scholarly journals Periodic variations of the geomagnetic activity indices Ap and Kp

2021 ◽  
Vol 23 (2) ◽  
Author(s):  
Pandey A.C. ◽  
◽  
Sham Singh ◽  
Dinesh Kumar Pathak ◽  
Archana Shukla ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
Interplanetary Magnetic Field ◽  
Wind Velocity ◽  
Geomagnetic Activity ◽  
Solar Wind Velocity ◽  
Data Sets ◽  
Time Intervals ◽  
Activity Indices

Yearly averages of geomagnetic activity indices Kp and Ap for the years 1984 to 2018 be compared to the relevant averages of VxBs, where V is the solar wind velocity and Bs is the southward interplanetary magnetic field (IMF) component. The correlation of both quantities is known to be rather good. Comparing the averages of Ap and Kp with V and Bs separately. We found that, during the declining phase of solar cycle, V and during the ascending phase Bs have more influence on Ap and Kp indices. According to this observation the 27 days and semiannual, Ap and Kp variations be analysed discretely for years after and before sunspot minima. The time intervals prior to sunspot minima with a significant 27-day recurrent period of the IMF structure and those intervals after sunspot minima with a significant 28 to28.5 day recurrent phase of the structure be used. The averaged spectra of the two Ap and Kp data sets obviously show a period of 27 days before and a period of 28 to 29 days after sunspot minimum.

scholarly journals Effect of large-scale inhomogeneity of solar wind velocity on distribution of directions of interplanetary magnetic field vector

2019 ◽  
Vol 5 (3) ◽  
pp. 50-63
Author(s):  
Дмитрий Ерофеев ◽  
Dmitry Erofeev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Angular Distribution ◽  
Solar Cycle ◽  
Interplanetary Magnetic Field ◽  
Wind Velocity ◽  
High Speed ◽  
Large Scale ◽  
Solar Wind Velocity ◽  
Statistical Characteristics

Using data with hourly resolution obtained in near-Earth heliosphere in 1965–2014, we have calculated statistical characteristics of the angles describing the direction of the interplanetary magnetic field (IMF): root-mean-square deviations of azimuthal and elevation angles, asymmetries of their distributions, and coefficient of correlation of the angles. It has been shown that the above characteristics varied in the course of solar cycle, and some of them changed their signs when solar polar magnetic field reversed. The results obtained from the experimental data analysis were compared with a model describing transport of large-scale disturbances of IMF lines by the inhomogeneous solar wind. The comparison has shown that the variations in the angular distribution of IMF in the course of solar cycle probably occur due to the appearance of the large-scale latitudinal gradient of solar wind velocity during solar minima. In addition, the angular distribution of IMF has been found to be substantially affected by the longitudinal velocity gradient in trailing parts of high-speed streams and short-term local-scale variations in velocity gradients.

scholarly journals Effect of large-scale inhomogeneity of solar wind velocity on distribution of directions of interplanetary magnetic field vector

2019 ◽  
Vol 5 (3) ◽  
pp. 42-53
Author(s):  
Дмитрий Ерофеев ◽  
Dmitry Erofeev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Angular Distribution ◽  
Solar Cycle ◽  
Interplanetary Magnetic Field ◽  
Wind Velocity ◽  
High Speed ◽  
Large Scale ◽  
Solar Wind Velocity ◽  
Statistical Characteristics

Using data with hourly resolution obtained in near-Earth heliosphere in 1965–2014, we have calculated statistical characteristics of the angles describing the direction of the interplanetary magnetic field (IMF): root-mean-square deviations of azimuthal and elevation angles, asymmetries of their distributions, and coefficient of correlation of the angles. It has been shown that the above characteristics varied in the course of solar cycle, and some of them changed their signs when solar polar magnetic field reversed. The results obtained from the experimental data analysis were compared with a model describing transport of large-scale disturbances of IMF lines by the inhomogeneous solar wind. The comparison has shown that the variations in the angular distribution of IMF in the course of solar cycle probably occur due to the appearance of the large-scale latitudinal gradient of solar wind velocity during solar minima. In addition, the angular distribution of IMF has been found to be substantially affected by the longitudinal velocity gradient in trailing parts of high-speed streams and short-term local-scale variations in velocity gradients.

scholarly journals Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity

2009 ◽  
Vol 27 (5) ◽  
pp. 1909-1914 ◽  
Author(s):  
A. Yoshida
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
Geomagnetic Activity ◽  
Physical Meaning ◽  
Solar Wind Velocity ◽  
Annual Variation ◽  
Geomagnetic Disturbance ◽  
Data Sets ◽  
Key Factor ◽  
Solar Wind Parameters

Abstract. Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity is investigated based on the three-hourly am index and solar wind parameters. When the z component of the interplanetary magnetic field (IMF) in geocentric solar magnetospheric (GSM) coordinates is southward, am indices are well correlated with BsVx2, where Bs is the southward component of the IMF and Vx is the solar wind velocity in the sun-earth direction. The am-BsVx2 relationship, however, depends on the range of Vx2: the am in higher ranges of Vx2 tends to be larger than am in lower ranges of Vx2 for the same value of BsVx2 for both equinoctial and solstitial epochs. Using the data sets of the same Vx2 range, it is shown that distribution of points in the am-BsVx2 diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each BsVx2 bin in solstitial epochs are closely consistent with those in equinoctial epochs, if Vx2 for each point at solstices are reduced to Vx2sin2 (Ψ) where Ψ is the geomagnetic colatitude of the sub-solar point. Further, it is shown that monthly averages of the am index in the long period is well correlated with the values of sin2(ψ) for the middle day of each month. These findings indicate that the factor that contributes to the generation of geomagnetic disturbance is not the velocity of the solar wind, but the component of the solar wind velocity perpendicular to the dipole axis of the geomagnetic field. The magnitude of the perpendicular velocity component varies semi-annually even if the solar wind velocity remains constant, which is considered to be the long-missed key factor causing the equinoctial effect.

The effects of the solar magnetic polarity and the solar wind velocity on Bz-component of the interplanetary magnetic field

2012 ◽  
Vol 49 (7) ◽  
pp. 1198-1202 ◽  
Author(s):  
M. Youssef ◽  
A. Mahrous ◽  
R. Mawad ◽  
E. Ghamry ◽  
M. Shaltout ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Wind Velocity ◽  
Solar Wind Velocity ◽  
Magnetic Polarity
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