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Forecasting the arrival time of coronal mass ejections (CMEs) and their associated shocks is one of the key aspects of space weather. In recent years many models have been developed by various research groups aiming to forecast CME arrival time. The models differ based on the input, approach, assumptions and complexity ranging from simple empirical and analytical to complex numerical and machine learning models. One of the commonly used models is, due to its simplicity and calculation speed, the analytical drag-based (ensemble) model [DB(E)M] for heliospheric propagation of CMEs. DB(E)M relies on the observational fact that slow CMEs accelerate whereas fast CMEs decelerate, and is based on the concept of MHD drag, which acts to adjust the CME speed to the ambient solar wind. However, regardless of the model, forecasting CME arrival time has proven to be exceedingly challenging. One of the major setbacks is the uncertainty of the CME observational input, which is still substantial despite state-of-the-art remote observational capacities such as high-resolution EUV imagers and stereoscopic observations. Another major setback is the uncertainty in the CME propagation itself, due to e.g. unrealistic background solar wind and/or complex interactions. These limits will be discussed in the scope of DB(E)M and the CME input analysis performed by the ISSI Bern team on the "Understanding Our Capabilities In Observing And Modeling Coronal Mass Ejections".

Understanding space weather driven by the solar activity is crucial as it can affect various human technologies, health as well as it can have important implications for the space environment near the Earth and the Earth's atmosphere. In order to better asses space weather forecasts various empirical, drag-based and MHD models have been developed to predict the arrival time of CMEs. One of them is the analytical Drag-based Model (DBM) applying the equation of CME motion which is determined by the drag force from the background solar wind acting on the CME. DBM predictions depend on various initial parameters such as CME launch speed, background solar wind speed and empirically derived drag parameter as well CME's angular half-width and longitude of CME source region for a DBM CME cone geometry. Since many of input parameters may be inaccurate or unreliable due to limited observations, the Drag-Based Ensemble Model (DBEM) was developed that considers the variability of model input parameters by making an ensemble of a number of different input parameters to calculate a distribution and significance of DBM results. DBM has the advantage of having very short computational time (< 0.01s) and DBEM ensemble runs with many thousand members can be performed within few seconds on a normal computer. Using such approach, DBEM can determine the most likely CME arrival times and speeds, quantify the prediction uncertainties and calculate the forecast confidence intervals. Recently, DBEM web interface was also integrated as one of the ESA Space Situational Awareness web portal space weather services (http://swe.ssa.esa.int/heliospheric-weather). We'll present the recent DBEM developments together with the validation of its predictions using observations and other models as well as the input parameter sensitivity tests.

In order to address the growing need for more accurate space-weather predictions, a new model named EUHFORIA (EUropean Heliospheric FORecasting Information Asset) was recently developed. We present the first results of the performance assessment for the solar-wind modeling with EUHFORIA and identify possible limitations of its present setup. Using the basic EUHFORIA 1.0.4 model setup with the default input parameters, we modeled background solar wind (no coronal mass ejections) and compared the obtained results with Advanced Composition Explorer (ACE) in-situ measurements. For the purposes of statistical study we developed a technique of combining daily EUHFORIA runs into continuous time series. The combined time series were derived for the years 2008 (low solar activity) and 2012 (high solar activity), from which in-situ speed and density profiles were extracted. We find for the low-activity phase a better match between model results and observations compared to the high-activity time interval considered. The quality of the modeled solar-wind parameters is found to be rather variable. Therefore, to better understand the results obtained we also qualitatively inspected characteristics of coronal holes, i.e. the sources of the studied fast streams. We discuss how different characteristics of the coronal holes and input parameters to EUHFORIA influence the modeled fast solar wind, and suggest possibilities for the improvement of the model.

