| “Extreme Ultraviolet （EUV） waves” are propagating large-scale wavelikebright transients in the corona, strongly associated with coronal mass ejections（CMEs）. The frst EUV wave was discovered by the EUV Imaging Telescope（EIT） on board the Solar and Heliospheric Observatory （SOHO） spacecraft, thusthey are originally named “EIT waves”. Though studied in detailed for almost15years, the understanding for EUV waves is still not very clear, and there aremany unresolved problems, especially that on the physical nature and drivingmechanism of EUV waves. Since the launch of the Solar Dynamic Observatory（SDO）, its high temporal and spatial resolution observations make it possible tostudy EUV waves in detail. Here, combining with the observations from the SDOand the Solar Terrestrial Relations Observatory （STEREO）, we studied somespecial EUV waves, trying to analysis the nature and origin for EUV waves.Moreover, we mainly chose the small-scale EUV waves, and want to get theirrelations and diferences with the large-scale ones. The main results are as follows.We present a possible detection of a fast-mode EUV wave associated with amini-CME observed by the SDO. On2010December1, a small-scale EUV waveerupted near the disk center associated with a mini-CME, which showed all thelow corona manifestations of a typical CME. The CME was triggered by theeruption of a mini-flament, with a typical length of about30′′. Although theeruption was tiny, the wave had the appearance of an almost semicircular frontand propagated at a uniform velocity of220–250km s-1with very little angulardependence. The CME lateral expansion was asymmetric with an inclinationtoward north, and the southern footprints of the CME loops hardly shifted. Thelateral expansion resulted in deep long-duration dimmings, showing the CMEextent. Comparing the onset and the initial speed of the CME, the wave waslikely triggered by the rapid expansion of the CME loops. Our analysis confrmsthat the small-scale EUV wave is a true wave, interpreted as the fast-mode MHDwave. Taking advantage of the high temporal and spatial resolution of the SDOobservations, we present four homologous EUV waves within3hours on2010November11. All EUV waves emanated from the same emerging fux region（EFR）, propagated into the same directions, and were accompanied by surges,weak fares and faint CMEs. The waves had the basically same appearance inall EUV wavebands of the Atmospheric Imaging Assembly on the SDO. Thewaves propagated at constant velocities in the range of280-500km s-1, withlittle angular dependence, which indicated that the homologous waves could belikely interpreted as fast-mode waves. The waves are supposed to likely involvemore than one driving mechanism, and it was most probable that the waveswere driven by the surges, due to their close timing and location relations. Wealso propose that the homologous waves were intimately associated with thecontinuous emergence and cancelation of magnetic fux in the EFR, which couldsupply sufcient energy and trigger the onsets of the waves.Taking advantage of the high temporal and spatial resolution of the SDOobservations, we present an EUV wave associated with a failed flament eruptionthat generated no CME on2011March1. We aim at understanding the natureand origin of this EUV wave. Combining the high-quality observations in thephotosphere, the chromosphere, and the corona, we studied the characteristicsof the wave and its relations to the associated eruption. The event occurred atan ephemeral region near a small active region. The continuous magnetic fuxcancelation in the ephemeral region produced pre-eruption brightenings and twoEUV jets, and excited the flament eruption, accompanying it with a microfare.After the eruption, the flament material appeared far from the eruption center,and the ambient loops seemed to be intact. It was evident that the flamenteruption had failed and was not associated with a CME. The wave happenedjust after the north jet arrived, and apparently emanated ahead of the north jet,far from the eruption center. The wave propagated at nearly constant velocitiesin the range of260-350km s-1, with a slight negative acceleration in the lastphase. Remarkably, the wave continued to propagate, and a loop in its passagewas intact when the wave and the loop met. Our analysis confrms that the EUVwave is a true wave, which we interpret as a fast-mode wave. In addition, the close temporal and spatial relationship between the wave and the jet providesevidence that the wave was likely triggered by the jet when the CME failed tohappen.The fast EUV waves (>1000km s-1) in the solar corona were very rare inthe past. Taking advantage of the high temporal and spatial resolution of theSDO observations, we present a fast EUV wave associated with a mini-flamenteruption, a C1.0fare, and a CME on2011September30. The event took placeat the periphery between two active regions （ARs）. The mini-flament rapidlyerupted as a blowout jet, associated with a fare and a CME. The CME front waslikely developed from the large-scale overlying loops. The wave onset was nearlysimultaneous with the start of the jet and the fare. The wave departed far fromthe fare center, and showed a closely location relation with the rapid jet. Thewave had a initial speed of about1100km s-1and a slight deceleration in the lastphase, and the velocity decreased to about500km s-1. The wave propagated ina narrow angle extent, likely because it wanted to avoid the ARs on both sides.All the results provide evidence that the fast EUV wave was a fast-mode MHDwave. The wave did not like to be driven the CME, because it opened up thelarge-scale loops and its front likely formed later than the wave. The wave wasmost likely triggered by the jet, due to their close timing and location relations. |
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