ST1.8

Intense photospheric magnetic fields manifest as enhanced emission in several spectral lines and parts of the continuum. Here we aim to improve the understanding of the relation between magnetic fields and radiative structures by using the seeing-free observations of the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI), both on-board Solar Dynamics Observatory (SDO). We use AIA 1600 Å band, which captures the far-ultraviolet continuum emission originating from the temperature minimum of the solar chromosphere.

We developed a novel, objective method to define thresholds separating the brightest AIA 1600 Å pixels ("bright pixels") and the least bright pixels ("dark pixels") from the AIA 1600 Å brightness distribution. According to the method bright pixels are pixels whose standardized contrast (ratio of brightness to the center-to-limb variation) exceeds the level of I = 1.93. This threshold maximizes the average size of bright clusters (4-connected regions of bright pixels). Dark pixels are pixels whose standardized contrast is below I = 0.5. This corresponds to a threshold below which there are practically no pixels on quiet days. Comparing the AIA 1600 Å intensity and HMI magnetic field observations, we found that the AIA 1600 Å dark pixels correspond to the strongest magnetic field (B > 1325 G) pixels. These pixels are typically within sunspots. On the other hand, we found the AIA bright pixels correspond to moderate (55 G < B < 475 G) magnetic field intensity pixels of HMI.

We found that the percentage of AIA bright pixels on the solar surface almost entirely explains the observed variability of the total AIA 1600 Å emission, even in the presence of large sunspot groups. We developed a multi-linear regression model, which reliably predicts the magnitude of the disk-averaged unsigned magnetic field using the measured percentages of bright and dark pixels. We found that the large bright clusters have a constant mean unsigned magnetic field, similarly as earlier found for, e.g., Ca II K plages. However, the magnetic field strength of bright clusters is 246.5 ± 0.1 G, which is roughly 100 G larger than found earlier for Ca II K plages.

How to cite: Tähtinen, I., Virtanen, I., Pevtsov, A., and Mursula, K.: Clarifying the relation between chromospheric emissions and photospheric magnetic fields using AIA 1600 Å and HMI data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9622, https://doi.org/10.5194/egusphere-egu22-9622, 2022.

The sun’s magnetic field drives the 11-year solar cycle, and predicting its strength has practical importance for many space weather applications. Previous studies have shown that analysing the solar activity of the two hemispheres separately instead of the full sun can provide more detailed information on the activity evolution. However, the existing Hemispheric Sunspot Number data series (1945 onwards) was too short for meaningful solar cycle predictions. Based on a newly created hemispheric sunspot number catalogue for the time range 1874-2020 (Veronig et al. 2021, http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56) that is compatible with the International Sunspot Number from World Data Centre SILSO, we investigate the evolution of the solar cycle for the two hemispheres and develop a novel method for predicting the solar cycle amplitude. We demonstrate a steady relationship between the maximal growth rate of activity in the ascending phase of a cycle and its subsequent amplitude and form a 3rd order regression for the predictions. Testing this method for cycles 12-24, we show that the forecast made by the sum of the maximal growth rate from the North and South Hemispheric Sunspot number is more accurate than the same forecast from the Total Sunspot Number: The rms error of predictions is smaller by 27%, the correlation coefficient r is higher by 11% on average reaching values in the range r = 0.8-0.9 depending of the smoothing window of the monthly mean data. These findings demonstrate that empirical solar cycle prediction methods can be enhanced by investigating the solar cycle dynamics in terms of the hemispheric sunspot numbers, which is a strong argument supporting regular monitoring, recording, and analysing solar activity separately for the two hemispheres.

How to cite: Jain, S., Podladchikova, T., Veronig, A. M., Sutyrina, O., Dumbović, M., Clette, F., and Pötzi, W.: Predicting the solar cycle amplitude with the new catalogue of hemispheric sunspot numbers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4178, https://doi.org/10.5194/egusphere-egu22-4178, 2022.

