Forbush Decreases Research Articles

Study of Forbush Decrease Recovery Times by the Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics (PAMELA) Experiment

Study of Forbush Decrease Recovery Times by the Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics (PAMELA) Experiment

Development of Forbush Decreases Associated with Coronal Ejections from Active Regions and non-Active Regions

In this paper, we study the development of Forbush decreases associated with coronal mass ejectionsfrom active regions accompanied by solar flares and filament eruptions from non-active regions usingthe database of Forbush effects and interplanetary disturbances created at IZMIRAN. We compared thedevelopment of two types of Forbush decreases during solar cycles 23–24, the maxima of these cycles, andthe minimum between them. Using statistical methods, we studied the distributions of time intervals from thebeginning of the Forbush decrease to registration: the minimum cosmic ray density, the maximum hourlydecrease in density, the maximum cosmic ray anisotropy, the maximum solar wind velocity, the maximumstrength of the interplanetary magnetic field, and the minimum of the Dst index. The difference in the developmentof two types of Forbush decreases was compared when the interplanetary disturbance contains ordoes not contain a magnetic cloud near the Earth. The results showed that flare-associated events developfaster than filament-associated events, even at close values of the solar wind parameters. The difference in thedevelopment of two types of Forbush decreases is more noticeable in the case of the presence of a magneticcloud near the Earth’s orbit. The largest difference between the time parameters in the two types of events isobserved for the time of registration of the maximum intensity of the interplanetary magnetic field. The mainphase of the two types of Forbush decreases is the same at the solar cycle 23 maximum and longer for filament-associated events at the cycle 24 maximum and 23–24 minimum. Considering all time parameters, thedifference in the development of the two types of Forbush decreases is more noticeable at the maximum ofcycle 23 and at the minimum of cycle 23–24 than at the maximum of cycle 24

Development of Forbush Decreases Associated with Coronal Ejections from Active Regions and non-Active Regions

Development of Forbush Decreases Associated with Coronal Ejections from Active Regions and non-Active Regions

Extended Cosmic Ray Decreases with Strong Anisotropy after Passage of Interplanetary Shocks

The passage of an interplanetary shock and/or interplanetary coronal mass ejection often causes a rapid decrease in the Galactic cosmic-ray (GCR) flux, known as a Forbush decrease, followed by a recovery of the flux over some days. These local effects are of short duration and strongly rigidity dependent, with higher-rigidity particles exhibiting much weaker effects. In contrast, we present data for two events in which the cosmic-ray flux gradually decreased for about 1 week after shock passage, then recovering over the following week, with the highest anisotropy levels observed throughout Solar Cycle 24. These extended decreases have a weak rigidity dependence and are much more prominent in observations at higher cutoff rigidity, where the initial Forbush decrease is not clearly detected and other variations are generally weak, as we demonstrate using data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand with a cutoff rigidity of about 17 GV. We propose that these extended decrease events were initiated upon the passage of an interplanetary shock that inhibited the inflow of GCRs along the interplanetary magnetic field, possibly due to magnetic mirroring at the shock. We also discuss the general behavior of GCR anisotropy as observed at this high cutoff rigidity.

The amplitude and phase distributions of cosmic ray variation at different conditions of Forbush decrease

The Forbush effect is one of the striking examples of irregular variations in the cosmic ray (CR) flux. It is a heliospheric phenomenon that includes a decrease and a recovery of the CR intensity and small changes in the CR density and anisotropy before the start of the main decrease. They were first noted as the effects of decreasing the intensity of cosmic rays, coinciding with geomagnetic storms. The increased interest is observed in recent years and it is primarily because their variables are strongly related to processes in solar-terrestrial physics. Forbush effects convey significant information regarding interplanetary disturbances. In the present work, fifty-three Forbush decrease (FD) events were categorized into four types according to their profile shape. From 1990 to 2020, cosmic ray intensity data from five neutron monitor stations (two subpolar and three mid-latitude) were used. The superposed epoch technique has been used to calculate the vectorial average of the observed diurnal vectors for every day of the four types of FD. It can be found that the subpolar stations (McMurdo and Thule) showed different behavior than the other stations. The solar-diurnal variation at the Thule and McMurdo subpolar stations is comparable on some days to the variation at mid-latitude stations, indicating that CR anisotropy on these days is not the only (and sometimes not the main) source of the solar-diurnal variation. The contribution of the solar-diurnal anisotropy to the diurnal variation at subpolar stations is small, much less than at other neutron monitors.

