Dual-peak solar cycle distribution of intense geomagnetic storms

González, W. D.; González, Alicia; Tsurutani, B. T.

doi:10.1016/0032-0633(90)90082-2

Cited by 136 publications

(97 citation statements)

References 16 publications

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“…The occurrence rate of CMEs increases with the enhanced solar activity (Gopalswamy et al, 2004), while the number of HSSs peaks during the declining phase of the sunspot cycle (Tanskanen et al, 2005). The first geomagnetic activity peak during the sunspot maximum is often related to an enhanced occurrence rate of CMEs, while the second peak mostly relates to the increased high-speed stream frequency later in the same spot cycle (Gonzalez et al, 1990;Richardson et al, 2001). The geomagnetic activity cycle is often described using geomagnetic indices, such as the aa index (Mayaud, 1972;Lockwood et al, 2013a).…”

Section: Introductionmentioning

confidence: 99%

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

2015

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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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Section: Introductionmentioning

confidence: 99%

“…The solar cycle evolution of geomagnetic activity often consists of two peaks during the solar maximum and in the declining phase (Gonzalez et al, 1990;Echer et al, 2004). The coronal mass ejections (CMEs) and high-speed solar wind streams (HSSs) drive the most severe geomagnetic variations.…”

Section: Introductionmentioning

confidence: 99%

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

2015

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“…Love (jlove@usgs.gov) The aa index has been widely used in the analysis of a number of inter-related issues, including: (1) magnetic-storm occurrence statistics and time-series analysis (Courtillot et al, 1977;Gonzalez et al, 1990;Willis et al, 1997), (2) spaceweather hazards (Boteler et al, 1998;Thomson et al, 2010), (3) solar-terrestrial interaction (Russell, 1975;Legrand and Simon, 1989;Pulkkinen et al, 2001;Lockwood, 2005), (4) solar activity and its prediction (Thompson, 1993;Hathaway et al, 1999;Fröhlich and Lean, 2004), (5) terrestrial climate change (Cliver et al, 1998;Friis-Christensen, 2001; Le Mouël et al, 2005), (6) atmospheric ozone depletion (Jarvis, 2005), and (7) cosmic rays and atmospheric radionuclide production (Stuiver and Quay, 1980;Beer et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

Long-term biases in geomagnetic <i>K</i> and <i>aa</i> indices

Love¹

2011

Ann. Geophys.

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Abstract. Analysis is made of the geomagnetic-activity aa index and its source K-index data from groups of groundbased observatories in Britain, and Australia, 1868.0-2009.0, solar cycles 11-23. The K data show persistent biases, especially for high (low) K-activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantly the result of changes in observatory location, localized induced magnetotelluric currents, changes in magnetometer technology, or the modernization of K-value estimation methods. Instead, the biases appear to be artifacts of the latitudedependent scaling used to assign K values to particular local levels of geomagnetic activity. The biases are not effectively removed by weighting factors used to estimate aa. We show that long-term averages of the aa index, such as annual averages, are dominated by medium-level geomagnetic activity levels having K values of 3 and 4.

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“…In principle, this situ ation arises only for ICMEs which are slower than the fast stream flow. However, this seems typical of ICMEs, which can rapidly decelerate even only out to 1 AU [e.g., Gopalswamy et al, 2000]. ICMEs also can contain southward fields which can be compressed in the CIR.…”

Section: Cirs and High Speed Streamsmentioning

confidence: 99%

The Solar Sources of Geoeffective Structures

Webb

Crooker

Plunkett

et al. 2013

Geophysical Monograph Series

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We review our current understanding of the solar sources of interplane tary structures that result in geomagnetic disturbances, especially storms. These sources have been broadly classified as: 1) transient or sporadic, or 2) recurrent, although we now know that these categories are not exclu sive. Transients usually refer to coronal mass ejections (CMEs). Recurrence refers to disturbances that repeat with the 27-day synodic rotation period of the Sun. CMEs are expulsions of large quantities of plasma and magnetic field from the Sun's corona. The occurrence rate of CMEs approximately follows that of the solar (sunspot) activity cycle. Recurrent sources are usu ally attributed to high-speed solar wind streams emanating from coronal holes. However, compression at the leading edge of the stream as it runs into the higher-density slow flow surrounding the heliospheric current sheet leads to a corotating interaction region (CIR), and it is passage of the CIR, not the high speed flow, that results in enhanced recurrent geomagnetic dis turbances. Moreover, the largest recurrent geomagnetic storms are actually caused by CMEs caught up in the CIRs.

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Dual-peak solar cycle distribution of intense geomagnetic storms

Cited by 136 publications

References 16 publications

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

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

Long-term biases in geomagnetic <i>K</i> and <i>aa</i> indices

The Solar Sources of Geoeffective Structures

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Dual-peak solar cycle distribution of intense geomagnetic storms

Cited by 136 publications

References 16 publications

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

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

Long-term biases in geomagnetic &lt;i&gt;K&lt;/i&gt; and &lt;i&gt;aa&lt;/i&gt; indices

The Solar Sources of Geoeffective Structures

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Long-term biases in geomagnetic <i>K</i> and <i>aa</i> indices