Magnetic helicity is a physical quantity of great importance in the study of magnetized plasmas as it is conserved in ideal magneto-hydrodynamics and slowly deteriorating in non-ideal conditions such as magnetic reconnection. A meaningful way of defining a density for helicity is with field line helicity, which, in solar conditions, is expressed by relative field line helicity (RFLH). Here, we study in detail the behaviour of RFLH in the large, well-studied, eruptive solar active region (AR) 11158. The computation of RFLH and of all other quantities of interest is based on a high-quality non-linear force-free reconstruction of the AR coronal magnetic field, and on the recent developments in its computational methodology. The derived photospheric morphology of RFLH is very different than that of the magnetic field or the electrical current, and also manages to depict the large decrease in the value of helicity during an X-class flare of the AR. Moreover, the area of the RFLH decrease coincides with the location of the magnetic structure that later erupted, the flux rope. Based on these results we review the necessary steps one needs to follow in order to identify the locations in an AR where magnetic helicity is more important. This task can provide crucial information for the conditions of an AR, especially during eruptive events.

How to cite: Moraitis, K., Patsourakos, S., and Nindos, A.: How to identify important magnetic helicity locations in solar active regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12590, https://doi.org/10.5194/egusphere-egu22-12590, 2022.

Remarkable works done in the last decades by many authors on the solar gyroresonance mechanism have illuminated the way to establish the relationship between this form of emission and magnetic fields in the solar atmosphere and to know the magnetic nature of the middle and upper layers of the active regions. Despite all these advances, solar physics still needs a direct means (without magnetograms) of identifying the sources of gyroresonance emission.
In search of a solution to this problem, we used solar images at 17 GHz synthesized by the Nobeyama Radioheliograph (NoRH) to map the likely sources of gyroresonance. 
To achieve this result, we first hypothesized that gyroresonance and bremsstrahlung mechanisms can generate a large brightness temperature intensification due to the close relationship such mechanisms have with magnetic fields and because of the role of the magnetic field in controlling the brightness of the solar atmosphere in the radiofrequency range.
To test this hypothesis regarding the gyroresonance process, we selected 8 large active regions (ARs) among the HMI magnetograms generated by the Solar Dynamics Observatory (SDO) corresponding to the 1st half of the 24th solar cycle.  We then analyzed each AR through its magnetogram and its image at 17 GHz. Aiming to verify, in these radio maps, whether there is a correspondence between brightness bumps and parameters associated with gyroresonance emission, we constructed three categories of brightness maps for each active region, respectively presenting the field of: brightness temperature in BT maps, brightness temperature gradient in BTG maps, and brightness temperature gradient to brightness temperature ratio in BTG/BT maps. Such parameters are the characteristic circular polarization, whose modulus is greater than 30%, and characteristic magnetic field strengths, associated with the gyroresonance radiation at 17 GHz for 3rd and 4th harmonics. Such a step also aimed to verify which of these categories would best map the putative sources of gyroresonance emission.
On these maps, we then plotted the contours of the characteristic parameters. 
For each AR, we also obtained the degree of correlation between its brightness variables and the characteristic polarization. We then observed that the contours of characteristic magnetic field strengths are predominantly enveloped by the area of the brightness bumps, while the contours of the characteristic polarization fit well to such areas, being better fitted to the relative bumps (in the BTG/BT maps). In the statistical analysis, we observe that for each active region, there is a predominance of strong correlations between the brightness variables and the modulus of the characteristic polarization. Such correlation tends to be highest for the brightness temperature. For each brightness variable, the highest correlations tend to occur for the predominant polarization direction of the active region.
The data, therefore, indicate a high probability that the gyroresonance emission mechanism was at least one of the important causes of the radio bumps produced in the observed active regions.

How to cite: Amaro, A., Rockenbach da Silva, M., and Rezende Costa, J. E.: Study on the association of solar gyroresonance emission sources with brightness temperature intensification at 17 GHz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-564, https://doi.org/10.5194/egusphere-egu22-564, 2022.

