A series of solar flares and fast solar wind streams are expected to stir up Earth’s magnetic field over the coming days, arriving at one of the best possible times for aurora chasers.
Geomagnetic storms are expected between March 20 and March 21 as a mix of incoming coronal mass ejections (CME) and high speed solar wind currents buffer the Earth’s magnetic field. NOAA’s Space Weather Prediction Center has issued a moderate (G2) geomagnetic storm watch through March 21, with a chance for conditions to briefly reach strong (G3) levels.
This means northern lights may spread further south than usual over the weekend, putting on a treat for mid-latitude skywatchers. What makes this event particularly exciting isn’t just the incoming space weather—it’s the timing.
Why spring equinox increases the northern lights
March 20 marks spring equinox in the Northern Hemisphere, a time known for increased geomagnetic activity and aurora borealis. Around both the spring and autumn equinoxes, the Earth’s orientation in space allows its magnetic field to interact more effectively with the solar wind. This seasonal boost is known as the Russell-McPherron effect.
What is the Russell-McPherron effect?
First described in 1973 by geophysicists Christophere Russell and Robert McPherron, the effect explains why geomagnetic storms – and the aurora displays they can trigger – tend to peak around the equinoxes.
At this time of year, the sun shining right above Earth‘s equator, giving almost equal day and night all over the world. The Earth is tilted on its axis by about 23.5 degrees, and as it orbits the Sun, this tilt changes how the planet’s magnetic field is oriented in space.
This seasonal shift brings Earth’s magnetic field into a more favorable alignment with the magnetic field carried by the solar wind and incoming CMEs – making it easier for energy to transfer into our magnetosphere.
Why timing can make storms stronger
With more energy directed into the Earth’s magnetosphere, geomagnetic storms become more likely and often more intense.
To put it simply, the same burst of solar activity can have a greater impact around the equinoxes than it would at other times of the year. That’s why March and September are often considered the best months to catch the Northern Lights. With several CMEs potentially hitting Earth along with a high-speed solar wind stream this week, conditions are already primed for geomagnetic unrest. Add in the seasonal lift from the Russell-McPherron effect and we could be in for a real treat tonight and into the weekend!
However, northern lights can be fickle creatures, so it’s possible that despite the seemingly perfect conditions, we could end up with a lackluster show.
The intensity and spread of aurora depends on how incoming solar flares interact with the Earth’s magnetic field. A key factor is the direction of the magnetic field carried by the solar wind – known as the interplanetary magnetic field. If it points south, it can more easily connect to the Earth’s north-pointing field, allowing more energy to flow in and supercharge the aurora borealis. If it points north, the Earth’s magnetic field can act more like a closed door, limiting how much energy gets through.
That said, conditions can change quickly, so make sure you’ve charged your cameras and turned on the Northern Lights!
