Why was the expected northern lights a bust? :: WRAL.com

While observers in Iceland along with parts of Northern Europe and Russia enjoyed the Northern Lights, Thursday’s X-Class solar eruption and Coronal Mass Ejection (CME) of charged particles thrown into space failed to put the show further south.

Why was this predicted G3 geomagnetic storm a bust?

Not unlike predicting how much snow a winter storm can bring, forecasters at NOAA’s Space Weather Prediction Center work with many variables, and each of them must line up just exactly to produce a significant event. This had several variables: the magnetic strength and polarity of the solar wind along with a small increase in the solar wind, indicating that Coronal Mass Ejections (CMEs) had reached Earth. None were significant enough to produce northern lights.

The effects of CME – which are large expulsions of plasma and magnetic fields from the Sun’s corona – reached Earth around 1 p.m. 6 EDT Halloween morning.

CME reached the level of a G1 geomagnetic storm, but was also close to sunrise to be visible throughout the United States.

2021 Halloween Geomagnetic Storm failed to produce significant aurora borealis

The effects were also too weak for the charged particles to reach deeper into the Earth’s magnetic field and enable interactions with air molecules high up in the upper atmosphere, creating the light of green, blue and red colors.

There are a number of elements to a geomagnetic storm that must line up to create the spectacular northern lights you see in pictures. Each of these measurements showed only minor changes as particles from Thursday’s CME passed NOAA’s DISCOVR probe located 1.5 million km away between Earth and the Sun.

Polarity (Bz)

The sun’s magnetic field, heliophysicists call it the Interplanetary Magnetic Field (IMF), was pointed to the right path to create northern lights. The Sun’s interplanetary magnetic field (IMF) pointed south (negative Bz), allowing it to connect better with the Earth’s more northerly magnetic field, allowing the solar wind to flow more freely into the upper atmosphere.

Like bar magnets or the magnets on your refrigerator, the Sun’s and Earth’s magnetic fields have an orientation. And like the smaller magnets, these large magnets can connect north to south, positive to negative.

This measurement went in the right direction to encourage charged particles to flow along magnetic field lines and collide with air molecules high in the upper atmosphere and create light displays of green, blue and red colors, it was not strong enough to reach deep into the Earth magnetic field should be further south into the lower 48 states.

Aurora is formed when charged particles flow in

Strength (Bt)

The sun’s magnetic field is about as strong as the magnets on your refrigerator (~ 50 gauss), Earth’s is about 100 times weaker. The higher the strength of the magnetic field in the solar wind when it reaches the Earth, the more intense the Northern Lights activity.

The weekend’s geomagnetic storm had only a small increase in this measurement.

Density

There was a slight increase in the density of the solar wind, a good indicator that CME had arrived. But this was also too small to have a significant effect.

Velocity

This is where you can see CME in the data. Where the speed of the solar wind suddenly increases for a period and then decreases again. NOAA estimates that CME left the Sun at 973 km / sec. This morning’s increase of only about 20-30 km / sec. indicates that the Earth received only a glance, and most of the CMEs missed us completely.

Taken together, these measurements suggest that this CME only produced a glimpse of the Earth, not the direct, stronger hit from previous geomagnetic storms such as …

Halloween 2003 Geomagnetic Storms

Compare DISCOVR measurements from Halloween 2021’s G1 geomagnetic storm with 2003’s G5 geomagnetic storm, which is visible from California to Texas to Florida, you can see how different the two storms were.

Halloween geomagnetic storms in 2003 and 2021 compared

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