This paper presents the results of the analysis of geomagnetic effects of solar flares (sfe) recorded at Ebre observatory (40.8° latitude N, 0.5° longitude E) during 33 years (1953‐1985). At Ebre, located near the focus latitude, two types of sfe can be observed: regular and reversed sfe. Regular sfe are those which have phase differences less than 90° with the regular diurnal magnetic variation of the day, SR. Reversed sfe are those which have phase differences greater than 90° with SR. From these 33 years, 140 sfe events were selected and a statistical study was performed. We found a local time dependence of the phase differences between the sfe and SR vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90°, concentrate between 10 and 12 hours. Reversed sfe show a dominant equinoctial character. Also, a weaker correlation was found between solar activity with reversed sfe (r=0.47) than with regular sfe (r=0.68). Using data from 67 observatories, we performed a global study of a sfe case, seen at Ebre as reversed sfe. In this case, in the northern hemisphere, the sfe system was about 1 hour of local time eastward of the SR system and formed 4° higher in latitude. Finally, we present a model of two elliptical ionospheric equivalent current systems with focus offset about 1 hour in local time to explain the phase difference between the sfe and Sq magnetic vectors observed at Ebre. The parameters of this model have been fitted from the results of a previous statistical analysis from Ebre data. Spatial and temporal distribution of the sfe and Sq vector phases are calculated with this model, and conditions for reversed sfe occurrence are predicted.

Sunspots are solar features located in active regions of the Sun, whose number is an indicator of the Sun's magnetic activity. Therefore accurate detection and classification of sunspots are fundamental for the elaboration of solar activity indices such as the Wolf number. However, irregularities in the shape of the sunspots and their variable intensity and contrast with the surroundings, make their automated detection from digital images difficult. Here, we present a morphological tool that has allowed us to construct a simple and automatic procedure to treat digital photographs obtained from a solar telescope, and to extract the main features of sunspots. Comparing the solar indices computed with our algorithm against those obtained with the previous method exhibit an obvious improvement. A favorable comparison of the Wolf sunspot number time series obtained with our methodology and from other reference observatories is also presented. Finally, we compare our sunspot and group detection to that of other observatories.

The interval 4-10 September 2017 was one of the most flare-productive periods of the solar cycle 24, producing strong-to-severe space weather episodes. Thus, on 6 September, the solar active region AR 30023 produced an X-9 level flare. The arrival of the associated coronal mass ejection produced severe geomagnetic storming on 7 and 8 September, preceded by two significant solar flare effects (Sfe) that could be seen in the lit hemisphere. In this article, we analyze the impact of these flares on the ionosphere as registered on the vertical incidence ionospheric sounder located at Ebre Observatory. We put the emphasis on the use of this instrument to detect solar flares by means of the absorption observed in its ionograms. We also analyze the impacts of these flares on the Earth's magnetic field and the temporal evolution of the second Sfe event using the technique of spherical elementary current systems, which allows tracing in detail the current system evolution during the Sfe lifetime. As expected, a sharp increase in current intensities occurred at the beginning. The peak of the disturbance was reached after a few minutes, when hard X-rays were dominant, while a slow decay followed the advent of soft X-rays and EUV rays. The modeled current systems appear abnormally displaced in longitude with respect to the subsolar point. The northern vortex shows up about 2 hr in advance of the subsolar point meridian, while the southern vortex is about 3 hr behind it. Both remain static, showing no significant shift over the whole episode. Although the event occurred during the equinox, a clear prevalence of the Northern Hemisphere was observed.Tracing the temporal evolution of the currents producing Sfe was already attempted by some authors (Van Sabben, 1961;Veldkamp & van Sabben, 1960). With a limited number of observatories, they only achieved CURTO ET AL.

[1] The solar eclipse of 11 August 1999 was total along a belt crossing Central Europe, where there is a high density of magnetic observatories. We studied the transient geomagnetic effects produced by the temporary cutoff of the ionizing solar radiations during the eclipse. It is the first case in which the phenomenon has been analysed in a multisite context. For observatories along the umbra path, a model based on the equivalent electric current schema is proposed.

Solar flare effects (Sfe) are rapid variations in the Earth’s magnetic field and are related to the enhancement of the amount of radiation produced during Solar flare events. They mainly appear in the Earth’s sunlit hemisphere at the same time as the flare observation and have a crochet-like shape. Much progress has been made since Carrington’s first observations in 1859 which are considered to represent the first direct evidence of the connection between the Sun and the Earth’s environment but there is still much to discover. In this paper, we review state-of-the-art developments and the advances made in the knowledge concerning Sfe phenomena while also looking at the challenges that lie ahead. First, we offer a historical approach with a comprehensive description that allows for a better understanding of the main characteristics of Sfe. This frames specific topics like the puzzling reversed-Sfe or the nighttime Sfe. The role played by the Service of Rapid Magnetic variations (SRMV) is also assessed, followed by a discussion of the main current limiting factors in the process of detection and proposed ways to overcome challenges such as by creating an automatic detection method. The paper clarifies some aspects related to the geo-effectiveness of the solar flares producing magnetic disturbances. The importance of the global modelling studies covering critical aspects needed to understand this Sun–Earth system is assessed. Also, we provide an overview of the temporal evolution of the electric currents producing Sfe. The importance of key subjects such as the dynamic aspects of Sfe is developed in another section. Finally, estimations of the size of large flares using ionospheric and magnetic data are reviewed as well as the prospects of these large flare events putting technological systems in danger.