Microwave radiation of solar active regions before X flares according to the RATAN-600 observations in 2011

The evolution of the microwave radiation from four active regions, where strong X-ray flares (X-class, GOES) occurred in 2011, has been studied. Daily multiwavelength RATAN-600 radio observations of the Sun in the 1.6–8.0 cm range have been used. It has been indicated that the radiosource above the photospheric magnetic field neutral line (above the region with the maximal convergence of the fields opposite in sign) becomes predominant in the structure of the active region microwave radiation one to two days before a powerful flare as in the eruptive events previously studied with RATAN-600. The appearance of such a radiosource possibly reflects the current sheet formation in the corona above the active region. The energy necessary for a flare is stored in the magnetic field of active region, which can be considered as a factor for predicting a powerful flare.     

Some Features of the Variation of the Magnetic Field Characteristics in the Umbra of Sunspots During Flares and Coronal Mass Ejections

The observed variations of the magnetic properties of sunspots during eruptive events (solar flares and coronal mass ejections (CMEs)) are discussed. Variations of the magnetic field characteristics in the umbra of the sunspots of active regions (ARs) recorded during eruptive events on August 2, 2011, March 9, 2012, April 11, 2013, January 7, 2014, and June 18, 2015, are studied. The behavior of the maximum of the total field strength B_max, the minimum inclination angle of the field lines to the radial direction from the center of the Sun α_min (i.e., the inclination angle of the axis of the magnetic tube from the sunspot umbra), and values of these parameters B_mean and α_mean mean within the umbra are analyzed. The main results of our investigation are discussed by the example of the event on August 2, 2011, but, in general, the observed features of the variation of magnetic field properties in AR sunspots are similar for all of the considered eruptive events. It is shown that, after the flare onset in six AR sunspots on August 2, 2011, the behavior of the specified magnetic field parameters changes in comparison with that observed before the flare onset.     

Features of Microwave Radiation and Magnetographic Characteristics of Solar Active Region NOAA 12242 Before the X1.8 Flare on December 20, 2014

This paper continues the cycle of authors’ works on the detection of precursors of large flares (M5 and higher classes) in active regions (ARs) of the Sun by their microwave radiation and magnetographic characteristics. Generalization of the detected precursors of strong flares can be used to develop methods for their prediction. This paper presents an analysis of the development of NOAA AR 12242, in which an X1.8 flare occurred on December 20, 2014. The analysis is based on regular multiazimuth and multiwavelength observations with the RATAN-600 radio telescope in the range 1.65–10 cm with intensity and circular polarization analysis and data from the Solar Dynamics Observatory (SDO). It was found that a new component appeared in the AR microwave radiation two days before the X-flare. It became dominant in the AR the day before the flare and significantly decreased after the flare. The use of multiazimuth observations from RATAN-600 and observations at 1.76 cm from the Nobeyama Radioheliograph made it possible to identify the radio source that appeared before the X-flare with the site of the closest convergence of opposite polarity fields near the neutral line in the AR. It was established that the X-flare occurred 20 h after the total gradient of the magnetic field of the entire region calculated from SDO/HMI data reached its maximum value. Analysis of the evolution of the microwave source that appeared before the X-flare in AR 12242 and comparison of its parameters with the parameters of other components of the AR microwave radiation showed that the new source can be classified as neutral line associated sources (NLSs), which were repeatedly detected by the RATAN-600 and other radio telescopes 1–3 days before the large flares.     

Studying the solar corona above active regions from microwave observations during solar flares recorded by CORONAS-F satellite

In 2001–2003, 45 flares of hard X ray (HXR) and gamma ray radiation, identified with a particular active region (AR) that produced each event, were recorded during the experiments onboard the Russian Solar Observatory CORONAS-F using the SONG (solar neutrons and gamma ray quanta) instrument. The solar corona structure and dynamics above these ARs is studied on the basis of the microwave observations with two Russian radio telescopes RATAN-600 and Siberian Solar Radio Telescope (SSRT). The results are illustrated using the active region NOAA 9601 and flare of September 5, 2001 (～ 1430 UT) as an example. The flare is interesting because the energy of its gamma radiation exceeded 1 MeV, while its power was only M6.0 in soft X rays. Such a combination of the event characteristics is not too frequent, which indicates that the spectrum of the studied event was rather hard. The type of the source of microwave radiation above NOAA 9601 has been determined. Some properties of this-type sources of a diagnostic value for detecting ARs capable of producing HXR and gamma radiation are indicated.     

