Effects Of Coronal Mass Ejections Research Articles

SODA - a tool to predict storm induced orbit decays for low Earth orbiting satellites

Due to the rapidly increasing technological progress in the last decades, the issue of space weather and its influences on our everyday life gains more and more importance. Today, satellite-based navigation plays a key role in aviation, logistics and transportation systems. With the strong rise of the current solar cycle 25 the number and intensity of solar eruptions increased. The forecasting tool SODA (Satellite Orbit DecAy) is based on an interdisciplinary analysis of space geodetic observations and solar wind in situ measurements. It predicts the effect of coronal mass ejections from their in-situ measured counterparts (ICME) on the altitude of low Earth orbiting satellites at 490 km with a lead time of about 20 hours. Additionally, it classifies the severeness of the expected geomagnetic storm in the form of the Space Weather G–scale from the National Oceanic and Atmospheric Administration (NOAA). For the establishment and validation of SODA, we examined 360 ICME events over a period of 21 years. Appropriated variations in the thermospheric neutral mass density, were derived mainly from measurements of the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Related changes in the interplanetary magnetic field component Bz were investigated from real-time measurements using data from spacecraft located at the Lagrange point L1. The analysis of the ICME induced orbit decays and the interplanetary magnetic field showed a strong correlation as well as a time delay between the ICME and the associated thermospheric response. The derived results are implemented in the real- forecasting tool SODA, which integrated in the Space Safety Program Ionospheric Weather Expert Service Center; I.161 of the Space Agency (ESA).

Effects of stealth CME to ion energisation at ionospheric altitudes of Mars

The declining phase of Solar cycle 24 produced a slow coronal mass ejection (CME), which was categorized as stealth CME based on the absence of associated low coronal signatures. This CME impacted Mars and caused a major space weather event during 27–28 August 2018 (max vsw = 580 km s−1 near 1.5 AU). The impact of the stealth CME on the topside of the Martian ionosphere is investigated using the data from Solar Wind Ion Analyzer (SWIA), Solar Energetic Particle (SEP) and Suprathermal and Thermal Ion Composition (STATIC) instruments onboard Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The variations of ion and electron fluxes within the plasma boundaries during the passage of ICME event were observed using Electron Spectrometer (ELS) and the Ion Mass Analyzer (IMA) sensors onboard Mars Express (MEX) mission. The plasma boundaries of the induced magnetosphere of Mars showed considerable enhancement in the observed fluxes during the event. SWIA observations during the interaction of the CME with Martian plasma environment showed enhancement in the ion flux. STATIC observations showed energisation of planetary heavy ions like O+ and O2+ to energies between 10 eV up to hundreds of eV at altitudes below 300 km. SEP measurements of energetic O+ pick-up ions at energies below 50 keV further support the claim on planetary ion energisation.

English

The solar sources of 884 geomagnetic storms have been studied for the solar cycles 23 and 24 (1996-2019), regardless of their size ranges; using the Kp index and the NOAA G criteria (minor to extreme storms). It claims from our investigation that fast solar wind streams (HSSWs) is the main factor of small (G1) and medium (G2) storms and occur mostly on the descending phase of the solar cycle. Fast solar wind has contributed to about 59% of G1 storms; 50% of G2; 29% G3; and 10% G4 storm. Large storms (G3 to G5) are the effects of coronal mass ejections (CMEs) and they are observed mainly during the maximum and the descending phases of the solar cycle. About 10% of G1 storms, 26% of G2 storms, 59% of G3 (strong) storms, 87% of G4 (severe) storms, and 100% of G5 (extreme) storms were the effect of CMEs. Magnetic clouds contributed 11% of G1 storms, 15% of G2 storms, 9% of G3 storms, and 3% of G4 storms. A comparative statistical occurrence shows that the number of storms decreased during solar cycle 24 when compared with the solar cycle 23. These results showed that the magnetospheric energy transfer decreased in solar cycle 24 and that the magnetosphere was under the influence of intense solar magnetic fields in solar cycle 23. The phenomenon observed in these investigations highlight a drop in solar plasma geoeffectiveness since the long minimum that followed the solar cycle 23. Key words: Magnetic storms, coronal mass ejections (CMEs), high speed solar winds stream (HSSWs), magnetic clouds (MCs), solar cycle.

