Science Scene Investigators

There was a tragic accident up north last month. A few minutes before 15:00 CET on March 15th a Norwegian military C-130 Hercules transport aircraft crashed into Kebnekaise - the highest mountain in Sweden – during a multi-national military exercise. All five officers on board died.

The aircraft was totally destroyed, and due to bad weather it took more than a day to find the crash site. One month after the crash pieces of debris are still being found in the snow up on the glacier. The ”black box” with the flight recorder has so far not been found, however.

The Forces of Nature

In the days after the tragic crash, questions were raised in the scientific community about geophysical phenomena that could possibly have contributed to the accident.

- Could high ionospheric activity have caused severe disturbances in GPS signal quality, thus affecting aircraft position accuracy?

- Could high geomagnetic activity have influenced the magnetic compass, and thus the heading of the aircraft?

- Could atmospheric lee-waves in the mountain area along the border between Norway and Sweden have caught the aircraft by surprise, thus bringing the plane down?

These were not only hypothetical questions. In fact, all three natural phenomena were observed on March15th, so a closer scrutiny was justified.

Also, solid-earth scientists volunteered. Could seismic instruments tell anything about the crash?

Geomagnetic storm

A chain of precise magnetometers is operated and monitored by Tromsø Geophysical Observatory (TGO). The measurements showed that there was indeed a geomagnetic storm raging that day, as the Earth’s magnetic field was hit around 14:00 CET by the flank of a Coronal Mass Ejection (CME) that was ejected from the Sun two days earlier. However, the largest variations in geomagnetic activity in Northern Norway appeared in the hour after the crash.

Disturbed ionosphere

The Norwegian Mapping Authority (NMA) is operating a real time chain of more than 100 GPS stations in Mainland Norway and on the Arctic islands. Looking at the signal delay along lines from each of the navigation satellites to each of these stations, one can get a good picture of the state of the ionosphere. When the NMA looked into their data, it showed much ionospheric disturbances later in the day on March 15th, but the ionospheric storm had not quite started over Scandinavia at the time of the crash.

Atmospheric lee waves

Scientists from the Nansen Environmental and Remote Sensing Center and the University of Bergen looked into satellite images showing the cloud conditions on March 15th. They found that on the day of the crash the satellites showed strong lee wave patterns in the clouds, due to strong south-westerly winds the mountain area. No such cloud patterns were present the day before or the day after the crash.

Seismology

Seismic instrument records for the period 14:30 – 15:30 CET have also been investigated by scientists in Norway, Sweden and Finland. Several small explosions due to mining activity were observed, but the impact of the aircraft did not provide a clear seismic signal. Experts say that this is somewhat unexpected, as impacting aircraft usually make a detectable signal. The lack of a seismic signal may be related to deep snow in the area and/or the impact angle with the terrain.

If a clear seismic signal had been present, the search and rescue teams would have got a much better indication of where to start looking for the wreck.

Summing up, so far

Scientists from many geophysical fields have contributed with valuable pieces of information for the investigation of the tragic C-130 Hercules crash. Magnetometers, GPS receivers, seismic arrays and weather satellites all carry relevant information.

As of today, atmospheric lee waves may seem more likely to have contributed to the crash than space weather effects.

Hopefully, the flight recorder will soon be found and a much more complete picture will emerge from the official commission investigating this tragic accident.

Photos:

Figure 1: Magnetometer readings on 15 March (UTC) at various sites from Svalbard (top) to Denmark (bottom). The fifth and the sixth curve from the top are located closest to the crash site. (Tromsø Geophysical Observatory)

Figure 2: Satellite image showing the area south of Lake Torneträsk on March 15th at 11:35 CET. The Kebnekaise area is covered by clouds, with several large lee-waves. (ESA ENVISAT)