Spectral Features of Forbush Decreases during Geomagnetic Storms

Geomagnetic storms and Forbush decreases (FD) on Earth are primarily caused by interplanetary coronal mass ejections (ICMEs) and stream/corotating interaction regions (SIRs/CIRs) originating in the Sun, which are propagated as a low-energy plasma disturbance through the interplanetary magnetic field (IMF). In this paper, we study the variations of the solar-wind parameters (solar wind velocity, plasma density, and IMF-Bz component) and the Earth's disturbance storm-time index (Dst) in relation to cosmic ray flux measurements from 8 neutron monitor stations distributed over Canada, Russia, Finland, and Greenland, during 3 intense geomagnetic storms occurred during the 24th solar cycle (March 16–18, 2015, June 21–23, 2015, and September 7–9, 2017). The wavelet analysis of the cosmic ray intensity reveals the clear evolution of the classical two-step FD with a peak period of approximately 2.1 h. The correlation-delay analysis shows a very strong correlation (∼0.9) between the relative count rate changes in cosmic ray intensity and the indices of solar wind speed and Dst. We obtain similar time-delay responses to the solar wind speed for all the cases (∼4 h), but large discrepancies are seen for the Dst index between the storms. We, therefore, recommend not using the Dst index for predicting Forbush decreases. Finally, we employ the resulting delay times to parameterise the Forbush decreases in terms of the solar wind, and we obtain a predictive model with R2 parameter of an approximate value of 0.8. Moreover, we observe a possible dependence on solar wind proton density which modulates the magnitude of Forbush decreases under similar solar wind speed conditions. Our results verify the suitability of using solar wind parameters to predict Forbush decreases in the cosmic ray flux.

23rd solar cycle: Solar activity parameters and associated Forbush decreases

We report Forbush decreases (FD) in cosmic ray intensity from January 1996 to December 2008, the whole Solar Cycle 23rd. Statistical analysis is done for only 152 events for which associated solar flare position, flare classes, and Coronal Mass Ejections (CME) speed are given. We applied FD parameters taken from the Forbush Effects and Interplanetary Disturbances databases maintained by the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation (IZMIRAN), obtained by processing the data of the worldwide neutron monitor network using the global survey method (GSM) (A. Belov et al., 2018). For the said number of events, we examine their effect on interplanetary space and the decrease of the galactic cosmic rays (GCR) near Earth. We found that the 11–20° latitudinal belt shows more FD- associated flare events than the other latitudinal belts, and on this belt, the Southern hemisphere is more active. The results reveal that FDs and solar flares are well correlated. Statistical analysis is carried out for the magnitude of the CR decrease with solar and geomagnetic parameters.

New insights from cross-correlation studies between solar activity indices and cosmic-ray flux during Forbush decrease events

Observed galactic cosmic ray intensity can be subjected to a transient decrease. These so-called Forbush decreases are driven by coronal mass ejection induced shockwaves in the heliosphere. By combining in situ measurements by space borne instruments with ground-based cosmic ray observations, we investigate the relationship between solar energetic particle flux, various solar activity indices, and intensity measurements of cosmic rays during such an event. We present cross-correlation study done using proton flux data from the SOHO/ERNE instrument, as well as data collected during some of the strongest Forbush decreases over the last two completed solar cycles by the network of neutron monitor detectors and different solar observatories. We have demonstrated connection between the shape of solar energetic particles fluence spectra and selected coronal mass ejection and Forbush decrease parameters, indicating that power exponents used to model these fluence spectra could be valuable new parameters in similar analysis of mentioned phenomena. They appear to be better predictor variables of Forbush decrease magnitude in interplanetary magnetic field than coronal mass ejection velocities.

