-
[show abstract]
[hide abstract]
ABSTRACT: An analysis of the coronal mass ejections (CMEs) during the ascending phase of solar cycle 23 (1996-2001) is performed; we study velocities, accelerations, widths and heliocentric latitude of emergence (position angle), their variation with time, as well as possible interdependences among them. The data set comes from the observations of CMEs by the SOHO LASCO C2 or C3 coronographs. An increase of the average CME velocity is found from solar minimum to solar maximum. The average acceleration however remains close to zero through the observation period, yet the standard deviation of the distribution of CME accelerations increases as the CME "ejection rate" increases with increasing solar activity. The average width is almost constant, while its standard deviation increases drastically.
SOLMAG 2002. Proceedings of the Magnetic Coupling of the Solar Atmosphere Euroconference; 10/2002
-
[show abstract]
[hide abstract]
ABSTRACT: The sun exhibits transient, large scale, energetic phenomena, namely solar flares, coronal mass ejections etc, directly affecting the space environment and the earth. The location and rate of appearance of these phenomena follow the general solar cycle, however there is a significant random component in their emergence. Also, the evolution and interactions between close magnetic structures of the sun is complicated and not a well understood process. We study the spatial and temporal distributions of transient energetic phenomena of the sun, investigating possible correlations and organization over wide range of scales. We also address the evolution of the distributions of energetic solar phenomena throughout the solar cycle.
SOLMAG 2002. Proceedings of the Magnetic Coupling of the Solar Atmosphere Euroconference; 10/2002
-
[show abstract]
[hide abstract]
ABSTRACT: The ideal induction of vector fields in fluids and plasmas is presented as invariance under local convection, `freezing' into flowlines and transfer of potential. Related consequences are discussed, namely the conservation of local flux and total helicity and the force-free relaxation state. In the framework of single-fluid Hall-MHD plasma flow model, the magnetic field and vorticity (which are formally analogous and generally anti-correlated, but each not ideally inducted, i.e. perfectly `frozen-into' the flow) are shown to combine in a unified magneto-vorticity field, which is ideally inducted in perfectly-conducting, however even forced, non-isentropic and viscous plasmas. Relaxation plasma states of conserved or extreme helicity magneto-vorticity fields are derived and shown to be generalized force-free states, similar to those previously derived in the framework of Hall-MHD and the multi-component plasma model. The magneto-vorticity induction in visco-resistive plasmas is also discussed. Application of the magneto-vorticity field concept in the study of type I superconductors and the spontaneous generation of magnetic fields are reviewed. The Cowling `anti-dynamo' theorem for axisymmetric flows is extended in Hall-MHD and for arbitrary flows and is shown that, in principle, the resistive (ohmic) dissipation of the magnetic field can be balanced by non-isentropic heating and/or helical forcing effects.
Plasma Physics and Controlled Fusion 01/2001; 43(2):195. · 2.42 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We make new applications of our previously proposed method for estimating the strain-rate tensor and vorticity vector in plasmas (concerning the local deformation and self rotation of the plasma fluid elements, respectively) solely from magnetic field time series. Here we use solar wind measurements of Ulysses spacecraft made in the outer heliosphere, on and off the ecliptic plane, during the period 1990-1998. The application results imply that the solar wind plasma is, to a good approximation, weakly incompressible , being nearly incompressible on the local magnetic field-normal plane, while expanding at maximum strain rate in the magnetic field direction. This property is theoretically expected, at least for low and intermediate beta plasmas, and supports previous arguments for two-dimensional MHD turbulence in the solar wind. In the magnetic induction equation the vorticity term is favoured, being at least an order of magnitude larger than the strain-rate term, thus explaining the magnetic field alignment of the minimum magnetic field variance and the random wandering of the magnetic field's vector tip on a sphere, both being well known, general features of the heliospheric magnetic field fluctuations. Further, the solar wind is found dominated by magnetized vortex sheet structures (MVS), on the tangential plane of which lie the, (not generally aligned) average vectors of magnetic field, vorticity and plasma velocity in the solar-corotating frame of reference. These coplanarity properties are shown to be consistent with a theoretically predicted force-free state, minimizing the total energy while conserving a generalized helicity function. The theory additionally implies that the (not directly measured by Ulysses) electric current density also lies on the MVS tangential plane, hence the MVS also constitute current sheets . The MVS spatial orientation implies that the MVS are wrapped in the form of magnetized vortex tubes with axes aligned to the average magnetic field. The vector couplings, characterizing the MVS, are found to weaken with increasing heliodistance and near the heliospheric current sheet.
