Cosmic Ray Decreases Research Articles

Interplanetary Causes and Impacts of the 2024 May Superstorm on the Geosphere: An Overview

The recent superstorm of 2024 May 10–11 is the second largest geomagnetic storm in the space age and the only one that has simultaneous interplanetary data (there were no interplanetary data for the 1989 March storm). The May superstorm was characterized by a sudden impulse (SI+) amplitude of +88 nT, followed by a three-step storm main-phase development, which had a total duration of ∼9 hr. The cause of the first storm main phase with a peak SYM-H intensity of −183 nT was a fast-forward interplanetary shock (magnetosonic Mach number M ms ∼ 7.2) and an interplanetary sheath with a southward interplanetary magnetic field component B s of ∼40 nT. The cause of the second storm's main phase with an SYM-H intensity of −354 nT was a deepening of the sheath B s to ∼43 nT. A magnetosonic wave (M ms ∼ 0.6) compressed the sheath to a high magnetic field strength of ∼71 nT. Intensified B s of ∼48 nT were the cause of the third and most intense storm main phase, with an SYM-H intensity of −518 nT. Three magnetic cloud events with B s fields of ∼25–40 nT occurred in the storm recovery phase, lengthening the recovery to ∼2.8 days. At geosynchronous orbit, ∼76 keV to ∼1.5 MeV electrons exhibited ∼1–3 orders of magnitude flux decreases following the shock/sheath impingement onto the magnetosphere. The cosmic-ray decreases at Dome C, Antarctica (effective vertical cutoff rigidity <0.01 GV) and Oulu, Finland (rigidity ∼0.8 GV) were ∼17% and ∼11%, respectively, relative to quiet-time values. Strong ionospheric current flows resulted in extreme geomagnetically induced currents of ∼30–40 A in the subauroral region. The storm period is characterized by strong polar-region field-aligned currents, with ∼10 times intensification during the main phase and equatorward expansion down to ∼50° geomagnetic (altitude-adjusted) latitude.

Analysis of the Cosmic Ray Decrease with Solar Activity and Geomagnetic Indices in Solar Cycle-24

Analysis of the Cosmic Ray Decrease with Solar Activity and Geomagnetic Indices in Solar Cycle-24

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.

Study of the development and mechanism of large amplitude decreases in cosmic ray intensity during geomagnetic disturbances in the magnetosphere

We analyze the time-variation of cosmic ray intensity during the periods when large and sudden disturbances occur and last for several days. We consider periods when there are sudden decreases of ≥5% in the galactic cosmic ray (GCR) intensity records. For the analysis, in addition to cosmic-ray intensity data, we utilize several solar wind plasma and field parameters. Time variation of changes in GCR intensity have been compared with simultaneous changes in solar wind plasma and field parameters, in order to gain insight about the physical processes responsible for large-amplitude cosmic ray disturbances. We utilize not only data about changes in the magnitude of some of the plasma and magnetic field parameters but also the parameters which provide information about the turbulent or quite (non-turbulent) nature of the parameters. Moreover, we also utilize the magnitude of a number of plasma and field parameters and their various products, during cosmic ray decrease of various magnitudes. The magnitudes of various plasma and field parameters and their various products including some newly tried products are subjected to correlation analysis with the magnitude of cosmic-ray decreases. We identify plasma and field parameters and their products which best correlates with cosmic-ray decreases. We provide an empirical relation that can be useful to estimate the amplitude of Forbush decreases using interplanetary plasma and field observations. Our results provide further insight about the physical processes playing important role during large cosmic ray disturbances in the heliosphere. Our results further demonstrate that large-amplitude Forbush decreases in GCR intensity occur due to passage of enhanced and turbulent magnetic field structure, consistent with the model that Forbush decreases are mainly due to scattering of cosmic ray particles by enhanced turbulent magnetic field regions in the heliosphere.