We analyse the 2010 April 3rd CME using spacecraft coronagraphic images at different vantage points (SOHO, STEREO-A and STEREO-B). We perform a 3D reconstruction of both the flux rope and shock using the Graduated Cylindrical Shell (GCS) model to calculate CME kinematic and morphologic parameters (e.g. velocity, acceleration, radius). The obtained results are fitted with empirical models describing the expansion of the CME radius in the heliosphere and compared with in situ measurements from Wind spacecraft: the CME is found to expand linearly towards Earth. Finally, we relate the event with decreases in the Galactic Cosmic Ray (GCR) Flux, known as Forbush decreases (FD), detected by EPHIN instrument onboard SOHO spacecraft. We use the analytical diffusion-expansion model (ForbMod) to calculate the magnetic field power law index, obtaining a value of approximately 1.6, thus estimating a starting magnetic field of around 0.01 G and an axial magnetic flux of around 5x1E20 Mx at 15.6 Rsun., 8 pages, 3 figures, Central European Astrophysical Bulletin

EUV waves are large-scale disturbances in the solar corona initiated by coronal mass ejections. However, solar EUV images show only the wave fronts projections along the line-of-sight of the spacecraft. We perform 3D reconstructions of EUV wave front heights using multi-point observations from STEREO-A and STEREO-B, and study their evolution to properly estimate the EUV wave kinematics. We develop two different methods to solve the matching problem of the EUV wave crest on pairs of STEREO-A/-B images by combining epipolar geometry with the investigation of perturbation profiles. The proposed approaches are applicable at the early and maximum stage of the event when STEREO-A/-B see different facets of the EUV wave, but also at the later stage when the wave front becomes diffusive and faint. The techniques developed are demonstrated on two events observed at different separation of the STEREO spacecraft (42$^\circ$ and 91$^\circ$). For the 7 December 2007 event, we find that the emission of the EUV wave front mainly comes from a height range up to 90-104 Mm, decreasing later to 7-35 Mm. Including the varying height of the EUV wave front allows us to correct the wave kinematics for the projection effects, resulting in velocities in the range 217-266 km/s. For the 13 February 2009 event, the wave front height doubled from 54 to 93 Mm over 10 min, and the velocity derived is 205-208 km/s. In the two events under study, the corrected speeds differ by up to 25% from the uncorrected ones, depending on the wave front height evolution., Comment: 19 pages, 10 figures, accepted for publication in the Astrophysical Journal

Coronal dimmings are distinct phenomena associated to coronal mass ejections (CMEs). The study of coronal dimmings and the extraction of their characteristic parameters helps us to obtain additional information of CMEs, especially on the initiation and early evolution of Earth-directed CMEs. We present a new approach to detect coronal dimming regions based on a thresholding technique applied on logarithmic base-ratio images. Characteristic dimming parameters describing the dynamics, morphology, magnetic properties and the brightness of coronal dimming regions are extracted by cumulatively summing newly dimmed pixels over time. It is also demonstrated how core dimming regions are identified as a subset of the overall identified dimming region. We successfully apply our method to two well-observed coronal dimming events. For both events the core dimming regions are identified and the spatial evolution of the dimming area reveals the expansion of the dimming region around these footpoints. We also show that in the early impulsive phase of the dimming expansion the total unsigned magnetic flux involved in the dimming regions is balanced and that up to 30% of this flux results from the localized core dimming regions. Furthermore, the onset in the profile of the area growth rate is co-temporal with the start of the associated flares and in one case also with the fast rise of the CME, indicating a strong relationship of coronal dimmings with both flare and CMEs., Comment: 17 pages, 11 figures, 1 table, accepted for publication in ApJ

