Modulation of Galactic Cosmic Ray Protons and Electrons During an Unusual Solar Minimum

Heber, B.; Kopp, A.; Gieseler, J.; Müller‐Mellin, R.; Fichtner, H.; Scherer, K.; Potgieter, M. S.; Ferreira, S. E. S.

doi:10.1088/0004-637x/699/2/1956

Cited by 86 publications

(83 citation statements)

References 31 publications

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“…In response, one could expect a corresponding increase of the galactic cosmic ray (GCR) flux recorded at Earth, in particular at low energy. While an increase by 20% was indeed observed in the low-energy GCRs compared to the previous minimum (Heber et al 2009;McDonald et al 2010;Mewaldt et al 2010;Jian et al 2011), no significant excess was observed relative to the range of the previous four solar minima. This apparent insensitivity of the GCR flux to the weaker solar wind can be due to a non-dipolar configuration of the corona and heliosphere, which is anomalous in the minimum phase of the solar cycle.…”

Section: Introductionmentioning

confidence: 69%

“…The IMF strength was 30% below past minima (McComas et al 2008;Smith & Balogh 2008;Fisk & Zhao 2009;Heber et al 2009;Cliver & Ling 2010;de Toma et al 2010;Jian et al 2011). This weakening can at least partly be associated with a parallel weakening of the observed polar magnetic field, by 40% (Sheeley 2008;Wang et al 2009;Janardhan et al 2010).…”

Section: Introductionmentioning

confidence: 93%

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Are the sunspots really vanishing?

Clette

Lefèvre

2012

J. Space Weather Space Clim.

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Context:The elapsed solar cycle (23) ended with an exceptionally long period of low activity and with unprecedented low levels for various series of solar irradiance and particle flux measurements. This unpredicted evolution of solar activity raised multiple questions about a future decline of the solar cycles and launched a quest for precursor signs of this possible deep solar transition over the last decade. Aim: We present here a review and overall interpretation of most current diagnostics of solar cycle 23, including the recent disagreements that appeared among solar reference indices and standard solar-based geo-indices, the indication of a changed pattern of internal torsional waves (helioseismology) or the announced fading and magnetic weakening of sunspots. Methods: Based on a statistical analysis of detailed sunspot properties over the last 24 years, we complete the picture with new evidence of a strong global deficit of the smallest sunspots starting around 2000, in order to answer the question: are all sunspots about to disappear? Results: This global scale-dependent change in sunspot properties is confirmed to be real and not due to uncontrolled biases in some of the indices. It can also explain the recent discrepancies between solar indices by their different sensitivities to small and weak magnetic elements (small spots). The International Sunspot Index R i , based on unweighted sunspot counts, proved to be particularly sensitive to this particular small-scale solar evolution. Conclusions: Our results and interpretation show the necessity to look backwards in time, more than 80 years ago. Indeed, the Sun seems to be actually returning to a past and hardly explored activity regime ending before the 1955-1995 Grand Maximum, which probably biased our current space-age view of solar activity.

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Section: Introductionmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 93%

Are the sunspots really vanishing?

Clette

Lefèvre

2012

J. Space Weather Space Clim.

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“…2a and 2b that the solar particle flux reached a minimum in 2009 ± 0.5. In addition to PAMELA observations, Mewaldt et al (2010) reported that cosmic rays with high rigidity reached record setting intensities during this time, while Heber et al (2009) and McDonald et al (2010) also noted this extraordinary event from space bound observations. It followed from these cosmic ray observations for this period that the delay between the time for minimum sunspot numbers and maximum cosmic ray intensities was at least three times longer than during previous even numbered solar cycles (see also e.g., Kane 2011;Aslam and Badruddin 2012;Mewaldt 2013).…”

Section: Cosmic Ray Observationsmentioning

confidence: 80%

A Remarkable Recent Transition in the Solar Dynamo

et al. 2016

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We summarize the major aspects of the remarkable, fairly long lasting period (∼ 2005 to ∼ 2010) of low solar activity, that we will call the Transition. It is the transitional stage between the Grand Maximum of the 20th century and a forthcoming (most probably Regular) episode of solar activity. The various kinds of activity in the functioning of the equatorial components of the solar dynamo before and during the Transition are summarized. While the behavior of unipolar magnetic regions and their rest-latitudes already gave very early indications -mid 20th century -of the forthcoming Transition, more such indications became available around 1995 and the main part of it occurred between 2005 and 2010. Some of the inferences are discussed. We submit the hypothesis that the solar tachocline undergoes pulsations and we present some helioseismic evidences. In that scenario we find that its equatorial part has moved downward over a fairly small semi-amplitude (∼ 0.03 solar radii) during the time of the Transition. There are several indications, apart from this 'pulsation', that the tachocline may even be pulsating with still smaller amplitudes in more modes. We speculate about the physical mechanism(s).

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“…It was followed by a high GCR count rate which breaks the previous record February 1987 level. Meanwhile, the solar wind (SW) density, pressure, and IMF strength all reached the lowest values ever observed during the latest measurements made by Ulysses [Heber et al, 2009].…”

Section: Introductionmentioning

confidence: 85%

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

et al. 2014

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During the recent solar minimum between cycles 23 and 24 (solar minimum P23/24), the intensity of galactic cosmic rays (GCR) measured at the Earth was the highest ever recorded since space age. It is the purpose of this paper to resolve the most plausible mechanism for this unusually high intensity. A GCR transport model in three‐dimensional heliosphere based on a simulation of Markov stochastic process is used to find the relation of cosmic ray modulation to various transport parameters, including solar wind (SW) speed, distance of heliospheric boundary, magnitude of interplanetary magnetic field (IMF) at the Earth, tilt angle of heliospheric current sheet, and values of parallel and perpendicular diffusion coefficients. We calculate GCR proton energy spectra at the Earth for the last three solar minima P21/22, P22/23, and P23/24, with the transport parameters obtained from observations. Besides weak IMF magnitude and slow SW speed, we find that a possible low magnetic turbulence, which increases the parallel diffusion and reduces the perpendicular diffusion in the polar direction, might be an additional possible mechanism for the high GCR intensity in the solar minimum P23/24.

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Modulation of Galactic Cosmic Ray Protons and Electrons During an Unusual Solar Minimum

Cited by 86 publications

References 31 publications

Are the sunspots really vanishing?

Are the sunspots really vanishing?

A Remarkable Recent Transition in the Solar Dynamo

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24

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