Extremely low geomagnetic activity during the recent deep solar cycle minimum

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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On solar wind speed distribution and geomagnetic activity during solar cycle 23 and the early ascending phase of solar cycle 24

International Journal of the Physical Sciences ◽

10.5897/ijps2015.4401 ◽

2015 ◽

Vol 10 (21) ◽

pp. 562-567

Author(s):

Louis Zerbo Jean ◽

Ouattara Fr eacute d eacute ric ◽

Nan eacute ma Emmanuel

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Wind Speed ◽

Geomagnetic Activity ◽

Solar Wind Speed ◽

Speed Distribution ◽

Wind Speed Distribution ◽

Solar Cycle 23 ◽

Solar Cycle 24 ◽

Cycle 24

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Peculiar Current Solar-Minimum Structure of the Heliosphere

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310010343 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 484-487

Author(s):

P. K. Manoharan

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Solar Minimum ◽

Large Scale ◽

Solar Wind Speed ◽

Heliospheric Current Sheet ◽

Coronal Density ◽

Current Minimum ◽

Similar Phase ◽

The Magnetic Field

AbstractIn this paper, I review the results of 3-D evolution of the inner heliosphere over the solar cycle 23, based on observations of interplanetary scintillation (IPS) made at 327 MHz using the Ooty Radio Telescope. The large-scale features of solar wind speed and density turbulence of the current minimum are remarkably different from that of the previous cycle. The results on the solar wind density turbulence show that (1) the current solar minimum is experiencing a low level of coronal density turbulence, to a present value of ~50% lower than the previous similar phase, and (2) the scattering diameter of the corona has decreased steadily after the year 2003. The results on solar wind speed are consistent with the magnetic field strength at the poles and the warping of heliospheric current sheet.

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Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds

Annales Geophysicae ◽

10.5194/angeo-24-3383-2006 ◽

2006 ◽

Vol 24 (12) ◽

pp. 3383-3389 ◽

Cited By ~ 12

Author(s):

C.-C. Wu ◽

R. P. Lepping

Keyword(s):

Solar Wind ◽

Geomagnetic Storm ◽

Solar Minimum ◽

Geomagnetic Storms ◽

Solar Maximum ◽

Solar Wind Speed ◽

Magnetic Clouds ◽

Active Period ◽

Quiet Period ◽

Solar Wind Parameters

Abstract. We investigated geomagnetic activity which was induced by interplanetary magnetic clouds during the past four solar cycles, 1965–1998. We have found that the intensity of such geomagnetic storms is more severe in solar maximum than in solar minimum. In addition, we affirm that the average solar wind speed of magnetic clouds is faster in solar maximum than in solar minimum. In this study, we find that solar activity level plays a major role on the intensity of geomagnetic storms. In particular, some new statistical results are found and listed as follows. (1) The intensity of a geomagnetic storm in a solar active period is stronger than in a solar quiet period. (2) The magnitude of negative Bzmin is larger in a solar active period than in a quiet period. (3) Solar wind speed in an active period is faster than in a quiet period. (4) VBsmax in an active period is much larger than in a quiet period. (5) Solar wind parameters, Bzmin, Vmax and VBsmax are correlated well with geomagnetic storm intensity, Dstmin during a solar active period. (6) Solar wind parameters, Bzmin, and VBsmax are not correlated well (very poorly for Vmax) with geomagnetic storm intensity during a solar quiet period. (7) The speed of the solar wind plays a key role in the correlation of solar wind parameters vs. the intensity of a geomagnetic storm. (8) More severe storms with Dstmin≤−100 nT caused by MCs occurred in the solar active period than in the solar quiet period.

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The heliospheric magnetic field and the solar wind during the solar cycle

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309029160 ◽

2008 ◽

Vol 4 (S257) ◽

pp. 109-120 ◽

Cited By ~ 7

Author(s):

Lennard A. Fisk ◽

Liang Zhao

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Cycle ◽

Solar Minimum ◽

Radial Component ◽

Heliospheric Magnetic Field ◽

Average Value ◽

Ram Pressure ◽

Current Minimum ◽

Coronal Electron

AbstractThe heliospheric magnetic field and the solar wind are behaving differently in the current solar minimum, compared to the previous minimum. The radial component of the heliospheric magnetic field, and thus the average value of the component of the solar magnetic field that opens into the heliosphere, the so-called open magnetic flux of the Sun, is lower than it was in the previous solar minimum; in fact, lower than in any previous solar minimum for which there are good spacecraft observations. The mass flux, the ram pressure, and the coronal electron temperature as measured by solar wind charge states are also lower in the current minimum compared to the previous one. This situation provides an opportunity to test some of the concepts for the behavior of the heliospheric magnetic field and the solar wind that have been developed; to improve these theories, and to construct a theory for the solar wind that accounts for the observed behavior throughout the solar cycle, including the current unusual solar minimum.

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Average auroral configuration parameterized by geomagnetic activity and solar wind conditions

Annales Geophysicae ◽

10.5194/angeo-28-1003-2010 ◽

2010 ◽

Vol 28 (4) ◽

pp. 1003-1012 ◽

Cited By ~ 20

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.

