Xenophon Moussas

Study of the solar and geomagnetic activity influence on the emergency proceedings in Greece, for selected months of solar cycle 23 and especially for the year 2005 is presented. We examined the time association between the magnetic storms (Dst geomagnetic index), daily numbers of solar flares and Coronal Mass Ejections (CMEs) with the emergency proceedings. The sample of about 30000

We present area and photometry measurements of all sunspots (aprox. 12000) for the 23rd solar cycle. The images that have been used for our analysis have been taken by the MDI instrument on board So.H.O during the last solar cycle through the years 1997 to 2007. At the completion of our analysis, with a simple algorithm, more than 3.300 images in photometry stage have been used. Initially we determined the sunspot pixel-positions from MDI images and registered them to the data base consisting of a complete record of sunspots during the last cycle, derived from the Mt. Wilson data base. We used a novel algorithm serving the purposes of this analysis, which measures the lowest intensity and the area of every sunspot umbra. Finally, groups penumbral and umbral data will be presented for all sunspot groups.

We present area and photometry measurements of all sunspots (aprox. 12000) for the 23rd solar cycle. The images that have been used for our analysis have been taken by the MDI instrument on board So.H.O during the last solar cycle through the years 1997 to 2007. At the completion of our analysis, with a simple algorithm, more than 3.300 images in photometry stage have been used. Initially we determined the sunspot pixel-positions from MDI images and registered them to the data base consisting of a complete record of sunspots during the last cycle, derived from the Mt. Wilson data base. We used a novel algorithm serving the purposes of this analysis, which measures the lowest intensity and the area of every sunspot umbra. Finally, groups penumbral and umbral data will be presented for all sunspot groups.

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 associated with several major SEP events. The association of the radio emission with the related flares and CMEs is also investigated.

The international contest 'Cassini Scientist for a Day', organized by the Cassini Outreach team at NASA's Jet Propulsion Laboratory, provides school students all around the world with the opportunity to get involved in astronomy and astrophysics and planetary sciences in particular. It gives excellent opportunity for outreach and publicity for the Cassini mission and ESA and NASA activities in Greece. For the years 2010 and 2011, the Space Physics Group of the Astronomy, Astrophysics and Mechanics section of the University of Athens in association with external colleagues has been selected as the co-ordinator of NASA for the competition in Greece. This kind of school competition in Greece is particularly important since Astronomy and Astrophysics and Space Sciences, although very popular, are not included in the school curricula and thus students rarely have the opportunity to experience and participate actively in these subjects. Under the guidance of Cassini Outreach t...

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 associated with several major SEP events. The association of the radio emission with the related flares and CMEs is also investigated.

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained data of Titan's surface from flybys performed during the last seven years. In the 0.8-5.2 µm range, these spectro-imaging data showed that the surface consists of a multivariable geological terrain hosting complex geological processes. The data from the seven narrow methane spectral "windows" centered at 0.93, 1.08, 1.27, 1.59, 2.03, 2.8 and 5 µm provide some information on the lower atmospheric context and the surface parameters that we want to determine. Atmospheric scattering and absorption need to be clearly evaluated before we can extract the surface properties. We apply here a statistical method [1, 2] and a radiative transfer method [3, 1] on three potentially "active" regions on Titan, i.e. regions possibly subject to change over time (in brightness and/or in color etc) [4]: Tui Regio (20°S, 130°W) [5], a 1,500-km long flow-like figure, Hotei Regio (26°S, 78°W) [6], a 700-km wide vol...

Saturn's largest satellite Titan is one of the most interesting planetary bodies. Since 2004 it is being explored by the Cassini-Huygens joint ESA/NASA mission, whose results indicate that it might be geologically active and may support local tectonic processes. Titan possesses a dynamic, multivariable and Earth-like (albeit with different materials) geology modified by fluvial, aeolian, impact and most probably tectonic and cryovolcanic processes as seen mainly from the Synthetic Aperture Radar (SAR), the Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini and Huygens probe's data. Morphotectonic-like structures such as ridges, mountains, faults and canyons [1; 2] as well as cryovolcanic structures like calderas, domes, flows and radial faults [3] are surficial evidence of the aforementioned dynamic activities. Herewith, we present the major morphotectonic structures seen on Titan and compare them with terrestrial ones in order to discover visual and constructio...