Studying the Effect of Coronal Mass Ejections and Solar Flares on Thunderstorms in the City of Mosul for Solar Cycles 23 and 24

The study of the impact of solar activity on the Earth's climate is an important matter for predicting the change of climate elements for long periods. Most research has been limited to studying the relationship of sunspots with a change in one of the climate elements. In this research, the effect of the solar activities of coronal mass ejections and solar flare on a climatic element in the troposphere, represented by thunderstorms during the winter season in the city of Mosul for the 23 and 24 solar cycles, respectively, was studied. The data on coronal mass ejections were collected from the SOHO/LASCO CME Catalog database and solar flare data were taken from the website National Oceanic and Atmosperic (NOAA). Climatic data on thunderstorms for the winter seasons from the period (1996-2019) were used from the monitoring station in the city of Mosul from the Iraqi General Authority for Meteorology and Seismic Monitoring.The parameters were analyzed using the statistical program (Minitab 19.0). The results showed that there is an inverse relationship between the monthly rates of solar activities with the monthly rate of thunderstorm frequency, with the exception of the rising phase of the solar cycle 24 for the time period (2008-2013), where the results showed the existence of a positive relationship between them

The impact of coronal mass ejections and flares on the atmosphere of the hot Jupiter HD189733b

ABSTRACT High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. For the exoplanet HD189733b, multiple observations in the Ly α line have shown that atmospheric evaporation is variable, going from undetected to enhanced evaporation in a 1.5-yr interval. Coincidentally or not, when HD189733b was observed to be evaporating, a stellar flare had just occurred 8 h prior to the observation. This led to the question of whether this temporal variation in evaporation occurred due to the flare, an unseen associated coronal mass ejection (CME), or even the simultaneous effect of both. In this work, we investigate the impact of flares (radiation), winds, and CMEs (particles) on the atmosphere of HD189733b using three-dimensional radiation hydrodynamic simulations that self-consistently include stellar photon heating. We study four cases: first, the quiescent phase including stellar wind; secondly, a flare; thirdly, a CME; and fourthly, a flare that is followed by a CME. Compared to the quiescent case, we find that the flare alone increases the evaporation rate by only 25 per cent, while the CME leads to a factor of 4 increments. We calculate Ly α synthetic transits and find that the flare alone cannot explain the observed high blueshifted velocities seen in the Ly α. The CME, however, leads to an increase in the velocity of escaping atmospheres, enhancing the blueshifted transit depth. While the effects of CMEs show a promising potential, our models are not able to fully explain the blueshifted transit depths, indicating that they might require additional physical mechanisms.

Statistical study of geomagnetic storm effects on the occurrence of ionospheric irregularities over equatorial/low-latitude region of Africa from 2001 to 2017

The effect of Coronal Mass Ejection (CME) and Corotating Interaction Region (CIR)-driven storms on the occurrence of ionospheric irregularities (OIIs) over the African equatorial and low-latitude region are studied statistically for the first time. In addition to the CME and CIRs’ catalogs, we have used the disturbance storm time (Dst) ≤ -30 nT and Kp ≥ 3 to identify the storm periods. The study was based on Global Navigation Satellite System (GNSS) total electron content (TEC) observation from three stations (nklg: 8.05°S, 81.05°E; mbar: 10.22°S, 102.36°E; and nazr: 0.25°S, 111.01°E, Geomagnetic) during 2001–2017. Based on the GNSS observations, the rate of change of total electron indices (ROTIROTI and ROTIave) have been used to observe the presence/absence of ionospheric irregularities. To examine the effect of the storms on the OIIs, ratio of ROTIave of the selected storm period to the quiet monthly mean of ROTIave, ROTIratio=ROTIobs/ROTI‾quiet, was applied. Based on our analysis, ROTIratio≥3.2, ROTIratio≤0.16 and 0.16<ROTIratio<3.2 were identified as threshold values indicating the enhancement (EN), suppression (SP), and no significant (NE) effect of the storms on the OIIs, respectively. Our results revealed that the SP in the OII during CME-and CIR-driven storms are more prevalent than the EN. During both CIR-and CME-driven storms, the percentage occurrence rate in EN observed over nklg was greater than mbar and nazr. Most of the SP effect of the storms, on the other hand, was predominantly observed over nazr and mbar stations. The occurrence rate of EN, SP and NE effect of both CME-and CIR-driven storms show dependence on the local time at which large decrease in Dst occurs. We also found that SP effect of both CIR-and CME-driven storm show a positive and linear correlation with sunspot number (SSN). While the EN effect of CIR-driven storm show a negative and linear relation with SSN, CME-driven storm effects show weak relation. The polarity and amplitude of different sources of disturbance electric field observed in the evening hours could play a dominant role in affecting the OIIs. The difference in the seasonal variation in the occurrence rate of EN, SP and NE effect of the storms observed over different stations were also discussed.