Prominences and filaments are manifestations of magnetised, levitated plasma within the solar coronal atmosphere. Expanding on our previous 2.5D work presented in Jenkins & Keppens (2021), we will present a state-of-the-art magnetohydrodynamic simulation that yields the first fully 3D model to successfully unite the extreme-ultraviolet and Hydrogen-α prominence views that contain radial striations with the equivalent on-disk filaments comprised of finite width threads. Owed to the unprecedented resolution with which this simulation is carried out, we complete a full observational synthesis and provide predictions of exactly what the instruments associated with the upcoming Solar Orbiter and DKIST will observe. We then begin with an analysis of all hydromagnetic sources of the vorticity evolution and find the internal plasma dynamics to be consistent with the nonlinear development of the magnetic Rayleigh-Taylor instability. A further stability analysis that drops the strict, idealised mRTi initial conditions then enables us to tentatively characterise the preceding linear development as the general (quasi-) interchange gravitational instability. Our simulations and analyses show clearly how this universal interchange process operates, and how our results and conclusions finally unify the contradictory prominence/filament perspectives.

How to cite: Jenkins, J. and Keppens, R.: The Role of the Magnetic Rayleigh-Taylor Instability in Resolving the Solar Prominence/Filament Paradox, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2438, https://doi.org/10.5194/egusphere-egu22-2438, 2022.

Large amplitude oscillations (LAO) are often detected in filaments. Their origin has been associated with shock waves or to interaction with eruptions and jets. In this study we present  two examples of LAOs due to solar jets interaction with filaments on February 3-5 2015 and March 14 2015.  The filament eruption on March 14 was followed by a two step filament eruption along with a CME and become the strong geomagnetic storm of Solar Cycle 24 on 17 March 2015. These LAOs are  analysed by using time-distance diagnostics. The detected LAOs have periods of around 60 minutes and are damped after three oscillations. The observations are consistent with the results of a recent developed theoretical model of jet and filament interaction. The jets are associated with very weak flares which did not initiate any EUV wave. The role of waves as trigger of these oscillations can be discarded for these two events. 

How to cite: Joshi, R., Luna, M., Schmieder, B., Moreno-Insertis, F., and Chandra, R.: Large Amplitude Oscillations in Solar Filaments Caused by Solar Jets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5443, https://doi.org/10.5194/egusphere-egu22-5443, 2022.

MHD avalanches involve small, narrowly localized instabilities spreading across neighbouring areas in a magnetic field. Cumulatively, many small events release vast amounts of stored energy. Straight cylindrical flux tubes are easily modelled, between two parallel planes, and can support such an avalanche: one unstable flux tube causes instability to proliferate, via magnetic reconnection, and then an ongoing chain of like events. True coronal loops, however, are visibly curved, between footpoints on the same solar surface. With 3D MHD simulations, we verify the viability of MHD avalanches in a more physical, curved geometry, in a coronal arcade. MHD avalanches thus amplify instability across strong astrophysical magnetic fields and disturb wide regions of plasma. Contrasting with the behaviour of straight cylindrical models, a modified ideal MHD kink mode occurs, more readily and preferentially upwards. Instability spreads over a region far wider than the original flux tubes and their footpoints. Consequently, sustained heating is produced in a series of 'nanoflares', collectively contributing substantially to coronal heating. Overwhelmingly, viscous heating dominates, generated in shocks and jets produced by individual small events. Reconnection is not the greatest contributor to heating, but rather facilitates those processes that are. Localized and impulsive, heating shows no strong spatial preference, except a modest bias away from footpoints, towards the loop's apex.

How to cite: Reid, J., Threlfall, J., and Hood, A. W.: MHD avalanches in truly curved coronal arcades: proliferation and heating, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13141, https://doi.org/10.5194/egusphere-egu22-13141, 2022.

