Alexander E. Hillaris

Alexander E. Hillaris
National and Kapodistrian University of Athens | uoa · Faculty of Physics

National and Kapodistrian University of Athens · Ph.D. in Physics, Section of Astronomy, Astrophysics and Mechanics, University of Athens. Dissertation: «Dynamics of Electron Beams Applied in Metre Wave Solar Bursts»

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89
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775
Citations
Citations since 2016
13 Research Items
363 Citations
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
2016201720182019202020212022020406080
Additional affiliations
January 2008 - present
National and Kapodistrian University of Athens
Description
  • Analysis of Solar Radio Bursts in the 650-20 MHz Range

Publications

Publications (89)
Article
Full-text available
We report the first detection of metric radio emission from a surge, observed with the Nançay Radioheliograph (NRH), STEREO and other instruments. The emission was observed during the late phase of the M9 complex event SOL2010-02-012T11:25:00, described in a previous publication and was associated with a secondary energy release, also observed in S...
Preprint
Full-text available
We report the first detection of metric radio emission from a surge, observed with the Nan\c{c}ay Radioheliograph (NRH), STEREO and other instruments. The emission was observed during the late phase of the M9 complex event SOL2010-02-012T11:25:00, described in a previous publication and was associated with a secondary energy release, also observed...
Article
Full-text available
Context. Narrowband bursts (spikes) are very small duration and bandwidth bursts which appear on dynamic spectra from microwave to decametric frequencies. They are believed to be manifestations of small-scale energy release through magnetic reconnection. Aims. We study the position of the spike-like structures relative to the front of type-II burst...
Preprint
Full-text available
Narrowband bursts (spikes) appear on dynamic spectra from microwave to decametric frequencies. They are believed to be manifestations of small-scale energy release through magnetic reconnection. We study the position of the spike-like structures relative to the front of type-II bursts and their role in the burst emission. We used high-sensitivity,...
Preprint
Full-text available
We have studied a complex metric radio event which originated in a compact flare, observed with the ARTEMIS-JLS radiospectro-graph on February 12, 2010. The event was associated with a surge observed at 195 and 304 {\AA} and with a coronal mass ejection observed by instruments on-board STEREO A and B near the East and West limbs respectively. On th...
Article
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Aims. We study the characteristics of intermediate drift bursts (fibers) embedded in a large type-IV event. Methods. We used high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay radioheliograph (NRH) and...
Article
Full-text available
Aims. We examined the characteristics of isolated intermediate drift bursts and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges. Furthermore we studied the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the intermediate drift bu...
Article
Full-text available
Aims . We examine high time resolution dynamic spectra for fine structures in type II solar radio bursts Methods . We used data obtained with the acousto-optic spectrograph receiver of the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph in the 450–270 MHz range at 10 ms cadence and identified more than 600 short, narrowband features. Their charac...
Article
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In this work we study the characteristics of moving type IV radio bursts which extend to the hectometric wavelengths (interplanetary type IV or type IV IP bursts) and their relationship with energetic phenomena on the Sun. Our dataset comprised 48 Interplanetary type IV bursts observed by the Wind/WAVES in the 13.825 MHz?20 KHz frequency range. The...
Article
Full-text available
On 2012 March 7, two large eruptive events occurred in the same active region within an hour from each other. Each consisted of an X-class are, a coronal mass ejection (CME), an EUV wave, and a shock wave. The eruptions gave rise to a major Solar Energetic Particle (SEP) event observed at widely-separated (~120o) points in the heliosphere. From mul...
Article
Full-text available
Transient and recurrent solar activity drive geomagnetic disturbances; these are quantified (among others) by DST, AE indices time-series. Transient disturbances are related to the Interplanetary Coronal Mass Ejections (ICMEs) while recurrent disturbances are related to co-rotating interaction regions (CIR). We study the relationship of the geomagn...
Article
Full-text available
Narrow band bursts appear on dynamic spectra from microwave to decametric frequencies as fine structures with very small duration and bandwidth. They are thought to mark small scale magnetic reconnection. We analyzed 27 metric type-IV events with narrow band bursts observed by the ARTEMIS-IV radiospectrograph in 30/6/1999-1/8/2010. We examined the...
Article
Full-text available
We study selected properties of Solar Energetic Particle (SEP) events as inferred from their associated radio emissions. We used a catalogue of 115 SEP events that consists of entries of proton intensity enhancements at one AU, with complete coverage over solar cycle 23, based on high-energy (~68 MeV) protons from SOHO/ERNE and we calculated the pr...