Characteristics of Forbush Decreases Measured by the PAMELA Instrument During 2006–2014

During the several decades of Forbush decrease (FD) studies the main properties of this phenomenon were established. Today is clear that Forbush decreases originate as the responses of cosmic ray particle fluxes to solar-induced processes inside interplanetary space. Moreover the profiles of FD’s are the manifestation of the complex structure of coronal mass ejections (CMEs) which are driving from the Sun and often accompanied by flares. So the investigation of FD’s is a useful tool for understanding the dynamics of CME processes and the effects they have on in the interplanetary space. Classification and theoretical interpretation of different FD’s are important for understanding the complex effect of CME’s as well as the search for new features of their behavior. Spectra of cosmic ray protons and helium nuclei obtained by the PAMELA experiment in the rigidity range between 1–15 GV were used to investigate the characteristics of Forbush decreases. Additional data on the interplanetary magnetic field and solar wind speed were taken from the ACE data center for correlation analysis. Rigidity dependences for selected Forbush decreases are also presented.

The Stellar CME–Flare Relation: What Do Historic Observations Reveal?

Abstract Solar coronal mass ejections (CMEs) and flares have a statistically well-defined relationship, with more energetic X-ray flares corresponding to faster and more massive CMEs. How this relationship extends to more magnetically active stars is a subject of open research. Here we study the most probable stellar CME candidates associated with flares captured in the literature to date, all of which were observed on magnetically active stars. We use a simple CME model to derive masses and kinetic energies from observed quantities and transform associated flare data to the Geostationary Operational Environmental Satellite 1–8 Å band. Derived CME masses range from ∼1015 to 1022 g. Associated flare X-ray energies range from 1031 to 1037 erg. Stellar CME masses as a function of associated flare energy generally lie along or below the extrapolated mean for solar events. In contrast, CME kinetic energies lie below the analogous solar extrapolation by roughly 2 orders of magnitude, indicating approximate parity between flare X-ray and CME kinetic energies. These results suggest that the CMEs associated with very energetic flares on active stars are more limited in terms of the ejecta velocity than the ejecta mass, possibly because of the restraining influence of strong overlying magnetic fields and stellar wind drag. Lower CME kinetic energies and velocities present a more optimistic scenario for the effects of CME impacts on exoplanets in close proximity to active stellar hosts.

Magnetic Fields on the Flare Star Trappist-1: Consequences for Radius Inflation and Planetary Habitability

We construct evolutionary models of Trappist-1 in which magnetic fields impede the onset of convection according to a physics-based criterion. In the models that best fit all observational constraints, the photospheric fields in Tr-1 are found to be in the range 1450-1700 G. These are weaker by a factor of about 2 than the fields we obtained in previous magnetic models of two other cool dwarfs (GJ65A/B). Our results suggest that Tr-1 possesses a global poloidal field which is some one hundred times stronger than in the Sun. In the context of exoplanets in orbit around Tr-1, the strong poloidal fields on the star may help to protect the planets from the potentially destructive effects of coronal mass ejections. This, in combination with previous arguments about beneficial effects of flare photons in ultraviolet and visible portions of the spectrum, suggests that conditions on Tr-1 are not necessarily harmful to life on a planet in the habitable zone of Tr-1.

