Northern Lights Superstorm Video: Aurora, Kp and the March 2015 Storm

Curtains of green light ripple across the sky, their lower edges flaring pink as they twist and fold. This real-time aurora video, uploaded by Rumble Viral on 5 October 2015, was billed as footage of the northern lights during a geomagnetic "superstorm" in March 2015, the month of the St Patrick's Day geomagnetic storm.

The St Patrick's Day storm of March 2015

On 17 March 2015, a cloud of solar material thrown out by the Sun two days earlier struck Earth's magnetic field and set off a G4, or "severe", geomagnetic storm. It became known as the St Patrick's Day storm, and it painted auroras far south of their usual range across North America, Europe and the Southern Hemisphere. NOAA's Space Weather Prediction Center later cited it as an example of a large storm that disrupted precise satellite-positioning users.

The uploader's description calls the footage real-time, links it to March 2015 and describes the activity as Kp 9. Near the end of the clip a brief streak, which the uploader identifies as a shooting star, crosses the scene.

What the Kp index and G scale measure

The Kp index measures disturbance in Earth's magnetic field on a scale from 0 to 9, and NOAA converts the top of that range into five storm levels:

• G1 (minor), Kp 5: about 1,700 times per 11-year solar cycle; aurora as far south as northern Michigan and Maine.
• G2 (moderate), Kp 6: about 600 per cycle; aurora down to New York and Idaho.
• G3 (strong), Kp 7: about 200 per cycle; aurora down to Illinois and Oregon.
• G4 (severe), Kp 8 to 9-: about 100 per cycle; aurora down to Alabama and northern California.
• G5 (extreme), Kp 9: about four per cycle; aurora seen as far south as Florida and southern Texas.

NOAA classes the 17 March 2015 event as G4. The scale tracks the magnetic disturbance, which is why the most colourful displays on camera do not always line up with the highest numbers.

Why the aurora is green, pink and red

Auroras form when charged particles from the Sun, funnelled by Earth's magnetic field towards the polar regions, collide with gases in the upper atmosphere. Each gas glows in its own colours. Atomic oxygen gives the familiar bright green at lower altitudes and a deep red (630 nm) at the very top of the display, where collisions are rare. Nitrogen adds blue and purple, and where red and green light mix, the eye sees the pink tones visible in this video. During strong storms the curtains move fast, ripple and fold across the sky.

Tips for seeing the northern lights

• Go where the oval sits: northern Norway, Swedish and Finnish Lapland, Iceland, Yukon, the Northwest Territories and Alaska see auroras on most clear, dark nights in season.
• Pick the dark months: roughly September to March in the far north, when nights are long enough.
• Watch the forecasts: NOAA's Space Weather Prediction Center and national services publish Kp and aurora forecasts; clear skies matter as much as the index.
• Use a tripod: a wide lens, high ISO and exposures of a few seconds capture moving curtains without blurring them.

For more, see our Yellowknife aurora photo essay, or watch NRK’s whales-and-aurora film from northern Norway.

Related reading

• Ten Northern-Lights Regions: Geography, Darkness and Realistic Expectations
• Mike Taylor’s Maine Aurora Photography and a Change of Direction
• Sun Halos over Finland: Understanding Pauli Hänninen’s Photographs
• The Mountain: Seven Days of Sky Photography at Teide

Sources