Article
Full-text available
Fine structures embedded in type-IV burst continua may be used as diagnostics of the magnetic field restructuring and the corresponding energy release associated with the low corona development of flare/CME events. A catalog of 36 type-IV bursts observed with the SAO receiver of the ARTEMIS-IV solar radio-spectrograph in the 450--270 MHz range at h...
Article
Full-text available
Context. The highest energies of solar energetic nucleons detected in space or through gamma-ray emission in the solar atmosphere are in the GeV range. Where and how the particles are accelerated is still controversial. Aims: We search for observational information on the location and nature of the acceleration region(s) by comparing the timing of...
Article
Full-text available
Solar radio emission records received at the IZMIRAN spectrograph (25–270 MHz) during the solar flare event of February 12, 2010 are analyzed. Different fine structures were observed in three large groups of type III bursts against a low continuum. According to data from the Nancay radioheliograph, sources of all three groups of bursts were located...
Article
Full-text available
On 13 June 2010, an eruptive event occurred near the solar limb. It included a small filament eruption and the onset of a relatively narrow coronal mass ejection (CME) surrounded by an extreme ultraviolet wave front recorded by the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was accompanied by...
Conference Paper
In this analysis we have identified the formation of coronal shock waves from 2007 to 2011, using as proxies the type II radio bursts from radio spectrograph ARTEMIS-IV and RSTN. For the 42 events we have identified, we combined data from STEREO, SOHO/LASCO και SDO with the characteristics of the composite radio spectra to investigate the propertie...
Conference Paper
Transient expulsions of gigantic clouds of solar coronal plasma into the interplanetary space in the form of Coronal Mass Ejections (CMEs) and sudden, intense flashes of electromagnetic radiation, solar flares, are well-established drivers of the variable Space Weather. Given the innate, intricate links and connections between the solar drivers and...
Conference Paper
The corona probed at meter and decimeter wavelengths is a crucial region for the acceleration and propagation of solar energetic particles (SEPs), and radio diagnostics in this plasma plays a major role in assessing the origin of SEP events. Using data from the ARTEMIS IV solar radio spectro-graph, we report the properties of the radio emission ass...
Conference Paper
High cadence observations in the low corona from AIA imagers combined with radiospectrograph high-resolution recordings give a new perspective of shock formation in the low corona. Using ARTEMIS-IV observations of drifting type-II metric radio emission and ultra-high resolution observations from the AIA imagers we present direct observation of shoc...
Conference Paper
We have studied a complex metric radio event,observed with the ARTEMIS radiospectrogarph on February 12, 2010. The event was associated with a surge observed at 195 and 304 A and with a coronal mass ejection observed by STEREO A and B instruments near the East wnd West limbs respectively. On the disk the event was observed at 10 frequencies by the...
Article
Full-text available
Context. Metric type II bursts are the most direct diagnostic of shock waves in the solar corona. Aims: There are two main competing views about the origin of coronal shocks: that they originate in either blast waves ignited by the pressure pulse of a flare or piston-driven shocks due to coronal mass ejections (CMEs). We studied three well-observed...
Article
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On 17 January 2005 two fast coronal mass ejections were recorded in close succession during two distinct episodes of a 3B/X3.8 flare. Both were accompanied by metre-to-kilometre type-III groups tracing energetic electrons that escape into the interplanetary space and by decametre-to-hectometre type-II bursts attributed to CME-driven shock waves. A...
Article
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We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present,...
Conference Paper
Full-text available
A number of metric (100-650 MHz) typeII bursts was recorded by the ARTEMIS-IV radiospectrograph in the 1998-2000 period; the sample includes both CME driven shocks and shocks originating from flare blasts. We study their characteristics in comparison with characteristics of associated CMEs and flares. Comment: Recent Advances in Astronomy and Astro...
Conference Paper
Full-text available
We present complex radio bursts recorded by the radiospectrograph ARTEMIS-IV in the active period of January 2005. The wide spectral coverage of this recorder, in the 650-20 MHz range, permits an analysis of the radio bursts from the base of the Solar Corona to 2 Solar Radii; it thus facilitates the association of radio activity with other types of...
Conference Paper
Full-text available
Although the energetic phenomena of the Sun (flares, coronal mass injections etc.) exhibit intermittent stochastic behavior in their rate of occurrence, they are well correlated to the variations of the solar cycle. In this work we study the spatial and temporal characteristics of transient solar activity in an attempt to statistically interpret th...
