Effects of magnetic clouds on the occurrence of geomagnetic storms: The first 4 years of Wind

Wu, Chin‐Chun

doi:10.1029/2001ja000161

Cited by 101 publications

(98 citation statements)

References 31 publications

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“…They found that storm intensity versus the maximum southward magnetic field (Bs) in either the ejecta or the adjacent disturbed solar wind has a correlation coefficient of -0.74. Using 34 MCs observed between 1995 and 1998, Wu and Lepping (2002a) found that the D st min is strongly correlated with V Bs max and |Bz min | with c.c.= -0.79 and -0.77, respectively. Both of the earlier studies (Cane et al, 2000;Wu and Lepping, 2002a) show that the intensity of a storm is strongly correlated with the magnitude of B z .…”

Section: Discussionmentioning

confidence: 99%

“…Using 34 MCs observed between 1995 and 1998, Wu and Lepping (2002a) found that the D st min is strongly correlated with V Bs max and |Bz min | with c.c.= -0.79 and -0.77, respectively. Both of the earlier studies (Cane et al, 2000;Wu and Lepping, 2002a) show that the intensity of a storm is strongly correlated with the magnitude of B z . However, both studies cover less than 1/4 of solar activity cycle (where 22 years is a full solar cycle).…”

Section: Discussionmentioning

confidence: 99%

“…Using 34 MCs that occurred during 1995-1998, Wu and Lepping (2002a) found that the correlation between storm intensity (D st min ) and the z-component of the interplanetary magnetic field, IMF (Bz), (or with V Bs) is very high. For solar cycle 23, previous studies have shown that the yearly average geomagnetic activity index (D st ) is not correlated well with solar activity , but the intensity of geomagnetic storms induced by MCs (observed during solar cycle 23) is related to solar activity .…”

Section: Discussionmentioning

confidence: 99%

“…Then there will be little or no negative B z . A geomagnetic storm might be driven by a MC itself or by the sheath fields upstream of a MC if an upstream exists (e.g., Lepping and Berdichevsky, 2001;Wu and Lepping, 2002a).…”

Section: Introductionmentioning

confidence: 99%

“…The intensity of a magnetic storm which is associated with a geomagnetic cloud is predictable (Wu and Lepping, 2005). Wu and Lepping (2002a) used the first four years of WIND magnetic field (Lepping et al, 1995) and plasma data (Ogilvie et al, 1995) to investigate the relationships between solar wind parameters and geomagnetic storms. They found that the intensity of geomagnetic storms (D st min ) is strongly related to the magnitude of solar wind parameters (B z , V B S or in Akasofu, 1981) within magnetic cloud complexes (including upstream sheath regions), and the occurrence timing of a geomagnetic storm is associated with the occurrence timing of Bz min , (V Bs) max or max .…”

Section: Introductionmentioning

confidence: 99%

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Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds

Lepping

2006

Ann. Geophys.

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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 Bz min 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) V Bs max in an active period is much larger than in a quiet period. (5) Solar wind parameters, Bz min , V max and V Bs max are correlated well with geomagnetic storm intensity, D st min during a solar active period. (6) Solar wind parameters, Bz min , and V Bs max are not correlated well (very poorly for V max ) 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 D st min ≤−100 nT caused by MCs occurred in the solar active period than in the solar quiet period.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds

Lepping

2006

Ann. Geophys.

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Two‐step forecast of geomagnetic storm using coronal mass ejection and solar wind condition

et al. 2014

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To forecast geomagnetic storms, we had examined initially observed parameters of coronal mass ejections (CMEs) and introduced an empirical storm forecast model in a previous study. Now we suggest a two-step forecast considering not only CME parameters observed in the solar vicinity but also solar wind conditions near Earth to improve the forecast capability. We consider the empirical solar wind criteria derived in this study (Bz ≤ −5 nT or Ey ≥ 3 mV/m for t≥ 2 h for moderate storms with minimum Dst less than −50 nT) and a Dst model developed by Temerin and Li (2002, 2006) (TL model). Using 55 CME-Dst pairs during 1997 to 2003, our solar wind criteria produce slightly better forecasts for 31 storm events (90%) than the forecasts based on the TL model (87%). However, the latter produces better forecasts for 24 nonstorm events (88%), while the former correctly forecasts only 71% of them. We then performed the two-step forecast. The results are as follows: (i) for 15 events that are incorrectly forecasted using CME parameters, 12 cases (80%) can be properly predicted based on solar wind conditions; (ii) if we forecast a storm when both CME and solar wind conditions are satisfied (∩), the critical success index becomes higher than that from the forecast using CME parameters alone, however, only 25 storm events (81%) are correctly forecasted; and (iii) if we forecast a storm when either set of these conditions is satisfied (∪), all geomagnetic storms are correctly forecasted.

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Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

et al. 2015

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We report on a study that compares the properties of magnetic clouds (MCs) during the first 73 months of solar cycles 23 and 24 in order to understand the weak geomagnetic activity in cycle 24. We find that the number of MCs did not decline in cycle 24, although the average sunspot number is known to have declined by ~40%. Despite the large number of MCs, their geoeffectiveness in cycle 24 was very low. The average Dst index in the sheath and cloud portions in cycle 24 was −33 nT and −23 nT, compared to −66 nT and −55 nT, respectively, in cycle 23. One of the key outcomes of this investigation is that the reduction in the strength of geomagnetic storms as measured by the Dst index is a direct consequence of the reduction in the factor VBz (the product of the MC speed and the out‐of‐the‐ecliptic component of the MC magnetic field). The reduction in MC‐to‐ambient total pressure in cycle 24 is compensated for by the reduction in the mean MC speed, resulting in the constancy of the dimensionless expansion rate at 1 AU. However, the MC size in cycle 24 was significantly smaller, which can be traced to the anomalous expansion of coronal mass ejections near the Sun reported by Gopalswamy et al. (2014a). One of the consequences of the anomalous expansion seems to be the larger heliocentric distance where the pressure balance between the CME flux ropes and the ambient medium occurs in cycle 24.

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Effects of magnetic clouds on the occurrence of geomagnetic storms: The first 4 years of Wind

Cited by 101 publications

References 31 publications

Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds

Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds

Two‐step forecast of geomagnetic storm using coronal mass ejection and solar wind condition

Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

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