Macrospicules are typically described as solar jets that are larger and longer-lived than spicules, and visible mostly in transition-region spectral lines. They show a broad variation in properties, which pose substantial difficulties for their identification, modelling, and the understanding of their role in the mass and energy balance of the solar atmosphere. In this study, we focused on a sub-population of these jets that undergo parabolic trajectories when observed in the He II 304Å line using high-cadence observations of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) to accumulate a statistically significant sample, which included 330 such events. We found these jets to be typically narrow (3-6 Mm), collimated flows of plasma, which reach heights of about 25 Mm, thus being among the smallest jets observed in the extreme ultraviolet (EUV). Combined with the rise velocities of 70-140 km s −1 and lifetimes of around 15 min, this makes them plausible candidates for the EUV counterpart of type II spicules. Moreover, we have found their dynamics to be inconsistent with a purely ballistic motion; instead, there is a strong correlation between the initial velocities and decelerations of the jets, which indicates that they may be driven by magneto-acoustic shocks with a dominant period of 10 ± 2 min. This makes these EUV jets similar in their dynamics to the conventional, or type I spicules, thus justifying the name of macro-spicules in this case, while a substantial difference in the shock periods (1-2 min for the chromospheric jets) suggests a dissimilarity in the formation conditions.

We employ an automated detection algorithm to perform a global study of solar prominence characteristics. We process four months of TESIS observations in the He ii 304Å line taken close to the solar minimum of 2008-2009 and focus mainly on quiescent and quiescent-eruptive prominences. We detect a total of 389 individual features ranging from 25 × 25 to 150 × 500 Mm 2 in size and obtain distributions of many their spatial characteristics, such as latitudinal position, height, size and shape. To study their dynamics, we classify prominences as either stable or eruptive and calculate their average centroid velocities, which are found to be rarely exceeding 3 km s −1 . Besides, we give rough estimates of mass and gravitational energy for every detected prominence and use these values to evaluate the total mass and gravitational energy of all simultaneously existing prominences (10 12 -10 14 kg and 10 29 -10 31 erg, respectively). Finally, we investigate the form of the gravitational energy spectrum of prominences and derive it to be a power-law of index −1.1 ± 0.2.

Macrospicules are relatively large spicule-like formations found mainly over the polar coronal holes when observing in the transition region spectral lines. In this study, we took advantage of the two short series of observations in the He ii 304 Å line obtained by the TESIS solar observatory with a cadence of up to 3.5 s to study the dynamics of macrospicules in unprecedented detail. We used a one-dimensional hydrodynamic method based on the assumption of their axial symmetry and on a simple radiative transfer model to reconstruct the evolution of the internal velocity field of 18 macrospicules from this dataset. Besides the internal dynamics, we studied the motion of the apparent end points of the same 18 macrospicules and found 15 of them to follow parabolic trajectories with high precision which correspond closely to the obtained velocity fields. We found that in a clear, unperturbed case these macrospicules move with a constant deceleration inconsistent with a purely ballistic motion and have roughly the same velocity along their entire axis, with the obtained decelerations typically ranging from 160 to 230 m s −2 , and initial velocities from 80 to 130 km s −1 . We also found a propagating acoustic wave for one of the macrospicules and a clear linear correlation between the initial velocities of the macrospicules and their decelerations, which indicates that they may be driven by magneto-acoustic shocks. Finally, we inverted our previous method by taking velocities from the parabolic fits to give rough estimates of the percentage of mass lost by 12 of the macrospicules. We found that typically from 10 to 30% of their observed mass fades out of the line (presumably being heated to higher coronal temperatures) with three exceptions of 50% and one of 80%.

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Due to the increase in the spatial and temporal resolution of observations of the solar atmosphere, which is mainly associated with progress in space research, we now understand that the Sun’s activity not only is associated with large centers, but also extends to significantly smaller scales. Each new advance in experimental technology over the past 60 years has led to the discovery of more and more numerous and small solar structures: X-ray active regions in the 1960s, hot X-ray points in the 1970s, solar microflares in the 1980s, and finally, from the end of the 20th century, solar nanoflares. At the same time, the total energy release, obtainable from observations, is still insufficient to ensure a balance between heating of the corona and its rapid radiative cooling. For the smallest-scale phenomena, nanoflares, it is still not possible to resolve their structure and mechanism, which raises the question of whether it is correct to classify them as flares. We present a review of the main results obtained so far in the field of small-scale solar activity, mainly microflares and nanoflares, and discuss the main issues that need to be solved in order to move forward.