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Исследование турбулентности магнитосферно-ионосферной плазмы в высокоширотной области

Исследование турбулентности магнитосферно-ионосферной плазмы в высокоширотной области. И.В.Головчанская, Б.В.Козелов. Observations. Dynamics Explorer 2 (DE2), altitudes 300-900 km, 1.5 year mission. D atabase:

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Исследование турбулентности магнитосферно-ионосферной плазмы в высокоширотной области

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  1. Исследование турбулентности магнитосферно-ионосферной плазмы в высокоширотной области И.В.Головчанская, Б.В.Козелов

  2. Observations • Dynamics Explorer 2 (DE2), altitudes 300-900 km, 1.5 year mission. • Database: • dc electric field (VEFI, double sounding technique), sensitivity 0.1 mV/m magnetometer data (IGRF subtracted), sensitivity 1.5 nT • Resolution:16 Hz (~500 m). • Optics: • Auroral Large Imaging System (ALIS) • Field of view ±17° from magnetic zenith, • Dynamical range 2·104 • Electrodynamics: • Signal-to-noise ratio 102-103 • One-pixel resolution ~ 400 m • Substorm conditions • OMNI database • Hourly IMF and solar wind parameters

  3. IMF By = -17.9 nT, IMF Bz = 13.4 nT Representative events Castaing distribution: where λ characterizes the degree of non-Gaussianity of data and lnα0 = - λ2 . Golovchanskaya I. V., Y. P. Maltsev, A. A. Ostapenko, High-latitude irregularities of the magnetospheric electric field and their relation to solar wind and geomagnetic conditions , J. Geophys. Res., 107, NA1, doi:10.1029/2001JA900092, 2002.

  4. Discrimination between fluctuations on the closed and open magnetic field lines. IMF By = -15.1 nT, IMF Bz = -6.7 nT Precipitation data: LAPI on DE2. Kozelov B. V., I. V. Golovchanskaya, A. A. Ostapenko, and Y. V. Fedorenko, Wavelet analysis of high-latitude electric and magnetic fluctuations observed by the Dynamic Explorer 2 satellite, J. Geophys. Res., 113, A03308, doi:10.1029/2007JA012575, 2008.

  5. Auroral zone Polar cap

  6. Turbulence occurrence regions. Relation to the IMF and large-scale Birkeland currents. Electric fields (VEFI on DE2) , where < > means ILAT-MLT bin averaged for ~5000 DE2 passes for 1.5 year.

  7. Magnetic fields (magnetometer on DE2) Golovchanskaya I. V., A. A. Ostapenko, B. V. Kozelov,Relationship between the high-latitude electric and magnetic turbulence and the Birkeland field-aligned currents, J. Geophys. Res., 111, A12301, doi:10.1029/2006JA011835, 2006.

  8. Electric field spectra and their interpretationKintner and Seyler [1985] Data: ac electric field spectrometer on Hawkeye 1, 2 Hz < f < 56 Hz Balloon measurements, Altitudes 30 –40 km f < 0.03 Hz Doppler shifted frequencies: 2f = Vsat·k Interpretation: Kraichnan regime of electrostatic (fluid type) ionospheric turbulence (?). Prediction: change of the slope at 1–10 km.

  9. Investigation of electric field spectrum slopes on larger statistics [Heppner et al., 1993]Data: ac electric field spectrometer on DE2, 4 Hz < f < 512 Hz Findings: (1) Peculiarity around local O+ gyrofrequency (32 – 64 Hz); (2) Seasonal variation of spectrum slopes;

  10. Turbulence source localization Ionospheric source Magnetospheric source Gurnett et al., 1985 (DE1,altitude 3–4 Re), Podgorny et al., 1988, 2003 (Bulgaria-1300 ,altitude 900 km) found predominantly downward direction of the associated Poynting flux, implying a magnetospheric source of the turbulence.

  11. DE2, 1981 day 304 DE2, 1981 day 290 Golovchanskaya I. V. and Y. P. Maltsev, On the direction of the Poynting flux related to the mesoscale electromagnetic turbulence at high latitudes, J. Geophys. Res., 109, A10203, doi:10.1029/2004JA010432, 2004 (DE2).

  12.  > 75° 60 ° <  < 75° Downward (black circles) and upward (white diamonds) turbulent Poynting flux averaged over the polar (left) and auroral (right) latitudes versus Bz IMF. Poynting flux δP in the auroral zone and the polar cap observed by DE2 on day 316 1981, UT = 00.

  13. Abry P. et al., Wavelets for the analysis, estimation and synthesis of scaling data , in Self-similar Network Traffic and Performance Evaluation, [2000]. Data: dataseries combined from DE2 observations in 10 dawn-to-dusk passes over the auroral zone and the polar cap (southward Bz IMF). Findings: (1) similar spectra in both regions; (2) a change in the spectrum slope at scale 32 km

  14. Non-perfect mapping of magnetospheric electric fields down to ionospheric heights? A diffusion range? Weimer et al., Auroral zone electric fields from DE 1 and 2 at magnetic conjunctions, J. Geophys. Res., 98, A8, 7479-7494, 1985.

