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Sunspot areas are one of the most important indices of solar activity. To obtain an extended time series covering multiple solar cycles, one must combine data from different observatories after a proper comparison and calibration of the individual datasets. We compare the daily and group values of sunspot areas provided by the different stations from the Solar Optical Observing Network, SOON, which are determined using similar instruments and techniques. We investigate if there are systematic differences among the stations and whether the differences in the daily values can be attributed to missing groups in the records or errors in the measurements. We find significant differences among the stations of the SOON network in terms of sizes (average daily and group values), quality of observations and coverage (considering the number of missing groups and data gaps). Our results indicate that calibration factors for daily values can be used with confidence to combine datasets from different stations. However, for some applications which require the location of the sunspot groups, the same correction factors should not be used. We estimate the irradiance deficit due to sunspot through the Photometric Sunspot Index and compare the output from similar datasets to quantify the effect of missing groups. We find differences as high as 150 ppm during the maximum of solar cycle. The effect increases for sunspot groups near the center of the disk accounting for about 80% of the observed differences.

The mid-infrared (mid-IR) range has been mostly unexplored for the investigation of solar flares. It is only recently that new mid-IR flare observations have begun opening a new window into the response and evolution of the solar chromosphere. These new observations have been mostly performed by the AR30T and BR30T telescopes that are operating in Argentina and Brazil, respectively. We present the analysis of SOL2019-05-15T19:24, a GOES class C2.0 solar flare observed at 30~THz (10$\ \mu$m) by the ground-based telescope AR30T. Our aim is to characterize the evolution of the flaring atmosphere and the energy transport mechanism in the context of mid-IR emission. We performed a multi-wavelength analysis of the event by complementing the mid-IR data with diverse ground- and space-based data from the Solar Dynamics Observatory (SDO), the H--$\alpha$ Solar Telescope for Argentina (HASTA), and the Expanded Owens Valley Solar Array (EOVSA). Our study includes the analysis of the magnetic field evolution of the flaring region and of the development of the flare. The mid-IR images from AR30T show two bright and compact flare sources that are spatially associated with the flare kernels observed in ultraviolet (UV) by SDO. We confirm that the temporal association between mid-IR and UV fluxes previously reported for strong flares is also observed for this small flare. The EOVSA microwave data revealed flare spectra consistent with thermal free-free emission, which lead us to dismiss the existence of a significant number of non-thermal electrons. We thus consider thermal conduction as the primary mechanism responsible for energy transport. Our estimates for the thermal conduction energy and total radiated energy fall within the same order of magnitude, reinforcing our conclusions., Comment: 10 pages, 8 figures. Accepted for publication in Astronomy and Astrophysics

The almost unexplored frequency window from submillimeter to mid-infrared (mid-IR) may bring new clues about the particle acceleration and transport processes and the atmospheric thermal response during solar flares. Because of its technical complexity and the special atmospheric environment needed, observations at these frequencies are very sparse. The High Altitude THz Solar Photometer (HATS) is a full-Sun ground-based telescope designed to observe the continuum from the submillimeter to the mid-IR. It has a 457-mm spherical mirror with the sensor in its primary focus. The sensor is a Golay cell with high sensitivity in a very wide frequency range. The telescope has a polar mount, and a custom-built data acquisition system based on a 32 ksamples per second, 24 bits (72 dB dynamic range), 8 channels analog-to-digital board. Changing only the composition of the low- and band-pass filters in front of the Golay cell, the telescope can be setup to detect very different frequency bands; making the instrument very versatile. In this article we describe the telescope characteristics and its development status. Moreover, we give estimates of the expected fluxes during flares., Accepted for publication in Solar Physics. 13 pages, 3 Figures and 2 Tables

We present a study of the M6.6 flare that occurred on 13 February 2011 in AR 11158. The flare was accompanied by a CME and EUV waves. We use multiwavelength observations from the ground: H-alpha Solar Telescope for Argentina (HASTA), and space: Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA), both onboard the Solar and Dynamic Observatory (SDO).

