Forbush Decreases Research Articles

Effects of Forbush Decreases on the Global Electric Circuit

AbstractThe suppression of high‐energy cosmic rays, known as Forbush decreases (FDs), represents a promising factor in influencing the global electric circuit (GEC) system. Researchers have delved into these effects by examining variations, often disruptive, of the potential gradient (PG) in ground‐based measurements taken in fair weather regions. In this paper, we aim to investigate deviations observed in the diurnal curve of the PG, as compared to the mean values derived from fair weather conditions, during both mild and strong Forbush decreases. Unlike the traditional classification of FDs, which are based on ground level neutron monitor data, we classify FDs using measurements of the Alpha Magnetic Spectrometer (AMS‐02) on the International Space Station. To conduct our analysis, we employ the superposed epoch method, focusing on PGs collected between January 2010 and December 2019 at a specific station situated at a low latitude and high altitude: the Complejo Astronómico El Leoncito (CASLEO) in Argentina (31.78°S, 2,550 m above sea level). Our findings reveal that for events associated with FDs having flux amplitude (A) decrease ≤10%, no significant change in the PG is observed. However, for FDs with A > 10%, a clear increase in the PG is seen. For these A > 10% events, we also find a good correlation between the variation of Dst and Kp indices and the variation of PG.

Catalogues of Forbush Decreases for the Period of 1957 - 1967

This work presents catalogues of Forbush Deceraeses (FDs) between the periods of 1957 – 1967. Forbush Decrease is a short-time decrease in the intensity of galactic cosmic rays. Such decreases are traced to solar wind disturbances. This work aims to study the catalogues of FDs. To achieve this aim, two approaches will be adopted namely; (1) downloading and presenting the IZMIRAN FDs from their website (2) applying the automated methods of FD identification developed by Okike and Umahi (2019) to identify and present FDs. The IZMIRAN catalog which applied the global survey method, identified a total of 450 FDs while the automated generated FDs (FD1 and FD2) which applied Fourier transformation, identified 500 and 458 FDs respectively. A close study on the three catalogues, pinpointed some differences and similarities. These were attributed to the differences in their methods of identification.

Forecasting solar wind disturbances and geomagnetic storms from ground-based cosmic ray measurements

This work reports on the methods developed by our group at ShICRA SB RAS to forecast negative manifestations of space weather from ground-based measurements of cosmic rays. Such manifestations are registered on the Earth in the form of decreases in galactic cosmic rays known as the Forbush effects, various types of geomagnetic and ionospheric disturbances, as well as auroras. Only the latters are directly visible to the naked eye, while the rest can only be detected with the help of various instruments. These occurrences are all caused by passage through the Earth’s orbit, such as the substantial influxes of charged particles from both solar and interplanetary sources, interplanetary shock waves, ejections of solar material and high-speed solar wind streams, all of which are attributed to the level of solar flares and coronal activity. The state of near-Earth space weather is determined by their presence. To monitor this state, we use data collected from ground-based cosmic ray stations and employ multiple methods to analyse these measurements. Additionally, we incorporate data from the Dst-index of the geomagnetic field and measurements of the interplanetary environmental parameters gathered by ACE, WIND, SOHO and DSCOVR spacecraft at the L1 libration point to confirm events. This has led to the development of techniques for predicting terrestrial effects of space weather in the short-term (1-3 days). Our findings suggest that it is feasible to predict the occurrence of severe geomagnetic storms in real-time through the utilisation of solely ground-based measurements from cosmic ray stations.