The Effects of Uncertainty in Initial CME Input Parameters on Deflection, Rotation, Bz, and Arrival Time Predictions

AbstractUnderstanding the effects of coronal mass ejections (CMEs) requires knowing if and when they will impact and their properties upon impact. Of particular importance is the strength of a CME's southward magnetic field component (Bz). Kay et al. (2013, https://doi:10.1088/0004-637X/775/1/5, 2015, https://doi:10.1088/948 0004-637X/805/2/168) have shown that the simplified analytic model Forecasting a CME's Altered Trajectory (ForeCAT) can reproduce the deflection and rotation of CMEs. Kay, Gopalswamy, Reinard, and Opher (2017, https://doi.org/10.3847/1538-4357/835/2/117) introduced ForeCAT In situ Data Observer, which uses ForeCAT results to simulate magnetic field profiles. ForeCAT In situ Data Observer reproduces the in situ observations on roughly hourly time scales, suggesting that these models could be extremely useful for predictions of Bz. However, as with all models, both models are sensitive to their input parameters, which may not be precisely known for predictions. We explore this sensitivity using ensembles having small changes in the initial latitude, longitude, and orientation of the erupting CME. We explore the effects of different background magnetic field models and find that the changes in deflection and rotation resulting from the uncertainty in the initial parameters tend to exceed the changes from different magnetic backgrounds. The range in the in situ profiles tends to scale with the range in the deflection and rotation. We also consider a simple arrival time model using ForeCAT results and find an average absolute error of only 3 hr. We show that an uncertainty in the CME position of 8.1° ± 6.9° leads to variations of 6 hr in the arrival time. This measure depends strongly on the location of impact within the CME with the arrival time changing less for impacts near the nose.

Geomagnetic field H, Z, and electromagnetic induction features of coronal mass ejections in association with geomagnetic storm at African longitudes

The largest geomagnetic disturbance caused by a coronal mass ejection (CME) of solar cycle 24 recorded on both 17 March and 22 June 2015 with minimum disturbance storm time values of −223 and −195 nT, respectively, was investigated. This study examines the effect of CME on Earth’s geomagnetic field, which includes the time derivatives of horizontal (H) and vertical (Z) components of the geomagnetic field and the rate of induction ΔZ/ΔH at African longitudes (AAE, MBO, HBK, HER, and TAM). The results demonstrated enhancement of dH/dt and dZ/dt in the daytime over the equatorial zone (AAE and MBO) and mid-latitudes (TAM, HER, and HBK) on 17 March 2015. Nighttime enhancement was observed on 22 June 2015 over the equatorial zones and mid-latitudes. Wavelet spectrum approach is used to investigate ΔZ/ΔH variation observed at AAE, MBO, HBK, HER, and TAM. The CME may have influence on time derivatives of geomagnetic field H, Z, and electromagnetic induction at the African longitudes, which may be associated with perturbations in electric fields and currents in the equatorial and low-latitude magnetic field linked with the changes in magnetospheric convection.

Determination of projection effects of CMEs using quadrature observations with the two STEREO spacecraft

Since 1995 coronal mass ejections (CMEs) have been routinely observed thanks to the sensitive Large Angle and Spectrometric Coronagraphs (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission. Their observed characteristics are stored, among other, in the SOHO/LASCO catalog. These parameters are commonly used in scientific studies. Unfortunately, coronagraphic observations of CMEs are subject to projection effects. This makes it practically impossible to determine the true properties of CMEs and therefore makes it more difficult to forecast their geoeffectiveness. In this study, using quadrature observations with the two Solar Terrestrial Relations Observatory (STEREO) spacecrafts, we estimate the projection effect affecting velocity of CMEs included in the SOHO/LASCO catalog. It was demonstrated that this effect depends significantly on width and source location of CMEs. It can be very significant for narrow events and originating from the disk center. The effect diminishes with increasing width and absolute longitude of source location of CMEs. For very wide (width ⩾ 250°) or limb events (|longitude ⩾ 70°) projection effects completely disappears.

Space Weather Forecasting at IZMIRAN

Since 1998, the Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (IZMIRAN) has had an operating heliogeophysical service—the Center for Space Weather Forecasts. This center transfers the results of basic research in solar–terrestrial physics into daily forecasting of various space weather parameters for various lead times. The forecasts are promptly available to interested consumers. This article describes the center and the main types of forecasts it provides: solar and geomagnetic activity, magnetospheric electron fluxes, and probabilities of proton increases. The challenges associated with the forecasting of effects of coronal mass ejections and coronal holes are discussed. Verification data are provided for the center’s forecasts.

