provided by the Icelandic MET office
How is the northern lights forecast done?
What are the northern lights?
Lets first have a quick glance at what they are so we will understand better how the northern lights forecast is done. The northern lights (aurora borealis) can be found both in the southern and the northern hemispheres and are a truly amazing natural phenomenon. The lights can rarely been seen outside of the polar areas but it can happen e.g. the lights have been seen down in the New York City. The southern lights have the name aurora australis. The sun is the origin of the auroras. On its surface solar activity ejects a cloud of gas, sometimes called coronal mass ejection (CME) by scientists. This cloud of gas takes normally 2-3 days to reach Earth´s magnetic field. When it collidies with this invisible field it causes complex changes to happen in the tail region of the field. Currents of charged particles are generated that flow then along the lines of the magnetic forces all the way into the Polar Regions. In the upper atmosphere these particles are boosted with energy, and when they collide with the oxygen and nitrogen atoms, the beautiful northern lights can be seen.
How are they monitored and expressed?
Satellites are the main tool for observing and monitoring the Sun and particles fluxes heading for Earth. Without them it would be difficult to do a reliable northern lights forecast. The National Oceanic and Athmospherice Admin of the USA (NOAA) operates couple of these, both for the back side and the front of the Sun. The satellites both generate images and have sensors for observing particle fluxes from the Sun. By using these observations we are able to create northern lights forecasts based on numerical simulations and forecast models. One of the most important element in these forecast models is that the Sun rotates about its axis in about 27 days, so any longer disturbances on the surface are repeated only every 27 days.
The above northern lights forecast from the Icelandic MET office is expressed on the quasi-logarithmic Kp-index as most other northern lights forecasts in the world. It is a numerical scale from 0 to 9. About 90% of the time it is 0-4 and very rarely reach 7-9 or only 1% of the time.
Key components of a northern lights forecast
The particles of the solar wind are traveling to the Earth at speeds of several hundred kilometers per sec.onds and it takes normally around 2-3 days to reach the Earth´s magnetic field. Using the satellites it is possible to predict major geomagnetic storms before they hit the Earth. As it get closer to the Earth the forecast becomes more reliable.
There are three key forecast models: a) 1-4 hours short term forecast, b) 3 days medium forecast and c) 2 weeks long term forecast.
1-4 hours short term forecast
This is the most reliable forecast and is based on particle flux from the Sun at the ACE-satellite. It hits the satellite approximately 1 hour before it hits Earth. Below is a sample image generated from the NOAA service via the Iceland MET office.
3 days medium forecast
The three day medium forecast can give rather good indications if there will be solar storms in the next 2-3 days or even within next 24 hours. Below is a sample image.
2 weeks long term forecast
In this forecast model you can see next 22 days.