Plasma Physics and Controlled Fusion 02/2000; 42(3):275. · 2.42 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It is shown that the magnetic field's local evolution in plasmas is directly affected by an interplay between the deformation (strain rate) and the self-rotation (vorticity) of the elementary plasma fluid volumes. At regions of strong strain rate, the fast local convergence or divergence of the flow causes exponential increase or decrease of the field's components, respectively. At regions of strong vorticity, faster directional than magnitude variations of the field occur, explaining the field alignment of the field minimum-variance direction and the random wandering of the field's tip on a sphere, both observed in the solar wind plasma, even in the absence of Alfvén waves. We further investigate the coupling between the maximum strain-rate direction and the local magnetic field, that was previously deduced from magnetic field measurements in the outer heliosphere. Cases of long-lasting, non-Parkerian, radial heliospheric magnetic field are also shown to be periods of field-aligned strain rate. A statistical proof for this alignment is given, assuming that the small-scale field fluctuations are weakly stationary and time reversible. We further propose a generalization of the Stokesian fluid stress-strain relation to the case of one-fluid, collisionless MHD plasmas, including the effects of turbulent viscosity and magnetically induced shearing motion. For a negligible or isotropic or `field-aligned' thermal pressure tensor, the proposed `Stokesian plasma' relation implies the field alignment of the solar wind plasma strain-rate direction and leads to anisotropic stress-strain balance equations, related to those of `firehose' plasma instability. The field alignment of a principal strain-rate direction leads to simplifications in the magnetic-induction equation, especially in the case of force-free fields. For the simplified case of homogeneous, isotropic and incompressible plasma turbulence, the proposed stress-strain-rate relation implies that the velocity and magnetic field inertial range spectra should be identical, further reducing to the Kolmogorov-like k-5/3 law for scale-invariant eddy cascade at constant energy-dissipation rate.
Plasma Physics and Controlled Fusion 08/1999; 41(8):967. · 2.42 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It is shown that the magnetic induction equation reduces to an autoregressive model equation. Assuming weakly ergodic field variations in steady mean plasma flow, this model permits the estimation of the mean flow deformation tensor, velocity divergence and kinetic vorticity from magnetic field time series. Applications, made to hourly-averaged, in-ecliptic interplanetary magnetic field (IMF) measurements from Ulysses spacecraft, showed that the direction of maximum deformation rate was, for most of the time, aligned to the mean field, while the vorticity tended to become perpendicular to the mean radial direction at large heliodistances.
Solar Physics 01/1996; 166(2):423-431. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A simplified, monoparametric model, based on the Van der Pol nonlinear RLC electric oscillator, is found capable of describing the shape and related morphological properties (such as the Waldmeier effect) of the sunspot cycles. The model can also exhibit long periods of sunspot inactivity of the Maunder Minimum type. According to the model, the significant rise-to-fall time asymmetry of the most recent cycles suggests that it is unlikely that another cycle suppression will occur in the forthcoming decades. The complete sunspot record and the system's attractor are successfully emulated, given the sunspot number at cycle maxima.
Solar Physics 12/1995; 163(1):193-203. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nonlinear dynamics in the solar wind and cometary plasma over small time scales are identified using sensitive entropy measures of the weak wave organization in the magnetic field polarized components. All possible linear Gaussian stochastic models are rejected at a high confidence level in all cases. The association of the detected correlations with a forward CIR shock is demonstrated using a large set of very high-resolution Pioneer-10 field measurements.
