Historical aurora borealis catalog for Anatolia and Constantinople (hABcAC) during the Eastern Roman Empire period: implications for past solar activity

Herein, Anatolian aurorae are reviewed based on the existing catalogs to establish a relationship between the aurora observations and past solar activity during the Medieval period. For this purpose, historical aurora catalogs for Constantinople and Anatolia are compiled based on the existing catalogs and compared with those in the Middle East region. The available catalogs in the literature are mostly related to the records observed in Europe, Japan, China, Russia, and the Middle East. There is no study dealing only with the historical aurora observations recorded in Anatolia and Constantinople. The data of the catalog show that there is a considerable relationship between the aurora activity and past strong solar activity. High auroral activity around the extreme solar particle storm in 774/775 and the Medieval grand maximum in the 1100s in Anatolia and the Middle East is quite consistent with the past solar variability reported in other scientific literature.

Grand minima of solar activity during the last millennia

In this review we discuss the occurrence and statistical properties of Grand minima based on the available data covering the last millennia. In particular, we consider the historical record of sunspot numbers covering the last 400 years as well as records of cosmogenic isotopes in natural terrestrial archives, used to reconstruct solar activity for up to the last 11.5 millennia, i.e. throughout the Holocene. Using a reconstruction of solar activity from cosmogenic isotope data, we analyze statistics of the occurrence of Grand minima. We find that: the Sun spends about most of the time at moderate activity, 1/6 in a Grand minimum and some time also in a Grand maximum state; Occurrence of Grand minima is not a result of long-term cyclic variations but is defined by stochastic/chaotic processes; There is a tendency for Grand minima to cluster with the recurrence rate of roughly 2000-3000 years, with a weak ≈210-yr periodicity existing within the clusters. Grand minima occur of two different types: shorter than 100 years (Maunder-type) and long ≈150 years (Spörer-type). It is also discussed that solar cycles (most possibly not sunspots cycle) could exist during the Grand minima, perhaps with stretched length and asymmetric sunspot latitudinal distribution.These results set new observational constraints on long-term solar and stellar dynamo models.

How well do we know the sunspot number?

We show that only two adjustments are necessary to harmonize the Group Sunspot Number with the Zürich Sunspot Number. The latter has been increased from the 1940s on to the present by 20% due to weighting of sunspot counts according to size of the spots and can be corrected by increasing the earlier values as well. The Group Sunspot Number before ~1885 is too low by ~50%. With these adjustments a single sunspot number series results. Of note is that there is no longer a distinct Modern Grand Maximum.

Solar activity and its influence on climate

Solar activity, as manifested by its many equatorial as well as high-latitude components of short-term variability is regulated by the Sun’s dynamo. This constitutes an intricate interplay between the solar toroidal and poloidal magnetic field components. The dynamo originates in the tachocline, which is a thin layer situated about 200,000 km beneath the solar surface. The dynamo is a non-linear system with deterministic chaotic elements, hence in principle unpredictable. Yet there are regularities in the past behaviour, such as the Grand Maxima (example: the recent high maximum of the 2nd half of the 20th century) the Grand Minima (e.g. the Maunder Minimum between 1650 and 1710) and the Regular Oscillations such as those between 1730 and 1923. Their occurrences are described by a phase diagram in which a specific point can be identified: the Transition Point. This diagram plays an essential role in determining the future solar activity. Guided by its quasi-regularities and by recent measurements of the solar magnetic fields we find that the Sun is presently undergoing a transition between the past Grand Maximum and a forthcoming period of Regular Oscillations. We forecast that this latter period will start in a few years and will continue for at least one Gleissberg cycle and that the next solar maximum (expected for 2014) will be low (Rmax ~ 68).We discuss the heliospheric drivers of Sun-climate interaction and find that the low-latitude magnetic regions contribute most to tropospheric temperatures but that also the influence of the - so far always neglected - polar activity is significant. Subtraction of these components from the observed temperatures of the past 400 years shows a residual series of relative peaks and dips in the temperature. These tops and lows last for periods of the order of the Gleissberg cycle. One of these is the recent period of global warming, which, from this point of view, is not an exceptional period.