Search

We present an optimized design of our recently realized disc dynamo. Like the original set-up, the optimized dynamo consists of a flatmulti-arm spiral coil and a co-axially placed disc which is connected to the former by sliding liquid metal contacts. In contrast to the original set-up, the disc and the coil in the optimized design have different sizes. This allows the disc to capture more of the high-density magnetic flux generated in the inner part of the coil and to avoid the reverse flux in the outer part of the coil. By optimizing the coil and dics radii, the critical magnetic Reynolds number can be reduced from -34.6 when the disc and the coil have equal inner and outer radii with the ratio ri/ro -0.36 to Rm-11.6. This lowest possible disc dynamo threshold is attained when the disc and the coil have relatively narrow widths. Using a slightly suboptimal but more practical set-up with the inner and outer radii of the disc and coil equal to (0.3,0.9) and (0.74,1), respectively, self-excitationis expected at Rm-14.6. [ABSTRACT FROM AUTHOR]

The magnetic fields take place in different astrophysical objects, such as stars, planets, galaxies, accretion discs etc. Their evolution is usually described by the dynamo model. The equations of the dynamo are quite difficult to be solved, so different approximations are often used. One of the most successful ones are connected with the no- model which has been developed for thin discs that can be a good model for galaxies and accretion discs. In this paper we study the magnetic field evolution in the case of Keplerian rotation law. The results have been obtained for the simplest case and for the model with helicity fluxes. This approach can be useful while researching the role of convective flows in the discs. It is shown that the magnetic field can have oscillations in this case. Also we show the evolution of the energy which can significantly change because of the convective flows. [ABSTRACT FROM AUTHOR]

Ionospheric disturbance dynamo is one of the main processes that causes perturbations in the upper atmosphere during a magnetic storm. We present a new method, based on the least square fitting, for estimation of the magnetic signatures associated with ionospheric disturbance currents. Using a wavelet semblance analysis, the durations of disturbance dynamo electric fields have been investigated at three longitudinal sectors. For that we have analyzed the disturbance dynamo (Ddyn) for 19 magnetic storms. It has been found that during CME generated storms magnetic signature of Ddyn may be observed—depending on strength of the storm as well as on the duration of interplanetary magnetic field (IMF) Bz southward—in one, two or all three longitudes. The Oscillatory behavior of IMF Bz during the high‐speed solar wind streams (HSSWs) generates Ddyn globally and the corresponding effects are observed at all low latitude magnetic observatories. In this regard, the Joule heating estimation shows that CME and HSSWs generated storms have very different patterns. The Ddyn duration is found to be maximum for the storms occurring during equinox season. Moreover, the HSSWs events are more likely to cause—because of the oscillatory IMF Bz—long lasting Ddyn as compared to CME generated counterpart. This study presents a detailed analysis of disturbance dynamo as affected by longitudinal and seasonal variations. In this regard the difference in magnetic signatures, of CME and HSSWs originated storms, have been highlighted. Plain Language Summary: Space weather activities significantly perturb the quiet time ionosphere through various coupling mechanisms. Ionospheric disturbance dynamo is one of the main processes that causes perturbations in the upper atmosphere during a magnetic storm. We present a new method for estimation of the magnetic signatures associated with ionospheric disturbance currents. The durations of disturbance dynamo electric fields have been investigated at three longitudinal sectors for 19 magnetic storms. It has been found that during CME generated storms magnetic signature of Ddyn may be observed in one, two or all three longitudes. The Oscillatory behavior of IMF Bz during the high speed solar wind streams (HSSWs) generates Ddyn globally and the corresponding effects are observed at all low latitude magnetic observatories. In this regard, the Joule heating estimation shows that CME and HSSWs generated storms have very different patterns. The Ddyn duration is found to be maximum for the storms occurring during equinox season. Moreover, the HSSWs events are more likely to cause long lasting Ddyn as compared to CME generated counterpart. This study presents a detailed analysis of disturbance dynamo of CME and HSSWs originated storms. Key Points: A least‐square fitting method has been used to evaluate the magnetic signatures disturbance dynamo electric fieldsDifferences in the magnetic signatures of CME and high‐speed solar wind streams generated magnetic storms are identifiedWe have analyzed disturbance dynamo in three different longitudinal sectors, as affected by seasonal and longitudinal variations [ABSTRACT FROM AUTHOR]