Effect of Coronal Mass Ejection on Earth’s Magnetic Field during Ascending Phase of Solar Cycles 23-24

We have studied the width and speed of coronal mass ejections (CMEs) and geomagnetic disturbance storm time (Dst) Index during ascending phase of solar cycles 23 and 24. We have classified total CMEs according to angular width and speed for the ascending period 1996-2002 and 2008-2014. We have found that the width of 62% CMEs is narrow, and 3% are Halo for the solar cycle 23 and 73% CMEs are narrow, and 2% CMEs are Halo for the solar cycle 24. The speed distribution of 65% CMEs has speed ≤ 500 km/sec and 4% CMEs has speed > 1000 km/sec for solar cycle 23 and 84% CMEs has speed ≤ 500 km/sec and 1% CMEs has speed > 1000 km/sec in cycle 24. The relationship between width and speed is more pronounced for fast ejecta (>1000 km/sec.), while slower ejecta shows more astronomically immense scatter. We have reported that the correlation between Dst and CMEs for ascending phase of solar cycle 24 is less than as compare to ascending phase of solar cycle 23.

PREDICTION OF GEOMAGNETIC STORM STRENGTH FROM INNER HELIOSPHERIC IN SITU OBSERVATIONS

ABSTRACT Prediction of the effects of coronal mass ejections (CMEs) on Earth strongly depends on knowledge of the interplanetary magnetic field southward component, B z . Predicting the strength and duration of B z inside a CME with sufficient accuracy is currently impossible, forming the so-called B z problem. Here, we provide a proof-of-concept of a new method for predicting the CME arrival time, speed, B z , and resulting disturbance storm time (Dst) index on Earth based only on magnetic field data, measured in situ in the inner heliosphere (&lt;1 au). On 2012 June 12–16, three approximately Earthward-directed and interacting CMEs were observed by the Solar Terrestrial Relations Observatory imagers and Venus Express (VEX) in situ at 0.72 au, 6° away from the Sun–Earth line. The CME kinematics are calculated using the drag-based and WSA–Enlil models, constrained by the arrival time at VEX, resulting in the CME arrival time and speed on Earth. The CME magnetic field strength is scaled with a power law from VEX to Wind. Our investigation shows promising results for the Dst forecast (predicted: −96 and −114 nT (from 2 Dst models); observed: −71 nT), for the arrival speed (predicted: 531 ± 23 km s−1; observed: 488 ± 30 km s−1), and for the timing (6 ± 1 hr after the actual arrival time). The prediction lead time is 21 hr. The method may be applied to vector magnetic field data from a spacecraft at an artificial Lagrange point between the Sun and Earth or to data taken by any spacecraft temporarily crossing the Sun–Earth line.

Source identification of moderate (−100 nT < Dst < −50 nT) and intense geomagnetic storms (Dst < −100 nT) during ascending phase of solar cycle 24

The origin of 39 moderate (−100nT<Dst<−50nT) and 12 intense (Dst<−100nT) geomagnetic storms has been investigated using fixed time window and adoptive time window. Coronal mass ejections (CMEs) and corotating interaction region (CIR) are found to be the primary sources. Out of 12 intense geomagnetic storms, 6 (50%) events are associated with unique FSH CMEs, 2 (17%) events with multiple FSH CMEs, 3 events (25%) with partial halo CME with no surface signature and 1 event (8%) is caused due to a CIR. Out of 39 moderate geomagnetic storms 21 (54%) are associated with full halo CME and 5 (13%) with partial halo CME, 4 (10%) storms associated with high speed solar wind from CIR whereas 1 storm has been found to be due to the combined effect of CME and CIR. The remaining 8 (20%) storms have unknown solar origins and were mostly observed when solar activity was at the minimum. The probability of a CIR causing a moderate storm is almost double as compared to an intense storm during the ascending phase of weak solar cycle 24.

Solar Transients Disturbing the Mid Latitude Ionosphere during the High Solar Activity

We investigate the effect of solar transients on the mid latitude ionosphere during the high solar activity period of solar cycle 23 i.e 2003 and 2004. A mid latitude station, Guangzhou (23.1N, 113.4E) was selected to carry out the investigation. The ionospheric behaviour at the selected station is characterized by considering the critical frequency of F2 layer (foF2) obtained by using the ground based Ionosonde observations. Then we selected two types of solar transients viz. solar flares and Coronal Mass Ejections (CMEs). To quantify the effect of solar flares we have considered the X-ray flux (1-8 Å) and EUV flux (26-34nm). Similarly to quantify the effect of CMEs, we have considered the geomagnetic storms, because during high solar activity the geomagnetic storms are caused by CMEs. From our analysis we conclude that during the geomagnetic storms the value of foF2 decreases as compared to quiet days thereby showing a negative effect. On the contrary we found that during solar flares there is sudden and intense increase in foF2. We also performed a correlation analysis to access the magnitude of association between changes in flux values and peak values of Dst during flares and storms with the corresponding changes and peak values of foF2. We found that a strong correlation exists between the enhancements/decrements in foF2 and enhancements in flux values and Dst. We conclude, while geomagnetic activity suppresses ionospheric activity the flares enhance the same.