  15. Assumptions: Scale-dependent ‘mapping’ function Basic equations: (1) (2) (3) In a static case: Integrating over z from z = i to z = h, we have (4) (5) Substitution of (5) into (3) yields where (6) Expanding the high-altitude potential and electric field in a Fourier series and substituting into Fourier transforms of (5) and (6): we finally have for each Fourier harmonics with wave number k

  16. Modeled diffusion range for different k0values

  17. Alfven wave turbulence Dubinin E. M. et al., Auroral electromagnetic disturbances at altitudes of 900 km: Alfven wave turbulence, Planet. Space Sci. ,36, N10, 949-962, 1988. Data: ICB-1300, 900 km altitude, f < 6 Hz. Qualitative scheme of the instability of Alfven wave with a finite amplitude. Variations of Ex and By components in séance 2931 (2 March 1982). Power spectra of electric and magnetic fields.

  18. Turbulence manifestations in aurora Auroral observations by ALIS during substorm conditions Golovchanskaya I. V., B. V. Kozelov, et al. Scaling behavior of auroral luminosity fluctuations observed by Auroral Large Imaging System (ALIS), J. Geophys. Res., 113, A10303, doi:10.1029/2008JA013217, 2008.

  19. Substorm auroral spots observed in the blue (λ = 4278 Å)emission

  20. Substorm auroral arcs observed in the blue (λ = 4278 Å)emission

  21. Corrections of the scaling characteristics for the effect of aspect angle broadening. Scaling characteristics of auroral fluctuations in the horizontal plane are distorted because of field-aligned extension of auroral structures, which is determined by a type of precipitation. KozelovB. V. and I. V. Golovchanskaya, Effect of the aspect angle broadening on the scaling characteristics of auroral fluctuations, 35th optical meeting, Maynooth, 24-29 August, 2008.

  22. Simulation of aspect angle distortions No distortion, fBm H=0.3 Narrow profile distortion Wide profile distortion • Fractional Brownian motion surface (H=0.3, 0..5, 0.7) was used as a precipitation pattern • Two types of altitude profile were used: narrow and wide • Region near magnetic zenith was simulated • The estimates of H derived in twenty realizations with applying the wavelet estimator [Abry et al., 2000] are found most robust. • It is shown that the true Hurst exponent H can be derived for self-similar (fractal) auroral data contaminated by the effect of aspect angle broadening. The necessary formulas are provided. Distorted values of scaling indices vs. the true ones. Hurst exponents deduced from the scaling indices.

  23. Relations between auroral and electrodynamical scaling parameters Intensity of auroral luminosityis proportional to the precipitation energy flux: I ~ ε. For monoenergetic precipitation: ε ~ (eV)2 where V is the field-aligned potential drop [Lyons et al., 1979] . Corrected for the effect of aspect angle broadening, scaling index αI = 0.6–0.98 and should be coincident with αV2. As shown by Lyons et al. [1979] j|| ~ V From current continuity equation in case  = const αj||=αE– 1 For substorm conditions [Golovchanskaya et al., 2008] αE ~ 1.2-1.4 Then αj||~ 0.2-0.4 Finally αV2 ~ 0.4-0.8 Considering a large number of simplifying assumptions, this is in a reasonable agreement with αI.

  24. Conclusions For the high-latitude low-frequency (f < i) plasma turbulence it was possible: 1. To show the relation to the IMF conditions. 2. To demonstrate the coincidence of the occurrence regions in the ILAT-MLT coordinates with the focuses of the large-scale Birkeland currents/convection velocity shears. 3. To provide evidence for the magnetospheric source. 4. Using particle precipitation data to discriminate between the turbulence in the auroral zone and the polar cap. 5. By application of a discrete wavelet transform method, developed for the analysis and estimation of scaling data, to find a peculiarity in the turbulence spectrum at f ~ 0.25 Hz (s ~ 30 km), and to show that it cannot be explained as a transition to the diffusion range. 6. To refute the interpretation in terms of electrostatic ionospheric turbulence. 7. To consider the finite amplitude Alfvén wave turbulence as a plausible alternative. 8. To study turbulence manifestations in the variations of auroral luminosity during substorm conditions with making corrections for aspect angle broadening distortions. 9. Under a number of simplifying assumptions, to relate the scaling parameters of electrodynamical and optical turbulent data. So far unresolved problems 1. A heavy need for higher resolution ( > 16 Hz) simultaneous electric and magnetic field measurements by a low-altitude polar-orbiting spacecraft. 2. A plausible interpretation for the higher-frequency spectral range, including the change of the slope at the local I of O+ . 3. Interpretation of the seasonal variation in the spectral slopes reported by Heppner et al. [1993]..

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