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Metric radio bursts and fine structures observed on 17 January, 2005  

Alexander Hillaris   Submitted: 2014-06-10 14:09

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 detection and analysis of the fine structure which this major radio event exhibits. The fine structure was found to match, almost, the comprehensive Ondřejov; Catalogue which it refers to the spectral range 0.8-2 GHz, yet seems to produce similar fine structure with the metric range.

Authors: Bouratzis, C.; Preka-Papadema, P.; Moussas, X.; Alissandrakis, C.; Hillaris, A.
Projects: None

Publication Status: Advances in Space Research, Volume 43, Issue 4, p. 605-611.
Last Modified: 2014-06-11 09:54
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Space storm measurements of the July 2005 solar extreme events from the low corona to the Earth  

Alexander Hillaris   Submitted: 2014-06-10 14:07

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 effect in cosmic rays. It rather appears as the effect of a special structure of interplanetary disturbances originating from a group of coronal mass ejections (CMEs) in the 13-14 July 2005 period. The initiation of the CMEs was accompanied by type IV radio bursts and intense solar flares (SFs) on the west solar limb (AR 786); this group of energetic phenomena appears under the label of Solar Extreme Events of July 2005. We study the characteristics of these events using combined data from Earth (the ARTEMIS IV radioheliograph, the Athens Neutron Monitor (ANMODAP)), space (WIND/WAVES) and data archives. We propose an interpretation of the unusual Forbush profile in terms of a magnetic structure and a succession of interplanetary shocks interacting with the magnetosphere.

Authors: Caroubalos, C.; Preka-Papadema, P.; Mavromichalaki, H.; Moussas, X.; Papaioannou, A.; Mitsakou, E.; Hillaris, A.
Projects: None

Publication Status: Advances in Space Research, Volume 43, Issue 4, p. 600-604.
Last Modified: 2014-06-11 09:54
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The improved ARTEMIS IV multichannel solar radio spectrograph of the University of Athens  

Alexander Hillaris   Submitted: 2014-06-10 14:03

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 the 20 100 MHz range. Two receivers are operating in parallel, one swept frequency for the whole range (10 spectrums/sec, 630 channels/spectrum) and one acousto-optical receiver for the range 270 to 450 MHz (100 spectrums/sec, 128 channels/spectrum). The data acquisition system consists of two PCs (equipped with 12 bit, 225 ksamples/sec ADC, one for each receiver). Sensitivity is about 3 SFU and 30 SFU in the 20 100 MHz and 100 650 MHz range respectively. The daily operation is fully automated: receiving universal time from a GPS, pointing the antenna to the sun, system calibration, starting and stopping the observations at preset times, data acquisition, and archiving on DVD. We can also control the whole system through modem or Internet. The instrument can be used either by itself or in conjunction with other instruments to study the onset and evolution of solar radio bursts and associated interplanetary phenomena.

Authors: Kontogeorgos, A.; Tsitsipis, P.; Caroubalos, C.; Moussas, X.; Preka-Papadema, P.; Hilaris, A.; Petoussis, V.; Bouratzis, C.; Bougeret, J.-L.; Alissandrakis, C. E.; Dumas, G.
Projects: None

Publication Status: Experimental Astronomy, Volume 21, Issue 1, pp.41-55
Last Modified: 2014-06-11 09:54
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Solar flares with and without SOHO/LASCO coronal mass ejections and type II shocks  

Alexander Hillaris   Submitted: 2014-06-10 14:01

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 more energetic than flares associated with type IIs only (without CME reported), as well as flares accompanied by type IV continua but not type II shocks. From the last two classes, flares with type II bursts (without CMEs reported) are the shortest in duration and the most impulsive.

Authors: Hillaris, A.; Petousis, V.; Mitsakou, E.; Vassiliou, C.; Moussas, X.; Polygiannakis, J.; Preka-Papadema, P.; Caroubalos, C.; Alissandrakis, C.; Tsitsipis, P.; Kontogeorgos, A.; Bougeret, J.-L.; Dumas, G.
Projects: None

Publication Status: Advances in Space Research, Volume 38, Issue 5, p. 1007-1010.
Last Modified: 2014-06-11 09:54
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Type II Radio Emission and Solar Particle Observations  

Alexander Hillaris   Submitted: 2014-06-10 13:59

The 28 October 2003 flare gave us the unique opportunity to compare the acceleration time of high-energy protons with the escaping time of those particles which have been measured onboard spacecraft and by neutron monitors network as GLE event. High-energy emission time scale and shock wave height and velocity time dependencies were also studied.