Signs of Preflare Situation in Solar Ultraviolet and Microwave Emission

Geomagnetism and Aeronomy - The spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) of active regions with a complex magnetic field configuration before powerful flares,...     

Evolution of Solar Active Regions Before Large Flares: Overview of the Events of 2010–2017

Geomagnetism and Aeronomy - The paper presents a study of the evolution of the photospheric magnetic field of active regions (ARs) of the Sun in which flares (larger than the M9 class in the...     

The July–August 2001 eruption of Mt. Etna (Sicily)

The July–August 2001 eruption of Mt. Etna stimulated widespread public and media interest, caused significant damage to tourist facilities, and for several days threatened the town of Nicolosi on the S flank of the volcano. Seven eruptive fissures were active, five on the S flank between 3,050 and 2,100 m altitude, and two on the NE flank between 3,080 and 2,600 m elevation. All produced lava flows over various periods during the eruption, the most voluminous of which reached a length of 6.9 km. Mineralogically, the 2001 lavas fall into two distinct groups, indicating that magma was supplied through two different and largely independent pathways, one extending laterally from the central conduit system through radial fissures, the other being a vertically ascending eccentric dike. Furthermore, one of the eccentric vents, at 2,570 m elevation, was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer, during both the initial and closing stages of the eruption. For 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer, permitting powerful explosive and effusive magmatic activity. While the eruption was characterized by a highly dynamic evolution, complex interactions between some of the eruptive fissures, and changing eruptive styles, its total volume (~25×10 ⁶ m ³ of lava and 5–10×10 ⁶ m ³ of pyroclastics) was relatively small in comparison with other recent eruptions of Etna. Effusion rates were calculated on a daily basis and reached peaks of 14–16 m ³ s ^-1, while the average effusion rate at all fissures was about 11 m ³ s ^-1, which is not exceptionally high. The eruption showed a number of peculiar features, but none of these (except the contemporaneous lateral and eccentric activity) represented a significant deviation from Etna's eruptive behavior in the long term. However, the 2001 eruption could be but the first in a series of flank eruptions, some of which might be more voluminous and hazardous. Placed in a long-term context, the eruption confirms a distinct trend, initiated during the past 50 years, toward higher production rates and more frequent eruptions, which might bring Etna back to similar levels of activity as during the early to mid seventeenth century.     

Skin-layer of the eruptive magnetic flux rope in large solar flares

The analysis of observations of large solar flares made it possible to propose a hypothesis on existence of a skin-layer in magnetic flux ropes of coronal mass ejections. On the assumption that the Bohm coefficient determines the diffusion of magnetic field, an estimate of the skin-layer thickness of ~10⁶ cm is obtained. According to the hypothesis, the electric field of ~0.01–0.1 V/cm, having the nonzero component along the magnetic field of flux rope, arises for ~5 min in the surface layer of the eruptive flux rope during its ejection into the upper corona. The particle acceleration by the electric field to the energies of ~100 MeV/nucleon in the skin-layer of the flux rope leads to their precipitation along field lines to footpoints of the flux rope. The skin-layer presence induces helical or oval chromospheric emission at the ends of flare ribbons. The emission may be accompanied by hard X-ray radiation and by the production of gamma-ray line at the energy of 2.223 MeV (neutron capture line in the photosphere). The magnetic reconnection in the corona leads to a shift of the skin-layer of flux rope across the magnetic field. The area of precipitation of accelerated particles at the flux-rope footpoints expands in this case from the inside outward. This effect is traced in the chromosphere and in the transient region as the expanding helical emission structures. If the emission extends to the spot, a certain fraction of accelerated particles may be reflected from the magnetic barrier (in the magnetic field of the spot). In the case of exit into the interplanetary space, these particles may be recorded in the Earth’s orbit as solar proton events.     

