Semiannual variation of the geomagnetic Dst index: Evidence for a dominant nonstorm component

Cliver, E. W.; Kamide, Y.; Ling, A. G.; Yokoyama, Noboru

doi:10.1029/2000ja000358

Cited by 39 publications

(55 citation statements)

References 29 publications

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“…Recently, Cliver et al (2000Cliver et al ( , 2001 argued, contrary to current popular thinking, that the R-M effect makes a relatively small contribution to the seasonal modulation of geomagnetic activity, while the equinoctial effect is most dominant. It was suggested that the efficiency of reconnection between the IMF and the geomagnetic field must be modulated by the angle between the flow direction of the solar wind and Earth's dipole axis.…”

Section: Seasonal Dependence Of Geomagnetic Activitymentioning

confidence: 78%

Space Storms and Space Weather Hazards

Daglis¹

2001

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Subject Terms Report Classification unclassified Classification of this page unclassified Classification of Abstract unclassified Limitation of Abstract UU Number of Pages 486REPORT DOCUMENTATION PAGE Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, -to review recent spacecraft measurements that have provided new insight into the dynamics and effects of space storms; -to review space weather hazards associated with space storms and pertinent to the operation of technological systems in space and on ground;-to discuss and assess methods of space weather forecasting, as well as national and international initiatives towards an efficient development of space climatology.Space weather, the invisible but nevertheless effective result of solar activity and solar-terrestrial coupling, has affected the operations of communication systems since the appearance of telegraph in the 19th century, though as an unknown trouble factor. Nowadays, the effects of space weather affect in various ways all communication modes, from cable to wireless to space-based systems. Moreover, space weather hazards include malfunction or even permanent damage of power distribution grids and of telecommunication, navigation and surveillance satellites, disturbances of over-the-horizon (OTH) radar, HF, VHF and UHF communications, surveying and navigation systems that use Global Positioning System (GPS) satellites, surveillance (optical and radar), and satellite tracking. Space weather influences on the Earth's weather and climate is still a developing topic. Little is known concerning the biological effects of space weather, especially regarding astronauts.This Institute could not be timelier. Space Weather, which has been defined as "conditions on the sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-and ground-based technological systems and can endanger human life", encompasses a broad range of phenomena impacting both space science and technology. The effects of Space Weather, while present throughout the solar cycle, gain particular prominence around the peak of the 11-year sunspot activity; the maximum of cycle 23 occurred in summer 2000.The fact that this ASI on Space Weather was held in Europe is particularly appropriate. European countries host a considerable repository of knowledge and world-class facilities in this field. Nevertheless, while Space Weather activities in c...

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Section: Seasonal Dependence Of Geomagnetic Activitymentioning

confidence: 78%

Space Storms and Space Weather Hazards

Daglis¹

2001

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“…The purpose of the present study is not to evaluate contribution of each effect to the phenomena, but to investigate physical meaning of the equinoctial effect. Recent detailed studies based on am and D st indices have shown that the equinoctial effect plays the dominant role in the semi-annual variation in geomagnetic activity (Cliver et al, 2000(Cliver et al, , 2001O'Brien and McPherron, 2002), but yet, the physical mechanism by which the equinoctial effect affects geomagnetic activity has not been clarified (Cliver et al, 2004). The present study proposes an idea how the equinoctial effect works.…”

Section: Introductionmentioning

confidence: 91%

“…A lot of studies have been done to clarify what a portion of the semi-annual variation in geomagnetic activity is attributed to each of the mechanisms (Cliver et al, 2000(Cliver et al, , 2002(Cliver et al, , 2001O'Brien and McPherron, 2002). de La Sayette and Berthelier (1996) pointed out another effect which would arise from the feature that B z in the geocentric solar equatorial (GSEQ) coordinate system has B z component in the GSM coordinates.…”

Section: Introductionmentioning

confidence: 99%

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

Yoshïda

2009

Ann. Geophys.

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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 B s V 2 x , where B s is the southward component of the IMF and V x is the solar wind velocity in the sun-earth direction. The am-B s V 2 x relationship, however, depends on the range of V 2 x : the am in higher ranges of V 2 x tends to be larger than am in lower ranges of V 2 x for the same value of B s V 2 x for both equinoctial and solstitial epochs. Using the data sets of the same V 2 x range, it is shown that distribution of points in the am-B s V 2 x diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each B s V 2 x bin in solstitial epochs are closely consistent with those in equinoctial epochs, if V 2 x for each point at solstices are reduced to V 2 x sin 2 ( ) where 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 sin 2 (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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“…7 Seasonal variations are another consideration. The quiettime D st exhibits seasonal dependence (Cliver et al, 2001;Mursula and Karinen, 2005), although its mechanism has not yet been clarified. On the other hand, the solar-wind conditions around Earth might exhibit seasonal dependence.…”

Section: Discussionmentioning

confidence: 99%

“…This non-storm long-term variation appears to be roughly periodic. In fact, the quiet-time D st index exhibits seasonal variations (Cliver et al, 2001;Mursula and Karinen, 2005). However, it does not seem that this periodic variation explains all the features of the non-storm long-term variation, which implies that the non-storm variation also includes some non-periodic irregular variation.…”

Section: Introductionmentioning

confidence: 98%

Non-storm irregular variation of the Dst index

Nakano

Higuchi

2012

Ann. Geophys.

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Abstract. The D st index has a long-term variation that is not associated with magnetic storms. We estimated the longterm non-storm component of the D st variation by removing the short-term variation related to magnetic storms. The results indicate that the variation of the non-storm component includes not only a seasonal variation but also an irregular variation. The irregular long-term variation is likely to be due to an anti-correlation with the long-term variation of solar-wind activity. In particular, a clear anti-correlation is observed between the non-storm component of D st and the long-term variation of the solar-wind dynamic pressure. This means that in the long term, the D st index tends to increase when the solar-wind dynamic pressure decreases. We interpret this anti-correlation as an indication that the long-term non-storm variation of D st is influenced by the tail current variation. The long-term variation of the solar-wind dynamic pressure controls the plasma sheet thermal pressure, and the change of the plasma sheet thermal pressure would cause the non-storm tail current variation, resulting in the non-storm variation of D st .

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Semiannual variation of the geomagnetic Dst index: Evidence for a dominant nonstorm component

Cited by 39 publications

References 29 publications

Space Storms and Space Weather Hazards

Space Storms and Space Weather Hazards

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

Non-storm irregular variation of the <I>D</I><sub>st</sub> index

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Semiannual variation of the geomagnetic Dst index: Evidence for a dominant nonstorm component

Cited by 39 publications

References 29 publications

Space Storms and Space Weather Hazards

Space Storms and Space Weather Hazards

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

Non-storm irregular variation of the &lt;I&gt;D&lt;/I&gt;&lt;sub&gt;st&lt;/sub&gt; index

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Non-storm irregular variation of the <I>D</I><sub>st</sub> index