scholarly journals Average auroral configuration parameterized by geomagnetic activity and solar wind conditions

2010 ◽  
Vol 28 (4) ◽  
pp. 1003-1012 ◽  
Author(s):  
S. E. Milan ◽  
T. A. Evans ◽  
B. Hubert
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
Geomagnetic Activity ◽  
Solar Wind Velocity ◽  
Solar Wind Speed ◽  
Auroral Oval ◽  
Similar Amount ◽  
Solar Wind Parameters ◽  
Upstream Solar Wind ◽  
The Imf

Abstract. Average proton and electron auroral images are compiled from three years of observations by the IMAGE spacecraft, binned according to concurrent KP and upstream solar wind conditions measured by the ACE spacecraft. The solar wind parameters include solar wind velocity, density, and pressure, interplanetary magnetic field (IMF) magnitude and orientation, and an estimate of the magnetopause reconnection rate. We use both (a) the overall variation in brightness in the images and (b) the variation in location of the aurorae with respect to the binning parameters to determine which parameters best order the auroral response. We find that the brightness varies by a factor of ~50 with KP, a similar amount with estimated dayside reconnection voltage, ~15 with the IMF, ~3 with solar wind density, ~2 with solar wind velocity, and ~5 with pressure. Clearly, geomagnetic activity as measured by KP and auroral dynamics are closely associated. In terms of the solar wind-magnetosphere coupling that drives auroral dynamics, the IMF is of paramount importance in modulating this, with solar wind speed and density playing a lesser role. Dayside reconnection voltage, derived from the solar wind velocity and IMF magnitude and orientation, orders the data almost as well as KP, though we find a plateau in the auroral response between voltages of 100 and 150 kV. We also discuss changes in configuration and overall size of the average auroral oval with upstream conditions.

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.

scholarly journals Extremely low geomagnetic activity during the recent deep solar cycle minimum

2011 ◽  
Vol 7 (S286) ◽  
pp. 200-209 ◽  
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.

scholarly journals Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 2: A new reconstruction of the interplanetary magnetic field

2013 ◽  
Vol 31 (11) ◽  
pp. 1979-1992 ◽  
Author(s):  
M. Lockwood ◽  
L. Barnard ◽  
H. Nevanlinna ◽  
M. J. Owens ◽  
R. G. Harrison ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Activity ◽  
Flow Speed ◽  
Range Data ◽  
Solar Wind Flow ◽  
Annual Means ◽  
Solar Wind Parameters ◽  
The Imf

Abstract. We present a new reconstruction of the interplanetary magnetic field (IMF, B) for 1846–2012 with a full analysis of errors, based on the homogeneously constructed IDV(1d) composite of geomagnetic activity presented in Part 1 (Lockwood et al., 2013a). Analysis of the dependence of the commonly used geomagnetic indices on solar wind parameters is presented which helps explain why annual means of interdiurnal range data, such as the new composite, depend only on the IMF with only a very weak influence of the solar wind flow speed. The best results are obtained using a polynomial (rather than a linear) fit of the form B = χ · (IDV(1d) − β)α with best-fit coefficients χ = 3.469, β = 1.393 nT, and α = 0.420. The results are contrasted with the reconstruction of the IMF since 1835 by Svalgaard and Cliver (2010).

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.

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