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Register a new userStudy of a Prominence Eruption using PROBA2/SWAP and STEREO/EUVI Data
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Observations of the early rise and propagation phases of solar eruptive prominences can provide clues about the forces acting on them through the behavior of their acceleration with height. We have analyzed such an event, observed on 13 April 2010 by SWAP on PROBA2 and EUVI on STEREO. A feature at the top of the erupting prominence was identified and tracked in images from the three spacecraft. The triangulation technique was used to derive the true direction of propagation of this feature. The reconstructed points were fitted with two mathematical models: i) a power-law polynomial function and ii) a cubic smoothing spline, in order to derive the accelerations. The first model is characterized by five degrees of freedom while the second one is characterized by ten degrees of freedom. The results show that the acceleration increases smoothly and it is continuously increasing with height. We conclude that the prominence is not accelerated immediately by local reconnection but rather is swept away as part of a large-scale relaxation of the coronal magnetic field.
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Context. Prominence eruptions provide key observations to understand the launch of coronal mass ejections as their cold plasma traces a part of the unstable magnetic configuration. Aims. We select a well observed case to derive observational constraints for eruption models. Methods. We analyze the prominence eruption and loop expansion and contraction observed on 02 March 2015 associated with a GOES M3.7 class flare (SOL2015-03-02T15:27) using the data from Atmospheric Imaging Assembly (AIA) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We study the prominence eruption and the evolution of loops using the time-distance techniques. Results. The source region is a decaying bipolar active region where magnetic flux cancellation is present for several days before the eruption. AIA observations locate the erupting prominence within a flux rope viewed along its local axis direction. We identify and quantify the motion of loops in contraction and expansion located on the side of the erupting flux rope. Finally, RHESSI hard X-ray observations identify the loop top and two foot-point sources. Conclusions. Both AIA and RHESSI observations support the standard model of eruptive flares. The contraction occurs 19 minutes after the start of the prominence eruption indicating that this contraction is not associated with the eruption driver. Rather, this prominence eruption is compatible with an unstable flux rope where the contraction and expansion of the lateral loop is the consequence of a side vortex developing after the flux rope is launched.
SWAP images from PROBA2 taken at 174 {AA} in the Fe IX/X lines are compared with simultaneous slitless flash spectra obtained during the solar total eclipse of 11 July, 2010. Myriads of faint low excitation emission lines together with the He I and He II Paschen {alpha} chromospheric lines are recorded on eclipse spectra where regions of limb prominences are obtained with space-borne imagers. We analyzed a deep flash spectrum obtained by summing 80 individual spectra to evaluate the intensity modulations of the continuum. Intensity deficits are observed and measured at the prominences boundaries in both eclipse and SWAP images. The prominence cavities interpreted as a relative depression of plasma density, produced inside the corona surrounding the prominences, and some intense heating occurring in these regions, are discussed. Photometric measurements are shown at different scales and different, spectrally narrow, intervals for both the prominences and the coronal background.
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.
We use The Sun Watcher with Active Pixel System detector and Image Processing (SWAP) imager onboard the Project for Onboard Autonomy 2 (PROBA2) mission to study the evolution of large-scale EUV structures in the solar corona observed throughout Solar Cycle 24 (from 2010 to 2019). We discuss the evolution of the on-disk coronal features and at different heights above the solar surface based on EUV intensity changes. We also look at the evolution of the corona in equatorial and polar regions and compare them at different phases of the solar cycle, as well as with sunspot number evolution and with the PROBA2/Lyman-Alpha Radiometer (LYRA) signal. The main results are as follows: The three time series (SWAP on-disk average brightness, sunspot number and LYRA irradiance) are very well correlated, with correlation coefficients around 0.9. The average rotation rate of bright features at latitudes of +15, 0, and -15 degrees was around 15 degree/day throughout the period studied. A secondary peak in EUV averaged intensity at the Poles was observed on the descending phase of SC24. These peaks (at North and South poles respectively) seem to be associated with the start of the development of the (polar) coronal holes. Large-scale off-limb structures were visible from around March 2010 to around March 2016, meaning that they were absent at the minimum phase of solar activity. A fan at the North pole persisted for more than 11 Carrington rotations (February 2014 to March 2015), and it could be seen up to altitudes of 1.6 Rs.
The solar photosphere, chromosphere and corona are known to rotate differentially as a function of latitude. To date, it is unclear if the solar transition region also rotates differentially. In this paper, we investigate differential rotational profile of solar transition region as a function of latitude, using solar full disk (SFD) images at 30.4 nm wavelength recorded by Extreme Ultraviolet Imager (EUVI) onboard Solar Terrestrial Relations Observatory (STEREO) space mission for the period from 2008 to 2018 (Solar Cycle 24). Our investigations show that solar transition region rotates differentially. The sidereal rotation rate obtained at +/- 5 degree equatorial band is quite high (~ 14.7 degree/day), which drops to ~ 13.6 degree/day towards both polar regions. We also obtain that the rotational differentiality is low during the period of high solar activity (rotation rate varies from 14.86 to 14.27 degree/day) while it increases during the ascending and the descending phases of the 24th solar cycle (rotation rate varies from 14.56 to 13.56 degree/day in 2008 and 14.6 to 13.1 degree/day in 2018). Average sidereal rotation rate (over SFD) follows the trend of solar activity (maximum ~ 14.97 degree/day during the peak phase of the solar activity, which slowly decreases to minimum ~ 13.9 degree/day during ascending and the descending phases of the 24th solar cycle). We also observe that solar transition region rotates less differentially than the corona.
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