On the relationship of power lines outages caused by thunderstorms with Forbush decreases of cosmic rays

It is known that power lines outages often occur during thunderstorms. Here are the results of comparing of power lines outages in Yakutia from 2012 to 2018 with the database of Forbush-Storm events. This database contains information on geomagnetic storms and Forbush-decreases of cosmic rays from 1996 to 2018. There are 3 classes of the events: if these two ground-based manifestations of solar wind disturbances occur simultaneously (Forbush with Storm, F+S) or separately (Forbush without Storm, F-S and Storm without Forbush, S-F). For 7 years in the summer time, 73 power lines outages associated with thunderstorms were recorded. It is shown that in 56 cases these outages occurred simultaneously with (F-S) class, 16 – with (F+S) class, and only in 1 case lightning outages were not associated with Forbush-Storm events (-F-S). In 19 cases of (S-F) class, not a single lightning outage was recorded. This means that lightning outages on power lines are mainly associated with decreases in the cosmic rays intensity, and during geomagnetic storms, power transmission disruptions occur when storms are simultaneous with Forbush-decreases of cosmic rays. Apparently, this indicates the significance of the effect of cosmic rays on atmospheric electricity, and it is more significant than the effect of geomagnetic storms.

Study of the recovery characteristics of intense cosmic-ray decreases

Study of the recovery characteristics of intense cosmic-ray decreases

Large Forbush Decreases and their Solar Sources: Features and Characteristics

One of the factors responsible for the wide variety of Forbush decreases is the different solar sources related to them. In this investigation the different features and characteristics of Forbush decreases, with emphasis on large Forbush decreases and their association with solar sources, are examined. Initially, a wider selection of events from the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation of the Russian Academy of Sciences Forbush decreases database served as a starting point for this study, which was then narrowed down to a group of large Forbush decreases. According to the helio-longitude of the solar source, the events under study were separated into three subcategories: western ( $21^{\circ} \leq \mbox{helio-longitude} \leq 60^{\circ}$ ), eastern ( $-60^{\circ} \leq \mbox{helio-longitude} \leq -21^{\circ}$ ), and central ( $-20^{\circ} \leq \mbox{helio-longitude} \leq 20^{\circ}$ ). The selected events cover the period 1967 – 2017. The “Global Survey Method” was used for analyzing the aforementioned Forbush decreases, along with data on solar flares, solar-wind speed, geomagnetic indices (Kp and Dst), and interplanetary magnetic field. The superimposed epoch method was applied to display the temporal profiles for the selected events. This detailed analysis reveals interesting results concerning the features of cosmic-ray decreases in relation to the helio-longitude of the solar sources. Specifically, Forbush decreases related to central or eastern solar sources are more often observed, have a greater magnitude, and present a slower development than Forbush decreases related to western sources, which are rarer, have a smaller magnitude, and have a shorter lifespan. Nevertheless, regardless of the helio-longitude of the solar source, large Forbush decreases are accompanied by increased geomagnetic activity and increased anisotropy, including anisotropy before the events, which can serve as a typical precursor of Forbush decreases.

Behavior of the Speed and Temperature of the Solar Wind during Interplanetary Disturbances Creating Forbush Decreases

Forbush decreases of cosmic rays are caused by two types of solar sources: coronal holes and coronal mass ejections. In some cases, the identification of the solar source with the interplanetary disturbance causing the Forbush decrease is difficult and requires a thorough and detailed analysis of the solar-wind characteristics. In these cases, it is useful to compare the behavior of the proton temperature and speed of the solar wind. In this paper, this comparison is carried out based on a large amount of experimental material summarized in the IZMIRAN databases. The dependence of temperature on speed for a quiet solar wind is found to have a power character with a steeper spectrum in the low-speed range (V < 425 km/s; exponent index 3.37 ± 0.02) than in the high-speed range (V ≥ 425 km/s; exponent index 2.21 ± 0.02). Based on the obtained T–V dependence, the expected proton temperature Texp and the temperature index KT = Tobs/Texp (Tobs is the observed temperature) are calculated for every hour with available data on the solar-wind parameters from July 1965 to December 2018. This index is anomalously high in the regions of the interaction different speed solar-wind streams and is anomalously low inside magnetic clouds. This makes it possible to detect the Forbush decreases associated with these interplanetary structures and to identify their solar sources.

