The analysis also
resolves a long standing controversy concerning the supersonic phase
velocities of these cross-field instabilities being observed in laboratory
experiments.
Full Article in PDF (3085 KB) |
|
|
