scholarly journals Magnetic Shear and Nonpotential Energy Evolution of Solar Minimum and the Onset of Solar Cycle 23

2001 ◽  
Vol 203 ◽  
pp. 267-269
Author(s):  
J. Dun ◽  
H. Zhang ◽  
B. Zhang ◽  
R. Li
Keyword(s):  
Solar Cycle ◽  
Relative Number ◽  
Transverse Field ◽  
Active Regions ◽  
Shear Angle ◽  
Magnetic Shear ◽  
Data Set ◽  
Solar Cycle 23 ◽  
Sunspot Relative Number ◽  
The Magnetic Field

Using a 1995-1998 data set of vector magnetograms, the magnetic field flux, shear angle of the transverse field and nonpotential energy of active regions were calculated. The evolution of these parameters were analyzed together with time series of the solar monthly sunspot relative number and area to study their relationships in the ascending phase of solar cycle 23. We find the magnetic flux and nonpotential energy have a good correlation with sunspot relative number and area. But the magnetic shear angle does not develop as above indices.

scholarly journals EUV Line Intensities and the Magnetic Field in Solar Active Regions

2001 ◽  
Vol 203 ◽  
pp. 276-279
Author(s):  
J. Ireland ◽  
A. Fludra
Keyword(s):  
Magnetic Field ◽  
Extreme Ultraviolet ◽  
Active Regions ◽  
Central Meridian ◽  
Coronal Emission ◽  
Data Set ◽  
Line Intensities ◽  
Doppler Imager ◽  
Synoptic Observations ◽  
The Magnetic Field

The Coronal Diagnostic Spectrometer (CDS) on SOHO carries out daily synoptic observations of the Sun in four EUV (extreme ultraviolet) spectra: He I 584 Å, O V 630 Å, Mg IX 368 Å and Fe XVI 360 Å, over a 4 arcmin-wide strip along the solar central meridian. Using 53 active regions observed in this data set along with co-temporally observed SOHO-MDI (Michelson Doppler Imager) magnetograms we study the correlation of the chromospheric, transition region and coronal emission with the photospheric magnetic field for meridional active regions, probing the relation between the radiative output and magnetic observables. We also establish empirical, quantitative relations among intensities of different lines, and between intensities and the magnetic field flux.

Three Super Active Regions in the Descending Phase of Solar Cycle 23

2003 ◽  
Vol 3 (6) ◽  
pp. 491-494 ◽  
Author(s):  
Hong-Qi Zhang ◽  
Xing-Ming Bao ◽  
Yin Zhang ◽  
Ji-Hong Liu ◽  
Shu-Dong Bao ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Active Regions ◽  
Solar Cycle 23

scholarly journals Flare Occurrence in the Solar Active Regions with Reversed Helicity Sign

2001 ◽  
Vol 203 ◽  
pp. 247-250
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Relative Number ◽  
Active Regions ◽  
Flare Activity ◽  
Sunspot Maximum ◽  
Solar Active Regions ◽  
Current Helicity

Based on the Huairou Solar Observing Station dataset, we computed the current helicity for several hundreds of active regions and found that: (1) Active regions that do not follow the hemispheric helicity sign rule show more flare activity than normal active regions. (2) The relative number of active regions with reversed helicity sign is higher near sunspot maximum. (3) It appears that during solar cycle 22 the southern hemisphere has more the reversed-sign active regions and stronger flare activity than the northern hemisphere.

scholarly journals The balance of magnetic fluxes in active regions

1968 ◽  
Vol 35 ◽  
pp. 47-49 ◽  
Author(s):  
Jan Olof Stenflo
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Active Region ◽  
Solar Surface ◽  
Active Regions ◽  
Basic Feature ◽  
The Sun ◽  
Magnetic Disturbance ◽  
The Magnetic Field

According to modern theories of the solar cycle, active regions on the Sun are caused by a magnetic disturbance penetrating the solar surface from below. Sunspots, filaments, flares and other conspicuous events in an active region seem to be only secondary phenomena, the basic feature being the magnetic field itself.

scholarly journals Properties and geoeffectiveness of magnetic clouds in the rising, maximum and early declining phases of solar cycle 23

2005 ◽  
Vol 23 (2) ◽  
pp. 625-641 ◽  
Author(s):  
K. E. J. Huttunen ◽  
R. Schwenn ◽  
V. Bothmer ◽  
H. E. J. Koskinen
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
Solar Maximum ◽  
Magnetic Storms ◽  
Magnetic Clouds ◽  
Solar Cycles ◽  
The North ◽  
Solar Cycle 23 ◽  
The Magnetic Field