Investigating The Dependence Of Forbush Decrease On Geomagnetic Cutoff Rigidity

The dependence of Forbush decreases on geomagnetic cutoff rigidity has been studied. The study aimed to investigate the implications of geomagnetic cutoff rigidity on forbush decrease. To achieve this aim, the data of cosmic ray daily count from six neutron stations of Tibet, Esoi, Tsumeb, Oulu, Apatity, and Magadan were used. These data covered a period of six (6) years from the year 2010 to 2015. An advanced manual method developed by Okike and Umahi (2019b) was used to select the FDs through R. statistical software. A sharp depression in the intensity of cosmic ray variation known as Forbush decrease (FD) was detected. A large number of FDs were recorded. The results of our analysis was grouped into stations of high, low and middle rigidity. The stations of low rigidity recorded the highest number of FDs followed by stations of middle rigidity while the stations of high rigidity recorded the least number of FDs. The magnitude of these FDs was determined. It was observed that FD magnitudes vary inversely with the station's rigidity. A correlation between the FD magnitudes of the cosmic ray (CR) stations was also tested. It was observed that stations of low rigidity indicated the best correlation followed by the stations of middle rigidity, while the stations of high rigidity indicated the least correlation. A regression was further tested between the FD magnitudes of the different stations. The result of the regression between FDs of different stations was 99.8% , 98% and 97.5% significant for stations low, high and middle rigidity stations respectively. In summary, this study used a large number of events to test the rigidity dependence of FDs, and it was observed that FDs are inversely related to the cutoff rigidity. Thus, FDs measured at the CR stations can be used to examine the effects of rigidity between the stations.
 

A new method of measuring Forbush decreases

Context. Forbush decreases (FDs) are short-term depressions in the galactic cosmic ray (GCR) flux and one of the common signatures of coronal mass ejections (CMEs) in the heliosphere. They often show a two-step profile, the second one associated with the CME’s magnetic structure. This second step can be described by the recently developed analytical FD model for flux ropes (FRs) – ForbMod. Aims. The aim of this study is to utilise ForbMod to develop a best-fit procedure to be applied on FR-related FDs as a convenient measurement tool. Our motivation is to develop a best-fit procedure that can be applied to a data series from an arbitrary detector. Thus, the basic procedure would facilitate measurement estimation of the magnitude of the FR-related FD, with the possibility of being adapted for the energy response of a specific detector for a more advanced analysis. Methods. The non-linear fitting was performed by calculating all possible ForbMod curves constrained within the FR borders to the designated dataset and minimising the mean square error (MSE). In order to evaluate the performance of the ForbMod best-fit procedure, we used synthetic measurements produced by calculating the theoretical ForbMod curve for a specific example CME and then applying various effects to the data to mimic the imperfection of the real measurements. We also tested the ForbMod best-fit function on the real data, measured by detector F of the SOHO/EPHIN instrument on a sample containing 30 events, all of which have a distinct FD corresponding to the magnetic obstacle. The extraction of FD profiles (from the onset to the end) was performed manually by an observer, whereby we applied two different versions of border selection and assigned a quality index to each event. Results. We do not find notable differences between events marked by a different quality index. For events with a selection of two different borders, we find that the best fit applied on extended interplanetary coronal mass ejection (ICME) structure borders results in a slightly larger MSE and differences compared to the traditional method due to a larger scatter of the data points. We find that the best-fit results can visually be categorised into six different FD profile types. Although some profiles do not show a visually pleasing FD, the ForbMod best-fit function still manages to find a solution with a relatively small MSE. Conclusions. Overall, we find that the ForbMod best-fit procedure performs similar to the traditional algorithm-based observational method, but with slightly smaller values for the FD amplitude, as it’s taking into account the noise in the data. Furthermore, we find that the best-fit procedure has an advantage compared to the traditional method as it can estimate the FD amplitude even when there is a data gap at the onset of the FD.

Forbush Decreases and Associated Geomagnetic Storms: Statistical Comparison in Solar Cycles 23 and 24

Forbush Decreases and Associated Geomagnetic Storms: Statistical Comparison in Solar Cycles 23 and 24