The ESA/NASA Solar Orbiter mission, launched in February 2020, has just completed its cruise phase. During its nominal mission, it will explore the Sun and heliosphere from close up and from out of the ecliptic plane. It aims to address the overarching questions of how the Sun creates and controls the heliosphere, and why solar activity changes with time. Among the instruments onboard Solar Orbiter  is the Polarimetric and Helioseismic Imager (SO/PHI), which is the first magnetograph to leave the Sun-Earth line and to observe the Sun from different directions. Already during the cruise phase of Solar Orbiter, SO/PHI has provided a few glimpses of its capabilities, including the excellent quality of the data. In spite of the very limited amount of data gathered during cruise, a few interesting results have already been obtained. A selection of such results will be presented.

How to cite: Solanki, S. K., Blanco, J., Kahil, F., Loeschl, P., Strecker, H., Hirzberger, J., Orozco Suárez, D., Del Toro Iniesta, J. C., Woch, J., Gandorfer, A., Alvarez-Herrero, A., Appourchaux, T., and Volkmer, R.: First results from the SO/PHI instrument on Solar Orbiter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4327, https://doi.org/10.5194/egusphere-egu22-4327, 2022.

Solar wind parameters, such as the velocity, density or pressure of the solar wind, are one of the most important factors in space physics, and their knowledge at as many points in the heliosphere as possible contributes to a broader understanding of our solar system.

Solar wind parameters at various points in the inner heliosphere are estimated using extrapolation methods. Currently, all spacecraft measuring solar wind parameters are in the ecliptic plane, thus it is enough to extrapolate the data from space probes to other spacecraft or celestial bodies near the ecliptic. Solar Orbiter, on the other hand, will soon leave the ecliptic and reach heliocentric latitudes of 34 degrees by the end of the mission, opening a new perspective.

The ballistic method extrapolates solar wind parameters in one dimension from the point of measurement to a chosen heliospheric position. The simple ballistic model considers the average rotation period of the Sun for the extrapolation in longitude while assuming a constant solar wind velocity during radial propagation. Our improved solar wind propagation model takes into account the interaction of slow and fast solar wind by applying a pressure correction during the extrapolation.

Applying this pressure-corrected ballistic method to data from solar corona models, we determined the solar wind parameters in the heliosphere in three dimensions. The advantage of our pressure-corrected ballistic method is that it is simple, it requires little calculation and it can be easily applied to the data of solar corona models in order to obtain a fast and efficient prediction in three dimensions.

How to cite: Timar, A., Opitz, A., Facsko, G., Dalya, Z., Koban, G., Biro, N., Madar, A., and Nemeth, Z.: Extrapolation of solar wind parameters in three-dimensions in the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2663, https://doi.org/10.5194/egusphere-egu22-2663, 2022.

Solar wind propagation models using in situ plasma observations as input can be improved by removing the signatures of Interplanetary Coronal Mass Ejections (ICMEs) from the input data. ICMEs are sporadic events that propagate in a given direction, hence their signatures in the plasma data should not be extrapolated to other heliocentric longitudes. As a result, in order to improve the prediction accuracy these should be filtered out. We create dedicated ICME lists providing the exact start and end times of ICMEs to numerous space probes such as ACE, STEREO A&B, SOHO, WIND, SolO, PSP, DSCOVER, VEX, MEX, Rosetta, BepiColombo, MAVEN and Messenger. We provide solar wind plasma and magnetic field predictions to any inner heliospheric position applying the ICME filter on the input dataset this way eliminating false alarms such as false ICME signature forecasts. Our corrected predictions contribute to the investigation of the background solar wind and related fields.

How to cite: Dalya, Z. and Opitz, A.: Removal of false alarms from solar wind predictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4987, https://doi.org/10.5194/egusphere-egu22-4987, 2022.

The Parker Solar Probe and Solar Orbiter spacecraft make whole new spatial and time scales available in the inner Heliosphere. With these new data, we study directional discontinuities that are common structures in the solar wind in this region. Their radial distribution can provide insight into the physical processes of this virtually collisionless plasma. Applying a method (Erdős & Balogh, 2008) based on minimum variance analysis to select directional discontinuities in magnetic field data, we determine their number as a function of distance from the Sun. How the directional discontinuity occurrence rate depends on the solar wind speed is also part of our analysis.

