Ask Captain Lim

Hi Capt Lim,

When airliners are flying the Polar Routes from the USA to Asia, do they have to avoid flying near aurora's? I think, at the very least they would wreak havoc on the HF radio but I am wondering if they are a threat to the aircraft itself? If so, are these covered in the International NOTAMS?

Also, how high are the auroras typically?

As always, I love visiting your site and learning about flying.

Andrew C.

Hi Andrew,

This is an interesting question. On my last flight from Stockholm to New York on the Boeing 777, the majestic sight of the Aurora Borealis greeted me as my First Officer alerted me during the changeover of shift. We were flying across the Atlantic using the shortest Great Circle route or OTS (Off Track System) where reporting points are transmitted at prescribed Latitudes and Longitudes. It was almost similar to a Polar Route because it took us over Greenland, then on a South Westerly track over the Canadian airspace, passing Gander and Boston before arriving New York. It did not occur to me as anything that would affect the safety of the flight except that I was fascinated by the clear view of this Northern Light at 38,000 feet!

What is the Aurora Borealis? To those who are not familiar with this, it is also known as the Northern Lights, common during the post-midnight hours. It blinks on and off every few seconds as though controlled by some mysterious unseen hand in the sky flicking a switch. It occurs along the ring-shaped regions around the North and South Geomagnetic Poles. Fairbanks, Alaska, is a good place for Aurora watching because it is under this region in the North, where people see them a lot; the Southern Aurora is Aurora Australis. My first experience of seeing the Aurora was in Sweden on a cold winter night. It was Captain Roland Nordmark (an ex-SAS friend) who first introduced it to me and it was awesome!

What cause this great auroral display? They are created by solar flares in the vicinity of major sunspots. The flares cast out a vast stream of electrically charged particles which stream down into the earth*s atmosphere. These particles, mostly electrons and protons, are steered away from the tropical regions by the earth*s magnetic field. When they strike the gases of the earth*s high atmosphere, the charged particles glow. So just like a neon sign, the auroral light is produced by a high-vacuum electrical discharge, powered by interactions between the sun and earth. The altitude of its lower edge is sixty or seventy miles, about ten times higher than a jet aircraft flies - too high to have any significant effect on planes!

So, aside from the distraction caused to pilots, does the aurora pose a hazard to flying? Well, there were talks that it does affect radio reception. How? During the solar flares, the incoming charged particles that stream down along the direction of the earth*s magnetic field do affect the ionosphere that both absorb and reflect radio waves. This has the effect of interfering with radio propagation in places like Alaska and other polar regions at lower latitudes. Sometimes, these aurora effects lead to weird and wondrous paths where people in Alaska can listen to AM radio from China or South America; or Fairbanks cab drivers receiving instructions from dispatchers from New York. This was probably caused by the radio waves bouncing several times between the ionosphere and the earth*s surface before reaching the destination (radio theory in ATP exams).

Surprisingly, on the night when we encountered the Aurora as we flew across the Atlantic, our HF (High Frequency) radio reception with Shannon and Gander stations was crystal clear when compared to the nightmares we used to experience over the Bay of Bengal with Mumbai, Chenai (Madras) or the Calcatta radio stations (without the Auroras)!

Does the auroras affect the weather? Researchers have found that storms beginning over the North Pacific during times of major auroral displays tended to grow more than did storms beginning at other times. It*s also known that auroral processes affect both electric fields and air temperatures high above the ground, and those changes could reach down into weather systems. Well, according to Dr Neil Davis, a seismologist at the Geophysical Institute, University of Alaska Fairbanks, the effects of auroral energies are relatively minor when compared to those driving primary weather processes...

Personally, I think the Aurora has very little effect on the safety of planes flying over the Polar Routes. With many modern form of communication, even with a loss of HF communication, it is not a problem at all. I have never seen any warnings in NOTAMS (Notice to Airmen) warning pilots to avoid the Auroras. Any anyway, at 60 miles high (ten times the normal airplane cruising height), the aurora is not a threat to any planes!