Large-amplitude Bidirectional Anisotropy of Cosmic-Ray Intensity Observed with Worldwide Networks of Ground-based Neutron Monitors and Muon Detectors in 2021 November

We analyze the cosmic-ray variations during a significant Forbush decrease observed with worldwide networks of ground-based neutron monitors and muon detectors during 2021 November 3–5. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first ∼2% decrease after the interplanetary shock arrival followed by the second ∼5% decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak amplitude of ∼5% at 15 GV, which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90°, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically, indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.

Topside ionosphere during solar cosmic ray bursts and Forbush decreases in galactic cosmic rays

The paper considers the behavior of the upper ionosphere at heights of the F2 layer during Forbush decreases in galactic cosmic rays (GCR FDs) and solar cosmic ray (SCR) bursts. We use the results of long-term continuous observations of cosmic rays and the ionosphere in Novosibirsk for the period from 1968 to 2021. The ionospheric disturbances in the F2 layer during GCR FDs, which were accompanied by a magnetic storm, took the form of an ionospheric storm negative phase. The scale of the negative phase of the ionospheric F-layer disturbance increases with increasing Dst index of the geomagnetic storm. This increase in the amplitude of the ionospheric disturbance becomes more and more significant depending on the magnitude of Forbush decreases. A burst of the amplitude of the daily variation in the F2-layer critical frequency occurred eight days after SCR bursts and GCR FD front. We assume that this burst might have been caused by disturbances in the lower atmosphere due to significant variations in the intensity of SCR and GCR fluxes.

Верхняя ионосфера в период вспышек солнечных космических лучей и форбуш-понижений галактических космических лучей

The paper considers the behavior of the upper ionosphere at heights of the F2 layer during Forbush decreases in galactic cosmic rays (GCR FDs) and solar cosmic ray (SCR) bursts. We use the results of long-term continuous observations of cosmic rays and the ionosphere in Novosibirsk for the period from 1968 to 2021. The ionospheric disturbances in the F2 layer during GCR FDs, which were accompanied by a magnetic storm, took the form of an ionospheric storm negative phase. The scale of the negative phase of the ionospheric F-layer disturbance increases with increasing Dst index of the geomagnetic storm. This increase in the amplitude of the ionospheric disturbance becomes more and more significant depending on the magnitude of Forbush decreases. A burst of the amplitude of the daily variation in the F2-layer critical frequency occurred eight days after SCR bursts and GCR FD front. We assume that this burst might have been caused by disturbances in the lower atmosphere due to significant variations in the intensity of SCR and GCR fluxes.

Solar Energetic Particle Events and Forbush Decreases Driven by the Same Solar Sources

The characteristics of Forbush decreases (FDs) and solar energetic particle (SEP) events driven by the same solar source (i.e., coronal mass ejection and associated solar flare) are investigated. The part of the solar disk (04∘ E–35∘ W) in which most of the solar events lead both to an FD and SEP event on Earth was chosen. SEPs for different energies (E > 10 MeV, E > 100 MeV, and Ground Level Enhancements) and with different flux thresholds were considered independently. The obtained results were compared with the control group of FDs that had solar sources within the same longitudinal zone but were not accompanied by any SEPs. It is shown that coronal mass ejections (CMEs) followed by SEPs have a very high probability of creating a large FD in the Earth’s orbit and to further cause a geomagnetic storm. It is also found that the accelerative and modulating efficiencies of powerful solar events are well correlated; this can be explained mostly by high speeds of the corresponding CMEs.