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Origins of the semiannual variation of geomagnetic activity in 1954 and 1996

Annales Geophysicae ◽

10.5194/angeo-22-93-2004 ◽

2004 ◽

Vol 22 (1) ◽

pp. 93-100 ◽

Cited By ~ 18

Author(s):

E. W. Cliver ◽

L. Svalgaard ◽

A. G. Ling

Keyword(s):

Solar Wind ◽

Geomagnetic Activity ◽

Solar Minimum ◽

High Speed ◽

Solar Wind Speed ◽

Coronal Holes ◽

Heliospheric Current Sheet ◽

Solar Cycles ◽

Axial Variation ◽

Semiannual Variation

Abstract. We investigate the cause of the unusually strong semiannual variation of geomagnetic activity observed in the solar minimum years of 1954 and 1996. For 1996 we separate the contributions of the three classical modulation mechanisms (axial, equinoctial, and Russell-McPherron) to the six-month wave in the aam index and find that all three contribute about equally. This is in contrast to the longer run of geomagnetic activity (1868-1998) over which the equinoctial effect accounts for ∼70% of the semiannual variation. For both 1954 and 1996, we show that the Russell-McPherron effect was enhanced by the Rosenberg-Coleman effect (an axial polarity effect) which increased the amount of the negative (toward Sun) [positive (away from Sun)] polarity field observed during the first [second] half of the year; such fields yield a southward component in GSM coordinates. Because this favourable condition occurs only for alternate solar cycles, the marked semiannual variation in 1954 and 1996 is a manifestation of the 22-year cycle of geomagnetic activity. The 11-year evolution of the heliospheric current sheet (HCS) also contributes to the strong six-month wave during these years. At solar minimum, the streamer belt at the base of the HCS is located near the solar equator, permitting easier access to high speed streams from polar coronal holes when the Earth is at its highest heliographic latitudes in March and September. Such an axial variation in solar wind speed was observed for 1996 and is inferred for 1954. Key words. Magnetosphere (solar wind – magnetosphere interactions; storms and substorms)

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Latitude dependence of long-term geomagnetic activity and its solar wind drivers

Annales Geophysicae ◽

10.5194/angeo-33-573-2015 ◽

2015 ◽

Vol 33 (5) ◽

pp. 573-581 ◽

Cited By ~ 5

Author(s):

M. Myllys ◽

N. Partamies ◽

L. Juusola

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Geomagnetic Activity ◽

High Speed ◽

Sunspot Cycle ◽

Horizontal Magnetic Field ◽

Geomagnetic Variations ◽

Latitude Dependence ◽

Latitude Region ◽

The Impact

Abstract. To validate the usage of global indices in studies of geomagnetic activity, we have examined the latitude dependence of geomagnetic variations in Fennoscandia and Svalbard from 1994 to 2010. Daily standard deviation (SD) values of the horizontal magnetic field have been used as a measure of the ground magnetic disturbance level. We found that the timing of the geomagnetic minimum depends on the latitude region: corresponding to the minimum of sunspot cycle 22 (in 1996), the geomagnetic minimum occurred between the geomagnetic latitudes 57–61° in 1996 and at the latitudes 64–67° in 1997, which are the average auroral oval latitudes. During sunspot cycle 23, all latitude regions experienced the minimum in 2009, a year after the sunspot minimum. These timing differences are due to the latitude dependence of the 10 s daily SD on the different solar wind drivers. In the latitude region of 64–67°, the impact of the high-speed solar wind streams (HSSs) on the geomagnetic activity is the most pronounced compared to the other latitude groups, while in the latitude region of 57–61°, the importance of the coronal mass ejections (CMEs) dominates. The geomagnetic activity maxima during ascending solar cycle phases are typically caused by CME activity and occur especially in the oval and sub-auroral regions. The strongest geomagnetic activity occurs during the descending solar cycle phases due to a mixture of CME and HSS activity. Closer to the solar minimum, less severe geomagnetic activity is driven by HSSs and mainly visible in the poleward part of the auroral region. According to our study, however, the timing of the geomagnetic activity minima (and maxima) in different latitude bands is different, due to the relative importance of different solar wind drivers at different latitudes.

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On the periodic variations of geomagnetic activity indices Ap and ap

Annales Geophysicae ◽

10.1007/s00585-998-0510-2 ◽

1998 ◽

Vol 16 (5) ◽

pp. 510-517 ◽

Cited By ~ 15

Author(s):

H. Schreiber

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Geomagnetic Activity ◽

Sunspot Cycle ◽

Solar Wind Plasma ◽

Sector Structure ◽

Interplanetary Physics ◽

Before And After ◽

Activity Indices ◽

The Imf

Abstract. Yearly averages of geomagnetic activity indices Ap for the years 1967–1984 are compared to the respective averages of ν2·Bs, 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 with ν2 and Bs separately we find that, during the declining phase of the solar cycle, ν2 and during the ascending phase Bs have more influence on Ap. According to this observation (using Fourier spectral analysis) the semiannual and 27 days, Ap variations for the years 1932–1993 were analysed separately for years before and after sunspot minima. Only those time-intervals before sunspot minima with a significant 27-day recurrent period of the IMF sector structure and those intervals after sunspot minima with a significant 28-28.5-day recurrent period of the sector structure were used. The averaged spectra of the two Ap data sets clearly show a period of 27 days before and a period of 28–29 days after sunspot minimum. Moreover, the phase of the average semiannual wave of Ap is significantly different for the two groups of data: the Ap variation maximizes near the equinoxes during the declining phase of the sunspot cycle and near the beginning of April and October during the ascending phase of the sunspot cycle, as predicted by the Russell-McPherron (R-M) mechanism. Analysing the daily variation of ap in an analogue manner, the same equinoctial and R-M mechanisms are seen, suggesting that during phases of the solar cycle, when ap depends more on the IMF-Bs component, the R-M mechanism is predominant, whereas during phases when ap increases as v increases the equinoctial mechanism is more likely to be effective.Key words. Interplanetary physics · Magnetic fields · Solar wind plasma · Solar wind · magnetosphere interaction

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