Heliospheric modulation of galactic cosmic rays : Effective energy of ground-based detectors

Variability of Galactic cosmic ray (GCR) is often expressed in terms of the modulation potential, which is typically assessed using energy-integrating ground-based detectors, such as neutron monitors (NMs) for the last decades or cosmogenic isotopes on the time scales of centuries and millennia. In order to estimate the energy dependence of the GCR variability we re-assess here the effective energy Eeff of each type of detector, which is defined so that the variability of the GCR particles at this energy is equal to that of the detector's count rate. We found that Eeff is 11-12 GeV/nuc for the standard polar sea-level neutron monitor, but it is essentially smaller for cosmogenic isotopes, being 6-7 GeV/nuc for 14C and 5.5-6 GeV/nuc for 10Be, respectively. It is also discussed that this effective energy is robustly defined and is hardly dependent on the primary assumptions on the local interstellar spectrum (LIS) of GCR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).Peer reviewe

Heliospheric modulation of galactic cosmic rays : Effective energy of ground-based detectors

Variability of Galactic cosmic ray (GCR) is often expressed in terms of the modulation potential, which is typically assessed using energy-integrating ground-based detectors, such as neutron monitors (NMs) for the last decades or cosmogenic isotopes on the time scales of centuries and millennia. In order to estimate the energy dependence of the GCR variability we re-assess here the effective energy Eeff of each type of detector, which is defined so that the variability of the GCR particles at this energy is equal to that of the detector's count rate. We found that Eeff is 11-12 GeV/nuc for the standard polar sea-level neutron monitor, but it is essentially smaller for cosmogenic isotopes, being 6-7 GeV/nuc for 14C and 5.5-6 GeV/nuc for 10Be, respectively. It is also discussed that this effective energy is robustly defined and is hardly dependent on the primary assumptions on the local interstellar spectrum (LIS) of GCR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).Peer reviewe

A new calibrated sunspot group series since 1749: statistics of active day fractions

Although the sunspot-number series have existed since the mid-19th century, they are still the subject of intense debate, with the largest uncertainty being related to the "calibration" of the visual acuity of individual observers in the past. Daisy-chain regression methods are applied to inter-calibrate the observers which may lead to significant bias and error accumulation. Here we present a novel method to calibrate the visual acuity of the key observers to the reference data set of Royal Greenwich Observatory sunspot groups for the period 1900-1976, using the statistics of the active-day fraction. For each observer we independently evaluate their observational thresholds [S_S] defined such that the observer is assumed to miss all of the groups with an area smaller than S_S and report all the groups larger than S_S. Next, using a Monte-Carlo method we construct, from the reference data set, a correction matrix for each observer. The correction matrices are significantly non-linear and cannot be approximated by a linear regression or proportionality. We emphasize that corrections based on a linear proportionality between annually averaged data lead to serious biases and distortions of the data. The correction matrices are applied to the original sunspot group records for each day, and finally the composite corrected series is produced for the period since 1748. The corrected series displays secular minima around 1800 (Dalton minimum) and 1900 (Gleissberg minimum), as well as the Modern grand maximum of activity in the second half of the 20th century. The uniqueness of the grand maximum is confirmed for the last 250 years. It is shown that the adoption of a linear relationship between the data of Wolf and Wolfer results in grossly inflated group numbers in the 18th and 19th centuries in some reconstructions

Forbush decreases of cosmic rays: Energy dependence of the recovery phase

Contains fulltext : 72446.pdf (publisher's version ) (Open Access

A test of the active-day fraction method of sunspot group number calibration:dependence on the level of solar activity

Abstract The method of active-day fraction (ADF) was proposed recently to calibrate different solar observers to standard observational conditions. The result of the calibration may depend on the overall level of solar activity during the observational period. This dependency is studied quantitatively using data of the Royal Greenwich Observatory by formally calibrating synthetic pseudo-observers to the full reference dataset. It is shown that the sunspot group number is precisely estimated by the ADF method for periods of moderate activity, may be slightly underestimated by 0.5 – 1.5 groups (≤10%) for strong and very strong activity, and is strongly overestimated by up to 2.5 groups (≤30%) for weak-to-moderate activity. The ADF method becomes inapplicable for the periods of grand minima of activity. In general, the ADF method tends to overestimate the overall level of activity and to reduce the long-term trends

An optical atmospheric phenomenon observed in 1670 over the city of Astrakhan was not a mid-latitude aurora

Abstract It has recently been claimed (Zolotova and Ponyavin Solar Phys., 291, 2869, 2016; ZP16 henceforth) that a mid-latitude optical phenomenon, which took place over the city of Astrakhan in July 1670, according to Russian chronicles, were a strong aurora borealis. If this were true, it would imply a very strong or even severe geomagnetic storm during the quietest part of the Maunder minimum. However, as we argue in this article, this conclusion is erroneous and caused by a misinterpretation of the chronicle record. As a result of a thorough analysis of the chronicle text, we show that the described phenomenon occurred during the daylight period of the day (“the last morning hour”), in the south (“towards noon”), and its description does not match that of an aurora. The date of the event was also interpreted incorrectly. We conclude that this phenomenon was not a mid-latitude aurora, but an atmospheric phenomenon, the so-called sundog (or parhelion), which is a particular type of solar halo. Accordingly, the claim of a strong mid-latitude aurora during the deep Maunder Minimum is not correct and should be dismissed

35th International Cosmic Ray Conference, ICRC, The Astroparticle Physics Conference

We performed an analysis of high-energy particle emission from the Sun in two extreme solar particle events observed even with ground-based neutron monitors (NMs). We model particle transport and interactions from near-Sun source through the solar wind and the Earth's magne-tosphere and atmosphere in order to make a deep analysis of the events. The time profile of the proton source at the Sun is deduced and compared with observed electromagnetic emissions. Several complementary to each other data sets are studied jointly with the broadband dynamic radio spectra EUV images as well as other data available for both events. We find a common scenario for both eruptions including the flare's dual impulsive phase the coronal mass ejection (CME)-launch-associated burst and the late low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch then trapped in large-scale magnetic loops and later released by the expanding CME.</p

Origin of two extreme solar particle events

Abstract We performed an analysis of high-energy particle emission from the Sun in two extreme solar particle events observed even with ground-based neutron monitors (NMs). We model particle transport and interactions from near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere in order to make a deep analysis of the events. The time profile of the proton source at the Sun is deduced and compared with observed electromagnetic emissions. Several complementary to each other data sets are studied jointly with the broadband dynamic radio spectra, EUV images as well as other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the coronal mass ejection (CME)-launch-associated burst and the late low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME