ST1.2

Galactic cosmic rays, and sporadic high energy solar energetic particles, are energetic enough to pierce the Earth’s protective magnetosphere and interact with the atmosphere. Here, a secondary particle cascade leads to enhanced radiation levels which is of importance, for instance, to aviation dosimetry and related studies. At ground level, these secondary particles can be observed (indirectly) by means of neutron monitors, and this has been done for more than 70 years, providing a valuable long-term cosmic ray record. In this talk, we introduce the different primary particle populations, discuss their acceleration and modulation, and connect this with long-term neutron monitor measurements.

How to cite: Strauss, D. T.: Cosmic rays at ground level; a brief introduction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6212, https://doi.org/10.5194/egusphere-egu21-6212, 2021.

SEPs are correlated with the 11-year solar cycle due to their production by flares and interaction with the inner heliosphere, while GCRs are anti-correlated with it due to the modulation of the heliospheric magnetic field. The solar magnetic field along the cycle varies in amplitude but also in geometry, causing diffusion of the particles along and across the field lines; the solar wind distribution also evolves, and its turbulence affects particle trajectories.

We combine 3D MHD compressible numerical simulations to compute the configuration of the magnetic field and the associated polytropic solar wind up to 1 AU, with analytical prescriptions of the corresponding parallel and perpendicular diffusion coefficients for SEPs and GCRs. First, we analyze separately the impact of the magnetic field amplitude and geometry for a 100 MeV proton. By varying the amplitude, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. By varying the geometry, we change the latitudinal gradients of diffusion by changing the position of the current sheets. We also vary the energy, and show that the statistical distribution of parallel diffusion is different for SEPs and GCRs. Then, we use realistic solar configurations, showing that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the Sun, especially at minimum of activity. With this model, we are thus able to study the direct influence of the Sun on Earth spatial environment in terms of energetic particles. 

How to cite: Perri, B., Brun, A. S., Strugarek, A., and Réville, V.: Energetic particles and the solar cycle: Impact of solar magnetic field amplitude and geometry on SEPs and GCRs diffusion coefficients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6394, https://doi.org/10.5194/egusphere-egu21-6394, 2021.

The random walk of magnetic field lines is an important ingredient in understanding how the connectivity of the magnetic field affects the spatial transport and diffusion of charged particles. As solar energetic particles (SEPs) propagate away from near-solar sources, they interact with the fluctuating magnetic field, which modifies their distributions. We develop a formalism in which the differential equation describing the field line random walk contains both effects due to localized magnetic displacements and a non-stochastic contribution from the large-scale expansion. We use this formalism together with a global magnetohydrodynamic simulation of the inner-heliospheric solar wind, which includes a turbulence transport model, to estimate the diffusive spreading of magnetic field lines that originate in different regions of the solar atmosphere. We first use this model to quantify field line spreading at 1 au, starting from a localized solar source region, and find rms angular spreads of about 20 – 60 degrees. In the second instance, we use the model to estimate the size of the source regions from which field lines observed at 1 au may have originated, thus quantifying the uncertainty in calculations of magnetic connectivity; the angular uncertainty is estimated to be about 20 degrees. Finally, we estimate the filamentation distance, i.e., the heliocentric distance up to which field lines originating in magnetic islands can remain strongly trapped in filamentary structures. We emphasize the key role of slab-like fluctuations in the transition from filamentary to more diffusive transport at greater heliocentric distances. This research has been supported in part by grant RTA6280002 from Thailand Science Research and Innovation and the Parker Solar Probe mission under the ISOIS project (contract NNN06AA01C) and a subcontract to University of Delaware from Princeton University (SUB0000165).  MLG acknowledges support from the Parker Solar Probe FIELDS MAG team.  Additional support is acknowledged from the  NASA LWS program  (NNX17AB79G) and the HSR program (80NSSC18K1210 & 80NSSC18K1648).

How to cite: Ruffolo, D., Chhiber, R., Matthaeus, W. H., Usmanov, A. V., Tooprakai, P., Chuychai, P., and Goldstein, M. L.: Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3719, https://doi.org/10.5194/egusphere-egu21-3719, 2021.

The influence of the heliospheric current sheet (HCS) on the propagation of high energy solar protons is explored using 3D test particle modelling. The test particle model, which includes drift effects, is used to simulate specific past ground level enhancement (GLE) events which cover a range of HCS configurations. For example, the effects of a source location close to and far from the HCS for events both poorly and well-connected to Earth are examined. Similarly, the effect of the Earth’s location relative to the HCS is explored. The modelling is performed for high energy (300-1200 MeV) protons to represent the energetic conditions under which GLEs occur. The derived intensity profiles at 1AU are compared to observations from HEPAD onboard GOES, as well as STEREO (at locations away from Earth) and neutron monitor data. 

How to cite: Waterfall, C. and Dalla, S.: Role of the heliospheric current sheet in high energy proton transport through modelling of historic GLE events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6223, https://doi.org/10.5194/egusphere-egu21-6223, 2021.

Solar wind stream interaction regions (SIRs)  are often characterised by energetic ion enhancements. The mechanisms accelerating these particles as well as the locations where the acceleration occurs, remains debated. Here, we report the findings of a simulation of a SIR-event observed by Parker Solar Probe at 0.56 au and the Solar Terrestrial Relations Observatory-Ahead at 0.96 au in September 2019 when both spacecraft were approximately radially aligned with the Sun. The simulation reproduces the solar wind configuration and the energetic particle enhancements observed by both spacecraft. Our results show that the energetic particles are produced at the compression waves associated with the SIR and that the suprathermal tail of the solar wind is a good candidate to provide the seed population for particle acceleration. The simulation confirms that the acceleration process does not require shock waves and can already commence within Earth's orbit, with an energy dependence on the precise location where particles are accelerated. The three-dimensional configuration  of the solar wind streams strongly modulates the energetic particle distributions, illustrating the necessity of advanced models to understand  these particle events.

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).

How to cite: Wijsen, N., Samara, E., Aran, À., Lario, D., Pomoell, J., and Poedts, S.: A self-consistent simulation of proton acceleration and transport near a high-speed solar wind stream, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8189, https://doi.org/10.5194/egusphere-egu21-8189, 2021.

In-situ observations of solar energetic particle events are determined by a combination of acceleration, injection, and transport processes which are often hard to disentangle. However, the energy spectrum of impulsive electron events is believed to carry the imprint of the flare acceleration process which can be studied by analyzing the hard X-ray (HXR) spectrum of the flare.

Using STEREO/SEPT electron data of the whole STEREO mission we have identified 64 solar energetic electron event candidates where the HXR solar counterpart of the event was observed by RHESSI. After cleaning of the data set and an independent verification by the timing of associated interplanetary type III radio bursts, we find 17 events which lend themselves for a comparison of the spectral indices observed in situ and at the Sun.

Special attention is paid to the choice of the in-situ electron spectral index used for comparison as most of the events show spectral transitions (breaks) in the measurement range of SEPT. We find that both the lower and higher spectral indices correlate similarly well with the HXR spectra yielding correlation coefficients of 0.8 but indicating opposite relations with the flare spectrum in terms of the thin- or thick target model. The correlations show no dependence on the electron onset delay, nor on the longitudinal separation between flare and spacecraft magnetic footpoint at the Sun. However, the correlations increase, if only events with significant anisotropy are used indicating that transport effects play a role in shaping the spectra observed in-situ. We will discuss the different transport effects that need to be taken into account and which may even lead to a vanishing imprint of the flare acceleration.

How to cite: Dresing, N., Warmuth, A., Effenberger, F., Klein, L., Glesener, L., Musset, S., and Bruedern, M.: Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9543, https://doi.org/10.5194/egusphere-egu21-9543, 2021.

How to cite: Mironova, I.: The effect of Forbush decreases on the polar-night HOx concentration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7498, https://doi.org/10.5194/egusphere-egu21-7498, 2021.

The solar system is constantly changing, and it is important for us to understand how our climate and weather changes in response to the solar activity during both long-time scales (e.g. the 11-year solar cycle) and short time scales (e.g. days to weeks during For-bush Decreases (FDs)). Solar variability causes a corresponding modulation of the incident number of cosmic rays in Earth's atmosphere. Previous work by [Veretenenko and Pudovkin, 1997], [Svensmark and Friis-Christensen, 1997], [Palle Bago and Butler, 2000], [Svensmark et al., 2016], [Harrison and Ambaum, 2010], and other researchers have discussed this cause-effect relationship from an experimental and theoretical approach. Since the 1970s, global observations of the Earth's system by satellites are offering an invaluable source of information about cloud parameters.