The propagation of 15 interplanetary coronal mass ejections (ICMEs) from Earth's orbit (1 AU) to Mars (∼1.5 AU) has been studied with their propagation speed estimated from both measurements and simulations. The enhancement of magnetic fields related to ICMEs and their shock fronts cause the so-called Forbush decrease, which can be detected as a reduction of galactic cosmic ray (GCR) intensity measured on-ground or on a spacecraft. This effect can be used to detect the passage of ICMEs at various locations in the heliosphere, for example at Earth (using neutron monitors), the STEREO A and B spacecraft (HET) as well the on the surface of Mars using the Radiation Assessment Detector (RAD) instrument on the Mars Science Laboratory (MSL) rover. A set of ICME events has been selected during the periods when Earth (or STEREO A or B) and Mars locations were nearly aligned on the same side of the Sun in the ecliptic plane (so-called opposition phase). Such lineups allow us to estimate the ICMEs' transit times between 1 and 1.5 AU by determining the time delay between the corresponding Forbush decreases measured at each location. We investigate the evolution of the ICME propagation speeds before and after passing Earth's orbit and find that their deceleration due to interaction with the ambient solar wind may continue beyond 1 AU. We also find a substantial variance of the speed evolution among different events revealing the dynamic and diverse nature of eruptive solar events. Furthermore, the results are compared to simulation data obtained from two CME propagation models, namely the Drag-Based Model and ENLIL plus cone model.

In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysis is to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere and corona. The study has an observational and a modeling part. In the observational part full-disc solar images are analyzed. Based on a modied FAL atmospheric model, radiation models for various observed solar structures are developed. Finally, the observational and modeling results are compared and discussed.

Forbush decreases (FDs) can be used as one of the "signatures" of an ICME passage. An analytical diffusion-expansion FD model (ForbMod) was developed that is based on the widely used approach of an initially empty, closed magnetic structure (i.e. flux rope) that fills up slowly with particles by diffusion perpendicular to the magnetic field of the flux rope. In our approach the FD amplitude is not only determined by the diffusion process but also by the expansion of the flux rope. While the first process leads to a smaller amplitude the second one leads again to a larger effect. Remote CME observations and 3D reconstruction is used to constrain initial and boundary conditions. CME evolutionary properties are taken into account by incorporating the flux rope expansion. Several options of flux rope expansion are regarded as competing mechanism to diffusion, which can lead to different FD characteristics, and forward modelling is used to analyse flux rope expansion and further constrain the model. In testing the model, a number of spacecraft and planetary observation is utilised, including those by the Radiation Assessment Detector aboard the Mars Rover Curiosity. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sk_odowska- Curie grant agreement No 745782.

Coronal mass ejections (CMEs) are the most dynamic phenomena in our solar system. They abruptly disrupt the continuous outflow of solar wind by expelling huge clouds of magnetized plasma into interplanetary space with velocities enabling to cross the Sun-Earth distance within a few days. Earth-directed CMEs may cause severe geomagnetic storms when their embedded magnetic fields and the shocks ahead compress and reconnect with the Earth's magnetic field. The transit times and impacts in detail depend on the initial CME velocity, size, and mass, as well as on the conditions and coupling processes with the ambient solar wind flow in interplanetary space. The observed CME parameters may be severly affected by projection effects and the constant changing environmental conditions are hard to derive. This makes it difficult to fully understand the physics behind CME evolution, preventing to do a reliable forecast of Earth-directed events. This short review focusing on observational data, shows recent methods which were developed to derive the CME kinematical profile for the entire Sun-Earth distance range as well as studies which were performed to shed light on the physical processes that CMEs encounter when propagating from Sun to Earth., Comment: accepted for publication in Astronomische Nachrichten

The drag-based model (DBM) is an analytical model appropriate for calculating kinematics of coronal mass ejections (CMEs) in the interplanetary space and allows the prediction of their arrival times and impact speeds at any point in the heliosphere (“target”). The model is based on the assumption that beyond a distance of about 20 solar radii from the Sun, the dominant force acting on CMEs is the “aerodynamic” drag force. In the previously used form of DBM, the input parameters of the model are chosen on statistical basis, considering average and unperturbed conditions in the interplanetary space and common CME properties which are not necessarily appropriate for a particular CME under study. Therefore, we advanced the model, providing a DBM usage in a perturbed and time dependent environment without constraint on the distances above 20 solar radii. A modified and extended version of DBM is suitable for various applications, starting from automatic least-square fitting on initially detected CME kinematic data suitable for a real-time space-weather forecasting system, and ending with an embedding of the DBM into various numerical simulations of the interplanetary ambient conditions (solar wind speed, density, CME– CME interactions, etc.). For example, the DBM could be embedded into numerical codes of ENLIL, EUHFORIA, and similar advanced numerical models. A demonstration and evaluation of already available versions of the tool are discussed, and their feasibility of synergy with different numerical models is presented. Various DBM versions are available at web-site: http://www.geof.unizg.hr/~tzic/dbm.html. We acknowledge the support of European Social Fund under the “PoKRet” project.

