Effects of the Weak Polar Fields of Solar Cycle 23: Investigation Using OMNI for the STEREO Mission Period

Lee, Christina O.; Luhmann, J. G.; Zhao, Xue; Liu, Y.; Riley, Pete; Arge, C. N.; Russell, C. T.; Pater, Imke de

doi:10.1007/s11207-009-9345-6

Cited by 53 publications

(57 citation statements)

References 24 publications

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“…It is well known that the late declining phase of solar cycle 23 and the following minimum were unusually long and deep when compared to three previous corresponding phases (e.g., Russell et al, 2010;Jian et al, 2011). The global solar magnetic field had significant differences between our study periods that were reflected throughout the heliosphere (e.g., Lee et al, 2009;Cremades et al, 2011;Jian et al, 2011) and as we will show, affected the solar wind structure surrounding magnetic clouds. The minimum following cycle 22 was a "typical" solar minimum featuring a dipole-like solar magnetic field and large polar coronal holes, while during the recent minimum, the global magnetic field of the Sun had a multipole structure, and as a consequence, low-and mid-latitude coronal holes were frequently present (Abramenko et al, 2010).…”

Section: Introductionmentioning

confidence: 42%

“…Our analysis shows that the low number of magnetic storms during Period 2 was attributed to the lack of both CME and non-CME associated storms. Several studies have shown that during the recent low solar activity period the near-ecliptic IMF and dynamic pressure were about 30 % weaker (e.g., Lee et al, 2009;Jian et al, 2011), CMEs were slower (Vourlidas et al, 2011) and ICMEs Kilpua et al, 2012;Jian et al, 2011) had weaker magnetic fields and lower speeds than reported during the previous solar minimum. This generally weaker IMF and dynamic pressure in stream interaction regions and in ICMEs presumably led to weaker geomagnetic consequences.…”

Section: Discussionmentioning

confidence: 95%

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On the relationship between magnetic cloud field polarity and geoeffectiveness

Kilpua

Luhmann

et al. 2012

Ann. Geophys.

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Abstract. In this paper, we have investigated geoeffectivity of near-Earth magnetic clouds during two periods concentrated around the last two solar minima. The studied magnetic clouds were categorised according to the behaviour of the Z-component of the interplanetary magnetic field (B Z ) into bipolar (B Z changes sign) and unipolar (B Z maintains its sign) clouds. The magnetic structure of bipolar clouds followed the solar cycle rule deduced from observations over three previous solar cycles, except during the early rising phase of cycle 24 when both B Z polarities were identified almost with the same frequency. We found a clear difference in the number of unipolar clouds whose axial field points south (S-type) between our two study periods. In particular, it seems that the lack of S-type unipolar clouds contributed to relatively low geomagnetic activity in the early rising phase of cycle 24. We estimated the level of magnetospheric activity using a Dst prediction formula with the measured B Z and by reversing the sign of B Z . We found that bipolar clouds with fields rotating south-to-north (SN) and north-to-south (NS) were equally geoeffective, but their geoeffectiveness was clearly modified by the ambient solar wind structure. Geoeffectivity of NS-polarity clouds was enhanced when they were followed by a higher-speed solar wind, while the majority of geoeffective SN-polarity clouds lacked the trailing faster wind. A leading shock increased the geoeffectiveness of both NS-and SN-polarity clouds, in particular, in the case of an intense storm. We found that in 1995-1998, SN-polarity clouds were more geoeffective, while in 2006-2011 NS-polarity clouds produced more storms. A considerably larger fraction of events were trailed by a higherspeed solar wind during our latter study period, which presumably increased geoeffectivity of NS-polarity. Thus, our study demonstrates that during low and moderate solar activity, geoeffectivity of opposite polarity bipolar clouds may depend significantly on the surrounding solar wind structure. In addition, different polarities also give different temporal storm evolutions: a storm from an SN-polarity cloud is expected to occur, on average, half-a-day earlier than a storm from an NS-polarity cloud.

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Section: Introductionmentioning

confidence: 42%

Section: Discussionmentioning

confidence: 95%

On the relationship between magnetic cloud field polarity and geoeffectiveness

Kilpua

Luhmann

et al. 2012

Ann. Geophys.