In this study, we used the newly calibrated PATMOS-x (Pathfinder Atmospheres Extended) data set during the period from 1978 to the present. A method for capturing the connection between cosmic rays and meteorological measurements has been conducted by superposition analysis of FD events for time series (36 days) and the Monte Carlo bootstrap test to evaluate significance level of the integrated signal for 9 days after the minimum in FD. We have reviewed results, primarily about cloud emissivity (Achieved Significance Level (ASL >99%), surface brightness temperature (ASL >99%), and cloud fraction (ASL >99%). Some of the results support the proposed relationship between solar activity and temperature. This result indicates that the amount of incident cosmic rays decreases due to FDs, global average temperature increases [Friis-Christensen and Lassen, 1991], [Harrison and Ambaum, 2010]. In addition, PATMOS-x parameters of cloud probability, cloud mask, and cloud fraction, which all means cloud coverage on the Earth shows statistically significant signals following FDs. In some previous research, IR-detected cloud fraction from International Satellite Cloud Climate Project (ISCCP) and combined liquid and ice cloud fraction, effective emissivity from the Moderate Resolution Imaging Spectroradiometer (MODIS) also show connection with FDs, see [Svensmark et al., 2009], [Svensmark et al., 2016], [Marsh and Svensmark, 2000a], Todd and Kniveton [2004]. The relationship between the observed changes in cloud amount and the resulting solar forcing is discussed. On the other hand, “Cloud water content" from Special Sensor Microwave Imager (SSM/I), “Liquid water path", and “Optical thickness" from MODIS also showed as significant signals by FDs, see [Svensmark et al., 2009], [Svensmark et al., 2016], however a similar parameter about “optical thickness" and “integrated total cloud water over whole column g/m2" from PATMOS-x dataset does not have high significant signals by a bootstrap test with ASL of 77.03 and 92.51% respectively. Moreover, significant results are reported for several new cloud parameters from the PATMOS-x dataset (e.g. cloud type, brightness temperature, measurements by different wavelength 0.65, 0.86, 3.75, 11.0, and 12.0 μm and others) and Fu-Liou model is used for estimation of changed radiations in the atmosphere. An interaction between CCN and radiation has not been investigated well yet. It is necessary to still more to learn about these results for further understanding of Earth’s atmosphere.

How to cite: Matsumoto, H., Svensmark, H., and Enghoff, M.: The Effect of Forbush Decreases on Atmospheric Aerosols and Clouds from The PATMOS-x Satellite from 1978 to 2018, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-858, https://doi.org/10.5194/egusphere-egu21-858, 2021.

The northern polar vortex experiences considerable inter-annual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near-Earth space into the polar atmosphere, which is mediated by EEP-induced chemical changes causing ozone loss in the mesosphere and stratosphere. However, the most dramatic changes in the polar vortex are due to strong enhancements of planetary wave activity, which typically result in a sudden stratospheric warming (SSW), a momentary breakdown of the polar vortex. Here we use the SSWs as an indicator of high planetary wave activity and consider their influence of SSWs on the atmospheric response to EEP in 1957-2017 using combined ERA-40 and ERA-Interim re-analysis data and geomagnetic activity as a proxy of EEP. We find that the EEP-related enhancement of the polar vortex and other associated dynamical responses are seen only during winters when a SSW occurs, and that the EEP-related changes take place slightly before the SSW onset. We show that the atmospheric conditions preceding SSWs favor enhanced wave-mean-flow interaction, which can dynamically amplify the initial polar vortex enhancement caused by ozone loss. These results highlight the importance of considering SSWs and sufficient level of planetary wave activity as a necessary condition for observing the effects of EEP on the polar vortex dynamics.

How to cite: Asikainen, T., Salminen, A., Maliniemi, V., and Mursula, K.: Influence of energetic particle precipitation on polar vortex mediated by planetary wave activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3376, https://doi.org/10.5194/egusphere-egu21-3376, 2021.

The Mansurov Effect is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit, which is further hypothesized to impact the polar troposphere through cloud generation processes. In this paper we investigate the connection between IMF By-component and polar surface pressure by using daily ERA5 reanalysis for geopotential height since 1980. Previous studies have shown to produce a significant 27-day cyclic response during solar cycle 23. However, when appropriate statistical tests are applied, the correlation is not significant at the 95% level. Our results also show that data from three other solar cycles, which have not been investigated before, produce similar cyclic responses as during solar cycle 23, but with seemingly random offset in the timing of the signal. We examine the origin of the cyclic pattern occurring in the super epoch/lead lag regression methods commonly used to support the Mansurov hypothesis in all recent papers, as well as other phenomena in this community. By generating random normally distributed noise with different levels of temporal autocorrelation, and using the real IMF By-index as forcing, we show that the methods applied to support the Mansurov hypothesis up to now, are highly susceptible, as cyclic patterns always occurs as artefacts of the methods. This, in addition to the lack of significance, suggests that there is no adequate evidence in support of the Mansurov Effect.

How to cite: Edvartsen, J., Maliniemi, V., Tyssøy, H., Asikainen, T., and Hatch, S.: The Mansurov Effect: Real or a statistical artefact?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2362, https://doi.org/10.5194/egusphere-egu21-2362, 2021.