On optimum solar wind – magnetosphere coupling functions for transpolar voltage and planetary geomagnetic activity

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.

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Introduction to special section on corotating solar wind streams and recurrent geomagnetic activity

Journal of Geophysical Research Atmospheres ◽

10.1029/2006ja011745 ◽

2006 ◽

Vol 111 (A7) ◽

Cited By ~ 11

Author(s):

Bruce T. Tsurutani ◽

Robert L. McPherron ◽

Walter D. Gonzalez ◽

Gang Lu ◽

Jose H. A. Sobral ◽

...

Keyword(s):

Solar Wind ◽

Geomagnetic Activity ◽

Special Section

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Extremely low geomagnetic activity during the recent deep solar cycle minimum

Proceedings of the International Astronomical Union ◽

10.1017/s174392131200484x ◽

2011 ◽

Vol 7 (S286) ◽

pp. 200-209 ◽

Cited By ~ 12

Author(s):

E. Echer ◽

B. T. Tsurutani ◽

W. D. Gonzalez

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Geomagnetic Activity ◽

Solar Minimum ◽

Solar Wind Speed ◽

Sunspot Cycle ◽

Cycle Minimum ◽

Current Minimum ◽

Solar Wind Parameters ◽

Xix Century

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

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Effect of geomagnetic activity, solar wind and parameters of interplanetary magnetic field on regularities in intermittency of Pi2 geomagnetic pulsations

Solnechno-Zemnaya Fizika ◽

10.12737/11551 ◽

2015 ◽

Vol 1 (3) ◽

pp. 11-20 ◽

Cited By ~ 3

Author(s):

Надежда Куражковская ◽

Nadezhda Kurazhkovskaya ◽

Борис Клайн ◽

Boris Klain

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interplanetary Magnetic Field ◽

Geomagnetic Activity ◽

Dynamic Pressure ◽

Cumulative Distribution ◽

Qualitative Assessment ◽

Geomagnetic Pulsations ◽

Magnetospheric Substorms ◽

Pi2 Pulsations

We present the results of investigation of the influence of geomagnetic activity, solar wind and parameters of the interplanetary magnetic field (IMF) on properties of the intermittency of midlatitude burst series of Pi2 geomagnetic pulsations observed during magnetospheric substorms on the nightside (substorm Pi2) and in the absence of these phenomena (nonsub-storm Pi2). We considered the index α as a main characteristic of intermittency of substorm and nonsubstorm Pi2 pulsations. The index α characterizes the slope of the cumulative distribution function of Pi2 burst amplitudes. The study indicated that the value and dynamics of the index α varies depending on the planetary geomagnetic activity, auroral activity and the intensity of magnetospheric ring currents. In addition, the forms of dependences of the index α on the density n, velocity V, dynamic pressure Pd of the solar wind and IMF Bx-component are different. The behavior of the index α depending on the module of B, By- and Bz-components is similar. We found some critical values of V, Pd, B, By- and Bz-components, after reaching of which the turbulence of the magnetotail plasma during substorm development is decreased. The revealed patterns of the intermittency of Pi2 pulsations can be used for qualitative assessment of turbulence level in the magnetotail plasma depending on changing interplanetary conditions.

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On the interplay between solar wind parameters and ULF wave power as a function of geomagnetic activity at high‐ and mid‐latitudes

Journal of Geophysical Research Space Physics ◽

10.1029/2021ja029693 ◽

2021 ◽

Author(s):

Stavros Dimitrakoudis ◽

Ian R. Mann ◽

Georgios Balasis ◽

Constantinos Papadimitriou ◽

Anastasios Anastasiadis ◽

...

Keyword(s):

Solar Wind ◽

Geomagnetic Activity ◽

Wave Power ◽

Ulf Wave ◽

Solar Wind Parameters

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Explicit IMF By-dependence in geomagnetic activity

10.5194/egusphere-egu21-850 ◽

2021 ◽

Author(s):

Lauri Holappa ◽

Timo Asikainen ◽

Kalevi Mursula

Keyword(s):

Solar Wind ◽

Geomagnetic Activity ◽

Space Weather ◽

High Latitude ◽

Coupling Function ◽

Future Space ◽

Weather Modeling ◽

Southern High Latitude ◽

Imf Clock Angle ◽

The Imf

The interaction of the solar wind with the Earth&#8217;s magnetic &#64257;eld produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic &#64257;eld (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the By component. However, recent studies have shown that IMF By is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By < 0). For NH summer the dependence on the By sign is reversed. We quantify the size of this explicit By-e&#64256;ect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We show that for a given value of solar wind coupling function, geomagnetic activity is about 40% stronger for By > 0 than for By < 0 in NH winter. We also discuss recent advances in the physical understanding of the By-effect. Our results highlight the importance of the IMF By-component for space weather and must be taken into account in future space weather modeling.

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