Conference Paper
Full-text available
We present a statistical study of dynamical and kinetic characteristics of CMEs which show temporal and spatial association with flares and type II radio bursts or complex radio events of type II bursts and type IV continua. This study is based on a set of earth‐directed full halo CMEs occurring during the present solar cycle, with data from the L...
Article
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A study and classification of super‐short structures (SSSs) recorded during metric type IV bursts is presented. The most important property of SSSs is their duration, at half power ranging from 4–50 ms, what is up to 10 times shorter than spikes at corresponding frequencies. The solar origin of the SSSs is confirmed by one‐to‐one correspondence bet...
Conference Paper
Full-text available
The Solar Radiospectrograph of the University of Athens (ARTEMIS-IV) is in operation at the Thermopylae Satellite Communication Station since 1996. The observations extend from the base of the Solar Corona (650 MHz) to about 2 Solar Radii (20 MHz) with time resolution 1/10-1/100 sec. The instruments recordings, being in the form of dynamic spectra,...
Article
Full-text available
We present the improved solar radio spectrograph of the University of Athens operating at the Thermopylae Satellite Telecommunication Station. Observations now cover the frequency range from 20 to 650 MHz. The spectrograph has a 7-meter moving parabola fed by a log-periodic antenna for 100 650 MHz and a stationary inverted V fat dipole antenna for...
Article
Full-text available
A complex radio event was observed on January 17, 2005 with the radio-spectrograph ARTEMIS-IV, operating at Thermopylae, Greece; it was associated with an X3.8 SXR flare and two fast Halo CMEs in close succession. We present dynamic spectra of this event; the high time resolution (1/100 s) of the data in the 450-270 MHz range, makes possible the de...
Conference Paper
Full-text available
The type III observations trace the propagation of energetic electron populations through the Solar Corona which, more often than not, precede or are associated with energy release on the Sun. A sample of Type III bursts in the range 20-650 MHz during the period of extraordinary solar activity (20 October to 4 November 2003) recorded by the ARTEMIS...
Conference Paper
Full-text available
On January 17, 2005 a complex radio event associated with an X3.8 SXR flare and two fast Halo CMEs (CME1 & CME2 henceforward) in close succession was observed. We present combined ARTEMIS-IV & WIND WAVES dynamic spectra which provide a complete view of the radio emission induced by shock waves and electron beams from the low corona to about 1 A.U....
Conference Paper
Full-text available
A major radio event, associated with an X7.1/2B flare in AR720 and a fast CME was observed on January 20, 2005 with the radio-spectrograph ARTEMIS-IV; it was particularly intense and with a complex radio signature with rich fine structure which was recorded in the 270-420 MHz range at high resolution (100 samples/sec). The fine structure is compare...
Conference Paper
Full-text available
We study the geoeffectiveness of a sample of complex events; each includes a coronal type II burst, accompanied by a GOES SXR flare and LASCO CME. The radio bursts were recorded by the ARTEMIS-IV radio spectrograph, in the 100-650 MHz range; the GOES SXR flares and SOHO/LASCO CMEs, were obtained from the Solar Geophysical Data (SGD) and the LASCO c...
Conference Paper
Type II bursts represent the passage of a shock wave through the tenuous plasma of the solar corona. Their exact origin has not been unambiguously determined, although they are associated with eruptive phenomena and are identified either with a flare blast wave or with a CME forward shock or with a shock driven by the flanks of a CME. We investigat...
Article
Full-text available
We present recent developments of the ARTEMIS IV solar radio spectrograph operating at Thermopylae, central Greece. Observations are obtained daily in total intensity and in the frequency range from 20 to 650MHz, using two antennas and two receivers. We are now in the process of developing a new system that will record consecutively the intensity o...
Article
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The Athens Neutron Monitor Data Processing (ANMODAP) Center recorded an unusual Forbush decrease with a sharp enhancement of cosmic ray intensity right after the main phase of the Forbush decrease on 16 July 2005, followed by a second decrease within less than 12 h. This exceptional event is neither a ground level enhancement nor a geomagnetic effe...
Conference Paper
Full-text available
We study a sample of complex events; each includes a coronal type II burst, accompanied by a GOES SXR flare and LASCO CME. The radio bursts were recorded by the ARTEMIS-IV radio spectrograph (100-650 MHz range); the GOES SXR flares and SOHO/LASCO CMEs, were obtained from the Solar Geophysical Data (SGD) and the LASCO lists respectively. The radio b...
