Modeling of the Lightning Return Stroke Current at a Tall Structure Using the Derivative of the Heidler Function

Traditionally tall structures have been modeled as simple lossless transmission lines. This model is inadequate for the CN Tower, which may be modeled as a series of transmission lines with different characteristic impedances resulting in a reflection coefficient at each discontinuity. Analysis shows that these vary significantly and are related to the ratio of the current derivative peak to the current derivative 10%-90% risetime, suggesting that they are frequency dependent. The magnitude of the reflection from the return stroke front, if it does exist, is much smaller that was previously proposed. An alternative approach to modeling, based on modeling the current derivative, is proposed and it is found to provide a better match with the measured waveforms. The CN Tower is modeled as a series of uniform lossless transmission lines and the channel is represented by the MTLL model. The features of the measured magnetic field waveform are well reproduced.

Modeling of the Lightning Return Stroke Current at a Tall Structure Using the Derivative of the Heidler Function

Traditionally tall structures have been modeled as simple lossless transmission lines. This model is inadequate for the CN Tower, which may be modeled as a series of transmission lines with different characteristic impedances resulting in a reflection coefficient at each discontinuity. Analysis shows that these vary significantly and are related to the ratio of the current derivative peak to the current derivative 10%-90% risetime, suggesting that they are frequency dependent. The magnitude of the reflection from the return stroke front, if it does exist, is much smaller that was previously proposed. An alternative approach to modeling, based on modeling the current derivative, is proposed and it is found to provide a better match with the measured waveforms. The CN Tower is modeled as a series of uniform lossless transmission lines and the channel is represented by the MTLL model. The features of the measured magnetic field waveform are well reproduced.

Magnetic vector inversion using XYZ measured by fluxgate magnetometer in UAV

<p>Traditionally, the inversion of magnetic data assumes the magnetization of the local geology to run parallel to the Earth’s internal magnetic field that is usually modelled using International Geomagnetic Reference Field (IGRF). Assuming the magnetization parallel to the main field, only the total (scalar) magnetic data are the sufficient input for the inversion of source susceptibility.</p><p>Local magnetization may alter from the main field direction in areas of remanent magnetization. Recently, magnetization vector inversion (MVI) using the total field has become an important tool trying to distinguish magnetic data affected by remanenence. Total field as a scalar field exclude all information of the direction of the internal magnetization and more information is required to reveal any remanent magnetization from the main field direction.  Compared to total field using the 3-component XYZ vector magnetic measurements provide more information of the source.  More measurements increase the unambiguous nature of data and may reveal the areas of possible remanence. </p><p>To measure XYZ vector magnetic field we use fluxgate 3-component magnetometer with rigid installation on a fixed-wing UAV. With the help of accurate inertial measurement units the measured magnetic field can be determined in the direction of fixed coordinate system. The components of the measured magnetic field rotated into the geographical coordinate represent the magnetic field at survey area.</p><p>UAV survey provided the data as the input for the inversions. We made the inversion separately for both susceptibility and magnetization vector. Susceptibility inversion means inversion of induced magnetization, i.e., a single component of magnetization parallel to the main field direction. Magnetization vector inversion, however, resolves all three components of magnetization, which may or may not include remanent magnetization in addition to induced one.</p><p>The benefits from utilizing XYZ components of the magnetic field with magnetization inversion seem promising in finding remanenence magnetization.</p><p> </p><p> </p>

Global current systems in Jupiter’s polar magnetosphere

<p>The Juno spacecraft has been in polar orbit around Jupiter since July 4, 2016 sampling Jupiter's environment from ~1.05 Jovian radii outwards, extending to the distant reaches of the Jovian magnetosphere. Juno’s polar orbit makes it possible to acquire direct observations of the Jovian magnetosphere and auroral emissions above the poles for the first time. We have quantitatively measured magnetic field-aligned (Birkeland) currents which are associated with Jupiter's auroral emissions and have modelled the morphology of the currents based on observations collected along one of Juno’s polar periJove passes. The structure of the field-aligned currents seems to be more complex than expected showing a dynamic filamentation in the azimuthal direction and strong asymmetries between the northern and southern regions. This complexity indicates a non-steady state generation of field-aligned currents possibly with non-linear processes involved. We present a way towards modeling the field-aligned currents more systematically extending the analysis with data from multiple periJove passes. We also show the development of a composite map of field-aligned current regions above the polar aurorae. This map gives us important information on the global structure of the field aligned currents and therefore on how angular momentum is transferred between Jupiter’s atmosphere and magnetosphere.</p>

To the question of constructing measuring devices based on fluxgate sensors

The article discusses the issues of feeding fluxgates from compact, low-power generators built on AND-NOT logic elements. The frequency of such generators depends on the magnitude of the measured magnetic field strength. This gives reason to consider the possibility of using frequency as a useful signal. The article discusses the issues of feeding fluxgates from compact, low-power generators built on AND-NOT logic elements. The frequency of such generators depends on the magnitude of the measured magnetic field strength. This gives reason to consider the possibility of using frequency as a useful signal. The article proposes to use modulated rectangular voltage pulses, that is, pulses with high-frequency filling, to power a fluxgate. Then, under the influence of the measured magnetic field, the filling frequency changes, according to which the magnitude of the intensity is determined, and the frequency of the modulating voltage corresponding to the passport frequency of the fluxgate remains constant. In this case, it becomes possible to increase the deviation of the filling frequency due to the use of the released output winding of the fluxgate as an additional element of the generator. It was also experimentally established that in order to increase the voltage on the excitation winding of the fluxgate and, as a consequence, to increase its sensitivity, it is advisable to power through the D-trigger, which makes it possible to obtain bipolar voltage on the excitation winding. In addition, it is necessary to use resonance phenomena (at the frequency of the modeling voltage) in the serial circuit “connecting capacitors - excitation coil of a fluxgate”, which allows increasing the voltage on the excitation winding without increasing the voltage of the power source.

Variations in ratio and correlation of solar magnetic fields in the Fe I 525.02 nm and Na I 589.59 nm lines according to Mount Wilson measurements during 2000–2012

Variations in the solar magnetic-field ratio over 13 years are analyzed, relying on the comparison of simultaneous measurements in two spectral lines at the Mount Wilson Observatory. The ratio and correlation coefficient are calculated over the general working range of measured magnetic-field values and in various ranges of field magnitudes. We study variations in both the parameters. We have found the following tenden-cies: i) the parameters show changes with solar cycle in the general case; ii) their dependence on magnetic-field magnitude is a nonlinear function of time, and this is especially pronounced in the ratio behavior; iii) several separate ranges of the field magnitudes can be distin-guished based on the behavioral patterns of variations in the ratio. We discuss correspondences between these ranges and the known structural objects of the solar atmosphere. This leads to a conclusion that the dependence of the parameters on magnetic-field magnitude and time is connected with the variety of magnetic structural components and their cyclic rearrangements. The reported results may be useful for solving interpretation problems of solar magnetic-field meas-urements and for the cross-calibration of applicable instruments. They can also be used for tasks related to the creation of a uniform long temporal series of solar magnetic-field data from various sources.