Solar-terrestrial storms of October 2003. 2. Five-phase dynamics of the substorm of October 28–30

The assumption that a solar-heliospheric storm has five phases is formulated based on the storm that occurred in October 2003. The first phase: slow (between solar rotations) convergent motions of photospheric sources of large-scale open solar fields (LOFs) with generation of active regions (ARs) between these fields. The second phase: magnetic energy pumping with adjustment of zero lines of the photospheric magnetic field in AR to the configuration of the LOF sector (subsector) boundaries. The third phase: AR destabilization with ordering of the complex of sporadic phenomena near ARs parallel to the zero line and fragments of the nearest LOF boundary. The fourth phase: propagation of disturbances in the near-Sun space with ordering relative to the LOF boundaries. The fifth phase: propagation of a coronal mass ejection (CME) in the inner heliosphere in the case when the axial axis of a magnetic cloud in CME is parallel to the LOF boundary and to the zero line in AR. Original results of LOF modeling and a number of substantial results of the known advanced studies of individual aspects of this storm are used to justify this dynamics as applied to the storm of October 28–30. Specific contents and features of each storm phases are presented. The specific feature of the first phase, responsible for the storm space-time scales and intensity, consisted in the displacement of the entire LOF negative magnetic flux (～5 × 10²² μs) from the north pole to the south with flowing around a midlatitude obstacle and with zonal convergent motions of LOF. The assumption of the AR configuration adjustment (the second phase) and ordering of disturbances (the third–five phases) during this storm near the subsector boundary between LOFs of identical polarity has been confirmed. It is noted that the pulse phase of the AR 0486 flare, coronal waves, and dimmings along the subsector boundary and the southwestern LOF “dam” joining ARs 0486 and 0484 (superposition of the third and fourth phases) originated almost simultaneously. The two-component disturbance structure is confirmed: halo-type CME with the axis along the LOF subsector boundary and a bright local ejection of magnetic plasma from the region above the southwestern LOF dam.     

Acoustic source characterization of impulsive Strombolian eruptions from the Mount Erebus lava lake

We invert for acoustic source volume outflux and momentum imparted to the atmosphere using an infrasonic network distributed about the erupting lava lake at Mount Erebus, Ross Island, Antarctica. By modeling these relatively simple eruptions as monopole point sources we estimate explosively ejected gas volumes that range from 1,000 m³ to 24,000 m³ for 312 lava lake eruptions recorded between January 6 and April 13, 2006. Though these volumes are compatible with bubble volumes at rupture (as estimated from explosion video records), departures from isotropic radiation are evident in the recorded acoustic wavefield for many eruptions. A point-source acoustic dipole component with arbitrary axis orientation and strength provides precise fit to the recorded infrasound. This dipole source axis, corresponding to the axis of inferred short-duration material jetting, varies significantly between events. Physical interpretation of dipole orientation as being indicative of eruptive directivity is corroborated by directional emissions of ejecta observed in Erebus eruption video footage. Although three azimuthally distributed stations are insufficient to fully characterize the eruptive acoustic source we speculate that a monopole with a minor amount of oriented dipole radiation may reasonably model the primary features of the recorded infrasound for these eruptions.     

