Finnish Aurora Observers Homepage

Aurora is a visual phenomena resulting from solar wind particles colliding with Earth's atmosphere. The light comes from the emissions of atmospheric atoms and molecules excited by collisions of solar particles at heights ranging from 70 to 1000 km. The solar particles are being captured by Earth's magnetic field, accelerated to high energy levels before hitting molecules and atoms of upper atmosphere, forming large Auroral ovals around both magnetic poles. 

Auroral displays are visually awesome to witness and all the more active events appear to be always different, than the ones seen before due to vast combination of forms and colours and their combinations. 

In winter time, Aurora is almost a nightly phenomena for people living in Lapland and it is no surprise the natives rarely pay much attention to it. For other Finns living in the mid- or southern parts of our country (or for the tourists), an active blazing Auroral display is always an exiting but unfortunately more rare experience. Sometimes warnings of Auroras and the strongest evening time Auroral displays may make it to TV news and on newspapers.

Why are Auroras so often seen in Finland?

During quiet geomagnetic conditions the Auroral oval remains dim, some 2500 km in diameter and is lies mostly over uninhabited Arctic areas. If a solar mass ejection occurs whose particles collide with Earth, the substantial increase in solar wind particle's flow and speed causes the Earth's magnetic field to become more and more compressed, expanding the Auroral oval over lower latitudes. This condition  correlates with geomagnetic indices, such as the 3 hour Kp-index. The chart below shows oval's  expansion as Kp-index reaches higher values. Auroras can be seen in the northern horizon at Kp values, which are lower by 1 to 3, than what is required to see it at zenith.

Kp-index vs. approximate southern edge of Aurora; the Aurora reaches observers zenith.

Since Scandinavia is located close to the oval, on the auroral and sub-auroral zone, Auroras (or Northern Lights) are an ideal and obvious observing object also for the Finnish amateur astronomers. While high latitude is a necessity to see any Aurora, in here the summer light suspends visual observing of Aurora from the end of April, till early August (only few brighter stars can be seen at midnight in Helsinki in June and the situation gets worse towards higher latitudes). The weather in Finland is often cloudy from late fall, to mid winter, but fortunately skies are more often clear near equinoxes, just when Auroras are more likely due to more favourable orientation of the Earth's magnetic field. 

The opportunities to see Auroras differ clearly between northern- and southern parts of Finland and there are some differences in the forms and activity also. While in the very northern parts of Finland, the number of Auroral displays may raise up to 200 per year (two nights out of three), on the southern coast, the number of fair displays remain less than 20/a. The frequency of Auroral display appearances depends up on solar activity, that varies in 11 year cycles. There are actually two peaks in the geomagnetic activity on both sides of the sunspot maxima. Sunspot maxima was in 2000 and now the solar activity is decreasing towards year 2007. 
 
 
 
 

History of the Aurora Section

Aurora observing in the association began in the late 1960's, when Mr. Matti Hänninen began reporting to Ursa on his Aurora observations. The association did not have any sections until mid 1970's, when six amateur astronomy activity groups were formed, mostly by younger members of Ursa, who were keen on observing celestial phenomena. Aurora observing was included in 1978. 

Initially the Aurora observers were just one part of a multi-field section observing the Sun, meteors, comets, etc. Kari Kaila was the first section leader, and later became a professional in Geophysics research. When this multi-field section grew too big, it became split and so the Aurora Section was finally under it's own banner in 1987. Around this time Ismo Luukkonen became the leader. His term ended in 1989. Markku Ruonala led the Aurora Section from 1989 to 1991. The 90's brought troubles in the form of finding a new leader. As a result, the activities diminished and most of the observers quit, which was a shame since it was an era with plenty of Auroral displays. Jani Katava took over the responsibilities in 1993 and was followed by Tom Eklund, the current section leader.

Aurora section is one of the smaller sections within Ursa, if rated by the number of observers, about 10 to 15, but we have been able to establish a unique observing network with good coverage in many aspects. There are some visual observers, who regularly record the information and mail their reports to section leader, who creates bimonthly summaries of observations. These summaries are published in "Korona", the section's column in Ursa Minor-magazine. 

Observing Aurora and Section's activities

The professionals have not abandoned Auroras. They are doing extensive research work using automatic imaging systems, radars, lidars, particle detectors, magnetometers, radio-emission detectors and other modern land and space based equipment on Aurora studies and Space Physics in general, also in Finland at SGO. Part of the interest to study this subject comes from the harmful effects the excessive solar particle emissions have on satellites and on terrestrial systems, such as electric power transmission and communication. 

Besides observing visually, some of our section members also take photographs, or radio- and magnetometer data. The primary radio data originates from an automated system monitoring VHF Auroral back scatter signal.

Our section has it's own mailing list (Finnish language) used presently mostly for, sharing unusual recent observations. Many of section's active members meet in July at "Cygnus", Ursa's annual summer event.

An expedition to Auroral radar systems STARE and CUTLAS in Hankasalmi, Finland, took place in October 1998. STARE is the 20 year old VHF radar with 40 kW peak output power and about 2 MW ERP, that is planned to be shut down with in a few years. CUTLAS is the new HF radar with 10 kW output power, based on solid state technology, while the STARE transmitter has a 3CPX1500A7 tube in the transmitter. Both radars are controlled by PCs running Unix. The author also visited the Swedish EISCAT radar receiving site near Kiruna in August 2001.

• Presentation of Ursa Astronomical Association
• Ursa homepage

Recent aurora observations in Finnish observation database

Observation source: www.taivaanvahti.fi

Predictions on solar and Auroral activity

Forecasts for longer periods are based on statistics. The 27-day period of Sun's rotation is quite evident in the occurrences of Aurora, at least after the peak of solar cycle. By using Bartels-diagram, which is based on this 27-day period, anyone can prepare predictions of Auroral displays for next month. This procedure works better, when coronal hole emissions are the primary cause for geomagnetic activity. Flares which dominate before the maxima, are quite hard to predict, since flares just "happen" (thought they do appear more often on potentially flare producing sunspot groups). There also exists a weaker event interval of 13.5 days besides the 182.5-day semi-annual period mentioned earlier. 

Internet is filled with forecasts made by professionals, but they should be treated with some caution, since the processes behind Auroral phenomena are fairly unpredictable by present means and the space based sensor network's spatial coverage is very poor. In spite of some severe geomagnetic storms have been properly predicted within the past few years, false alarms have still been numerous. Severe geomagnetic storms may occur even near sunspot minima in mid summer, when statistically the odds are against them. Though the scientists are improving the prediction tools and models and new space based sensors become operational, the quality of  Space Weather forecasts improves slowly. To see as may Auroral displays as possible, we just have to be alert and watch real time data and northern sky.