How to cite: Madár, Á., Erdos, G., Opitz, A., Nemeth, Z., Facsko, G., Timar, A., Biro, N., Koban, G., and Dalya, Z.: Directional Discontinuities in the Inner Heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6620, https://doi.org/10.5194/egusphere-egu22-6620, 2022.

Suprathermal ions from coronal jets, characterized by enhanced ³He and heavy-ion abundances, are an essential component of the seed population accelerated by coronal mass ejection (CME)-driven shocks in gradual solar energetic particle (GSEP) events. However, the mechanisms through which CME-driven shocks gain access to these suprathermal ions and produce spectral and abundance variations in GSEP events remain largely unexplored. We study GSEP events simultaneously measured on at least two spacecraft, such as ACE, STEREO, and Solar Orbiter, where ³He finite mass peak is measured at least on one spacecraft. This presentation discusses the origin of vastly different abundances and spectral shapes in terms of variable remnant population from preceding impulsive SEP events. Furthermore, with the help of imaging observations from SDO and STEREO, we examine a possible direct contribution from parent active regions of GSEP events.

How to cite: Bucik, R., Mason, G. M., Gómez-Herrero, R., Dayeh, M. A., Desai, M. I., Hart, S. T., Ho, G. C., Lario, D., Krupar, V., Wimmer-Schweingruber, R. F., Rodríguez-Pacheco, J., and Asfaw, T. T.: Multi-Spacecraft Observations of Gradual Solar Energetic Particle Events with Enhanced 3He Abundance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6726, https://doi.org/10.5194/egusphere-egu22-6726, 2022.

Interplanetary (IP) shocks can be driven in the solar wind by fast coronal mass ejections and by the interaction of fast solar wind with slow streams of plasma. These shocks can be preceded by extended wave and suprathermal ion foreshocks. We use STEREO data to study wave modes upstream and downstream of IP shocks. Understanding these waves is important because they contribute to shock acceleration processes and modify the solar wind as the shocks propagate in the heliosphere. We find that upstream regions can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) right-handed waves (f~10^-2–10^-1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. In contrast with planetary bow shocks, most IP shocks have a small Mach number (<4) and most of the upstream waves studied here are mainly transverse and no steepening occurs. Downstream of the shocks ion cyclotron and mirror mode waves can grow due to temperature anisotropy. The waves observed downstream of IP quasi-parallel shocks have larger amplitudes than waves in the regions downstream of quasi-perpendicular shocks. A variety of waves can be found in the sheath regions of IP shocks, even when IP shocks are weak, mostly for quasi-perpendicular shocks. These include ion cyclotron waves (ICW) with well defined peaks in frequency, broad spectra ICW, and mirror mode storms, which tend to occur for higher plasma beta.

How to cite: Blanco-Cano, X., Kajdic, P., Rojas-Castillo, D., Preisser, L., Jian, L., Russell, C., and Luhmann, J.: ULF waves upstream and downstream of interplanetary shocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6088, https://doi.org/10.5194/egusphere-egu22-6088, 2022.

The solar wind properties at a given point in the heliosphere depend strongly on the source surface characteristics, the dynamical effects during propagation and the transient events. We study the background solar wind structures after modelling their propagation throughout the 3-dimensional heliosphere. We remove the transient events from the observations, then apply the ballistic propagation method corrected for pressure gradients at stream interactions. A detailed multi-spacecraft investigation of the radial and latitudinal effects improves our model. These results are applied to study the temporal evolution of the solar wind by excluding the spatial effects through adjusting for the timelag calculated from the spacecraft separations.

How to cite: Opitz, A., Timar, A., Nemeth, Z., Dalya, Z., Koban, G., Biro, N., and Madar, A.: Temporal evolution of the background solar wind throughout the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5466, https://doi.org/10.5194/egusphere-egu22-5466, 2022.