Low Latitude Lightning Activity Responses to Cosmic Ray Forbush Decreases

AbstractThe relation between low latitude lightning activity and Forbush decreases (FDs) of galactic cosmic rays was studied, with flash rates observed by the Lightning Image Sensor aboard the Tropical Rainfall Measuring Mission satellite and FDs selected from the events with decreases more than 2% measured by the Mexico City neutron monitor. The effect of spacecraft precession on Lightning Image Sensor data complicates the analysis, but this can be dealt with by the approach we use. Applying a superposed epoch analysis to all of the 70 FD cases, we found the low latitude lightning activity decreases by about 10% after the Forbush minimum, with a 95% confidence level tested by Monte Carlo simulation, and recovers 3 days later. The response is more significant in the Southern Hemisphere. Our result provides evidence for a proposed link between solar activity, cosmic rays, the global atmospheric electric circuit, and cloud microphysics.

The Identification of a Planar Magnetic Structure within the ICME Shock Sheath and Its influence on Galactic Cosmic-Ray Flux

Abstract A Forbush decrease is a sudden decrease in cosmic-ray intensity caused by transient interplanetary disturbances. The substructure of an interplanetary counterpart of a coronal mass ejection (ICME) such as a shock sheath and/or a magnetic cloud independently contributes to cosmic-ray decrease, which is evident as a two-step decrease. Our earlier work has shown multistep decrease and recovery within the ICME-driven shock-sheath region. Further, we have suggested that the presence of a small-scale flux rope within the shock-sheath region causes a steady/gradual recovery in cosmic-ray intensity. Here, we demonstrate the presence of a planar magnetic structure (PMS) and small-scale flux rope within a single shock sheath of an ICME. The plot of the elevation (θ) versus azimuthal (ϕ) angle of the interplanetary magnetic field (IMF) is used for the identification of the PMS. The planarity, efficiency, and a plane-normal vector are estimated by employing a minimum variance analysis (MVA) technique, which confirmed the presence of the PMS. In addition, a 2D-hodogram method in conjunction with the MVA technique is utilized to identify the flux-rope structure and turbulent conditions in the corresponding ICME region. The observation in the visible suggests that the PMS region within the ICME shock sheath caused the decrease in the cosmic-ray flux observed at Earth. It has also been observed that the sharp variations in the IMF (i.e., turbulence) cause a decrease, whereas the flux-rope structure is responsible for the recovery of the CR flux. Further studies are needed to investigate their origins and to confirm their effects on space weather.

Forbush Decrease: A New Perspective with Classification

The sudden short duration decrease in cosmic ray flux is known as Forbush decrease which is mainly caused by interplanetary disturbances. Generally accepted view is that the first step of Forbush decrease is due to shock sheath and second step is due to Magnetic Cloud (MC) of Interplanetary Coronal Mass Ejection (ICME). However, there are few questions which needs detail investigation. (i) Does the complete (or part of) ICME shock or MC contribute in cosmic ray decrease? (ii) Is there any internal structure associated with the ICMEs shock/MC which precisely contribute in decrease? To address these questions we have studied a total of 18 large ($>=8 \%$) Forbush decrease events and associated ICMEs. Majority of events shows multi-steps Forbush decrease profile. This leads into re-classification of Forbush decrease events depending upon the number of steps observed in their respective profile. The present study clearly indicates that not only broad regions (shock-sheath and MC) contribute to Forbush decrease but also localized structures within shock-sheath and MC have very much significant importance in Forbush decrease profile.

Forbush decrease of cosmic rays in a toroidal model of a magnetic cloud

The intensity of cosmic rays in a magnetic cloud is calculated. It is found that the duration of the Forbush decrease recovery is determined by the magnetic cloud orientation and the reduction in the magnetic field inside the magnetic cloud as it expands. The formation of the Forbush decrease is described in terms of the contributions from different sources of particles.

Comparative analysis of short-term effects of solar and galactic cosmic rays on the evolution of baric systems at middle latitudes

Effects of solar proton events (SPEs) and Forbush decreases of galactic cosmic rays (GCRs) on the evolution of baric systems at middle latitudes are compared. It is shown that SPEs with particle energies >90МeV contribute to more intensive regeneration of cyclones at Arctic fronts, while Forbush decreases of GCRs are accompanied by intensification of anticyclonic processes at Polar fronts. The data show that changes in the ionization rate caused by cosmic ray variations play an important part in solar-atmospheric relationships.