We examine the capability of a blast-wave scenario - associated with a coronal flare or to the expansion of CME flanks - to reproduce a chromospheric Moreton phenomenon. We also simulate the Moreton event of 2006 December 06, considering both the corona and the chromosphere. To obtain a sufficiently strong coronal shock - able to generate a detectable chromospheric Moreton wave - a relatively low magnetic field intensity is required, in comparison with the active region values. Employing reasonable coronal constraints, we show that a flare ignited blast-wave or the expansion of the CME flanks emulated as an instantaneous or a temporal piston model, respectively, are capable to reproduce the observations. Fil: Krause, Gustavo Javier. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Ténicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentina Fil: Cécere, Mariana Andre. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Francile, Carlos Natale. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina Fil: Costa, Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Elaskar, Sergio Amado. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Ténicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentina Fil: Schneiter, Ernesto Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina

Considering the chromosphere and a stratified corona, we examine, by performing 2D compressible magnetohydrodynamics simulations, the capability of a coronal mass ejection (CME) scenario to drive a Moreton wave. We find that given a typical flux rope (FR) magnetic configuration, in initial pseudo-equilibrium, the larger the magnetic field and the lighter (and hotter) the FR, the larger the amplitude and the speed of the chromospheric disturbance, which eventually becomes aMoreton wave.We present arguments to explain why Moreton waves are much rarer than CME occurrences. In the frame of the present model, we explicitly exclude the action of flares that could be associated with the CME. Analysing the Mach number, we find that only fast magnetosonic shock waves will be able to produce Moreton events. In these cases an overexpansion of the FR is always present and it is the main factor responsible for the Moreton generation. Finally, we show that this scenario can account for the Moreton wave of the 2006 December 6 event (Francile et al. 2013). Fil: Krause, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina Fil: Cécere, Mariana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Zurbriggen, Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Costa, Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Francile, Carlos Natale. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Informática. Observatorio Astronómico Félix Aguilar; Argentina Fil: Elaskar, Sergio Amado. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina

To contribute to the understanding of the physical mechanisms at work during the initial phase and early evolution of erupting prominences, we analyze combined observations from ground-based and space-borne instruments. We present two case studies, which occurred at two different phases of the solar cycle, namely on March 2, 2002 and on April 16, 2012. In particular, we show the results of a morphological and kinematical analysis and interpret them in terms of available theoretical models.

A Moreton wave was detected in active region (AR) 12017 on 29 March 2014 with very high cadence with the Halpha Solar Telescope for Argentina (HASTA) in association with an X1.0 flare (SOL2014-03-29T17:48). Several other phenomena took place in connection with this event, such as low coronal waves and a coronal mass ejection (CME). We analyze the association between the Moreton wave and the EUV signatures observed with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. These include their low-coronal surface-imprint, and the signatures of the full wave and shock dome propagating outward in the corona. We also study their relation to the white-light CME. We perform a kinematic analysis by tracking the wavefronts in several directions. This analysis reveals a high-directional dependence of accelerations and speeds determined from data at various wavelengths. We speculate that a region of open magnetic field lines northward of our defined radiant point sets favorable conditions for the propagation of a coronal magnetohydrodynamic shock in this direction. The hypothesis that the Moreton wavefront is produced by a coronal shock-wave that pushes the chromosphere downward is supported by the high compression ratio in that region. Furthermore, we propose a 3D geometrical model to explain the observed wavefronts as the chromospheric and low-coronal traces of an expanding and outward-traveling bubble intersecting the Sun. The results of the model are in agreement with the coronal shock-wave being generated by a 3D piston that expands at the speed of the associated rising filament. The piston is attributed to the fast ejection of the filament-CME ensemble, also consistent with the good match between the speed profiles of the low-coronal and white-light shock-waves., 37 pages, 14 Figures, published in Solar Physics

Impulsive 30 THz continuum bursts have been recently observed in solar flares, utilizing small telescopes with a unique and relatively simple optical setup concept. The most intense burst was observed together with a GOES X2 class event on October 27, 2014, also detected at two sub-THz frequencies, RHESSI X-rays and SDO/HMI and EUV. It exhibits strikingly good correlation in time and in space with white light flare emission. It is likely that this association may prove to be very common. All three 30 THz events recently observed exhibited intense fluxes in the range of 104 solar flux units, considerably larger than those measured for the same events at microwave and sub-mm wavelengths. The 30 THz burst emission might be part of the same spectral burst component found at sub-THz frequencies. The 30 THz solar bursts open a promising new window for the study of flares at their origin, Comment: 11 pages, 4 Figures J. Geophys. Res - Space Physics, accepted, May 21, 2015

In this work we have tracked coronal mass ejections observed with the ground based Mirror Coronagraph for Argentina (MICA) and the Large Angle and Spectroscopic Coronagraph (LASCO) C2 and C3 on board of the Solar and Heliospheric Observatory (SOHO). The MICA telescope is located at El Leoncito (31.8 S, 69.3 W), San Juan (Argentina), since 1997 as part of a bilateral scientific project between Germany and Argentina. SOHO is a project of international cooperation between ESA and NASA. Together these instruments are able to observe the solar corona ranging from 1.05 to 32 solar radii. MICA images the Fe XIV emission line corona and LASCO coronagraphs observe the Thomson scattered white light corona. We have selected events for which there are observations from the three coronagraphs. Using the composite data we were able to obtain height-time diagrams for the corresponding dynamical coronal features traveling outwards in order to determine some of their kinematical properties, i.e., plane of sky velocity and acceleration.