Forbush Effects Observed by the Helios Spacecraft

Forbush Effects Observed by the Helios Spacecraft

Forbush decreases associated with coronal mass ejections from active and non-active regions: statistical comparison

ABSTRACT In this paper, Forbush decreases (FDs) from 1997 to 2020 associated with coronal mass ejections from active and non-active regions are compared between themselves and to FDs caused by high-speed streams from coronal holes. The two types of sporadic FDs are also compared when corresponding solar wind (SW) disturbances contain, or do not contain, magnetic clouds (MCs) near Earth. Cosmic ray density and anisotropy variations, SW speed, interplanetary magnetic field (IMF) strength, and geomagnetic indices have been examined using statistical methods. The results reveal that these parameters are larger for FDs associated with active region (AR) ejections and have highly skewed distributions for both types of sporadic events. In the same ranges of SW parameters, FD magnitude is larger for flare-associated events; more efficient modulation occurs in FDs associated with AR ejections. Differences between FDs associated with AR and non-AR ejections are more pronounced when an MC is registered. For IMF strength and geomagnetic indices, differences between the distributions depend more upon MC presence or absence than on the type of solar source. Correlation of IMF strength and SW speed differs slightly between FDs caused by AR and non-AR ejections regardless of the presence or absence of an MC, akin to the partial correlation between FD magnitude and IMF strength. Difference between the speeds of disturbed and background SW is larger for FDs associated with AR ejections especially when an MC is registered; the interaction region of different-speed SW streams occurs more frequently in interplanetary disturbances induced by AR ejections.

On the Magnetosphere‐Ionosphere Coupling During the May 2021 Geomagnetic Storm

AbstractOn 12 May 2021 the interplanetary doppelgänger of the 9 May 2021 coronal mass ejection impacted the Earth's magnetosphere, giving rise to a strong geomagnetic storm. This paper discusses the evolution of the various events linking the solar activity to the Earth's ionosphere with special focus on the effects observed in the circumterrestrial environment. We investigate the propagation of the interplanetary coronal mass ejection and its interaction with the magnetosphere—ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analyzing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm was correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a net and rapid loss of relativistic electrons from the entire outer radiation belt. Our analysis shows no evidence for any short‐term recovery to pre‐storm levels during the days following the main phase. Storm effects also included a small Forbush decrease driven by the interplay between the interplanetary shock and subsequent magnetic cloud arrival.

Similarities and Differences between Forbush Decreases Associated with Streams from Coronal Holes, Filament Ejections, and Ejections from Active Regions

Similarities and Differences between Forbush Decreases Associated with Streams from Coronal Holes, Filament Ejections, and Ejections from Active Regions

Влияние изменений потока космических лучей на общую циркуляцию атмосферы

A comparison of average daily values time series of the axial component of the global wind angular moment and galactic cosmic ray (GCR) flux was made. Using the superposed epoch method it is shown that the Forbush decreases of the GCR flux are accompanied by an increase in the average angular velocity of atmosphericcirculation and, accordingly, by an increase in the zonal transfer.

Correction to: Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

Correction to: Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

Solar and interplanetary causes of x-class, x-ray solar flare related forbush decreases of higher magnitude in cosmic ray intensity during the period of solar cycle 23 and rising phase of solar cycle 24

Solar and interplanetary causes of x-class, x-ray solar flare related forbush decreases of higher magnitude in cosmic ray intensity during the period of solar cycle 23 and rising phase of solar cycle 24

Testing the Empirical Relationship between Forbush Decreases and Cosmic Ray Diurnal Anisotropy

The abrupt aperiodic modulation of cosmic ray (CR) flux intensity, often referred to as Forbush decrease (FD), plays a significant role in our understanding of the Sun–Earth electrodynamics. Accurate and precise determinations of FD magnitude and timing are among the intractable problems in FD-based analysis. FD identification is complicated by CR diurnal anisotropy. CR anisotropy can increase or reduce the number and amplitude of FDs. It is therefore important to remove its contributions from CR raw data before FD identification. Recently, an attempt was made, using a combination of the Fourier transform technique and FD-location machine, to address this. Thus, two FD catalogs and amplitude diurnal variation (ADV) were calculated from filtered (FD1 and ADV) and raw (FD2) CR data. In the current work, we test the empirical relationship between FD1, FD2, ADV and solar-geophysical characteristics. Our analysis shows that two types of magnetic fields - interplanetary and geomagnetic (Dst) - govern the evolution of CR flux intensity reductions.