The response of clouds and aerosols to cosmic ray decreases

AbstractA method is developed to rank Forbush decreases (FDs) in the galactic cosmic ray radiation according to their expected impact on the ionization of the lower atmosphere. Then a Monte Carlo bootstrap‐based statistical test is formulated to estimate the significance of the apparent response in physical and microphysical cloud parameters to FDs. The test is subsequently applied to one ground‐based and three satellite‐based data sets. Responses (&gt;95%) to FDs are found in the following parameters of the analyzed data sets. AERONET: Ångström exponent (cloud condensation nuclei changes), SSM/I: liquid water content, International Satellite Cloud Climate Project (ISCCP): total, high, and middle, IR‐detected clouds over the oceans, Moderate Resolution Imaging Spectroradiometer (MODIS): cloud effective emissivity, cloud optical thickness, liquid water, cloud fraction, liquid water path, and liquid cloud effective radius. Moreover, the responses in MODIS are found to correlate positively with the strength of the FDs, and the signs and magnitudes of the responses agree with model‐based expectations. The effect is mainly seen in liquid clouds. An impact through changes in UV‐driven photo chemistry is shown to be negligible and an impact via UV absorption in the stratosphere is found to have no effect on clouds. The total solar irradiance has a relative decrease in connection with FDs of the order of 10−3, which is too small to have a thermodynamic impact on timescales of a few days. The results demonstrate that there is a real influence of FDs on clouds probably through ions.

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of galactic cosmic rays (GCRs) decreases. The main aims of this paper are to find: common plasma and magnetic properties of different ICME sub-structures, and which ICME properties affect the flux of GCRs near Earth. We use a superposed epoch method applied to a large set of ICMEs observed \insitu\ by the spacecraft ACE, between 1998 and 2006. We also apply a superposed epoch analysis on GCRs time series observed with the McMurdo neutron monitors. We find that slow MCs at 1 AU have on average more massive sheaths. We conclude that it is because they are more effectively slowed down by drag during their travel from the Sun. Slow MCs also have a more symmetric magnetic field and sheaths expanding similarly as their following MC, while in contrast, fast MCs have an asymmetric magnetic profile and a compressing sheath in compression. In all types of MCs, we find that the proton density and the temperature, as well as the magnetic fluctuations can diffuse within the front of the MC due to 3D reconnection. Finally, we derive a quantitative model which describes the decrease of cosmic rays as a function of the amount of magnetic fluctuations and field strength. The obtained typical profiles of sheath/MC/GCR properties corresponding to slow, mid, and fast ICMEs, can be used for forecasting/modelling these events, and to better understand the transport of energetic particles in ICMEs. They are also useful for improving future operative space weather activities.

Solar Activity Parameters and Associated Forbush Decreases During the Minimum Between Cycles 23 and 24 and the Ascending Phase of Cycle 24

We study the Forbush decreases in cosmic-ray intensity from January 2008 to December 2013, covering the minimum between Solar Cycles 23 and 24 and the ascending phase of Cycle 24. We performed a statistical analysis of 617 events and concentrated on three of the most important ones. We used the IZMIRAN database of Forbush effects obtained by processing the data of the worldwide neutron monitor network using the global survey method. The first event occurred on 18 February 2011 with a \({\sim}\,5~\%\) decrease of cosmic rays with 10 GV rigidity, the second on 8 March 2012 with an amplitude of \({\sim}\,12~\%\), and the third on 14 July 2012 with an amplitude of \({\sim}\,6~\%\). For these three events, we also studied the events that occurred on the Sun and the way that these affected the interplanetary space, and finally provoked the decreases of the galactic cosmic rays near Earth. We found that each neutron monitor records these decreases, which depend on the cut-off rigidity of the station. We carried out a statistical analysis of the amplitude of the cosmic-ray decreases with solar and geomagnetic parameters.

Effects of Forbush decreases of galactic cosmic rays on anticyclone activity at middle latitudes

The baric response of the lower atmosphere to Forbush decreases of galactic cosmic rays (GCRs) is investigated. It is shown that Forbush decreases are accompanied by a weakening of cyclonic activity and a strengthening of anticyclonic activity at the extratropical latitudes (45°–70°) of the Northern and Southern hemispheres. These results show an important role of cosmic rays in solar-terrestrial relationships.

