New Sunspot Catalog to Enhance Area Climate Forecasts – Watts Up With That?


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Scientists from the University of Graz, the Kanzelhöhe Observatory, Skoltech and the World Data Center SILSO at the Royal Observatory of Belgium have presented the catalog of hemispherical sunspot numbers. It will enable more accurate predictions of the solar cycle and space weather, which can affect man-made infrastructure both on Earth and in orbit. The study was published in the journal Astronomy & Astrophysics, and the catalog is available from SILSO – the World Data Center for the production, maintenance and dissemination of the international sunspot number.

Our sun is a large boiling sphere of gas, most of which are so hot that electrons are torn from atoms, creating a circulating mixture of charged particles known as plasma. These moving charges give the sun an enormous magnetic field, which is bundled when it rises from the interior of the sun and creates dark areas, so-called sunspots, on the surface.

Sunspots are the main sources of solar flares and coronal mass ejections, or CMEs. These are huge magnetic plasma clouds that are released from the sun at great speed. When directed at the earth, they cause strong magnetic interference that can damage satellite equipment, paralyze telecommunications and even cause power outages in a city – with devastating economic effects.

The appearance and disappearance of sunspots varies over an approximately 11-year cycle. It starts with almost no sunspots. In the further course more and more spots appear in the middle latitudes and migrate to the solar equator. Since the sun’s equator rotates faster than the poles, its magnetic field is entangled and strengthened to form bundles in the course of the cycle. Eventually, the field line bundles become strong enough to be pushed out as loops through the photosphere, trapping and ejecting plasma as CME.

Sunspot monitoring is therefore critical to predicting dangerous space weather events and their impact on air travelers, astronauts, and equipment and infrastructure – both on Earth, in orbit and on long-term space missions.

Originally observed by Galileo in the 17th century, today sunspots are observed daily by around 80 observatories around the world. The World Data Center SILSO at the Royal Observatory of Belgium is the global hub for all sunspot data. Systematic data on the total number of sunspots are available from the 18th century. However, newer models suggest that solar activity is better understood as an interplay between the separately considered activities in the northern and southern hemispheres. Such data are much rarer because the most important solar activity index – the International Sunspot Number – has only recorded sunspots by hemisphere since 1992.

The authors of the current study in Astronomy & Astrophysics have developed a method to significantly expand the available data by reconstructing historical hemispherical sunspot numbers. As a result, they published a continuous catalog of daily and monthly data on sunspot numbers for the northern and southern hemispheres, dating back to 1874. The team showed its high agreement with the existing hemispheric data and showed that the predictions of the solar cycle are actually more accurate if the sunspot numbers are considered separately for the two hemispheres.

“Our sun is a fascinating star and its physics are both simple and complicated. We have learned from our study that we can better understand the long-term development of solar activity by simply treating the two hemispheres separately first and only then adding up the two contributions to get the total activity. The newly reconstructed data on the number of hemispherical sunspots will be available to the scientific community and we believe that they can provide an important basis for the development of new, more accurate prediction schemes for solar activity, ”said Astrid Veronig, first author of the study, professor at the University of Graz and head of the observatory for solar and environmental research Kanzelhöhe.

Shantanu Jain, PhD student and co-author of Skoltech, highlighted the practicality of the new catalog: “We believe that this new catalog will be essential for accurately predicting space weather as we now have continuous hemispherical data over a longer period of time, to create a meaningful solar cycle. ”Predictions. If we were faced with extreme solar flares in today’s age of technological dependence, our power grids, satellite communications, and the Internet could easily fail, causing economic losses of up to trillion dollars. An accurate forecast of space weather can help prepare us and avoid such a scenario. “

“For permanent technical infrastructures, for long-term issues such as ozone depletion or climate and with regard to future manned long-term missions to the moon or Mars, there is a growing need for medium and long-term trend forecasts.” As part of an emerging discipline called “space climate”, such long-term predictions of the strength of the solar cycle can only be based on detailed knowledge of the actual development of many past solar cycles. Our new extended data series is one of the most important steps in the growing efforts to revise and fully utilize legacy data collections with the modern tools of the 21st century, ”commented the co-author of the study and head of the World Data Center SILSO Frédéric Clette.

“At the moment we don’t fully understand how the solar dynamo works and how the solar magnetic field is generated during the 11-year solar cycle. All planets in our solar system orbit the sun in what is known as an ecliptic plane. This means that observatories on earth or instruments on board an orbiting satellite that take pictures of the sun never really see what is happening at the solar poles. However, in February 2020, a groundbreaking space mission – the Solar Orbiter – was launched to fly very close to the Sun. It will perform gravitational maneuvers to get out of the ecliptic and get a glimpse of the poles for the first time in history. The first polar pass is expected to take place in March 2025, with the spacecraft tilting 17 degrees above the ecliptic plane and rising to 33 degrees in July 2029. We think that the newly developed product of hemispherical sunspot numbers along with the unprecedented observations and fundamentally new insights from the Solar Orbiter will help us advance solar cycle studies and space weather forecasting. And whatever storms may be raging, we wish everyone good weather in space, ”said Tatiana Podladchikova, co-author of the paper and assistant professor at the Skoltech Space Center.



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