For the past 60, 000 years our Sun and its protective heliosphere have been plowing through the Local Interstellar Cloud (LIC), but is now in a historic transition region towards the G-cloud that could have dramatic consequences for the global heliospheric structure. An Interstellar Probe mission to the Very Local Interstellar Medium (VLISM) would bring new scientific discoveries of the mechanisms upholding our vast heliosphere and directly sample the Local Interstellar Clouds to allow us, not only to understand the current dynamics and shielding, but also how the heliosphere responded in the past and how it will respond in the new interstellar environment. An international team of scientists and experts have now completed a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for an Interstellar Probe with a nominal design lifetime of 50 years. The team has analyzed dozens of launch configurations and demonstrated that asymptotic speeds in excess of 7.5 Astronomical Units (AU) per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 AU/year. An Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.

In this presentation we provide an overview of the study, the science mission concept, discuss the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.

How to cite: Brandt, P. and the The Interstellar Probe Study Team: Interstellar Probe: A Mission to the Heliospheric Boundary and Interstellar Medium to Understand our Home in the Galaxy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6802, https://doi.org/10.5194/egusphere-egu22-6802, 2022.

Knowing the temporal and spatial behavior of the main plasma parameters in the solar wind is important because of both an academic interest and the necessity to build theoretical models. Meanwhile, the solar wind characteristics are available with good accuracy only from in situspacecraft observations. There are a very limited number of studies that analyzed the radial evolution of the interplanetary magnetic field, the speed, the density, and the temperature of the solar wind. Previously, data from missions carried out in the 1970s were used for these purposes. Meanwhile, none of them approached the Sun closer than ~0.3 AU, and the information available did not allow describing the processes occurring near the solar corona. The launch of the Parker Solar Probe mission has opened up vast opportunities for studying the solar wind, starting from distances of the order of the Alfven radius. At the moment, Parker Solar Probe data are available with approaches to the Sun up to 0.08 AU.

An analysis of data obtained from Parker Solar Probe and Helios 2 (up to 1 AU), and from IMP8 and Voyager 1 (further from the Earth's orbit and up to 7 AU) was performed. The dependencies of the interplanetary magnetic field, the temperature, the speed, and the density of the solar wind on heliocentric distance are revealed and their typical profiles are analyzed. The nature of deviations of observed values from theoretical expectations is discussed. A particular attention is paid to the comparison of the results from the Parker Solar Probe and Helios missions.

How to cite: Antsiferova, U. and Khabarova, O.: Radial evolution of the key solar wind parameters according to the Parker Solar Probe and other missions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11910, https://doi.org/10.5194/egusphere-egu22-11910, 2022.

How to cite: Krafft, C. and Savoni, P.: Electromagnetic radiation emitted at fundamental and harmonic plasma frequencies by weak electron beams in inhomogeneous solar wind plasmas : 2D PIC simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13146, https://doi.org/10.5194/egusphere-egu22-13146, 2022.

This research provides an analysis of extreme events in the solar wind and in the magnetosphere due to disturbances of the solar wind. Extreme value theory has been applied to a 20-year data set from the Advanced Composition Explorer spacecraft for the period 1998–2017. The solar proton speed, solar proton temperature, solar proton density, and magnetic field have been analyzed to characterize extreme events in the solar wind. The solar wind electric field, vBz has been analyzed to characterize the impact from extreme disturbances in the solar wind to the magnetosphere. These extreme values were estimated for 1-in-40- and 1-in-80-year events, which represent two and four times the range of the original data set. The estimated values were verified in comparison with measured values of extreme events recorded in previous years. Finally, our research also suggests the presence of an upper boundary in the magnitudes under study.

How to cite: Larrodera, C., Nikitina, L., and Cid, C.: Estimation of the solar wind extreme events., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-730, https://doi.org/10.5194/egusphere-egu22-730, 2022.