Integrated field, satellite and petrological observations of the November 2010 eruption of Erta Ale

Erta Ale volcano, Ethiopia, erupted in November 2010, emplacing new lava flows on the main crater floor, the first such eruption from the southern pit into the main crater since 1973, and the first eruption at this remote volcano in the modern satellite age. For many decades, Erta Ale has contained a persistently active lava lake which is ordinarily confined, several tens of metres below the level of the main crater, within the southern pit. We combine on-the-ground field observations with multispectral imaging from the SEVIRI satellite to reconstruct the entire eruptive episode beginning on 11 November and ending prior to 14 December 2010. A period of quiescence occurred between 14 and 19 November. The main eruptive activity developed between 19 and 22 November, finally subsiding to pre-eruptive levels between 8 and 15 December. The estimated total volume of lava erupted is ??0.006?km³. The mineralogy of the 2010 lava is plagioclase?+?clinopyroxene?+?olivine. Geochemically, the lava is slightly more mafic than previously erupted lava lining the caldera floor, but lies within the range of historical lavas from Erta Ale. SIMS analysis of olivine-hosted melt inclusions shows the Erta Ale lavas to be relatively volatile-poor, with H₂O contents ??1,300?ppm and CO₂ contents of ??200?ppm. Incompatible trace and volatile element systematics of melt inclusions show, however, that the November 2010 lavas were volatile-saturated, and that degassing and crystallisation occurred concomitantly. Volatile saturation pressures are in the range 7?C42?MPa, indicating shallow crystallisation. Calculated pre-eruption and melt inclusion entrapment temperatures from mineral/liquid thermometers are ??1,150?°C, consistent with previously published field measurements.     

Time delay in pulsations of the nonthermal radiation of solar flares

The oscillations with a period of about 6 and 12 s in the nonthermal radiation of a solar flare occurred on November 5, 1992, are identified. The time-translated profiles of hard X-ray and microwave radiation flux are characterized by an anticorrelation. The specific features of the radiation fine time structure are interpreted using the model of the coronal magnetic mirror where fast magnetoacoustic modes are excited.     

Time-lapse camera observations of gas piston activity at Pu‘u ‘ō‘ō, Kīlauea volcano, Hawai‘i

Gas pistoning is a type of eruptive behavior described first at K??lauea volcano and characterized by the (commonly) cyclic rise and fall of the lava surface within a volcanic vent or lava lake. Though recognized for decades, its cause continues to be debated, and determining why and when it occurs has important implications for understanding vesiculation and outgassing processes at basaltic volcanoes. Here, we describe gas piston activity that occurred at the Pu??u ???????? cone, in K??lauea??s east rift zone, during June 2006. Direct, detailed measurements of lava level, made from time-lapse camera images captured at close range, show that the gas pistons during the study period lasted from 2 to 60?min, had volumes ranging from 14 to 104?m³, displayed a slowing rise rate of the lava surface, and had an average gas release duration of 49?s. Our data are inconsistent with gas pistoning models that invoke gas slug rise or a dynamic pressure balance but are compatible with models which appeal to gas accumulation and loss near the top of the lava column, possibly through the generation and collapse of a foam layer.     

Peculiar transient events in the Schumann resonance band and their possible explanation

Superimposed on the continuous Schumann resonance (SR) background in the extremely low frequency (ELF) band, transient signals (e.g. bursts) can be observed, which originate from intense lightning discharges occurring at different locations on the globe. From the many transients that were observed at the Astronomical and Geophysical Observatory (AGO) of Comenius University near Modra, western Slovakia, in the vertical electric field component mainly during May and June of 2006, a peculiar group of events could be recognized. According to the waveform analysis, these peculiar events in most cases consist of two overlapping transients with a characteristic time difference of 0.13–0.15 s between the onsets. On the other hand, the spectrum of these peculiar transients showed discernible SR peaks for higher modes as well (n>7). The same events could be found in the records of the Széchenyi István Geophysical Observatory of the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences near Nagycenk, Hungary (NCK). The natural origin of the peculiar events was verified from the NCK data and the source location was determined from the second transient. The results suggest that the two consecutive transients originated in the same thunderstorm. Furthermore, the phase spectrum analysis indicates that the sources have coherently excited the Earth-ionosphere cavity. These findings seem to support the idea that electromagnetic waves orbiting the Earth might trigger lightning discharges. The possibility that electromagnetic waves may trigger discharges was first considered by Nikola Tesla.     

Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano.     

