Abstract:Our knowledge of the long-term evolution of solar activity and of its primary modulation, the 11-year cycle, largely depends on a single direct observational record: the visual sunspot counts that retrace the last 4 centuries, since the invention of the astronomical telescope. Currently, this activity index is available in two main forms: the International Sunspot Number initiated by R. Wolf in 1849 and the Group Number constructed more recently by Hoyt and Schatten (1998a,b). Unfortunately, those two series do not match by various aspects, inducing confusions and contradictions when used in crucial contemporary studies of the solar dynamo or of the solar forcing on the Earth climate. Recently, new efforts have been undertaken to diagnose and correct flaws and biases affecting both sunspot series, in the framework of a series of dedicated Sunspot Number Workshops. Here, we present a global overview of our current understanding of the sunspot number calibration.After retracing the construction of those two composite series, we present the new concepts and methods used to self-consistently re-calibrate the original sunspot series. While the early part of the sunspot record before 1800 is still characterized by large uncertainties due to poorly observed periods, the more recent sunspot numbers are mainly affected by three main inhomogeneities: in 1880-1915 for the Group Number and in 1947 and 1980-2014 for the Sunspot Number.After establishing those new corrections, we then consider the implications on our knowledge of solar activity over the last 400 years. The newly corrected series clearly indicates a progressive decline of solar activity before the onset of the Maunder Minimum, while the slowly rising trend of the activity after the Maunder Minimum is strongly reduced, suggesting that by the mid 18 th century, solar activity had already returned to levels equivalent to those observed in recent solar cycles in the 20 th century. We finally conclude with future prospects opened by this epochal revision of the Sunspot Number, the first one since Wolf himself, and its reconciliation with the Group Number, a long-awaited modernization that will feed solar cycle research into the 21 st century.

We describe a revised collection of the number of sunspot groups from 1610 to the present. This new collection is based on the work of Hoyt and Schatten (Solar Phys. 179, 189, 1998). The main changes are the elimination of a considerable number of observations during the Maunder Minimum (hereafter, MM) and the inclusion of several long series of observations. Numerous minor changes are also described. Moreover, we have calculated the active-day percentage during the MM from this new collection as a reliable index of the solar activity. Thus, the level of solar activity obtained in this work is greater than the level obtained using the original Hoyt and Schatten data, although it remains compatible with a grand minimum of solar activity. The new collection is available in digital format.Comment: 27 pages, 6 figures, accepted for publication in Solar Physic

Aims. Although the time of the Maunder minimum (1645-1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle #24. We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum. Methods. We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.Results. The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets. Conclusions. We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level.

Early observations of sunspot were realised by the naked eye. Possible utilization of these records for studying the long-term change in the Sun is discussed here. Other historical sunspot observations with camera obscuras are also discussed. Moreover, the best record of the behaviour of the Sun exists for the last four centuries thanks to the observations of sunspots with telescope. These observations should allow us to know the number, position, and area of sunspots as well as some relevant episodes (Maunder Minimum, optical flares, etc.). Rudolf Wolf developed the first reconstruction of solar activity in the 19th century. The next reconstruction was made by Hoyt and Schatten in 1998 by improving the database and using a new methodological approach. Here some mistakes, pending tasks and minor improvements are discussed.

Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with longterm solar activity evolution. Here we reconsider the current paradigm of the Grand minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636-1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60-70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.

Aims. The Maunder minimum (MM) of greatly reduced solar activity took place in 1645-1715, but the exact level of sunspot activity is uncertain because it is based, to a large extent, on historical generic statements of the absence of spots on the Sun. Using a conservative approach, we aim to assess the level and length of solar cycle during the MM on the basis of direct historical records by astronomers of that time. Methods. A database of the active and inactive days (days with and without recorded sunspots on the solar disc) is constructed for three models of different levels of conservatism (loose, optimum, and strict models) regarding generic no-spot records. We used the active day fraction to estimate the group sunspot number during the MM.

In this study trends in extreme rainfall over the Iberian Peninsula at a daily scale in the second half of the twentieth century have been detected and analyzed. For this goal 35 stations evenly distributed over the region of study covering the period 1958-97 have been studied. Two different approaches have been used. The first one consists of the nonparametric Mann-Kendall test and the Sen method. The second approach is based on the statistical theory of extreme values, involving time-dependent parameters in order to be able to reflect possible temporal changes in the frequency distribution. Results from both methods agree, confirming the reliability of the analysis. Negative trends are found for the west and southwest of the Iberian Peninsula in spring and winter. In autumn a spatial dipolar pattern appears, but trends are not so evident.

ABSTRACT:The year 1816 was characterized by unusual weather conditions, in particular, by a cold and wet summer season ('year without a summer') on both the European and North American continents. The eruption of Tambora, an active stratavolcano, on the Island of Sumbaya (Indonesia) in April 1815 has been identified as the main driving force for the strong 1816 temperature anomaly. This climate anomaly has been relatively well studied in central Europe, France, Scandinavia and the United Kingdom. The unusual unsettled weather and climate at mid-latitudes in 1816 and 1817 had major socioeconomic impacts, particularly in terms of a poor yield of agricultural production, malnutrition and consequentially an increased potential for diseases and epidemics. The Iberian Peninsula was also affected by the intense climate anomalies during those years. Documentary sources describe the impact that the cold and wet summer of 1816 had on agriculture, namely the bad quality of fruits, delayed ripening of vineyards and cereals.It is within this context that we stress the relevance of recently recovered meteorological observed data, from 1816 onwards, for stations located in Portugal (Lisbon) and also for a longer period for the Spanish stations of Madrid, Barcelona and San Fernando-Cadiz. We have compared observed (station-based) and large-scale reconstructed seasonal temperature anomalies computed for the winter and summer seasons after the eruption (1816-1818). There is qualitative agreement between the two independent data sets, though some stations partly indicate stronger departures from the long-term averages for single years compared to neighbouring grid points. In particular, all available stations reveal a cold summer of 1816, mainly in July and August. In comparison to the 1871-1900 reference period, those two months were 2-3°C cooler, close to what has been reported for central Europe. We also discuss the regional climate anomalies for those years (1816-1818) using independently reconstructed atmospheric circulation fields.