The heliospheric current sheet (HCS) is the largest known solar wind structure that exists persistently and continuously within the heliosphere. While it is discovered for more than half a century ago, owing to very limited and scattered in-situ solar wind observations in the heliosphere, the shape and evolution of the HCS are still little known and constitute the key subject in the study of global-scale solar wind. Currently the morphology of the HCS is derived largely from simple kinematic approaches that map the neutral sheet observed at 2.5 solar radii outward into the heliosphere. The dynamical effect of solar wind interactions on the evolution and global structure of the HCS is still poorly understood. Here we present results from a study of the HCS from 1995 to 2009 using time-dependent, three-dimensional, global magnetohydrodynamic (MHD) model simulations. We focus on the radial and solar cycle variations of the HCS tilt angle from 18 solar radii to 7 AU. We also compare our result with those obtained from ballistic outward projections of the neutral sheet observed at 2.5 solar radii. We present our analysis result and discuss possible implications.

How to cite: Liou, K. and Wu, C.-C.: Evolution and variation of the heliospheric current sheet during 1995-2009, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10969, https://doi.org/10.5194/egusphere-egu22-10969, 2022.

Our research group has carried out several studies on space climate in the past. One of our lines of work is the recovery and analysis of the catalogues including historical sunspot observations. We have already published in digital version some sunspot catalogues made in observatories, for example, of the Iberian Peninsula (Aparicio et al. 2018). Recently, we have also digitized the catalogue from the sunspot observations made in the Stonyhurst College Observatory for 1921 – 1935 (Carrasco et al. 2021) and completed the first step for the publication of the Sacramento Peak Observatory sunspot catalogue (1947 – 2004) (Carrasco et al. 2020). Currently, we are analyzing the sunspot observations from drawings made in Boulder (U.S.A) for the period 1966 – 1992 to create a sunspot group catalogue including that information. Furthermore, we have also analyzed long-term observation series made by individual astronomers. Two examples of this kind of studies can be the analysis of the sunspot observations made by David Hadden during the period 1890 – 1931 (Carrasco et al. 2013) and those made by Eric Strach for 1969 – 2008 (Carrasco et al. 2019). Nowadays, in collaboration with other Italian research group, we are studying all the sunspot drawings made by Father Angelo Secchi in the second half of the 19th century. We are constructing the Wolf number, group number and the area series from these drawings. As future work, our objective is to publish a sunspot group catalogue from these observations.

References

Aparicio, A.J.P., Lefèvre, L., Gallego, M.C., Vaquero, J.M., Clette, F., Bravo-Paredes, N., Galaviz, P., Bautista, M.L.: 2018, A Sunspot Catalog for the Period 1952 – 1986 from Observations Made at the Madrid Astronomical Observatory, Solar Physics 293, 164.

Carrasco, V.M.S., Vaquero, J.M., Gallego, M.C., Trigo, R.M.: 2013, Forty two years counting spots: Solar observations by D.E. Hadden during 1890–1931 revisited. New Astronomy 25, 95.

Carrasco, V.M.S, Vaquero, J.M., Olmo-Mateos, V.M.: 2019, Eric Strach: Four Decades of Detailed Synoptic Solar Observations (1969‐2008), Space Weather 17, 796.

Carrasco, V.M.S., Pevtsov, A.A., Nogales, J.M., Vaquero, J.M.: 2020, The Sunspot Drawing Collection of the National Solar Observatory at Sacramento Peak (1947–2004), Solar Physics 296, 3.

Carrasco, V.M.S., Muñoz-Jaramillo, A., Nogales, J.M., Gallego, M.C., Vaquero, J.M.: 2021, Sunspot Catalog (1921–1935) and Area Series (1886–1940) from the Stonyhurst College Observatory, Astrophysical Journal Supplement Series 256, 38.

How to cite: Carrasco, V. M. S., Aparicio, A. J. P., Nogales, J. M., Bravo-Paredes, N., Tovar, I., Gallego, M., and Vaquero, J. M.: Studies on Space Climate Made in the University of Extremadura (Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8435, https://doi.org/10.5194/egusphere-egu22-8435, 2022.