In this work we have tracked coronal mass ejections observed with the ground based Mirror Coronagraph for Argentina (MICA) and the Large Angle and Spectroscopic Coronagraph (LASCO) C2 and C3 on board of the Solar and Heliospheric Observatory (SOHO). The MICA telescope is located at El Leoncito (31.8 S, 69.3 W), San Juan (Argentina), since 1997 as part of a bilateral scientific project between Germany and Argentina. SOHO is a project of international cooperation between ESA and NASA. Together these instruments are able to observe the solar corona ranging from 1.05 to 32 solar radii. MICA images the Fe XIV emission line corona and LASCO coronagraphs observe the Thomson scattered white light corona. We have selected events for which there are observations from the three coronagraphs. Using the composite data we were able to obtain height-time diagrams for the corresponding dynamical coronal features traveling outwards in order to determine some of their kinematical properties, i.e., plane of sky velocity and acceleration.

It is well known that chromospheric observations in the hydrogen alpha line give relevant information about solar flares, plages and protuberances, among other typical features of the Sun. From 1998 to 2006, the HAlpha Solar Telescope of Argentina (HASTA) has provided solar images to the scientific community with the technological resources available at that time. Starting in 2007, major improvements have been incorporated, like a new CCD camera with enhanced spatial and temporal resolution, filter replacement, the automatic focusing system, and a new flat-fielding procedure. The hardware changes also called for software improvements, and a new solar-flare classification routine was implemented. At present, the Félix Aguilar Observatory (OAFA) of the University of San Juan (UNSJ) has a permanent staff of observers which now permits continuous solar monitoring. We expect that all these advances will allow to analyze chromospheric solar activity, especially solar flares, in more detail.

We present high temporal resolution observations of a Moreton wave event detected with the Hα Solar Telescope for Argentina (HASTA) in the Hα line 656.3 nm, on December 6, 2006. The aim is to contribute to the discussion about the nature and triggering mechanisms of Moreton wave events. We describe the HASTA telescope capabilities and the observational techniques. We carried out a detailed analysis to determine the flare onset, the radiant point location, the kinematics of the disturbance and the activation time of two distant filaments. We used a 2D reconstruction of the HASTA and corresponding TRACE observations, together with conventional techniques, to analyze the probable origin of the phenomenon. Results. The kinematic parameters and the probable onset time of the Moreton wave event are determined. A small-scale ejectum and the winking of two remote filaments are analyzed to discuss their relation with the Moreton disturbance. The analysis of the Moreton wave event favors the hypothesis that the phenomenon can be described as the chromospheric imprint of a single fast coronal shock triggered from a single source in association with a coronal mass ejection. Its onset time is concurrent with a Lorentz force peak measured in the photosphere, as stated by other authors. However, the existence of multiple shock waves that were generated almost simultaneously cannot be discarded. Fil: Francile, Carlos Natale. Universidad Nacional de San Juan. Observatorio Astronómico Félix Aguilar; Argentina Fil: Costa, Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina Fil: Luoni, Maria Luisa. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Elaskar, Sergio Amado. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

As part of the new German-Argentinian Solar-Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA: Mirror Coronagraph for Argentina) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges, corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way it is a good complement for the LASCO-C1 instrument. We present a brief review of the characteristics of the instrument, and some recent observations.

As part of the new German-Argentinian Solar Observatory in El Leoncito, San Juan, Argentina, a new ground-based solar telescope (MICA) began to operate in August 1997. MICA is an advanced mirror coronagraph, its design being an almost exact copy of the LASCO-C1 instrument. Since its installation, it has been imaging the inner solar corona (1.05 to 2.0 solar radii) in two spectral ranges corresponding to the emission lines of the Fe XIV and Fe X ions. The instrument can image the corona as fast as every minute. Thus, it is ideally suited to study fast processes in the inner corona. In this way, it is a good complement for the LASCO-C 1 instrument. After a brief review of the instrument, we present some recent observations showing the capabilities of the instrument.