ABSTRACT We present a study of Titan's complex geology with a focus on the satellite's surface regions that are showing spectral variations with time possibly linked to geological activity. We apply a statistical method, the Principal Component Analysis (PCA) [1] and a radiative transfer method (RT) [1,2] on three potentially 'active' regions on Titan, i.e. surface areas possibly subject to change over time (in brightness and/or in color etc.), namely Tui Regio (20°S, 130°W), a 1,500-km long flow-like figure, Hotei Regio (26°S, 78°W), a 700-km wide volcanic-like terrain, and Sotra Facula (15°S, 42°W), a 235-km in diameter area. With our PCA method we manage to isolate regions of distinct spectral response in all data available for our three study areas. Then, with our follow-up radiative transfer code we retrieve the surface albedo of the isolated regions with respect to the Huygens landing site albedo, which we use as a reference region and we compare them. Using this double procedure, we study the temporal surface variations of the three regions witnessing albedo changes with time for Tui Regio from 2005-2009 (darkening) and Sotra Facula from 2005-2006 (brightening) at all wavelengths. Hotei Regio has been suggested to present brightness variations over a two-year period (2004-2005) by Nelson et al. 2009 [3]. However, we find that the to-date available observations of that region present issues (geometry, resolution) that prevent an accurate application of our radiative transfer model to infer surface information with the desired accuracy. Therefore, we do not detect any significant surface albedo variations over time from 2004 and until 2009 given the uncertainties involved. The surface albedo variations, which we currently investigate in terms of chemical composition, and the volcanic-like features such as calderas, domes and lobate flows, which are present within the regions as shown by RADAR data analysis [e.g. 4], suggest that these features are compatible with internal phenomena such as cryovolcanism. Another study focusing on these areas suggests that Tui Regio and Hotei Regio could be paleolake clusters [5]. In the future, considering that the extracted surface albedos contain information on the chemical composition of the regions and their nature, we plan to better evaluate the temporal changes and to associate chemical composition inferences with morphological information to determine the nature of these regions. References: [1] Solomonidou, A., et al.: in prep. [2] Hirtzig, M., et al.: submitted to Icarus. [3] Nelson, R., et al.: Icarus 199, 429-441, 2009. [4] Lopes, R.M.C., et al.: JGR, in press. [5] Moore, J.M., and Howard, A.D.: GRL 37, L22205, 2010.

ABSTRACT Spectro-imaging and radar measurements by the Cassini-Huygens mission suggest that some of the Saturnian satellites may be geologically active and could support tectonic processes. In particular, Titan, Saturn's largest moon, possesses a complex and dynamic geology as witnessed by its varied surface morphology resulting from aeolian, fluvial, and possibly tectonic and endogenous cryovolcanic processes [e.g. 1]. The Synthetic Aperture Radar (SAR) instrument on board Cassini spacecraft indicates the possibility for morphotectonic features on Titan's surface such as mountains, ridges, faults and canyons [e.g.2]. We suggest that contractional tectonism followed by atmospheric modifications has resulted in the observed morphotectonic features. To test the possibility of morphotectonics on Titan, we provide in this work a comparative study between Cassini observations of the satellite versus terrestrial tectonic systems and infer suggestions for possible formation mechanisms [3]. A significantly interesting type of the morphotectonic features are the cryovolcanic features, which even if they are not yet identified, they considered to have formed due to correlation between volcanic and tectonic actions. Nowadays there are three locations on Titan suggestive as strong cryovolcanic candidates, namely Tui Regio, Hotei Regio and Sotra Facula [4]. Data analysis using statistical and radiative transfer methods [5] and the retrieval of meaningful surface albedos without the atmospheric contribution, enhance the supposition for a cryovolcanic origin by showing temporal variations in surface albedo for at least two candidate areas [6]. Furthermore, methane on Titan seems to follow the same pattern that water does on Earth, while its preservation limit is 100 Myr [7] suggesting that a methane reservoir that supplies the atmosphere is required. Cryovolcanic eruptions emanating from the candidate active regions could potentially provide the observed amount of methane. Both the typical morphotectonic features, such as mountains (30°S and 30°N) and faults (10°S-26°S), and the cryovolcanic features (20°S-30°S) are concentrated in equatorial latitudes and are likely associated with surface stress field. Thus, within the 30°S - 30°N zone, elevated, fractured and volcanic-like crustal features are observed while this association indicates a morphotectonic pattern. The presence of morphotectonic features and the recent data analysis indicating changes within the candidate cryovolcanic regions, suggest that similarities do exist between surficial features observed on the Earth, where both tectonic and volcanic activities are dominant, and on Titan. In addition, a recent study [8] that calculates Titan's tidal response and investigates the possible correlation between tidal deformation, near-surface processes and geological features, provides significant indications for the connection of the interior with the cryovolcanic candidate and morphotectonic features with implications for the satellite's astrobiological potential. [1] Soderblom, L.A. et al.: Icarus 204, 610-618, 2009. [2] Lopes, R.M.C. et al.: Icarus 205, 540-558, 2010. [3] Solomonidou, A., et al.: Planetary and Space Science, in press, 2012. [4] Lopes, R.M.C., et al.: JGR, in press, 2012. [5] Hirtzig, M., et al.: submitted to Icarus. [6] Solomonidou, A., et al.: in prep. [7] Lunine, J.I., Atreya, S.K.: Nature Geoscience 1, 159-164, 2008. [8] Sohl, F., et al.: in prep.

