|
Principal Component Analysis of Background and Sunspot Magnetic Field Variations During Solar Cycles 21-23
|
|
Valentina Zharkova Submitted: 2012-07-05 06:42
The aim of this paper is to derive principal components (PCs) in variations of (a) the solar background magnetic field (SBMF) measured by the Wilcox Solar Observatory with low spatial resolution for solar cycles 21-23, and, (b) the sunspot magnetic field (SMF) in cycle 23 obtained by SOHO/MDI.
For reduction of the component dimensions, the Principal Component Analysis (PCA) is carried out to identify global
patterns in the data and to detect the pairs of principal components and corresponding empirical orthogonal functions (EOFs).
PCA analysis reveals two main temporal PCs in SBMF of opposite polarities originating in the opposite
hemispheres and running noticeably off-phase (with about a two and half year delay), with their maximums overlapping in the most active hemisphere for a given cycle. Their maximum magnitudes are reduced by factor 3
from cycle 21 to 23 overlapping in the Northern hemisphere for cycle 21, the Southern one in cycle 22 and in the
Northern again in cycle 23. The reduction of magnitudes and slopes of the maximums of the SBMF waves from cycle 21 towards cycle 23 leads us to expect lower magnitudes of the SBMF wave in cycle 24. Also PCA allowed us to detect 4 pairs of EOFs in the SBMF latitudinal components: the two main latitudinal EOFs attributed to symmetric and another three pairs of EOFs assigned to asymmetric types of meridional flows. The results allow us to postulate the existence of dipole and quadruple (or triple dipole) magnetic structures in the SBMF, which varies from cycle to cycle and takes the form of two waves travelling off phase, with a phase shift of one quarter of the 11 year period. Similar PC and EOF components were found in temporal and latitudinal distributions of the sunspot magnetic field for cycle 23 revealing the polarities opposite to the SBMF polarities and double maximum in time or maximums in latitude corresponding to the maximums of the SBMF PC residuals or minimums in SBMF EOFs, respectively. This allows to suggest that the SBMF waves also modulate the occurrence and magnitudes of sunspot magnetic field in time and latitude.
Authors: Zharkova V.V., Shepperd, S.J. and Zharkov S.I.
Projects: SoHO-MDI
|
Publication Status: 2012, MNRAS, in press
Last Modified: 2012-07-05 07:17
|
 
 
|
|
|
Particle dynamics in the reconnecting heliospheric current sheet: solar wind data versus 3D PIC simulations
|
|
Valentina Zharkova Submitted: 2012-04-20 11:07
In this paper we apply an assumption of the reconnecting heliospheric current sheet (HCS) for explanation of some contradictory results in the experimental detection of the sector boundaries (SBs) from the interplanetary magnetic field (IMF) and electron pitch angle measurements. Trajectories, densities, velocity and pitch angle distributions of particles accelerated by a super-Dreicer electric field are investigated with 2.5D full kinetic particle-in-cell (PIC) approach in the heliospheric current sheet (HCS) assumed to undergo a slow magnetic reconnection process with magnetic field configurations deduced from the solar wind observations. This approach reveals that during motion in a current sheet both kinds of particles, electrons and protons, are to be separated, either fully or partially, with respect to its midplane that can lead to their ejection to the opposite semiplanes that was also observed during the HCS crossings. This separation is found to form Hall's currents and polarisation electric field across the current sheet, which distribution over the current sheets allows to reproduce the magnitudes and temporal profiles of proton and ion velocities measured across the sector boundary (current sheet midplane). This separation process, in turn, divides both kinds of particles on 'transit' and 'bounced' ones depending on a side of the current sheet where they enter it and where they are supposed to be ejected. The transit and bounced protons reproduce rather closely the measured distributions of proton/ion densities about the current sheet midplane with a larger maximum occurring at the heliospheric sector boundary to be formed by the bounced protons and the other two smaller maximums on both sides from the central one to be formed by 'transit' protons. The observed electron distributions of density and energy before and after SBCs are found to fit the simulated ones for electrons accelerated in a current sheet revealing a sharp increase of density from one side from the HCS boundary and a depression from the other side. The transit electrons are shown to gain energies up to ten of keVs while the bounced ones gain only a few tens eVs as often measured in the HCS with a single crossing that results in the bump-in-tail electron distributions leading to Langmuir turbulence. The bounced electrons are shown to be responsible for the increased density of electrons detected at some distance from the HCS boundary (midplane) with the horse shoe-like or medallion- (or locket)-type distributions in pitch angles with the distance, at which electrons turn away from the HCS, being dependent on a magnitude of the guiding magnetic field.
Authors: Zharkova V.V. and Khabarova O.V.
Projects: None
|
Publication Status: Astrophysical Journal, 2012, 750/1, in press
Last Modified: 2012-04-25 12:45
|
 
 
|
|
|
Diagnostics of electron beam properties from the simultaneous hard X-ray and microwave emission in the 10 March 2001 flare
|
|
Valentina Zharkova Submitted: 2011-05-23 08:56
Simultaneous simulation of HXR and MW emission with the same populations of
electrons is still a great challenge for interpretation of observations in real
events. In this paper we apply the FP kinetic model of precipitation of
electron beam with energy range from 12 keV to 1.2 MeV to the interpretation of
X-ray and microwave emissions observed in the flare of 10 March 2001. Methods.
The theoretical HXR and MW emissions were calculated by using the distribution
functions of electron beams found by solving time-dependent Fokker-Planck
approach in a converging magnetic field (Zharkova at al., 2010; Kuznetsov and
Zharkova, 2010) for anisotropic scattering of beam electrons on the ambient
particles in Coloumb collisions and Ohmic losses. The simultaneous observed HXR
photon spectra and frequency distribution of MW emission and polarization were
fit by those simulated from FP models which include the effects of electric
field induced by beam electrons and precipitation into a converging magnetic
loop. Magnetic field strengths in the footpoints on the photosphere were
updated with newly calibrated SOHO/MDI data. The observed HXR energy spectrum
above 10 keV is shown to be a double power law which was fit precisely by the
photon HXR spectrum simulated for the model including the self-induced electric
field but without magnetic convergence. The MW emission simulated for different
models of electron precipitation revealed a better fit to the observed
distribution at higher frequencies for the models combining collisions and
electric field effects with a moderate magnetic field convergence of 2. The MW
simulations were able to reproduce closely the main features of the MW emission
observed at higher frequencies.
Authors: Zharkova, V.V., Meshalkina, N.S., Kashapova, L.K., Kuznetsov, A.A. and Altyntsev A.T.
Projects: RHESSI
|
Publication Status: Astronomy and Astrophysics, in press
Last Modified: 2011-05-24 09:44
|
 
 
|
|
|
|
Key
|
 | Go to main E-Print page. |
 | Download Preprint. |
 | Submitters Homepage. |
 | Edit Entry. |
 | Delete abstract. |
|
|
|