Equatorial coronal holes, solar wind high-speed streams, and their geoeffectiveness

Context. Solar wind high-speed streams (HSSs), originating in equatorial coronal holes (CHs), are the main driver of the geomagnetic activity in the late-declining phase of the solar cycle.Aims. We analyze correlations between CH characteristics, HSSs parameters, and the geomagnetic activity indices, to establish empirical relationships that would provide forecasting of the solar wind characteristics, as well as the effect of HSSs on the geomagnetic activity in periods when the effect of coronal mass ejections is low.Methods. We apply the cross-correlation analysis to the fractional CH area (CH ) measured between central meridian distances ± 10°, solar wind parameters (flow velocity V , proton density n , temperature T , and the magnetic field B ), and the geomagnetic indices Dst and Ap .Results. The cross-correlation analysis reveals a high degree of correlation between all studied parameters. In particular, we show that the Ap index is considerably more sensitive to HSS and CH characteristics than Dst . The Ap and Dst indices are most tightly correlated with the solar wind parameter B V 2 . Conclusions. From the point of view of space weather, the most important result is that the established empirical relationships provide a few-days-in-advance forecasting of the HSS characteristics and the related geomagnetic activity at the six-hour resolution.

Dependence of successive GMSs with Dst &lt; −100 nT on solar and interplanetary parameters

The intense Geomagnetic Storms (GMSs) with Dst < −100 nT have been investigated for the period from Jan 1996 to Dec 2006. Seven GMSs of doublet and four of triplet nature are observed. Firstly, each GMS has been studied separately as if they are associated with independent Coronal Mass Ejections (CMEs). Secondly, for each doublet and triplet, the accumulated effect on GMS has been investigated and correlated with Dst index so as to understand the geoeffectiveness of Successive Intense GMSs. Majority of the successive intense GMSs have occurred during maximum phase of Solar cycle. During the occurrence of overlapping successive storms Dst falls abruptly. For non-overlapping successive storms, the Dst value falls gradually to minimum, showing a trend of recovery before the geosphere is hit by another storm. It is observed that the combined effect on GMSs is due to the Solar Wind (SW) being complex, having a very high value of SW velocity (Vsw) continuously for a very long period of 2 to 6 days. Further, Bz falls to a much lower value and B rises to a pretty high value for accumulated effect than for isolated GMS. When the GMSs are considered as separate entity, the correlation coefficient of Interplanetary Magnetic Field (IMF) parameters B and Bz and further, their products Vsw.B and Vsw.Bz correlated with Dst index are found to be −0.65, 0.72, −0.66 and 0.77 respectively; whereas, the coefficients are much better with the respective values of −0.7, 0.87, −0.78 and 0.90, for the accumulated effect of GMSs. Thus, it is preferable to investigate the accumulated effect of CMEs causing successive GMSs as compared to their isolated effects.

Small-scale magnetic helicity losses from a mean-field dynamo

Using mean-field models with a dynamical quenching formalism, we show that in finite domains magnetic helicity fluxes associated with small-scale magnetic fields are able to alleviate catastrophic quenching. We consider fluxes that result from advection by a mean flow, the turbulent mixing down the gradient of mean small-scale magnetic helicity density or the explicit removal which may be associated with the effects of coronal mass ejections in the Sun. In the absence of shear, all the small-scale magnetic helicity fluxes are found to be equally strong for both large- and small-scale fields. In the presence of shear, there is also an additional magnetic helicity flux associated with the mean field, but this flux does not alleviate catastrophic quenching. Outside the dynamo-active region, there are neither sources nor sinks of magnetic helicity, so in a steady state this flux must be constant. It is shown that unphysical behaviour emerges if the small-scale magnetic helicity flux is forced to vanish within the computational domain.