Evolution of the cosmic ray spectrum during a Forbush decrease

The Antarctic Cosmic Ray Observatory (ORCA) has been in continuous operation since January 2020 and in nominal phase since March 2021 at the Spanish Antarctic Base Juan Carlos I (Livingston Island, Antarctica 62°39′46′′S,60°23′20′′W at 12 m above sea level) at an effective vertical cutoff rigidity of R=2.37 GV. ORCA consists of two neutron monitors, ORC-A with three BF3 counter tubes following the NM64 standard, and ORC-B, with three bare BF3 counter tubes; and a muon telescope, ORC-M consisting of two 1 m2 scintillators with the neutron monitors between them. ORCA provides neutron count rates at two different energy thresholds (provided by ORC-A and ORC-B) and muon count rates and muon incidence directions throughout the ORCA volume. The neutron-producing cosmic rays observed in ORC-A have a lower rigidity threshold than the muon-producing ones observed in ORC-M. The relationship between them gives an idea about the change in the slope of the cosmic ray spectrum at the corresponding thresholds, 2.37 GV for ORC-A and ≈12 GV for ORC-M. This relation allows to investigate the change in the cosmic ray spectrum along the different regions in an Interplanetary Coronal Mass Ejection, i.e. the shock, the sheath and the magnetic cloud. ORCA first observations are presented, focusing on the analysis of the Forbush Decrease (FD) that happened at the beginning of November 2021. We present these observations and show the promising capabilities of the Antarctic Cosmic Ray Observatory, which represents a new concept of cosmic ray and solar energetic particle detector. The cosmic ray spectrum changes during the Forbush decrease detected in early November 2021 as seen in the change in the ratio of ORC-A to ORC-M count rates. This change is clear after the arrival of the shock and during the magnetic cloud being smoother or even flat in the sheath. In addition, the secondary muons show changes in their arrival directions along the ICME, being clear the different behavior in shock, sheath and magnetic cloud.

Forbush decreases and geomagnetic disturbances: 2. Comparison of solar cycles 23–24 and events with sudden and gradual onset

Statistical relationships between the values of geomagnetic indices and the characteristics of cosmic rays and interplanetary disturbances are studied for Forbush decreases with sudden and gradual onset associated with different types of solar sources: a) coronal mass ejections from active regions accompanied by solar flares; b) filament eruptions outside active regions; c) high-speed streams from coronal holes; d) several sources. Using statistical methods, the dependence of geomagnetic indices on cosmic ray and solar wind parameters for Forbush decreases in solar cycles 23 and 24 is also compared. The results obtained showed: a) interplanetary disturbances associated with coronal mass ejections from active regions cause mainly magnetic storms with a sudden onset; b) interplanetary disturbances associated with high-speed streams from coronal holes cause mainly storms with a gradual onset; c) interplanetary disturbances associated with filament eruptions outside active regions cause equally probable storms with a sudden and gradual onset. For sporadic Forbush decreases the values of cosmic ray and geomagnetic activity parameters are, on average, higher for events with a sudden onset; for recurrent Forbush decreases, the nature of the event onset does not affect the value of these parameters. For all types of solar sources the parameters of the disturbed solar wind are, on average, higher in events with a sudden onset. The geoefficiency of interplanetary disturbances is much higher in the 23rd cycle for events associated with ejections from active regions; for other types of disturbances, the difference between the cycles is weak.

Forbush Decreases and Geomagnetic Disturbances: 2. Comparison of Solar Cycles 23–24 and Events with Sudden and Gradual Commencement

Forbush Decreases and Geomagnetic Disturbances: 2. Comparison of Solar Cycles 23–24 and Events with Sudden and Gradual Commencement

Geomagnetic and Cosmic Ray Activity Effect on Heart Rate during the Solar Cycle 24

The number of investigations relevant to the study of geomagnetic activity, solar events, and cosmic rays, i.e., space weather phenomena, and their impact on human health has increased dramatically over the past few years. Numerous studies examine the reaction of the cardiovascular, nervous, and other functional systems to variations observed in geospace. These studies examine the behavior of human physiological parameters not only during different levels of activity of the Sun and in the interplanetary space (from no activity to remarkably intense activity) but also through geomagnetic activity storms and Forbush decreases. Here, individuals from the Hippocratio General Hospital in Athens, the cardiology clinics of Nikaia General Hospital in Piraeus, and the Heraklion University Hospital in Crete, Greece, were assessed during the time period from 2011 until 2018. The heart rate of the individuals was recorded every hour via the Holter electrocardiogram method. Data were analyzed using the analysis of variance (ANOVA) and the method of superimposed epochs. The investigation covers not only the ascending but also the descending phase of the solar cycle 24 (lasting until 2019 and with its maximum in the year 2014).