Article
Full-text available
A high-speed, halo-type coronal mass ejection (CME), associated with a GOES M4.6 soft X-ray flare in NOAA AR 0180 at S12W29 and an EIT wave and dimming, occurred on 9 November 2002. A complex radio event was observed during the same period. It included narrow-band fluctuations and frequency-drifting features in the metric wavelength range, type III...
Article
Full-text available
The solar radiospectrograph of the University of Athens is installed at the Thermopylae Satellite Telecommunication Station. The observations cover the frequency range from 20 to 650 MHz. The spectrograph has a 7-m moving parabola feeding by a log-period antenna for 100–650 MHz and a stationary inverted V fat dipole antenna for 20–100 MHz. Two rece...
Article
We present the improved solar radiospectrograph of the University of Athens operating at the Thermopylae Satellite Station. Observations now cover the frequency range from 20 to 650 MHz. The spectrograph has a 7-meter moving parabola feeding by a log-period antenna for 100 to 650MHz and a stationary inverted V fat dipole antenna for the 20 to 100 M...
Article
Full-text available
Abstract We present a fast algorithm for slope detection on gray scale images, based on 2D Fourier transform and standard filters; this may be used for line or edge detection. Our approach is based on the calculation of “energy” per direction of the image, thus obtaining the “energy spectrum,on slope” (). This exhibits local maxima,at the points wh...
Article
Full-text available
We analyse of a set of radio rich (accompanied by type IV or II bursts) solar flares and their association with SOHO/LASCO Coronal Mass Ejections in the period 1998–2000. The intensity, impulsiveness and energetics of these events are investigated. We find that, on the average, flares associated both with type IIs and CMEs are more impulsive and mo...
Conference Paper
Full-text available
In this report we present the Type II and IV radio bursts observed and analyzed by the radio spectrograph ARTEMIS IV1, in the 650-20MHz frequency range, during the active period October-November 2003. These bursts exhibit very rich fine structures such fibers, pulsations and zebra patterns which is associated with certain characteristics of the ass...
Conference Paper
Full-text available
A study of periodicities appearing in the type-IV bursts fine structure (fibers and pulsations in particular) is presented. Our data set includes recordings by ARTEMIS IV with high time resolution; this facilitates the detection of lower than 1 sec periodicities. We introduce a method which employs directional filtering for the separation of intert...
Conference Paper
Full-text available
We present a fast algorithm for slope detection on grey scale images, based on 2D-FFT, which may be used for line or edge detection. Our approach is based on the calculation of "energy" per direction of the image, thus obtaining the Energy Spectrum on Slope ($alpha$). This exhibits local maxima at the points where $alpha$ equals the slopes of linea...
Article
Full-text available
Characteristics of supershort structures (SSSs) occurring in the metric solar type IV radio bursts are described. The most important property of SSSs is their duration, which, at half-power, ranges from 4 to 60 ms and is thus much shorter than generally expected for the bursts in the metric range. The comparison of the distributions of SSS duration...
Article
Full-text available
The large flare/CME event that occurred close to the west solar limb on 3 November 2003 launched a large-amplitude large-scale coronal wave that was observed in H$\alpha$ and Fe xii 195 Å spectral lines, as well as in the soft X-ray and radio wavelength ranges. The wave also excited a complex decimeter-to-hectometer type II radio burst, revealing t...
Article
Full-text available
Fine structure of type IV radio solar bursts with a great variety and complexity often give much information in different ways and enable estimation of various coronal characteristics. In this work, we expose our new method for fine structure revealing and separation of two basic kinds of type IV fine structure, as fibers and pulsations. We also es...
Conference Paper
Full-text available
Large-scale dimmings in the form of disappearing transequatorial loops have been observed on several occasions in association with the onset of coronal mass ejections (CMEs). The opening of the CME magnetic field can be revealed by radio observations since the radio emission sources trace the propagation paths of electrons (along the large-scale lo...
Conference Paper
Full-text available
We present dynamic spectra of three out of six complex events observed in the period October 23 - November 3 with the radio-spectrograph ARTEMIS-IV, operating at Thermopylae, Greece. Combined with data from WIND-WAVES, these observations provide a complete view of the radio emission induced by shock waves and electron beams from the low corona to a...
Article
Full-text available
A fast "halo"-type coronal mass ejection (CME) associated with a two-ribbon flare, GOES class M 1.3, was observed on February 8, 2000. Soft X-ray and EUV images revealed several loop ejections and one wave-like moving front that started from a remote location, away from the flare core region. A radio type-II burst was observed near the trajectory o...