The drag-based model (DBM) is an analytical model which is usually used for calculating kinematics of coronal mass ejections (CMEs) in the interplanetary space, prediction of the CME arrival times and impact speeds at arbitrary “target” in the heliosphere. The main assumption of the model is that beyond a distance of about 20 solar radii from the Sun, the drag is dominant in the interplanetary space. The previous version of DBM relied on the rough assumption of averaged, unperturbed and constant surrounding and CME properties throughout entire interplanetary CME propagation. The continuation of our work consists of enhancing the model into a form where is used a time dependent and perturbed environment without constraints on CME properties and distance forecasting. The extension provides the possibility of application in various scenarios, such as automatic least-square fitting on initial CME kinematic data suitable for a real-time forecasting of CME kinematics, or embedding the DBM into pre-calculated interplanetary ambient conditions provided by advanced numerical simulations (for example, codes of ENLIL, EUHFORIA, etc.). A demonstration of enhanced DBM is available on the web-site: http://www.geof.unizg.hr/~tzic/dbm.html. We acknowledge the support of European Social Fund under the “PoKRet” project.

High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the ACE spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed solar wind speed (root-mean-square error, RMSE $\approx$ 100 km/s) but tend to either overestimate (ESWF) or underestimate (WSA) the number of high-speed solar wind streams (threat score, TS $\approx$ 0.37). The predicted high-speed streams show typical uncertainties in the arrival time of about 1 day and uncertainties in the speed of about 100 km/s. General advantages and disadvantages of the investigated solar wind models are diagnosed and outlined.

The severe geomagnetic effects of solar storms or coronal mass ejections (CMEs) are to a large degree determined by their propagation direction with respect to Earth. There is a lack of understanding of the processes that determine their non-radial propagation. Here we present a synthesis of data from seven different space missions of a fast CME, which originated in an active region near the disk centre and, hence, a significant geomagnetic impact was forecasted. However, the CME is demonstrated to be channelled during eruption into a direction + 37+/-10 degree (longitude) away from its source region, leading only to minimal geomagnetic effects. In situ observations near Earth and Mars confirm the channelled CME motion, and are consistent with an ellipse shape of the CME-driven shock provided by the new Ellipse Evolution model, presented here. The results enhance our understanding of CME propagation and shape, which can help to improve space weather forecasts., 6 figures, published in Nature Communications as open access

We demonstrate the use of machine learning algorithms in combination with segmentation techniques in order to distinguish coronal holes and filaments in SDO/AIA EUV images of the Sun. Based on two coronal hole detection techniques (intensity-based thresholding, SPoCA), we prepared data sets of manually labeled coronal hole and filament channel regions present on the Sun during the time range 2011 - 2013. By mapping the extracted regions from EUV observations onto HMI line-of-sight magnetograms we also include their magnetic characteristics. We computed shape measures from the segmented binary maps as well as first order and second order texture statistics from the segmented regions in the EUV images and magnetograms. These attributes were used for data mining investigations to identify the most performant rule to differentiate between coronal holes and filament channels. We applied several classifiers, namely Support Vector Machine, Linear Support Vector Machine, Decision Tree, and Random Forest and found that all classification rules achieve good results in general, with linear SVM providing the best performances (with a true skill statistic of ~0.90). Additional information from magnetic field data systematically improves the performance across all four classifiers for the SPoCA detection. Since the calculation is inexpensive in computing time, this approach is well suited for applications on real-time data. This study demonstrates how a machine learning approach may help improve upon an unsupervised feature extraction method., in press for SWSC

Some essential outcomes of a detailed analysis of the formation and evolution of the coronal EUV wave of 15 February 2011 are presented, focused on the relationship between the source region expansion, wave kinematics, and the evolution of the wave amplitude. The observations are explained in terms of the results of the numerical MHD simulations, providing new insights into the physical background of coronal waves, especially considering the nature of the relationship of the wave amplitude and propagation velocity in different phases of the wave evolution.