Solar Physics 03/1995; 158(1):159-172. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new method to calculate the mean free paths of energetic particles propagating parallel and anti-parallel to the interplanetary magnetic field, based on quasi-linear theory and the complex spectral polarization analysis of the field, is developed and presented. Applications of the method using HEOS 2 (1 AU), Pioneer 10 (5 AU), Pioneer 11 (20 AU), ICE (Giacobini-Zinner's comet) data have been made, showing that: (a) The mean free paths parallel and anti-parallel to the field can be completely different in various regions of the interplanetary medium and different time periods. (b) Particles are preferentially scattered in one direction. (c) The parallel and anti-parallel mean free paths become equal at certain energy. Comparisons with the results from another computational method are made.
Solar Physics 06/1994; 152(2):445-455. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Strong indications of chaotic dynamics underlying in the interplanetary and cometary magnetic field fluctuations over short time scales are identified using HEOS-2 spacecraft (at 1 AU), Pioneer 10 (at 4.8 AU), Pioneer 11 (at 20 AU) and ICE (Giacobini-Zinner cometary environment) high-resolution measurements. Other non-chaotic candidate processes, such as linear deterministic models, fractal Brownian motion, and linear gaussian stochastic models are rejected at a high confidence level using nonlinear prediction methods. Experimental proofs of phase correlations are obtained. Assuming chaotic dynamics, estimations of the Kolmogorov-Sinai entropy are provided.
Solar Physics 04/1994; 151(2):341-350. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new computational method and algorithm, based on complex Fourier analysis, is used to derive the spectral density of plane and circularly polarized fluctuation components of the interplanetary magnetic field. Applications of the method have been made using HEOS 2 (1 AU), Pioneer 10 (5 AU), Pioneer 11 (20 AU), and International Cometary Explorer (ICE) (Giocabini-Zinner's comet) data sets. The results show the existence of circularly polarized magnetohydrodynamic (MHD) waves in all cases.
03/1994;
-
[show abstract]
[hide abstract]
ABSTRACT: The fractal nature of the magnetic field fluctuations is verified using
HEOS 2 (at 1 AU), Pioneer 10 (at 4.8 AU), Pioneer 11 (at 20 AU)
interplanetary and ICE (Giacobini-Zinner) cometary environment high
resolution measurements. The fractal dimension of the time series
profiles is estimated and the self-affinity property is tested. The
results show significant diversions from the powerlaw model. Certain
properties of the field scaling, exhibited in most of the cases,
indicate that deterministic, chaotic dynamics may exist in the solar
wind turbulence.
Astronomy and Astrophysics 02/1994; 283:990. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The Sun is the nearest stellar and astrophysical laboratory, available for detailed studies in several fields of physics and astronomy. It is a sphere of hot gas with a complex and highly variable magnetic field which plays a very important role. The Sun shows an unprecedented wealth of phenomena that can be studied extensively and to the greatest detail, in a way we will never be in a position to study in other stars. Humans have studied the Sun for millennia and after the discovery of the telescope they realized that the Sun varies with time, i.e., solar activity is highly variable, in tune scales of millennia to seconds. The study of these variabilities helps us to understand how the Sun works and how it affects the interplanetary medium, Earth and the other planets. Solar power varies substantially and greatly affects the Earth and humans. Solar activity has several important periodicities, and quasi-periodicities. Knowledge of these periodicities helps us to forecast, to an extent, solar events that affect our planet. The most prominent periodicity of solar activity is the one of 11 years. The actual period is in fact 22 years because the magnetic field polarity of the Sun has to be taken into account. The Sun can be considered as a non-linear RLC electric circuit with a period of 22 years. The RLC equivalent circuit of the Sun is a van der Pol oscillator and such a model can explain many solar phenomena, including the variability of solar energy with time. Other quasi-periodicities such as the ones of 154 days, the 1.3, 1.7 to 2 years, etc., some of which might be harmonics of the 22 year cycle are also present in solar activity, and their study is very interesting and important since they affect the Earth and human activities. The period of 27 days related to solar rotation plays also a very important role in geophysical phenomena. It is noticeable that almost all periodicities are highly variable with time as wavelet analysis reveals. It is very important for humans to be in a position to forecast solar activity during the next hour, day, year, decade and century, because solar phenomena affect life on Earth and such predictions will help politicians and policy makers to better serve their countries and our planet.
Advances in Space Research.