Solar and Interplanetary Causes of Magnetic Cloud Related Forbush Decreases During Solar Cycle 23,24

Solar and Interplanetary Causes of Magnetic Cloud Related Forbush Decreases During Solar Cycle 23,24

Measurement of muon flux variations with scintillators in Mexico City and their correlation to solar activity

In this work we report the variations of the atmospheric muons flux in Mexico City. The measurements were performed from September to December 2023 at the Institute of Nuclear Sciences of UNAM, located at coordinates 19.32°N 99.18°W with an altitude of 2274 meters above sea level and a cutoff rigidity of 8.24 GV. The experimental setup consists of a pair of scintillators, with dimensions of 50cm x 1m. To compensate for fluctuations in air pressure, we calculate the barometric coefficient using data, which is determined to be -0.21%/mb. The observed muon flux corresponds to 98.3 ± 2.6 m−2 s−1 sr−1 and is consistent with other measurements at the same location. We have identified three variations in the pressure-corrected muon flux that exhibit a pattern similar to those observed by a neutron cosmic ray detector at UNAM. Through an extensive analysis of the publicly available geomagnetic data, we have correlated these variations with a phenomenon known as a Forbush decrease.

A Comparative Study of Two Contrasting Cosmic-Ray Events Caused by Solar Eruptions from NOAA AR 12673 in 2017 September

Two major solar eruptions on AR 12673 produced a Forbush decrease (FD) event (reduction of cosmic rays) on 2017 September 8 and ground-level enhancement (GLE; enhancement of cosmic rays) on 2017 September 10. The occurrence of two contrasting cosmic-ray events within 2 days that are associated with two similar X-class solar flares (X9.3 and X8.2) and share the same active region on the Sun provides us a rare opportunity to understand the dominant factors in determining the properties of transient cosmic-ray events. Using a suite of modern-day instruments continuously tracking solar eruptions from the Sun to the Earth with ground-based cosmic-ray detectors, we reveal the complete cause–effect chain of activities for these two events. We conclude that the different consequences on the ground arise from two effects of the eruptions near the Sun: (1) the geometric effect of CMEs and (2) the intensity effect of CME-driven shocks. The first eruption, which originated at the heliographic longitude of W34° on 2017 September 6, had its CME ejecta and CME-driven shock intercept the Earth, leading to the FD event. The second eruption, which occurred on September 10 at W88°, only had its far flank reach the Earth. The peak shock speed of 3344 km s−1 of the second eruption, much faster than the 2175 km s−1 of the first eruption, is the dominant factor producing the GLE event, even though the first eruption is better connected magnetically to the Earth and has a similar flare. The results indicate that the production of GLE particles can be dominated by fast-enough CME-driven shocks.

The Effect of Magnetic Field Line Topology on ICME-related GCR Modulation

The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to affect the galactic cosmic-ray (GCR) flux measured in situ by spacecraft, causing temporary decreases known as Forbush decreases (FDs). In some ICMEs, the magnetic ejecta exhibits a magnetic flux rope (FR) structure; the strong magnetic field strength and closed field line geometry of such ICME FRs have been proposed to act as a shield to GCR transport. In this study, we identify four ICMEs near Earth that drove FDs with similar mean magnetic field strengths (20–25 nT), two ICMEs with more typical mean speeds (∼400 km s−1), and two fast (∼750 km s−1) ICMEs. Within each speed pairing, we identify an ICME that exhibited an open magnetic field line topology and compare its effect on the GCR flux to that which exhibited a mostly closed topology. We investigate the different mechanisms that contribute to the resulting ICME-related FDs and their recovery and determine which properties, if any, play a more important role than others in driving FDs. We find that much of the GCR response to the ICME events in this study is independent of the open or closed magnetic field line topology of the FR and that features such as the fluctuations in speed, magnetic field structure, and expansion within the FR may play more of a role in determining the smaller-scale structure of the FD profile.