The severe geomagnetic effects of solar storms or coronal mass ejections (CMEs) are to a large degree determined by their propagation direction with respect to Earth. There is a lack of understanding of the processes that determine their non-radial propagation. Here we present a synthesis of data from seven different space missions of a fast CME, which originated in an active region near the disk centre and, hence, a significant geomagnetic impact was forecasted. However, the CME is demonstrated to be channelled during eruption into a direction þ37±10 (longitude) away from its source region, leading only to minimal geomagnetic effects. In situ observations near Earth and Mars confirm the channelled CME motion, and are consistent with an ellipse shape of the CME-driven shock provided by the new Ellipse Evolution model, presented here. The results enhance our understanding of CME propagation and shape, which can help to improve space weather forecasts.

New space‐weather forecast‐tool for predicting the arrival of Interplanetary Coronal Mass Ejections (ICMEs) is presented. The forecast‐tool is based on the "Drag‐Based Model" (DBM), developed in the frame of the European Commission FP7 Project SOTERIA (SOlar‐TERrestrial Investigations and Archives) and advanced within FP7 Project COMESEP (Coronal Mass Ejections and Solar Energetic Particles). The DBM is based on a hypothesis that the driving Lorentz force that launches CME ceases in the upper corona, and that beyond certain distance the dynamics becomes governed solely by the interaction of the ICME and the ambient solar wind. This assumption is founded on the fact that in the interplanetary space fast ICMEs decelerate, whereas slow ones accelerate, showing a tendency to adjust their velocity with the ambient solar wind. In particular, we consider the option where the drag acceleration has the quadratic dependence on the ICME relative speed, which is expected in the collisionless environment, where the drag is caused primarily by emission of MHD waves. This is the simplest version of DBM, where the equation of motion can be solved analytically, providing explicit solutions for the Sun‐Earth ICME transit time and the impact speed. DBM offers easy handling and straightforward application in the real‐ time space‐weather forecasting. DBM results are compared with remotely‐measured interplanetary kinematics of several ICMEs, whereas forecasting abilities are tested on the statistical basis by employing in situ measurements. Finally, the advantages and drawbacks of DBM are summarized. This work has received funding from the European Commission FP7 Project COMESEP (263252).

We investigate the interaction of three consecutive large-scale coronal waves with a polar coronal hole, simultaneously observed on-disk by the Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on January 27, 2011. All three extreme-ultraviolet(EUV) waves originate from the same active region NOAA 11149 positioned at N30E15 in the STEREO-A field-of-view and on the limb in PROBA2. We derive for the three primary EUV waves start velocities in the range of ~310 km/s for the weakest up to ~500 km/s for the strongest event. Each large-scale wave is reflected at the border of the extended coronal hole at the southern polar region. The average velocities of the reflected waves are found to be smaller than the mean velocities of their associated direct waves. However, the kinematical study also reveals that in each case the end velocity of the primary wave matches the initial velocity of the reflected wave. In all three events the primary and reflected waves obey the Huygens-Fresnel principle, as the incident angle with ~10{\deg} to the normal is of the same size as the angle of reflection. The correlation between the speed and the strength of the primary EUV waves, the homologous appearance of both the primary and the reflected waves, and in particular the EUV wave reflections themselves implicate that the observed EUV transients are indeed nonlinear large-amplitude MHD waves., Comment: 22 pages, 8 figures, accepted for publication in Solar Physics

The Atacama Large Mm/sub-mm array (ALMA) will be suitable for solar observations thanks to a specifically designed surface that prevents overheating of the telescope structure, and solar filters that attenuate the incoming signals to a suitable level. Preliminary results from the commissioning of solar observations are presented.

