Speaker
Description
Space plasmas display fluctuations and nonlinear behavior at a broad range of scales, being in most cases in a turbulent state. The majority of these plasmas are also considered to be heated, with dissipation of turbulence as a possible explanation. Despite of many studies and advances in research, many aspects of the turbulence, heating and their interaction with several space plasma phenomena (e.g., shocks, reconnection, instabilities, waves), remain to be fully understood and many questions are still open.
Plasma irregularities and turbulence are believed common in the F-region ionosphere and because of their impact on the GNSS and the human activity [1, 2, 3] in the polar regions, a detailed understanding is required.
This study provides a characterization of the turbulence developed inside the polar-cusp ionosphere, including features as intermittency, not extensively addressed so far.
The electron density of ICI-2 and ICI-3 missions have been analyzed using advanced time-series analysis techniques and a standard diagnostics for intermittent turbulence. The following parameters have been obtained: the autocorrelation function, that gives useful information about the correlation scale of the field [4]; the energy power spectra, which show the average spectral indexes ∼ −1.7, not far from the Kolmogorov value observed at MHD scales [5], while a steeper power law is suggested below kinetic scales [6]. In addition, the PDFs of the scale-dependent increments display a typical deviation from Gaussian that increase towards small scales due to intense field fluctuations, indication of the presence of intermittency and coherent structures [7, 8, 9]. Finally, the kurtosis-scaling exponent [10, 11] reveals an efficient intermittency, usually related to the occurrence of structures.
References
[1] V. Bothmer, and I. A. Daglis, “Space Weather: Physics and Effects”, 2007, Springer, New York.
[2] H. C. Carlson, 2012, “Sharpening our thinking about polar cap ionospheric patch morphology, research, and mitigation techniques”, Radio Sci., 47, RS0L21.
[3] J. I. Moen, H. C. Carlson, S. E. Milan, N. Shumilov, B. Lybekk, P.E. Sandholt,, and M. Lester, “Space weather
challenges of the polar cap ionosphere”, J. Space Weather Space Clim., 2000, 3(A02), 13.
[4] S. Pope, Turbulent Flows, Cambridge University Press, 2000, Cambridge.
[5] R. J. Leamon, C. W. Smith, N. F. Ness, W. H. Matthaeus, “Observational constraints on the dynamics of the
interplanetary magnetic field dissipation range”, J. of Geophys. Res., 1998, 103(A3), 4775-4787.
[6] A. Spicher, W. J. Miloch, and J. I. Moen, “Direct evidence of double-slope power spectra in the highlatitude ionospheric plasma”, Geophys. Res. Lett., 2014, 41, 1406–1412.
[7] U. Frisch, “Turbulence. The Legacy of A. N. Kolmogorov”, Cambridge University Press, 1995, Cambridge.
[8] K. R. Sreenivasan, “Fluid Turbulence”, Rev. Mod. Phys., 1999, Vol. 71, 2.
[9] R. Bruno, and V. Carbone, “The Solar Wind as a Turbulence Laboratory”, Living Rev. Sol. Phys., 2005, 10, 2.
[10] F. Anselmet, Y. Gagne, E. J. Hopfinger, and R. A. Antonia,“High order velocity structure functions in turbulent shear flows”, J. Fluid Mech., 1984, 140, 25, 63-89.
[11] K. R. Sreenivasan, and R. Antonia, Ann. Rev. Fluid Mech., 1997, 29, 435-472.
Keywords: Sounding rocket observations, Turbulence, Ionospheric Irregularities
