How much does the sun influence our daily or monthly weather, climate, and meteorological events like lightning? Surprisingly, a new study found the answers to this question in a set of diaries dating back to the 1700s.
A collaborative research team from several universities in Japan and the National Institute of Polar Research set out to better understand the sun’s impact on terrestrial weather, and the results were published in the journal Annales Geophysicae.
Solar activity, like the sun’s rotation, increases the number of ultraviolet rays on Earth, but it is not well understood how this activity impacts weather.
“It is well known that long-term–centennial to millennial-scale–variations of solar activity influences terrestrial climate,” said Hiroko Miyahara, first author on the paper. “However, it is not well established whether the sun influences the daily or monthly weather.”
Every 27 days, the sun rotates on its axis and when areas of high solar activity like sunspots turn to face the Earth, ultraviolet rays increase. The researchers examined a set of diaries that were kept for more 150 years to see if the sun’s rotation correlated with an increase in lightning and other weather events.
The first diary, “Diary of Ishikawa Family,” was kept by a farm family in Hachioji, Japan and the second diary was kept by civil servants from Hirosaki.
The researchers read through the daily logs to find any reference to thunder and lightning between May and September and found an increase in meteorological activity every 24 to 31 days.
This time frame matches the rotational period of the sun’s axis and shows that sunspots and high solar activity influence lightning on Earth.
“The cyclic behavior of the sun is playing a very important role in the changes of weather in Japan,” said Miyahara.
The researchers plan to continue their research on solar influences on meteorological events and hope to one day find a way to include solar activity in weather forecasts.
“It would improve the accuracy of the forecast, and it may even enable a longer-term weather forecast,” said Miyahara.