Authors: Kuznetsov, S. N.; Kurt, V. G.; Yushkov, B. Yu.; Myagkova, I. N.; Kudela, K.; Belov, A. V.; Caroubalos, C.; Hilaris, A.; Mavromichalaki, H.; Moussas, X.; Preka-Papadema, P.
Projects: None

Publication Status: International Journal of Modern Physics A, Volume 20, Issue 29, pp. 6705-6707 (2005).
Last Modified: 2014-06-11 09:54
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ARTEMIS IV Radio Observations of the 14 July 2000 Large Solar Event  

Alexander Hillaris   Submitted: 2014-06-10 13:57

In this report we present a complex metric burst, associated with the 14 July 2000 major solar event, recorded by the ARTEMIS-IV radio spectrograph at Thermopylae. Additional space-borne and Earth-bound observational data are used, in order to identify and analyze the diverse, yet associated, processes during this event. The emission at metric wavelengths consisted of broad-band continua including a moving and a stationary type IV, impulsive bursts and pulsating structures. The principal release of energetic electrons in the corona was 15 20 min after the start of the flare, in a period when the flare emission spread rapidly eastwards and a hard X-ray peak occurred. Backward extrapolation of the CME also puts its origin in the same time interval, however, the uncertainty of the extrapolation does not allow us to associate the CME with any particular radio or X-ray signature. Finally, we present high time and spectral resolution observations of pulsations and fiber bursts, together with a preliminary statistical analysis.

Authors: Caroubalos, C.; Alissandrakis, C. E.; Hillaris, A.; Nindos, A.; Tsitsipis, P.; Moussas, X.; Bougeret, J.-L.; Bouratzis, K.; Dumas, G.; Kanellakis, G.; Kontogeorgos, A.; Maroulis, D.; Patavalis, N.; Perche, C.; Polygiannakis, J.; Preka-Papadema, P.
Projects: None

Publication Status: Solar Physics, v. 204, Issue 1/2, p. 165-177 (2001).
Last Modified: 2014-06-11 09:54
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Radio Observations of the 20 January 2005 X-class Flare  

Alexander Hillaris   Submitted: 2014-06-10 13:55

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, in the flare - ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV - Wind/ Waves - HiRAS, with 2000 MHz - 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the Standard Flare - CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.

Authors: Bouratzis, C.; Preka-Papadema, P.; Hillaris, A.; Tsitsipis, P.; Kontogeorgos, A.; Kurt, V. G.; Moussas, X..
Projects: None

Publication Status: Solar Physics, Volume 267, Issue 2, pp.343-359
Last Modified: 2014-06-11 09:54
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On the relationship of shock waves to flares and coronal mass ejections  

Alexander Hillaris   Submitted: 2014-06-10 13:52

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 type II bursts in an attempt to place tighter constraints on their origins. Methods: The type II bursts were observed by the ARTEMIS radio spectrograph and imaged by the Nançay Radioheliograph (NRH) at least at two frequencies. To take advantage of projection effects, we selected events that occurred away from disk center. Results: In all events, both flares and CMEs were observed. In the first event, the speed of the shock was about 4200 km s-1, while the speed of the CME was about 850 km s-1. This discrepancy ruled out the CME as the primary shock driver. The CME may have played a role in the ignition of another shock that occurred just after the high speed one. A CME driver was excluded from the second event as well because the CMEs that appeared in the coronagraph data were not synchronized with the type II burst. In the third event, the kinematics of the CME which was determined by combining EUV and white light data was broadly consistent with the kinematics of the type II burst, and, therefore, the shock was probably CME-driven. Conclusions: Our study demonstrates the diversity of conditions that may lead to the generation of coronal shocks.

Authors: Nindos, A.; Alissandrakis, C. E.; Hillaris, A.; Preka-Papadema, P.
Projects: None

Publication Status: Astronomy & Astrophysics, Volume 531, id.A31, 12 pp
Last Modified: 2014-06-11 09:55
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The 17 January 2005 Complex Solar Radio Event Associated with Interacting Fast Coronal Mass Ejections  

Alexander Hillaris   Submitted: 2014-06-10 13:49

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 peculiar type-III burst group was observed below 600 kHz 1.5 hours after the second type-III group. It occurred without any simultaneous activity at higher frequencies, around the time when the two CMEs were expected to interact. We associate this emission with the interaction of the CMEs at heliocentric distances of about 25 R ⊙. Near-relativistic electrons observed by the EPAM experiment onboard ACE near 1 AU revealed successive particle releases that can be associated with the two flare/CME events and the low-frequency type-III burst at the time of CME interaction. We compare the pros and cons of shock acceleration and acceleration in the course of magnetic reconnection for the escaping electron beams revealed by the type-III bursts and for the electrons measured in situ.

