On the nature of steady short-period oscillations of the earth's magnetic field /Pc3 and Pc4/

Investigation of steady short period type-Pc3 and Pc4 geomagnetic field oscillation

Certain peculiarities in the distribution of plasma concentration and of the field of Alfven waves in the earth's magnetosphere

Peculiarities in plasma density and Alfven wave velocity in magnetospher

Variations of phase velocity and gradient values of ULF geomagnetic disturbances connected with the Izu strong earthquakes

Results of study of anomaly behavior of amplitudes, phase velocities and gradients of ULF electromagnetic disturbances (<i>F</i> = 0.002 – 0.5 Hz) before and during a seismic active period are presented. Investigations were carried out in Japan (Izu and Chiba peninsulas) by two groups of magnetic stations spaced apart at a distance ~ 140 km. Every group (magnetic gradientometer) consists of three 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at distance 4–7 km. Kakioka magnetic station (>200 km to the North from Izu) was used as a reference point. Available data (only night-time intervals 00:00–07:00 LT) were preliminary filtrated by narrow pass-band filters (16 frequency bands – periods <i>T</i> = 2–512 s). The amplitude, gradient and phase velocity values and probabilities of directions of gradient and phase velocity vectors were constructed for the every frequency band. Apparent resistivities of the Earth’s crust in the every frequency band were calculated using the phase velocity values. It was found that Z component amplitudes of the ULF magnetic disturbances increased at Izu peninsula 2–4 weeks before the seismic active period and 2–4 days before the strongest seismic shocks (<i>M</i> > 6). Ratio of Z component amplitudes of Kamo (Izu) and Kakioka data (<i>Z_k</i>/<i>Z_kk</i>) increased during 2–4 weeks before the seismic activity start (27 June 2000) and reached a maximum just before a moment of the strongest seismic shock (EQ with <i>M</i> = 6.4). The gradient and the phase velocity values had an anomaly behavior during the same 2–4 weeks before the start of seismic active period. The gradient vectors of the total horizontal component of the ULF magnetic pulsations were probably directed to the regions with increased conductivity. New additional direction of the gradient vectors appeared 2–3 weeks before the seismic activity start – the direction to the seismic active area which appeared due to a magma rising

ULF magnetic emissions connected with under sea bottom earthquakes

Measurements of ULF electromagnetic disturbances were carried out in Japan before and during a seismic active period (1 February 2000 to 26 July 2000). A network consists of two groups of magnetic stations spaced apart at a distance of &#x2248;140 km. Every group consists of three, 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at a distance of 4–7 km. The results of the ULF magnetic field variation analysis in a frequency range of <i>F</i> = 0.002–0.5 Hz in connection with nearby earth-quakes are presented. Traditional <i>Z</i>/<i>G</i> ratios (<i>Z</i> is the vertical component, <i>G</i> is the total horizontal component), magnetic gradient vectors and phase velocities of ULF waves propagating along the Earth’s surface were constructed in several frequency bands. It was shown that variations of the <i>R</i>(<i>F</i>) = <i>Z</i>/<i>G</i> parameter have a different character in three frequency ranges: <i>F</i>₁ = 0.1 ± 0.005, <i>F</i>₂ = 0.01 ± 0.005 and <i>F</i>₃ = 0.005 ± 0.003 Hz. Ratio <i>R</i>(<i>F</i>₃)/<i>R</i>(<i>F</i>₁)</i> sharply increases 1–3 days before strong seismic shocks. Defined in a frequency range of <i>F</i>₂ = 0.01 ± 0.005 Hz during nighttime intervals (00:00–06:00 LT), the amplitudes of <i>Z</i> and <i>G</i> component variations and the <i>Z</i>/<i>G</i> ratio started to increase &#x2248; 1.5 months before the period of the seismic activity. The ULF emissions of higher frequency ranges sharply increased just after the seismic activity start. The magnetic gradient vectors (<b>&#x2207; <i>B</i></b> &#x2248; 1 – 5 pT/km), determined using horizontal component data (<i>G</i> &#x2248; 0.03 – 0.06 nT) of the magnetic stations of every group in the frequency range <i>F</i> = 0.05 ± 0.005 Hz, started to point to the future center of the seismic activity just before the seismoactive period; furthermore they continued following space displacements of the seismic activity center. The phase velocity vectors (<i>V</i> &#x2248; 20 km/s for <i>F</i> = 0.0067 Hz), determined using horizontal component data, were directed from the seismic activity center. Gradient vectors of the vertical component pointed to the closest seashore (known as the 'sea shore' effect). The location of the seismic activity centers by two gradient vectors, constructed at every group of magnetic stations, gives an &#x2248; 10 km error in this experiment

Physics of Auroral Phenomena

Abstract. On February 16, 2003 EISCAT-Heating experiment was carried out on observation of heating induced disturbances in the magnetosphere. A pump wave of 4.04 MHz in X-mode was used for the ionosphere modification from 19:55 to 23:59:59 UT in square modulation regime with 5 minutes ON / 5 minutes OFF cycle. During the interval of good conjugation of CLUSTER with the heating facility spacecraft 4 (Tango) recorded clear variations of electric field at modulation frequency lasting around 30 minutes. Spectral peak of the variations at 1.67 mHz is more pronounced in the y-component. Slow temporal variations of the conductivity in the heated volume due to electron density increasing in the E-region related with the heating duty cycle provide the same variations of disturbed electric field. Polarization of the disturbances is almost linear; it corresponds to constant ratio of Hall to Pedersen conductivity variations. The analysis of the signal waveform shows that at ~ 23.30 UT the phase of the variations is changed together with a sign of DC electric field. The transverse size of the disturbed structure in the magnetosphere is near 0.1 R E . The observed behavior of the disturbances may be interpreted in terms of Alfven mode propagation of the disturbed ionospheric electric field into the magnetosphere. The electric field disturbances being uniform in the region of modified conductivity have a discontinuity at its border of the region and decay as two-dimensional dipole outside it. Field-aligned currents are related with conductivity gradients and distinct magnetic field variations are clear seen in quick-look plots around 20.30 UT. For further study of this event records of magnetic variations onboard CLUSTER satellites would be very important