Forbush Decreases and Geomagnetic Disturbances: 1. Events Associated with Different Types of Solar and Interplanetary Sources

Forbush Decreases and Geomagnetic Disturbances: 1. Events Associated with Different Types of Solar and Interplanetary Sources

Analyzing solar activity with Belgrade muon station: case study of 2021 November 4th Forbush decrease

Analyzing solar activity with Belgrade muon station: case study of 2021 November 4th Forbush decrease

Solar Activity, Weather, and Climate: The Elusive Connection

Abstract The search for an explanation of correlations of weather and climate with solar activity has uncovered some subtle effects of the varying solar inputs, which include irradiance, energetic particles, electric fields induced by the solar wind, and the modulation of the galactic cosmic ray flux. Relevant phenomena have been identified in stratospheric chemistry and dynamics and in aerosols, atmospheric electricity, and clouds. The effects are small and appear intermittently in statistical analyses of observations. Correlations and theory permit responses to several solar inputs effective on the decadal time scales, making it difficult to distinguish them observationally. No mechanism for tropospheric decadal change can be considered to be definitely established, but for the day-to-day time scale there is clear observational evidence for clouds responding to solar wind–induced current flow (JZ) in the global electric circuit, due to changes in ionospheric potential, and independently from Forbush decreases of the cosmic ray flux. The responses to JZ also correlate separately with ionospheric potential changes due to changes in day-to-day thunderstorm activity. The identified mechanism is for electric charge effects on in-cloud scavenging, and this implies a decadal response, in view of decadal changes in JZ. However, a complete and quantitative model of the inferred electrically induced changes in cloud microphysics is not yet available. The failures, successes, and controversies of the search illustrate the somewhat chaotic process of scientific discovery.

Forbush Decreases and Geomagnetic Disturbances: 1. Events Associated with Different Types of Solar and Interplanetary Sources

In this paper we study the statistical relations between geomagnetic indices and the characteristics of cosmic rays and interplanetary disturbances for Forbush decreases associated with (a) coronal mass ejections from active regions accompanied by solar flares, (b) filament eruptions outside active regions, (c) high-speed streams from coronal holes, and (d) multiple sources. For sporadic Forbush decreases, the dependence of geomagnetic indices on cosmic ray and solar wind parameters in the presence or absence of a magnetic cloud is compared using statistical methods. The results show that (a) the highest geoeffectiveness is characteristic of interplanetary disturbances associated with solar matter eruptions from active regions in the presence of a magnetic cloud (and the lowest one for recurrent disturbances), (b) sporadic and recurrent events differ not only in the magnitude of geomagnetic indices and the southern component of the magnetic field but also in the nature of the relationship between them, (c) the geoeffectiveness of transient solar wind disturbances depends more strongly on the presence or absence of a magnetic cloud than on the type of solar source, and (d) for interplanetary disturbances associated with filament eruptions outside active regions, in the presence of a magnetic cloud, the geoeffectiveness depends only on the southern component of the magnetic field, while for other types of disturbances it depends on other solar wind parameters.

Comparison of Solar Activity Parameters and Associated Forbush Decreases in Solar Cycles 23 and 24

Comparison of Solar Activity Parameters and Associated Forbush Decreases in Solar Cycles 23 and 24

The role of extreme geomagnetic storms in the Forbush decrease profile observed by neutron monitors

The Forbush decrease (FD) and Geomagnetic storm (GS) are the two distinct space weather events having common causing agents like interplanetary coronal mass ejection (ICME) or corotating interacting region (CIR). Generally, large-amplitude FDs and extreme GSs are caused by ICME. Here, we studied eight ICME induced extreme storms and their effects on respective FD profiles as observed by neutron monitors. We observed the sudden storm commencement of the GS coincides with the FD onset. Interestingly, we also noted a gradual increase in neutron counts during the main and recovery phases of GS. The maximum enhancement in neutron counts coincides with the minimum value of the Sym-H index. The enhancement is visible primarily in all the neutron monitors but significantly pronounced in high-energy neutrons compared to low-energy neutrons. We observed that the enhancement in cosmic ray flux during Forbush decrease as observed by neutron monitors is contributed by magnetospheric disturbance of geomagnetic storm. Thus we conclude that the weakening of Earth’s magnetic shield due to ICME-Magnetosphere interaction allows more cosmic rays to reach the ground. Thus, we conclude that the geomagnetic storm conditions highly influence the FD profile along with the external causing agent. Therefore, it is essential to include the effect of geomagnetic field variation in the models that are used to reproduce the FD profile.