Abstract. The magnetic structure and geomagnetic response of 73 magnetic clouds (MC) observed by the WIND and ACE satellites in solar cycle 23 are examined. The results have been compared with the surveys from the previous solar cycles. The preselected candidate MC events were investigated using the minimum variance analysis to determine if they have a flux-rope structure and to obtain the estimation for the axial orientation (θC, φC). Depending on the calculated inclination relative to the ecliptic we divided MCs into "bipolar" (θC<45°) and "unipolar" (θC>45°). The number of observed MCs was largest in the early rising phase, although the halo CME rate was still low. It is likely that near solar maximum we did not identify all MCs at 1AU, as they were crossed far from the axis or they had interacted strongly with the ambient solar wind or with other CMEs. The occurrence rate of MCs at 1AU is also modified by the migration of the filament sites on the Sun towards the poles near solar maximum and by the deflection of CMEs towards the equator due to the fast solar wind flow from large polar coronal holes near solar minimum. In the rising phase nearly all bipolar MCs were associated with the rotation of the magnetic field from the south at the leading edge to the north at the trailing edge. The results for solar cycles 21-22 showed that the direction of the magnetic field in the leading portion of the MC starts to reverse at solar maximum. At solar maximum and in the declining phase (2000-2003) we observed several MCs with the rotation from the north to the south. We observed unipolar (i.e. highly inclined) MCs frequently during the whole investigated period. For solar cycles 21-22 the majority of MCs identified in the rising phase were bipolar while in the declining phase most MCs were unipolar. The geomagnetic response of a given MC depends greatly on its magnetic structure and the orientation of the sheath fields. For each event we distinguished the effect of the sheath fields and the MC fields. All unipolar MCs with magnetic field southward at the axis were geoeffective (Dst<-50nT) while those with the field pointing northward did not cause magnetic storms at all. About half of the all identified MCs were not geoffective or the sheath fields preceding the MC caused the storm. MCs caused more intense magnetic storms (Dst<-100nT) than moderate magnetic storms (-50nT ≥Dst≥-100nT).

scholarly journals Relationship between the minima of the horizontal magnetic component measured in Mexico and the Dst and SYM-H indices for geomagnetic storms with Dst≤ -100nT during the descending phase of solar cycle 23

2016 ◽  
Vol 55 (2) ◽  
Author(s):  
Julia Lénica Martínez-Bretón ◽  
Blanca Mendoza Ortega ◽  
Esteban Hernández-Quintero
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Storms ◽  
Universal Time ◽  
The Other ◽  
Magnetic Component ◽  
Magnetic Observatory ◽  
Solar Cycle 23 ◽  
The Difference ◽  
Current Systems ◽  
The Magnetic Field

In this paper, we analyze the time delay between the occurrence of the minima in the geomagnetic Dst, SYM-H indices and the horizontal magnetic component (H) measured in the Teoloyucan Magnetic Observatory (TEO) of Mexico. This difference was calculated in Universal Time for 15 geomagnetic storms (Dst≤-100nT) occurred during the descending phase of solar cycle 23. We found that, when the TEO was at the dayside, dawn and dusk, the time difference was negative, indicating that the minimum appeared first in the Dst, SYM-H reported by Kyoto, and afterwards in the H reported by TEO. On the other hand, when the TEO was close to midnight the difference was positive, indicating that the minimum occurred first at TEO and afterwards in Dst. We noticed that 14 out of 15 geomagnetic storms followed this behavior, except the most intense one of the sample. For the rest of the storms, it seems that the cause of the delay is not the intensity of the magnetic field at minimum but the intensity of the current systems present during the storm occurrences.

The Photospheric Flow near the Flare Locations of Active Regions

2000 ◽  
Vol 179 ◽  
pp. 249-250
Author(s):  
Debi Prasad Choudhary
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Field Of View ◽  
Image Motion ◽  
Line Center ◽  
Flare Activity ◽  
Data Set ◽  
Zero Crossing ◽  
Left And Right ◽  
The Magnetic Field

Extended AbstractThe observation of the photospheric velocity field along with the magnetic field is very important for understanding the origin and evolution of these locations of active regions. Earlier measurements have shown a general down flow with velocities of 0.2 to 0.3 km s−1in the active regions along with few locations of upflows. The localised upflows are observed in the light bridges and emerging flux regions with different speeds (Beckers &amp; Schröter 1969). The flow patterns of flare locations in the active regions are observed by using the tower vector magnetograph (TVM) of Marshall Space Flight Centre. The line-center-magnetogram (LCM) technique has been employed to determine the active region velocities (Giovanelli &amp; Ramsay 1971). The LCM is based on finding the wavelength in the line profile where two opposite circularly polarised Zeeman-split components change sign. If the material in the magnetic field of different locations have relative line of sight velocities, their cross-over wavelength will be seen to be Doppler shifted. In order to use the LCM with TVM, a series of Stoke-V images are made as a function of wavelength and their cross-over wavelength at each pixel is determined. We have observed 12 active regions between June 25th and August 25th, 1998. Three of these active regions (NOAA 8253, 8264 and 8307) show flare activity associated with the flux emergence and/or changes in magnetic shear during their disk passage. The images of a selected field of view in left and right circularly polarised Zeeman components in the wavelength range of 5250.12 to 5250.30 Å are obtained at 10 mÅ steps. The time taken for obtaining one set of observations is about 10–15 minutes. In this mode of operation, the start and end wavelengths are specified and the filter is tuned at desired wavelength steps. In one observing sequence, two sets of left and right circularly polarized images are produced as a function of wavelength. These sets of images are processed and merged following a certain procedure to produce a data cube. The most important requirement for the Doppler shift measurements is the repeatability of the wavelength steps. In the recent improvement, the filter tuning was achieved with accuracy better than 0.3 mÅ by using an optical encoder. However, it has been shown that insufficient spectral resolution would lead to spurious zero-crossing shift of asymmetric Stokes-V. This effect of spectral smearing in the case of observations with TVM and the present data analysis procedure has been estimated by simulation. The individual images are flat fielded and registered in order to remove the pixel sensitivity variation over the field of view and image motion during the observations. The two Zeeman components are subtracted to obtain a set of difference images as a function of wavelength. These processed images are merged to make Stokes-V data cubes, with two spatial and one-wavelength dimensions. The integrated Stokes-V profiles are obtained by averaging the profiles of the pixels with magnetic field values higher than a certain cut-off value depending on the noise level in each data set.

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