Authors: Hillaris, A.; Malandraki, O.; Klein, K.-L.; Preka-Papadema, P.; Moussas, X.; Bouratzis, C.; Mitsakou, E.; Tsitsipis, P.; Kontogeorgos, A.
Projects: None

Publication Status: Solar Physics, Volume 273, Issue 2, pp.493-509
Last Modified: 2014-06-11 09:54
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The relativistic solar particle event of 2005 January 20: prompt and delayed particle acceleration  

Alexander Hillaris   Submitted: 2014-06-10 13:46

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. We search for observational evidence on the acceleration region(s) by comparing the timing of relativistic protons detected at Earth and radiative signatures in the solar atmosphere. To this end a detailed comparison is undertaken of the double-peaked time profile of relativistic protons, derived from the worldwide network of neutron monitors during the large particle event of 2005 January 20, with UV imaging and radio petrography over a broad frequency band from the low corona to interplanetary space. We show that both relativistic proton releases to interplanetary space were accompanied by distinct episodes of energy release and electron acceleration in the corona traced by the radio emission and by brightenings of UV kernels in the low solar atmosphere. The timing of electromagnetic emissions and relativistic protons suggests that the first proton peak was related to the acceleration of gamma-ray emitting protons during the impulsive flare phase, as shown before. The second proton peak occurred together with signatures of magnetic restructuring in the corona after the CME passage. We attribute the acceleration to reconnection and possibly turbulence in large-scale coronal loops. While type II radio emission was observed in the high corona, there is no evidence of a temporal relationship with the relativistic proton acceleration.

Authors: Klein, K.-L.; Masson, S.; Bouratzis, C.; Grechnev, V.; Hillaris, A.; Preka-Papadema, P
Projects: None

Publication Status: Submitted to A&A
Last Modified: 2014-06-11 09:55
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Fine Structure of Metric Type-IV Radio Bursts Observed with the ARTEMIS-IV Radio Spectrograph: Association with Flares and Coronal Mass Ejections  

Alexander Hillaris   Submitted: 2014-06-10 13:44

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 high cadence (0.01 sec) was compiled; the fine structures were classified into five basic classes with two or more sub-classes each. The time of fine structure emission was compared with the injection of energetic electrons as evidenced by HXR and microwave emission, the SXR light-curves and the CME onset time. Our results indicate a very good temporal association between energy release episodes and pulsations, spikes, narrow-band bursts of the type-III family and zebra bursts. Of the remaining categories, the featureless broadband continuum starts near the time of the first energy release, between the CME onset and the SXR peak, but extends for several tens of minutes after that, covering almost the full extent of the flare-CME event. The intermediate drift bursts, fibers in their majority, mostly follow the first energy release but have a wider distribution, compared to other fine structures.

Authors: Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A.
Projects:

Publication Status: Solar Physics 290 (1), 219-286. Topical Issue
Last Modified: 2016-06-23 15:23
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CME Expansion as the Driver of Metric Type II Shock Emission as Revealed by Self-consistent Analysis of High-Cadence EUV Images and Radio Spectrograms  

Alexander Hillaris   Submitted: 2014-06-10 13:41

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 (EUV) wave front recorded by the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst; high-resolution dynamic spectra of the latter were obtained by the Appareil de Routine pour le Traitement et l'Enregistrement Magnetique de l'Information Spectral (ARTEMIS IV) radio spectrograph. The combined observations enabled a study of the evolution of the ejecta and the EUV wave front and its relationship with the coronal shock manifesting itself as metric Type-II burst. By introducing a novel technique, which deduces a proxy of the EUV compression ratio from AIA imaging data and compares it with the compression ratio deduced from the band-split of the Type-II metric radio burst, we are able to infer the potential source locations of the radio emission of the shock on that AIA images. Our results indicate that the expansion of the CME ejecta is the source for both EUV and radio shock emissions. Early in the CME expansion phase, the Type-II burst seems to originate in the sheath region between the EUV bubble and the EUV shock front in both radial and lateral directions. This suggests that both the nose and the flanks of the expanding bubble could have driven the shock.

Authors: Kouloumvakos, A.; Patsourakos, S.; Hillaris, A.; Vourlidas, A.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A.
Projects: None

Publication Status: Solar Physics, Volume 289, Issue 6, pp.2123-2139
Last Modified: 2014-06-11 09:55
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Abstracts by Author
Metric radio bursts and fine structures observed on 17 January, 2005
Space storm measurements of the July 2005 solar extreme events from the low corona to the Earth
The improved ARTEMIS IV multichannel solar radio spectrograph of the University of Athens
Solar flares with and without SOHO/LASCO coronal mass ejections and type II shocks
Type II Radio Emission and Solar Particle Observations
ARTEMIS IV Radio Observations of the 14 July 2000 Large Solar Event
Radio Observations of the 20 January 2005 X-class Flare
On the relationship of shock waves to flares and coronal mass ejections
The 17 January 2005 Complex Solar Radio Event Associated with Interacting Fast Coronal Mass Ejections
The relativistic solar particle event of 2005 January 20: prompt and delayed particle acceleration
Fine Structure of Metric Type-IV Radio Bursts Observed with the ARTEMIS-IV Radio Spectrograph: Association with Flares and Coronal Mass Ejections
CME Expansion as the Driver of Metric Type II Shock Emission as Revealed by Self-consistent Analysis of High-Cadence EUV Images and Radio Spectrograms

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