The Massive Solar Storm of June 1st Caused the Largest Forbush Decline on Earth in the Past 20 Years

Not all solar storms are created equal, and some can produce effects that are often overlooked, such as the massive Forbush storm that hit Earth on June 1, the largest in 20 years.

solar storm hitting Earth
Earth was struck by a coronal mass ejection that drastically reduced the number of galactic cosmic rays reaching our planet.

The solar storm on June 1st produced a rather strange effect known as the “Forbush decrease.”

This effect is named after American physicist Scott Forbush, who discovered and theorized this particular phenomenon in 1937. It refers to a rapid decrease in the intensity of galactic cosmic rays observed following a coronal mass ejection (CME).

A coronal mass ejection is a significant release of material, or plasma, from the solar corona into the heliosphere. This phenomenon is usually associated with other solar activity events like flares.

Technically speaking, one might think that increased solar activity should always result in more cosmic rays, but that's not always the case—as seen on June 1st.

The Strange "Forbush Decrease"

More precisely, we can define the Forbush effect as a sudden decrease in cosmic rays of more than 20%, lasting from a few hours to several weeks. This drop is usually caused by sudden intensifications of the solar wind due to solar flares or coronal mass ejections.

This phenomenon typically occurs during periods of intense solar activity, and as we know, the peak of the 11-year solar cycle occurred at the end of 2024.

But why do fewer cosmic rays reach Earth when solar activity increases?

Solar storm
The Forbush effect often occurs alongside intensified solar activity.

We know that when solar activity increases, the solar wind also intensifies—this is the stream of charged particles emitted by the Sun’s upper atmosphere. These moving charged particles, mainly protons and electrons, generate a magnetic field that can deflect some galactic cosmic rays away from Earth.

The recent Forbush decrease was also the largest drop in cosmic radiation recorded in the last 20 years. In fact, the Oulu Cosmic Ray Station in Finland measured a 25% decrease in cosmic rays.

The last coronal mass ejection to trigger such an intense Forbush effect occurred on October 30, 2003.

Studying this phenomenon and galactic cosmic rays in general is crucial; in fact, these radiations pose the greatest health risk to astronauts, making it essential to understand them thoroughly.

We Could Turn This Phenomenon to our Advantage

Ideally, this rare phenomenon could be used in future space missions to help reduce radiation exposure for astronauts. It's important to know that just one day in space exposes someone to the same amount of radiation as a full year on Earth.

However, it’s important to note that this cosmic ray decrease was measured on Earth—satellites in orbit may not have been so lucky.

Currently, our planet is still experiencing the ongoing Forbush decrease, which is expected to fade in about one to two weeks, when cosmic radiation levels return to normal.

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