North-south Component Of Interplanetary Magnetic Field Research Articles

Geomagnetic indices ASY-H and SYM-H and their relation to interplanetary parameters

The dependences of the geomagnetic indices SYM-H and ASY-H on interplanetary parameters for the period from 1981 to 2015 according to their daily averages are studied. The study is carried out in two ways: the first — the entire data array is analyzed, the second — the data are divided into 9 activity groups in accordance with the average daily values of the planetary geomagnetic index Ap. A correlation analysis of the indices with the solar wind speed, magnitude, and the north-south component of the interplanetary magnetic field (IMF) has been performed. The search for a relationship between the ASY-H and SYM-H indices and interplanetary parameters turned out to be more successful when considering the entire data array than in the case of splitting the data into groups of magnetic activity. Regression equations relating ASY-H and SYM-H to interplanetary parameters are determined. It has been found that when describing the relationship between the ASY-H and SYM-H indices and the IMF north-south component, it is necessary to take into account the contribution of the IMF modulus.

Геомагнитные индексы ASYH и SYMH и их связь с межпланетными параметрами

The dependences of the geomagnetic indices SYM-H and ASY-H on interplanetary parameters for the period from 1981 to 2015 according to their daily averages are studied. The study is carried out in two ways: the first — the entire data array is analyzed, the second — the data are divided into 9 activity groups in accordance with the average daily values of the planetary geomagnetic index Ap. A correlation analysis of the indices with the solar wind speed, magnitude, and the north-south component of the interplanetary magnetic field (IMF) has been performed. The search for a relationship between the ASY-H and SYM-H indices and interplanetary parameters turned out to be more successful when considering the entire data array than in the case of splitting the data into groups of magnetic activity. Regression equations relating ASY-H and SYM-H to interplanetary parameters are determined. It has been found that when describing the relationship between the ASY-H and SYM-H indices and the IMF north-south component, it is necessary to take into account the contribution of the IMF modulus.

The longitudinal polar cusp displacement from geomagnetic measurements in Antarctica

We used ULF geomagnetic field measurements in the Pc5 frequency range (1.7-7 mHz) attwo Antarctic stations to statistically investigate the longitudinal location of the polar cusp.The two stations are located at the same geomagnetic latitude, ~80° S (just poleward of thecusp), and are separated by one hour in magnetic local time. Since at each station the Pc5power maximizes when the station approaches the cusp, the comparison between their Pc5power allows to estimate the longitudinal position of the cusp and to examine its movements.We found that there is a displacement of the cusp depending on interplanetary conditions;in particular, the cusp shifts to later hours for negative values of the interplanetary magneticfield and solar wind velocity east-west components (By and Vy), while moves to earlier hoursfor positive values of Vy. Conversely, no dependence of the cusp longitudinal position onpositive By values nor on the interplanetary magnetic field north-south component (Bz) emerges.

Shape of the equatorial magnetopause affected by the radial interplanetary magnetic field

The ability of a prediction of the magnetopause location under various upstream conditions can be considered as a test of our understanding of the solar wind-magnetosphere interaction. The present magnetopause models are parametrized with the solar wind dynamic pressure and usually with the north-south interplanetary magnetic field (IMF) component. However, several studies pointed out an importance of the radial IMF component, but results of these studies are controversial up to now. The present study compares magnetopause observations by five THEMIS spacecraft during long lasting intervals of the radial IMF with two empirical magnetopause models. A comparison reveals that the magnetopause location is highly variable and that the average difference between the observed and predicted positions is ≈+0.7RE under this condition. The difference does not depend on the local times and other parameters, like the upstream pressure, IMF north-south component, or tilt angle of the Earth dipole. We conclude that our results strongly support the suggestion on a global expansion of the equatorial magnetopause during intervals of the radial IMF.

Solar-wind control of plasma sheet dynamics

Abstract. The purpose of this study is to quantify how solar-wind conditions affect the energy and plasma transport in the geomagnetic tail and its large-scale configuration. To identify the role of various effects, the magnetospheric data were sorted according to different solar-wind plasma and interplanetary magnetic field (IMF) parameters: speed, dynamic pressure, IMF north–south component, epsilon parameter, Auroral Electrojet (AE) index and IMF ultra low-frequency (ULF) fluctuation power. We study variations in the average flow speed pattern and the occurrence rate of fast flow bursts in the magnetotail during different solar-wind conditions using magnetospheric data from five Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission spacecraft and solar-wind data from NASA's OMNIWeb. The time interval covers the years from 2008 to 2011 during the deep solar minimum between cycles 23 and 24 and the relatively quiet rising phase of cycle 24. Hence, we investigate magnetospheric processes and solar-wind–magnetospheric coupling during a relatively quiet state of the magnetosphere. We show that the occurrence rate of the fast (|Vtail| > 100 km s−1) sunward flows varies under different solar-wind conditions more than the occurrence of the fast tailward flows. The occurrence frequency of the fast tailward flows does not change much with the solar-wind conditions. We also note that the sign of the IMF BZ has the most visible effect on the occurrence rate and pattern of the fast sunward flows. High-speed flow bursts are more common during the slow than fast solar-wind conditions.