In Pursuit of the Northern Lights

The Science Behind the Northern Lights

The Northern Lights, or Aurora Borealis, are one of the most awe-inspiring natural phenomena on Earth. Whilst catching sight of them requires patience and a bit of luck, understanding the science and data behind auroral activity can dramatically improve your chances of seeing them. This fact sheet explains how to interpret the key metrics for predicting auroras and highlights some common mistakes made by chasers who rely too heavily on apps without understanding the full picture.

Key Metrics for Aurora Prediction

1. Auroral Electrojet Index (AE):

   The AE index measures magnetic activity in the auroral zone, showing the strength of ionospheric currents that contribute to auroras.

   • AE ≤ 100 nT: Little or no auroral activity.
   • AE 100 – 500 nT: Moderate auroras possible in higher latitudes (near the poles).
   • AE 500 – 1000 nT: Strong auroras may be visible in mid-latitude regions.
   • AE > 1000 nT: Intense activity, auroras likely visible much farther south.

   Key takeaway: Look for AE values above 500 nT for a good chance of auroras.

2. Kp Index:

   A global measure of geomagnetic storm strength, ranging from 0 to 9.

   • Kp 0 – 1: Little activity, auroras confined to polar regions.
   • Kp 2 – 3: Minor activity, visible in northernmost latitudes.
   • Kp 4 – 5: Active, potential for auroras in northern U.S., Canada, and northern U.K.
   • Kp 6 – 9: Strong storms, auroras visible in mid-latitude or even lower-latitude regions.

   Key takeaway: A Kp value of 4 or higher suggests strong auroral activity, but don’t rely on this number alone.

3. Solar Wind Speed and Density:

   The solar wind is a stream of charged particles from the Sun that interact with Earth’s magnetic field to produce auroras.

   • Solar Wind Speed:
   • 300 – 400 km/s: Minimal auroral activity.
   • 400 – 500 km/s: Moderate auroral chances.
   • 500+ km/s: High likelihood of auroras.
   • Solar Wind Density: 6+ particles/cm³: Better chances for auroral displays.

   Key takeaway: High wind speeds (500+ km/s) and moderate-to-high density boost the chances of auroras.

4. Bz Component of the Interplanetary Magnetic Field (IMF):

   The Bz component indicates the orientation of the solar wind’s magnetic field. A negative Bz allows for greater interaction with Earth’s magnetic field, increasing auroral activity.

   • Bz positive: Less favorable for auroras.
   • Bz negative: Favorable for auroras, especially with high solar wind speeds.

   Key takeaway: When Bz is negative, your chances of seeing auroras significantly improve.

Additional Factors to Consider

• Cloud Cover and Local Weather: Even with strong auroral activity, overcast skies will block the view. Always check weather forecasts for clear skies.
• Moon Phase: A bright moon can wash out weaker auroras. Aim for new moon periods for optimal viewing conditions.
• Light Pollution: Urban areas reduce visibility. Head to dark-sky areas for the best results.

Common Mistakes of Aurora Chasers

1. Over-reliance on the Kp Index: While useful, the Kp Index isn’t the sole predictor of auroras. Consider other metrics, such as AE, Bz, and local conditions.
2. Chasing Instead of Waiting: Constantly driving around can result in missed opportunities. Find a dark, clear location and wait patiently.
3. Ignoring Local Weather: Even the best space weather data won’t help if there’s heavy cloud cover. Check forecasts beforehand.

Join the 2025 Great Aurora Hunt

Let Andy Keen and his expert team guide you on an unforgettable journey into Swedish Lapland. With years of experience and an unparalleled understanding of auroral activity, they’ll ensure you have the best chance to witness and photograph the magic of the Northern Lights.

Find out more and book your spot here.