Results from computer experiments based on high resolution interplanetary magnetic field and plasma data from spacecrafts Pioneer 10 and 11 are presented. Energetic particle acceleration and propagation play an important role in high energy astrophysics and especially to the origin of cosmic rays. Spacecraft measurements of cosmic rays and of the solar wind (plasma velocity and magnetic field) give a

We investigate the relationship of metric type III radio bursts obtained with radio spectrograph ARTEMIS IV (20-650 MHz) in Thermopylae, to GOES SXR/Ha and SOHO/LASCO CMEs within the period of intense activity 20 October to 5 November 2003. Our sample consists of 123 type III radio bursts, 115 SXR Flares (mostly C-type) and 12 CMEs. 69% of type III bursts

ABSTRACT We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titan's stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm{sup -1} range for latitudes from 50 Degree-Sign S to 50 Degree-Sign N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50 Degree-Sign N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary.

The procedure employed in the present study is based on techniques reported by Jones et al. (1973) and Mousas et al. (1975). The problems investigated are related to the spatial and energy dependence of the parallel diffusion mean free path (derived from the pitch angle scattering coefficient), the energy dependence of the diffusion coefficients in energy space due to the interplanetary acceleration process studied by Fisk (1976), and the modification of the guiding center drift motion by scattering. The considered modification may have implications for the conclusions of Jokipii et al. (1976) concerning off-ecliptic modulation effects. Attention is given to details regarding the employed data and the numerical method, questions concerning the validity of the employed flux equation, results on space diffusion, and results on acceleration coefficients.

Within a period of intense activity (20 October to 5 November 2003), the injection and propagation of near relativistic electrons, resulted in hundreds of type III bursts recorded by the ARTEMISIV radio spectrograph (20–650 MHz). For a number of these type III events association with GOES SXR/Hα flare and/or SOHO/LASCO CME was established. We study the variation of characteristic type III parameters and their relationship with features of the associated flares and/or CMEs.

A couple of years ago, a broad study of ancient temples and oracles in Greece was published by M. Ranieri in 2014 [1]. In this interesting work, Ranieri describes a very special behaviour of the orientation for the majority of the studied temples, by identifying the diagonals of the temples to be oriented, mainly, towards one of the cardinal points. Furthermore, he establishes that the dimensions of each temple obeys a condition related to a Pythagorean triangle, as already identified in a previous study. [2]

Abstract The purpose of the present research is to study the latitudinal distribution and its asymmetry of solar flares during the period 2002–2017 and make a comparison between the studied data from two different satellites (GOES and RHESSI). We tried to benefit from available advantages of GOES and RHESSI satellites, where GOES satellite is providing classes associated to each flare, while RHESSI is providing the location of the recorded solar flare events. The distribution of the solar flares' location during the period 2002–2017 shows that most of the flares are located in the southern hemisphere (57% of C – class, 61% of B – class, 56% of M – class and 61% of X – class). The study of the solar flare events from RHESSI flare catalog during each phase of the solar cycles 23 and 24 (during the period 2002–2017) showed that the most of flare events are happening during the declining phase of the solar cycle and keeping the tendency to have more southern events (61%) than the northern ones, while there are more flares found in the northern hemisphere (64%) than the southern hemisphere during the rising phase of the solar cycle 24. We calculated the mean latitude value in the northern hemisphere and found it to be about +13° (about 7.5% of all solar flare records are located on this latitude) using flare events recorded by GOES and RHESSI, but there is a slight difference between the mean latitude values calculated using GOES (about −13°) and RHESSI (about −15°), about 6% of all solar flares recorded by RHESSI in the southern hemisphere are located on this latitude.