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“…The consequences of these weaker solar magnetic fields were visible in changes of the solar wind plasma flow through the interplanetary medium. Observations near the Earth orbit during the end-phase of solar cycle 23 demonstrated that the IMF strength and solar wind density were about 30 % lower than in the minimum 22/23, and the momentum flux was about 38 % lower , whereas the solar wind speed remained unchanged compared with the previous solar minimum (Lee et al, 2009). At the same time, the Ulysses (Balogh et al, 1992;Bame et al, 1992) out-of-ecliptic observations show comparable changes throughout the heliosphere, namely a reduction in the radial magnetic field by about 64 %, of the dynamic pressure by about 22 %, and of the thermal pressure by about 25 % (Smith and Balogh, 2008;McComas et al, 2008).…”

Section: Introductionmentioning

confidence: 96%

The 27-Day Cosmic Ray Intensity Variations During Solar Minimum 23/24

Modzelewska

Alania

2013

Sol Phys

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We have studied the 27-day variations and their harmonics in Galactic cosmic ray (GCR) intensity, solar wind velocity, and interplanetary magnetic field (IMF) components during the recent prolonged solar minimum 23/24. The time evolution of the quasiperiodicity in these parameters connected with the Sun's rotation reveals that the synodic period of these variations is ≈ 26 -27 days and is stable. This means that the changes in the solar wind speed and the IMF are related to the Sun's near-equatorial regions in considering the differential rotation of the Sun. However, the solar wind parameters observed near the Earth's orbit provide only the conditions in the limited local vicinity of the equatorial region in the heliosphere (within ± 7• in latitude). We also demonstrate that the observed period of the GCR intensity connected with the Sun's rotation increased up to ≈ 33 -36 days in 2009. This means that the process that drives the 27-day GCR intensity variations takes place not only in the limited local surroundings of the equatorial region but in the global 3-D space of the heliosphere, covering also higher latitude regions. A relatively long period (≈ 34 days) found for 2009 in the GCR intensity gives possible evidence of the onset of cycle 24 due to active regions at higher latitudes and rotating slowly because of the Sun's differential rotation. We also discuss the effect of differential rotation on the theoretical model of the 27-day GCR intensity variations.

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“…As discussed in Sect. 1 also coronal and heliospheric magnetic fields were significantly lower during the SC 23 minimum than during a few previous solar cycles (Wang et al, 2009;Lee et al, 2009). In addition, the warped and high-latitude streamer belt configuration observed during the SC 23 minimum (Sect.…”

Section: Discussion and Summarymentioning

confidence: 73%

“…This extended period of low solar activity and uncommon solar magnetic field configuration produced interesting consequences throughout the heliosphere. Lee et al (2009) investigated the effects of the weak polar fields in the ecliptic near-Earth interplanetary medium and they found that the interplanetary magnetic field (IMF), density and momentum flux were lower by 30 %, 30 % and 38 %, respectively, compared to a similar phase of the SC 22 minimum.…”

Section: Introductionmentioning

confidence: 99%

Interplanetary coronal mass ejections in the near-Earth solar wind during the minimum periods following solar cycles 22 and 23

et al. 2011

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Abstract. In this paper we examine the occurrence rates and properties of interplanetary coronal mass ejections (ICMEs) and solar activity levels during the minima following solar cycle 22 (January 1995-December 1997) and 23 (January 2007-April 2010) minima using observations from the OMNI data base. Throughout the minimum following cycle 22 the CME and ICME rates roughly tracked each other, while for the minimum following cycle 23 they diverged. During the minimum after solar cycle 23, there were large variations in the streamer belt structure. During the lowest activity period of cycle 23 (based on sunspot numbers), the ICME rate was about four times higher than during a similar activity period of cycle 22. We propose that this relatively high ICME rate may be due to CME source regions occurring at lower heliolatitudes and due to equatoward deflection of slow and weak CMEs originating from the midand high-heliolatitudes. The maximum magnetic fields of the ICMEs identified during the minimum following cycle 23 were ∼ 30 % lower and their radial widths were ∼15 % lower compared to the ICMEs observed during the minimum following solar cycle 22. The weak and small ICMEs may result from intrinsically weak CMEs and/or they may represent stronger CMEs that are encountered far away from the center.

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Effects of the Weak Polar Fields of Solar Cycle 23: Investigation Using OMNI for the STEREO Mission Period

Cited by 53 publications

References 24 publications

On the relationship between magnetic cloud field polarity and geoeffectiveness

On the relationship between magnetic cloud field polarity and geoeffectiveness

The 27-Day Cosmic Ray Intensity Variations During Solar Minimum 23/24

Interplanetary coronal mass ejections in the near-Earth solar wind during the minimum periods following solar cycles 22 and 23

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