Impulsive expansion of coronal mass ejections frequently results in the formation of global MHD wave in the solar corona. Such a large-amplitude disturbance is often observed as a EUV coronal wave and chromospheric Moreton wave. We present results of numerical simulations linking the low-coronal signatures of the wave with its chromospheric counterpart. The coronal wave is created by an explosive eruption of the coronal arcade that is anchored in the chromosphere/photosphere. Results of simulations are quantitatively analyzed and confronted with the observations, as well as with results of a simple analytical modeling. It is shown that the lateral expansion of the arcade is viable of creating the coronal wave, having characteristics that are fully consistent with the observations. This work has received funding from European Physical Society and the European Commission FP7 Projects eHEROES (284461) and COMESEP (263252).

We study three CME/ICME events (2008 June 1-6, 2009 February 13-18, 2010 April 3-5) tracked from Sun to 1 AU in remote-sensing observations of STEREO Heliospheric Imagers and in situ plasma and magnetic field measurements. We focus on the ICME propagation in IP space that is governed by two forces, the propelling Lorentz force and the drag force. We address the question at which heliospheric distance range the drag becomes dominant and the CME gets adjusted to the solar wind flow. To this aim we analyze speed differences between ICMEs and the ambient solar wind flow as function of distance. The evolution of the ambient solar wind flow is derived from ENLIL 3D MHD model runs using different solar wind models, namely Wang-Sheeley-Arge (WSA) and MHD-Around-A-Sphere (MAS). Comparing the measured CME kinematics with the solar wind models we find that the CME speed gets adjusted to the solar wind speed at very different heliospheric distances in the three events under study: from below 30 Rs, to beyond 1 AU, depending on the CME and ambient solar wind characteristics. ENLIL can be used to derive important information about the overall structure of the background solar wind, providing more reliable results during times of low solar activity than during times of high solar activity. The results from this study enable us to get a better insight into the forces acting on CMEs over the IP space distance range, which is an important prerequisite in order to predict their 1 AU transit times., accepted for publication in ApJ

One of central issues of space weather is the propagation of interplanetary coronal mass ejections (ICMEs). At the heliospheric distances beyond R=20 solar radii the “aerodynamic” drag is presumably the dominant force governing ICME propagation ; therefore, a drag based model (DBM) was established, which can be used to forecast the ICME arrival at the Earth. First, the model was tested on a sample of CMEs by combining remote observations of the CME take-off gained by the LASCO onboard SOHO, and in situ measurements from ACE and Wind satellites. The results of the DBM were compared to observational data and a fairly good agreement of the two was found. The model was then tested against STEREO observations. The ICME kinematics was inferred from STEREO observations by applying the Harmonic Mean method and compared to the DBM results. In this way we were able to reproduce the propagation of both slow and fast ICMEs, as well as to identify ICME- ICME interactions and a transition from fast-to-slow solar wind regimes. Finally, a statistical study was performed, where parameters were varied within a model in order to obtain optimal values, for which the average difference in the observed and calculated TT is zero (O-C=0) and the O-C scatter gets minimum. The source of the scatter in O–C values was investigated. The research leading to the results presented in this paper has received funding from European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 218816.

We analyze the evolution and kinematics of the fast, globally propagating Moreton wave of 2003 October 28 associated with the extreme X17.2 solar flare/CME event. This Moreton wave is distinct due to its strengths and azimuthal span of span 360. We study the wave kinematics in different propagation directions, and compare it with the following associated phenomena: EIT wave, coronal dimmings, fast halo CME, flare, and type II burst. The sectoral analysis yield mean velocity values in the range 900-1000 km/s ; two sectors show wave deceleration. The perturbation profile evolution indicates an amplitude growth followed by amplitude weakening and broadening, which is consistent with a disturbance first driven and then evolving into a freely propagating wave. We find two `'radiant points" for the Moreton wave fronts on opposite east-west edges of the source region, roughly co-spatial with the bipolar coronal dimming. The co-spatiality of the associated radio type II burst source and the first Moreton wave fronts indicate that the wave was launched from an extended region. These findings indicate that the wave is initiated by the CME expanding flanks.

