Long Data: Predicting Solar Storms

As Samuel Arbesman’s recent article on Long Data might suggest, all the data in the world on the Sun’s activities today can’t tell us what it will do tomorrow. But careful observation over the last several centuries has allowed us to develop a predictive understanding of the patterns in solar storm activity.  This collection of long data and the insights it provides won’t guarantee you only see ads that are relevant to you, but it does keep our global electrical and telecommunications infrastructure running.

Long Now intern Sandy Curth writes:

Researchers at NASA’s Marshall Space Flight Center recently posted their solar cycle predictions for 02013. This coming fall is predicted to be the peak of the twenty-fourth 11- year sunspot cycle on record. Though that might sound scary, this peak is actually anticipated to be the lowest since 01906. While the expected solar activity and its impacts for this year aren’t likely to break many records, the source of these predictions is an exceptional example of long term thinking with data stretching back over 350 years.

Since the start of the 18th century, astronomers have been consistently noting the number of spots on the sun, with records of sunspot observation dating back to 364BCE in the star catalogue of Chinese astronomer Gan De. Belgium’s Solar Influences Data Analysis Center offer sunspot data yearly from 01700, monthly from 01750 and daily beginning in 01874. Modern solar predictions are created by analyzing trends in this data and measuring activity in the Earths magnetic field caused by the sun.

NASA solar physicist Dr. David Hathaway explains the details:

A number of techniques are used to predict the amplitude of a cycle during the time near and before sunspot minimum. Relationships have been found between the size of the next cycle maximum and the length of the previous cycle, the level of activity at sunspot minimum, and the size of the previous cycle.

Among the most reliable techniques are those that use the measurements of changes in the Earth’s magnetic field at, and before, sunspot minimum. These changes in the Earth’s magnetic field are known to be caused by solar storms but the precise connections between them and future solar activity levels is still uncertain.

Another indicator of the level of solar activity is the flux of radio emission from the Sun at a wavelength of 10.7 cm (2.8 GHz frequency). This flux has been measured daily since 1947. It is an important indicator of solar activity because it tends to follow the changes in the solar ultraviolet that influence the Earth’s upper atmosphere and ionosphere. Many models of the upper atmosphere use the 10.7 cm flux (F10.7) as input to determine atmospheric densities and satellite drag.

Predicting the behavior of a sunspot cycle is fairly reliable once the cycle is well underway (about 3 years after the minimum in sunspot number occurs [see Hathaway, Wilson, and Reichmann Solar Physics; 151, 177 (1994)]). Prior to that time the predictions are less reliable but nonetheless equally as important. Planning for satellite orbits and space missions often require knowledge of solar activity levels years in advance.

Even though many of the Sun’s systems are still a mystery, scientists are able to predict its activity well enough to keep our communication satellites on track and give us time to prepare for powerful geomagnetic storms that can black out whole cities.

The first solar storm recorded was in September of 01859 and reportedly caused major failures in the world’s developing telegraph system and auroras as far south as the Caribbean. More recently, a less severe storm in 01989 left six million Canadians without power for nine hours. Predicting the next major solar event is becoming as important to maintaining our infrastructure as predicting the next hurricane.

Taking the past seriously is a clear route to a good prediction, but having the presence of mind to collect seemingly useless data to make predictions easier for future thinkers is worth contemplating. Astronomers centuries ago did not have tangible applications for the data they recorded on the sun. Luckily, though, they took the time to carefully collect and compile what they could see so that today, as scientists realize the potentially devastating impact of a severe solar storm, their data becomes priceless.

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