arXiv subjects

X. Moussas

Publications and source records attributed to X. Moussas.

27 records · Page 2Linked to original sources

arXiv2010

ARTEMIS IV Radio Observations of the 14 July 2000 Large Solar Event

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.

astro-ph.SR↗

arXiv2010

Type II Radio Emission and Solar Particle Observations

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.

astro-ph.SR↗

arXiv2010

Space storm measurements of the July 2005 solar extreme events from the low corona to the Earth

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.

astro-ph.SR↗

arXiv2010

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

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 Ondrejov Catalogue which it refers to the spectral range 0.8-2 GHz, yet seems to produce similar fine structure with the metric range.

astro-ph.SR↗

arXiv2010

Type III events, flares and CMEs, in the extremely active period October-November 2003

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-IV1 radio spectrograph is analysed; its parameters are compared with characteristics of associated flares (Ha and GOES SXR) and CMEs, observed in the same period and reported in the SGR and the LASCO archives respectively. In this report we attempt to establish a correlation between energetic particles and major manifestations of solar activity such as flares and CMEs.

astro-ph.SR↗

arXiv2010

CME on CME Interaction on January 17, 2005

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. These are supplemented with data, from the Nançay Radioheliograph (NRH), GOES, EIT and LASCO for the study of the associated flare and CME activity.

astro-ph.SR↗

arXiv2010

Metric Radio Bursts and Fine Structures Observed on January 20, 2005

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 compared with similar results in the decimetric and microwave frequency range. It was found to approximately match the comprehensive Ondrejov Classification in the spectral range 0.8-2 GHz.

astro-ph.SR↗

arXiv2009

The correlation of fractal structures in the photospheric and the coronal magnetic field

This work examines the relation between the fractal properties of the photospheric magnetic patterns and those of the coronal magnetic fields in solar active regions.Our results show no correlation between the fractal dimensions of the observed 2d photospheric structures and the extrapolated unstable volumes in the corona, when nonlinear force-free extrapolation is used. This result is independent of efforts to (1) bring the photospheric magnetic fields closer to a nonlinear force-free equilibrium and (2) omit the lower part of the modeled magnetic field volume that is almost completely filled by unstable volumes. A significant correlation between the fractal dimensions of the photospheric and coronal magnetic features is only observed at the zero level (lower limit) of approximation of a current-free (potential) magnetic field extrapolation. We conclude that the complicated transition from photospheric non-force-free fields to coronal force-free ones hampers any direct correlation between the fractal dimensions of the 2d photospheric patterns and their 3d counterparts in the corona at the nonlinear force-free limit.

astro-ph.SR↗

arXiv2003

On signal-noise decomposition of timeseries using the continuous wavelet transform: Application to sunspot index

We show that the continuous wavelet transform can provide a unique decomposition of a timeseries in to 'signal-like' and 'noise-like' components: From the overall wavelet spectrum two mutually independent skeleton spectra can be extracted, allowing the separate detection and monitoring in even non-stationary timeseries of the evolution of (a) both stable but also transient, evolving periodicities, such as the output of low dimensional dynamical systems and (b) scale-invariant structures, such as discontinuities, self-similar structures or noise. An indicative application to the monthly-averaged sunspot index reveals, apart from the well-known 11-year periodicity, 3 of its harmonics, the 2-year periodicity (quasi-biennial oscillation, QBO) and several more (some of which detected previously in various solar, earth-solar connection and climate indices), here proposed being just harmonics of the QBO, in all supporting the double-cycle solar magnetic dynamo model (Benevolenskaya, 1998, 2000). The scale maximal spectrum reveals the presence of 1/f fluctuations with timescales up to 1 year in the sunspot number, indicating that the solar magnetic configurations involved in the transient solar activity phenomena with those characteristic timescales are in a self-organized-critical state (SOC), as previously proposed for the solar flare occurence (Lu and Hamilton, 1991).

physics.data-an↗