Seminars
Lecturer: Irina Golovchanskaya (PGI)
Date: 2007-09-04 10:00
Place: Aniara
Small scale variations of electric and magnetic fields at high latitudes and associated optical manifestationsIrina Golovchanskaya
Polar Geophysical Institute
Apatity
Russia
High-latitude electric and magnetic field fluctuations are investigated using 16 Hz (~500 m) measurements of the polar-orbiting Dynamics Explorer 2 spacecraft (altitudes from 300 km to 900 km) for 1.5 year. A relation of the fluctuations to the IMF and geomagnetic conditions, as well as to the large-scale Birkeland currents, is demonstrated. A seasonal variation in the amplitudes of fluctuations is revealed and interpreted. On the whole, it is shown that the statistical properties of the fluctuations are similar to those of the discrete aurora. In order to discriminate between the ionospheric (feedback) and magnetospheric generators of the fields, the direction of the Pointing flux δP = δE× δB associated with the fluctuations is examined. It is found that in about 95% of cases this flux is directed downward, suggesting a magnetospheric origin of the fluctuations. By applying the wavelet transform of the data, the magnetic-to-electric field ratios are computed at different frequencies (scales). These ratios appear more consistent with the values of ionospheric Pedersen conductance (5- 10 mhos) than with the inverse impedance of the Alfvén waves (< 1mho), pointing toward spatial (quasi-static) rather than temporal character of the field variations. Turbulent nature of the fluctuations are supported by the power-law form of the spectra, leptokurtic shape of the probability distribution functions (PDFs), collapse of the re-scaled PDFs onto a single curve (a property of self-affinity), and flatness in excess of 3, which increases with scale decreasing. First attempts have been performed to reveal the signatures of the turbulence in the fluctuations of auroral luminosity by examining auroral images obtained by ALIS under substorm conditions.
Created 2007-08-30 09:32:59 by Mats HolmströmLast changed 2007-08-31 07:54:25 by Mats Holmström