Symmetrie Cosmic Ray Intensity Decreases in Relation with Coronal Mass Ejections and Disturbances In Solar Wind Plasma Parameters

We have studied symmetric cosmic ray intensity decreases (V Shape, and U Shape) magnitude ≥ 2.0%, observed at Oulu super neutron monitor, during the period of 1986-2006 with coronal mass ejections CMEs), interplanetary shocks and disturbances in solar wind plasma parameters (solar wind temperature, velocity, density). We have found that 76.92% V shape symmetric cosmic ray intensity decreases are associated with halo and partial halo coronal mass ejections (CMEs). The association rate between halo and partial halo coronal mass ejections are found 40.00%and 60.00% respectively. Most of the V Shape symmetric cosmic ray intensity decreases are related to interplanetary shocks (61.53%) and the related shocks are forward shocks. We have also found positive co-relation with co-relation co-efficient 0.54 between magnitude of V shape symmetric cosmic ray intensity decreases and speed of associated coronal mass ejections. From the further study it is concluded that V shape symmetric cosmic ray decreases are strongly related to the disturbances in solar wind plasma parameters. Negative co-relation has been found between magnitudes of V Shape symmetric cosmic ray intensity decreases and magnitude of jump in solar wind plasma density of associated JSWD events with co-relation co-efficient -0.152 between these two events. Negative co-relation has also been found between magnitude of V Shape asymmetric cosmic ray intensity decreases and magnitude of jump in solar wind plasma velocity of the associated JSWV events with co-relation co-efficient -0.48 between these two events. From the study of U Shape symmetric cosmic ray intensity decreases and disturbances in solar wind plasma parameters, we found negative co-relation with correlation coefficient, -0.473 between magnitude of U shape symmetric cosmic ray intensity decreases and magnitude of jump in solar wind plasma temperature of associated JSWT events, -0.468 between magnitude of U shape symmetric cosmic ray intensity decreases and magnitude of jump in solar wind plasma density of associated JSWD events and -0.26 between U shape symmetric cosmic ray intensity decreases and magnitude of jump in solar wind plasma velocity of associated JSWV events.

Atmospheric pressure variations at extratropical latitudes associated with Forbush decreases of galactic cosmic rays

Changes of troposphere pressure associated with short-time variations of galactic cosmic rays (GCRs) taking place in the Northern hemisphere’s cold months (October–March) were analyzed for the period 1980–2006, NCEP/NCAR reanalysis data being used. Noticeable pressure variations during Forbush decreases of GCRs were revealed at extratropical latitudes of both hemispheres. The maxima of pressure increase were observed on the 3rd–4th days after the event onsets over Northern Europe and the European part of Russia in the Northern hemisphere, as well as on the 4th–5th days over the eastern part of the South Atlantic opposite Queen Maud Land and over the d’Urville Sea in the Southern Ocean. According to the weather chart analysis, the observed pressure growth, as a rule, results from the weakening of cyclones and intensification of anticyclone development in these areas. The presented results suggest that cosmic ray variations may influence the evolution of extratropical baric systems and play an important role in solar-terrestrial relationships.

Investigation of cosmic ray–cloud connections using MISR

Numerous empirical studies have analyzed International Satellite Cloud Climatology Project data and reached contradictory conclusions regarding the influence of solar‐modulated galactic cosmic rays on cloud fraction and cloud properties. The Multiangle Imaging Spectroradiometer (MISR) instrument on the Terra satellite has been in continuous operation for 13 years and thus provides an independent (and previously unutilized) cloud data set to investigate purported solar‐cloud links. Furthermore, unlike many previous solar‐climate studies that report cloud fraction MISR measures albedo, which has clearer climatological relevance. Our long‐term analysis of MISR data finds no statistically significant correlations between cosmic rays and global albedo or globally averaged cloud height, and no evidence for any regional or lagged correlations. Moreover, epoch superposition analysis of Forbush decreases reveals no detectable albedo response to cosmic ray decreases, thereby placing an upper limit on the possible influence of cosmic ray variations on global albedo of 0.0029 per 5% decrease. The implications for recent global warming are discussed.