The EUVI instruments onboard the twin STEREO spacecraft provide high-cadence full-disk imaging of the solar atmosphere with four different filters at EUV wavelengths. These observations are highly suitable to study the kinematics and dynamics of flare/CME associated coronal waves, so-called "EIT waves". We present a detailed analysis of one coronal wave captured by the EUVI instruments, with particular emphasis on the wave dynamics and its connection to the associated flare (RHESSI hard X-rays) and CME (STEREO COR1) in terms of blast wave versus driven wave scenario.

The flare wave associated with the 3B/X3.8 flare and coronal mass ejection (CME) of January 17, 2005 are studied using imaging data in the Hα and EUV spectral channels. Due to the high-cadence Hα observations from Kanzelhöhe Solar Observatory (KSO), a distinct Moreton wave can be identified in ˜ 40 Hα frames over a period of ˜ 7 minutes. The associated coronal EIT wave is identifiable in only one EUV frame and appears close to the simultaneously observed Moreton wave front, indicating that they are closely associated phenomena. Beside the morphology of the wave across the solar disc (covering an angular extend of ˜ 130°), the evolution in different directions is studied to analyse the influence of a coronal hole (CH) on the wave propagation. The Moreton wave shows a decelerating character which can be interpreted in terms of a freely propagating fast-mode MHD shock. The parts of the wave front moving towards the CH show a lower initial and mean speed, and a greater amount of deceleration than the segments moving into the undisturbed direction. This is interpreted as the tendency of high Alfvén velocity regions to influence the propagation of wave packets.

Multi-wavelength study of coronal waves associated with the CME-flare event of 03 November 2003

The timing of 503 solar flares observed simultaneously in hard X-rays, soft X-rays and H-alpha is analyzed. We investigated the start and the peak time differences in different wavelengths, as well as the differences between the end of the hard X-ray emission and the maximum of the soft X-ray and H-alpha emission. In more than 90% of the analyzed events, a thermal preheating seen in soft X-rays is present prior to the impulsive flare phase. On average, the soft X-ray emission starts 3 min before the hard X-ray and the H-alpha emission. No correlation between the duration of the preheating phase and the importance of the subsequent flare is found. Furthermore, the duration of the preheating phase does not differ for impulsive and gradual flares. For at least half of the events, the end of the nonthermal emission coincides well with the maximum of the thermal emission, consistent with the beam-driven evaporation model. On the other hand, for about 25% of the events there is strong evidence for prolonged evaporation beyond the end of the hard X-rays. For these events, the presence of an additional energy transport mechanism, most probably thermal conduction, seems to play an important role., 21 pages, 9 figures, in press at Solar Physics (2002)

In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysis is to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere and corona. The study has an observational and a modeling part. In the observational part full-disc solar images are analyzed. Based on a modied FAL atmospheric model, radiation models for various observed solar structures are developed. Finally, the observational and modeling results are compared and discussed.

Forbush decreases (FDs), which are short-term drops in the flux of galactic cosmic rays, are caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, especially interplanetary coronal mass ejections (ICMEs) and their associated shocks, as well as corotating interaction regions. Such events can be observed at Earth, for example, using neutron monitors, and also at many other locations in the solar system, such as on the surface of Mars with the Radiation Assessment Detector instrument onboard Mars Science Laboratory. They are often used as a proxy for detecting the arrival of ICMEs or corotating interaction regions, especially when sufficient in situ solar wind measurements are not available. We compare the properties of FDs observed at Earth and Mars, focusing on events produced by ICMEs. We find that FDs at both locations show a correlation between their total amplitude and the maximum hourly decrease, but with different proportionality factors. We explain this difference using theoretical modeling approaches and suggest that it is related to the size increase of ICMEs, and in particular their sheath regions, en route from Earth to Mars. From the FD data, we can derive the sheath broadening factor to be between about 1.5 and 1.9, agreeing with our theoretical considerations. This factor is also in line with previous measurements of the sheath evolution closer to the Sun.