A weak phreatic eruption of June 2010 on Ekarma Volcano, Kuril Islands as a possible precursor of a future large magmatic eruption

We provide data concerning a weak phreatic eruption of Ekarma Volcano on Ekarma Island, in the Kurils, in June 2010. The ash plumes did not rise higher than 3 km above sea level. A preliminary estimate of the volume of erupted resurgent material (mostly tephra) is on order 2 × 10⁵ m³. Reconstruction of the volcano??s history and the dynamics of its eruptive activity for the last 4500?C5000 years suggests that a larger eruption can occur during the next few decades that will discharge juvenile pyroclastics and/or lava.     

Plinian eruptions and their products

Plinian eruptions are amongst the most powerful of explosive volcanic events, and the extensive pumice deposits which they produce have an exceptionally wide dispersal because of the great eruptive plume height. Historical data on 12 plinian eruptions, and available quantitative data on the deposits of these and 37 other plinian eruptions are collated in this review to characterise further the plinian eruptive style and its products and to establish the known limits of their variation. The deposit volumes have been recomputed according to a standard procedure to provide a better basis for comparison, and they vary over 4 orders of magnitude to reach a maximum of about 100 km³. Almost all volcanic magma compositions apart from the most mafic are represented among the juvenile products; rhyolitic and dacitic deposits account for 80% of the total volume and basaltic ones less than 1%. Compositional zoning is very common. Plinian eruptions are of open vent type and produce deposits which tend to be homogeneous in grain size and constitution through their thickness. Considerable departures from homogeneity often however exist. Finer grained beds which often interrupt the continuity can be produced by a number of different mechanisms, the features of which are summarised. In a significant proportion of plinian deposits the finer beds are the deposits of intraplinian pyroclastic flows, or are related to such flows; pyroclastic flows such as may be attributable to column collapse thus do not form exclusively at the end of the plinian phase. The most recent work indicates that major phreatoplinian eruptions dominated by the copious inflow of water into the vent can produce deposits quite as widely dispersed and as voluminous as the biggest plinian eruptions, and it appears that the characteristics of the grain size populations of the two types tend to converge in the most powerful eruptions.     

Quilotoa volcano — Ecuador: An overview of young dacitic volcanism in a lake-filled caldera

Quilotoa volcano, an example of young dacitic volcanism in a lake-filled caldera, is found at the southwest end of the Ecuador's volcanic front. It has had a long series of powerful plinian eruptions of moderate to large size (VEI = 4–6), at repetitive intervals of roughly 10–15 thousand years. At least eight eruptive cycles (labeled Q-I to Q-VIII with increasing age) over the past 200 ka are recognized, often beginning with a phreatomagmatic onset and followed by a pumice-rich lapilli fall, and then a sequence of pumice, crystal, and lithic-rich deposits belonging to surges and ash flows. These unwelded pyroclastic flows left veneers on hillsides as well as very thick accumulations in the surrounding valleys, the farthest ash flow having traveled about 17 km down the Toachi valley. The bulk volumes of the youngest flow deposits are on the order of 5 km³, but that of Q-I's 800 yr BP ash-fall unit is about 18 km³. In the last two eruption cycles water has had a more important role.     

Impact of the geomagnetic field and solar radiation on climate change

Recent studies have shown that, in addition to the role of solar variability, past climate changes may have been connected with variations in the Earth??s magnetic field elements at various timescales. An analysis of variations in geomagnetic field elements, such as field intensity, reversals, and excursions, allowed us to establish a link between climate changes at various timescales over the last millennia. Of particular interest are sharp changes in the geomagnetic field intensity and short reversals of the magnetic poles (excursions). The beginning and termination of the examined geomagnetic excursions can be attributed to periods of climate change. In this study, we analyzed the possible link between short-term geomagnetic variability (jerks) and climate change, as well as the accelerated drift of the north magnetic pole and surface temperature variations. The results do not rule out the possibility that geomagnetic field variations which modulate the cosmic ray flux could have played a major role in climate change in addition to previously induced by solar radiation.